Initial Commit

include/asio/impl/any_completion_executor.ipp

@@ -0,0 +1,126 @@
+//
+// impl/any_completion_executor.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_ANY_COMPLETION_EXECUTOR_IPP
+#define ASIO_IMPL_ANY_COMPLETION_EXECUTOR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if !defined(ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+#include "asio/any_completion_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+any_completion_executor::any_completion_executor() noexcept
+  : base_type()
+{
+}
+
+any_completion_executor::any_completion_executor(nullptr_t) noexcept
+  : base_type(nullptr_t())
+{
+}
+
+any_completion_executor::any_completion_executor(
+    const any_completion_executor& e) noexcept
+  : base_type(static_cast<const base_type&>(e))
+{
+}
+
+any_completion_executor::any_completion_executor(std::nothrow_t,
+    const any_completion_executor& e) noexcept
+  : base_type(static_cast<const base_type&>(e))
+{
+}
+
+any_completion_executor::any_completion_executor(
+    any_completion_executor&& e) noexcept
+  : base_type(static_cast<base_type&&>(e))
+{
+}
+
+any_completion_executor::any_completion_executor(std::nothrow_t,
+    any_completion_executor&& e) noexcept
+  : base_type(static_cast<base_type&&>(e))
+{
+}
+
+any_completion_executor& any_completion_executor::operator=(
+    const any_completion_executor& e) noexcept
+{
+  base_type::operator=(static_cast<const base_type&>(e));
+  return *this;
+}
+
+any_completion_executor& any_completion_executor::operator=(
+    any_completion_executor&& e) noexcept
+{
+  base_type::operator=(static_cast<base_type&&>(e));
+  return *this;
+}
+
+any_completion_executor& any_completion_executor::operator=(nullptr_t)
+{
+  base_type::operator=(nullptr_t());
+  return *this;
+}
+
+any_completion_executor::~any_completion_executor()
+{
+}
+
+void any_completion_executor::swap(
+    any_completion_executor& other) noexcept
+{
+  static_cast<base_type&>(*this).swap(static_cast<base_type&>(other));
+}
+
+template <>
+any_completion_executor any_completion_executor::prefer(
+    const execution::outstanding_work_t::tracked_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_completion_executor any_completion_executor::prefer(
+    const execution::outstanding_work_t::untracked_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_completion_executor any_completion_executor::prefer(
+    const execution::relationship_t::fork_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_completion_executor any_completion_executor::prefer(
+    const execution::relationship_t::continuation_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // !defined(ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+#endif // ASIO_IMPL_ANY_COMPLETION_EXECUTOR_IPP

include/asio/impl/any_io_executor.ipp

@@ -0,0 +1,134 @@
+//
+// impl/any_io_executor.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_ANY_IO_EXECUTOR_IPP
+#define ASIO_IMPL_ANY_IO_EXECUTOR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if !defined(ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+#include "asio/any_io_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+any_io_executor::any_io_executor() noexcept
+  : base_type()
+{
+}
+
+any_io_executor::any_io_executor(nullptr_t) noexcept
+  : base_type(nullptr_t())
+{
+}
+
+any_io_executor::any_io_executor(const any_io_executor& e) noexcept
+  : base_type(static_cast<const base_type&>(e))
+{
+}
+
+any_io_executor::any_io_executor(std::nothrow_t,
+    const any_io_executor& e) noexcept
+  : base_type(static_cast<const base_type&>(e))
+{
+}
+
+any_io_executor::any_io_executor(any_io_executor&& e) noexcept
+  : base_type(static_cast<base_type&&>(e))
+{
+}
+
+any_io_executor::any_io_executor(std::nothrow_t, any_io_executor&& e) noexcept
+  : base_type(static_cast<base_type&&>(e))
+{
+}
+
+any_io_executor& any_io_executor::operator=(const any_io_executor& e) noexcept
+{
+  base_type::operator=(static_cast<const base_type&>(e));
+  return *this;
+}
+
+any_io_executor& any_io_executor::operator=(any_io_executor&& e) noexcept
+{
+  base_type::operator=(static_cast<base_type&&>(e));
+  return *this;
+}
+
+any_io_executor& any_io_executor::operator=(nullptr_t)
+{
+  base_type::operator=(nullptr_t());
+  return *this;
+}
+
+any_io_executor::~any_io_executor()
+{
+}
+
+void any_io_executor::swap(any_io_executor& other) noexcept
+{
+  static_cast<base_type&>(*this).swap(static_cast<base_type&>(other));
+}
+
+template <>
+any_io_executor any_io_executor::require(
+    const execution::blocking_t::never_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).require(p);
+}
+
+template <>
+any_io_executor any_io_executor::prefer(
+    const execution::blocking_t::possibly_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_io_executor any_io_executor::prefer(
+    const execution::outstanding_work_t::tracked_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_io_executor any_io_executor::prefer(
+    const execution::outstanding_work_t::untracked_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_io_executor any_io_executor::prefer(
+    const execution::relationship_t::fork_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+template <>
+any_io_executor any_io_executor::prefer(
+    const execution::relationship_t::continuation_t& p, int) const
+{
+  return static_cast<const base_type&>(*this).prefer(p);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // !defined(ASIO_USE_TS_EXECUTOR_AS_DEFAULT)
+
+#endif // ASIO_IMPL_ANY_IO_EXECUTOR_IPP

include/asio/impl/append.hpp

@@ -0,0 +1,169 @@
+//
+// impl/append.hpp
+// ~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_APPEND_HPP
+#define ASIO_IMPL_APPEND_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/utility.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Class to adapt an append_t as a completion handler.
+template <typename Handler, typename... Values>
+class append_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename H>
+  append_handler(H&& handler, std::tuple<Values...> values)
+    : handler_(static_cast<H&&>(handler)),
+      values_(static_cast<std::tuple<Values...>&&>(values))
+  {
+  }
+
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    this->invoke(
+        index_sequence_for<Values...>{},
+        static_cast<Args&&>(args)...);
+  }
+
+  template <std::size_t... I, typename... Args>
+  void invoke(index_sequence<I...>, Args&&... args)
+  {
+    static_cast<Handler&&>(handler_)(
+        static_cast<Args&&>(args)...,
+        static_cast<Values&&>(std::get<I>(values_))...);
+  }
+
+//private:
+  Handler handler_;
+  std::tuple<Values...> values_;
+};
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    append_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+      this_handler->handler_);
+}
+
+template <typename Signature, typename... Values>
+struct append_signature;
+
+template <typename R, typename... Args, typename... Values>
+struct append_signature<R(Args...), Values...>
+{
+  typedef R type(decay_t<Args>..., Values...);
+};
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename... Values, typename Signature>
+struct async_result<append_t<CompletionToken, Values...>, Signature>
+  : async_result<CompletionToken,
+      typename detail::append_signature<
+        Signature, Values...>::type>
+{
+  typedef typename detail::append_signature<
+      Signature, Values...>::type signature;
+
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        std::tuple<Values...> values, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          detail::append_handler<decay_t<Handler>, Values...>(
+            static_cast<Handler&&>(handler),
+            static_cast<std::tuple<Values...>&&>(values)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        std::tuple<Values...> values, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          detail::append_handler<decay_t<Handler>, Values...>(
+            static_cast<Handler&&>(handler),
+            static_cast<std::tuple<Values...>&&>(values)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<CompletionToken, signature>(
+        declval<init_wrapper<decay_t<Initiation>>>(),
+        token.token_,
+        static_cast<std::tuple<Values...>&&>(token.values_),
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<CompletionToken, signature>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_,
+        static_cast<std::tuple<Values...>&&>(token.values_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename... Values, typename DefaultCandidate>
+struct associator<Associator,
+    detail::append_handler<Handler, Values...>, DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const detail::append_handler<Handler, Values...>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::append_handler<Handler, Values...>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_APPEND_HPP

include/asio/impl/as_tuple.hpp

@@ -0,0 +1,276 @@
+//
+// impl/as_tuple.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_AS_TUPLE_HPP
+#define ASIO_IMPL_AS_TUPLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <tuple>
+#include "asio/associated_executor.hpp"
+#include "asio/associator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/type_traits.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Class to adapt a as_tuple_t as a completion handler.
+template <typename Handler>
+class as_tuple_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename CompletionToken>
+  as_tuple_handler(as_tuple_t<CompletionToken> e)
+    : handler_(static_cast<CompletionToken&&>(e.token_))
+  {
+  }
+
+  template <typename RedirectedHandler>
+  as_tuple_handler(RedirectedHandler&& h)
+    : handler_(static_cast<RedirectedHandler&&>(h))
+  {
+  }
+
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    static_cast<Handler&&>(handler_)(
+        std::make_tuple(static_cast<Args&&>(args)...));
+  }
+
+//private:
+  Handler handler_;
+};
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    as_tuple_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+}
+
+template <typename Signature>
+struct as_tuple_signature;
+
+template <typename R, typename... Args>
+struct as_tuple_signature<R(Args...)>
+{
+  typedef R type(std::tuple<decay_t<Args>...>);
+};
+
+template <typename R, typename... Args>
+struct as_tuple_signature<R(Args...) &>
+{
+  typedef R type(std::tuple<decay_t<Args>...>) &;
+};
+
+template <typename R, typename... Args>
+struct as_tuple_signature<R(Args...) &&>
+{
+  typedef R type(std::tuple<decay_t<Args>...>) &&;
+};
+
+#if defined(ASIO_HAS_NOEXCEPT_FUNCTION_TYPE)
+
+template <typename R, typename... Args>
+struct as_tuple_signature<R(Args...) noexcept>
+{
+  typedef R type(std::tuple<decay_t<Args>...>) noexcept;
+};
+
+template <typename R, typename... Args>
+struct as_tuple_signature<R(Args...) & noexcept>
+{
+  typedef R type(std::tuple<decay_t<Args>...>) & noexcept;
+};
+
+template <typename R, typename... Args>
+struct as_tuple_signature<R(Args...) && noexcept>
+{
+  typedef R type(std::tuple<decay_t<Args>...>) && noexcept;
+};
+
+#endif // defined(ASIO_HAS_NOEXCEPT_FUNCTION_TYPE)
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename... Signatures>
+struct async_result<as_tuple_t<CompletionToken>, Signatures...>
+  : async_result<CompletionToken,
+      typename detail::as_tuple_signature<Signatures>::type...>
+{
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          detail::as_tuple_handler<decay_t<Handler>>(
+            static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          detail::as_tuple_handler<decay_t<Handler>>(
+            static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        typename detail::as_tuple_signature<Signatures>::type...>(
+          init_wrapper<decay_t<Initiation>>(
+            static_cast<Initiation&&>(initiation)),
+          token.token_, static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      typename detail::as_tuple_signature<Signatures>::type...>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_, static_cast<Args&&>(args)...);
+  }
+};
+
+#if defined(ASIO_MSVC)
+
+// Workaround for MSVC internal compiler error.
+
+template <typename CompletionToken, typename Signature>
+struct async_result<as_tuple_t<CompletionToken>, Signature>
+  : async_result<CompletionToken,
+      typename detail::as_tuple_signature<Signature>::type>
+{
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          detail::as_tuple_handler<decay_t<Handler>>(
+            static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          detail::as_tuple_handler<decay_t<Handler>>(
+            static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        typename detail::as_tuple_signature<Signature>::type>(
+          init_wrapper<decay_t<Initiation>>(
+            static_cast<Initiation&&>(initiation)),
+          token.token_, static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      typename detail::as_tuple_signature<Signature>::type>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_, static_cast<Args&&>(args)...);
+  }
+};
+
+#endif // defined(ASIO_MSVC)
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::as_tuple_handler<Handler>, DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const detail::as_tuple_handler<Handler>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::as_tuple_handler<Handler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+template <typename... Signatures>
+struct async_result<partial_as_tuple, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&&, Args&&... args)
+    -> decltype(
+      async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        as_tuple_t<
+          default_completion_token_t<associated_executor_t<Initiation>>>{},
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        as_tuple_t<
+          default_completion_token_t<associated_executor_t<Initiation>>>{},
+        static_cast<Args&&>(args)...);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_AS_TUPLE_HPP

include/asio/impl/awaitable.ipp

@@ -0,0 +1,48 @@
+//
+// impl/awaitable.ipp
+// ~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_AWAITABLE_IPP
+#define ASIO_IMPL_AWAITABLE_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_CO_AWAIT)
+
+#include "asio/awaitable.hpp"
+#include "asio/detail/call_stack.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+void awaitable_launch_context::launch(void (*pump_fn)(void*), void* arg)
+{
+  call_stack<awaitable_launch_context>::context ctx(this);
+  pump_fn(arg);
+}
+
+bool awaitable_launch_context::is_launching()
+{
+  return !!call_stack<awaitable_launch_context>::contains(this);
+}
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // defined(ASIO_HAS_CO_AWAIT)
+
+#endif // ASIO_IMPL_AWAITABLE_IPP

include/asio/impl/buffered_read_stream.hpp

@@ -0,0 +1,404 @@
+//
+// impl/buffered_read_stream.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_BUFFERED_READ_STREAM_HPP
+#define ASIO_IMPL_BUFFERED_READ_STREAM_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/associator.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/type_traits.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+template <typename Stream>
+std::size_t buffered_read_stream<Stream>::fill()
+{
+  detail::buffer_resize_guard<detail::buffered_stream_storage>
+    resize_guard(storage_);
+  std::size_t previous_size = storage_.size();
+  storage_.resize(storage_.capacity());
+  storage_.resize(previous_size + next_layer_.read_some(buffer(
+          storage_.data() + previous_size,
+          storage_.size() - previous_size)));
+  resize_guard.commit();
+  return storage_.size() - previous_size;
+}
+
+template <typename Stream>
+std::size_t buffered_read_stream<Stream>::fill(asio::error_code& ec)
+{
+  detail::buffer_resize_guard<detail::buffered_stream_storage>
+    resize_guard(storage_);
+  std::size_t previous_size = storage_.size();
+  storage_.resize(storage_.capacity());
+  storage_.resize(previous_size + next_layer_.read_some(buffer(
+          storage_.data() + previous_size,
+          storage_.size() - previous_size),
+        ec));
+  resize_guard.commit();
+  return storage_.size() - previous_size;
+}
+
+namespace detail
+{
+  template <typename ReadHandler>
+  class buffered_fill_handler
+  {
+  public:
+    buffered_fill_handler(detail::buffered_stream_storage& storage,
+        std::size_t previous_size, ReadHandler& handler)
+      : storage_(storage),
+        previous_size_(previous_size),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    buffered_fill_handler(const buffered_fill_handler& other)
+      : storage_(other.storage_),
+        previous_size_(other.previous_size_),
+        handler_(other.handler_)
+    {
+    }
+
+    buffered_fill_handler(buffered_fill_handler&& other)
+      : storage_(other.storage_),
+        previous_size_(other.previous_size_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec,
+        const std::size_t bytes_transferred)
+    {
+      storage_.resize(previous_size_ + bytes_transferred);
+      static_cast<ReadHandler&&>(handler_)(ec, bytes_transferred);
+    }
+
+  //private:
+    detail::buffered_stream_storage& storage_;
+    std::size_t previous_size_;
+    ReadHandler handler_;
+  };
+
+  template <typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      buffered_fill_handler<ReadHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename Stream>
+  class initiate_async_buffered_fill
+  {
+  public:
+    typedef typename remove_reference_t<
+      Stream>::lowest_layer_type::executor_type executor_type;
+
+    explicit initiate_async_buffered_fill(
+        remove_reference_t<Stream>& next_layer)
+      : next_layer_(next_layer)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return next_layer_.lowest_layer().get_executor();
+    }
+
+    template <typename ReadHandler>
+    void operator()(ReadHandler&& handler,
+        buffered_stream_storage* storage) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      non_const_lvalue<ReadHandler> handler2(handler);
+      std::size_t previous_size = storage->size();
+      storage->resize(storage->capacity());
+      next_layer_.async_read_some(
+          buffer(
+            storage->data() + previous_size,
+            storage->size() - previous_size),
+          buffered_fill_handler<decay_t<ReadHandler>>(
+            *storage, previous_size, handler2.value));
+    }
+
+  private:
+    remove_reference_t<Stream>& next_layer_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename ReadHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::buffered_fill_handler<ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::buffered_fill_handler<ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::buffered_fill_handler<ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+template <typename Stream>
+template <
+    ASIO_COMPLETION_TOKEN_FOR(void (asio::error_code,
+      std::size_t)) ReadHandler>
+inline auto buffered_read_stream<Stream>::async_fill(ReadHandler&& handler)
+  -> decltype(
+    async_initiate<ReadHandler,
+      void (asio::error_code, std::size_t)>(
+        declval<detail::initiate_async_buffered_fill<Stream>>(),
+        handler, declval<detail::buffered_stream_storage*>()))
+{
+  return async_initiate<ReadHandler,
+    void (asio::error_code, std::size_t)>(
+      detail::initiate_async_buffered_fill<Stream>(next_layer_),
+      handler, &storage_);
+}
+
+template <typename Stream>
+template <typename MutableBufferSequence>
+std::size_t buffered_read_stream<Stream>::read_some(
+    const MutableBufferSequence& buffers)
+{
+  using asio::buffer_size;
+  if (buffer_size(buffers) == 0)
+    return 0;
+
+  if (storage_.empty())
+    this->fill();
+
+  return this->copy(buffers);
+}
+
+template <typename Stream>
+template <typename MutableBufferSequence>
+std::size_t buffered_read_stream<Stream>::read_some(
+    const MutableBufferSequence& buffers, asio::error_code& ec)
+{
+  ec = asio::error_code();
+
+  using asio::buffer_size;
+  if (buffer_size(buffers) == 0)
+    return 0;
+
+  if (storage_.empty() && !this->fill(ec))
+    return 0;
+
+  return this->copy(buffers);
+}
+
+namespace detail
+{
+  template <typename MutableBufferSequence, typename ReadHandler>
+  class buffered_read_some_handler
+  {
+  public:
+    buffered_read_some_handler(detail::buffered_stream_storage& storage,
+        const MutableBufferSequence& buffers, ReadHandler& handler)
+      : storage_(storage),
+        buffers_(buffers),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    buffered_read_some_handler(const buffered_read_some_handler& other)
+      : storage_(other.storage_),
+        buffers_(other.buffers_),
+        handler_(other.handler_)
+    {
+    }
+
+    buffered_read_some_handler(buffered_read_some_handler&& other)
+      : storage_(other.storage_),
+        buffers_(other.buffers_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec, std::size_t)
+    {
+      if (ec || storage_.empty())
+      {
+        const std::size_t length = 0;
+        static_cast<ReadHandler&&>(handler_)(ec, length);
+      }
+      else
+      {
+        const std::size_t bytes_copied = asio::buffer_copy(
+            buffers_, storage_.data(), storage_.size());
+        storage_.consume(bytes_copied);
+        static_cast<ReadHandler&&>(handler_)(ec, bytes_copied);
+      }
+    }
+
+  //private:
+    detail::buffered_stream_storage& storage_;
+    MutableBufferSequence buffers_;
+    ReadHandler handler_;
+  };
+
+  template <typename MutableBufferSequence, typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      buffered_read_some_handler<
+        MutableBufferSequence, ReadHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename Stream>
+  class initiate_async_buffered_read_some
+  {
+  public:
+    typedef typename remove_reference_t<
+      Stream>::lowest_layer_type::executor_type executor_type;
+
+    explicit initiate_async_buffered_read_some(
+        remove_reference_t<Stream>& next_layer)
+      : next_layer_(next_layer)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return next_layer_.lowest_layer().get_executor();
+    }
+
+    template <typename ReadHandler, typename MutableBufferSequence>
+    void operator()(ReadHandler&& handler,
+        buffered_stream_storage* storage,
+        const MutableBufferSequence& buffers) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      using asio::buffer_size;
+      non_const_lvalue<ReadHandler> handler2(handler);
+      if (buffer_size(buffers) == 0 || !storage->empty())
+      {
+        next_layer_.async_read_some(mutable_buffer(0, 0),
+            buffered_read_some_handler<MutableBufferSequence,
+              decay_t<ReadHandler>>(
+                *storage, buffers, handler2.value));
+      }
+      else
+      {
+        initiate_async_buffered_fill<Stream>(this->next_layer_)(
+            buffered_read_some_handler<MutableBufferSequence,
+              decay_t<ReadHandler>>(
+                *storage, buffers, handler2.value),
+            storage);
+      }
+    }
+
+  private:
+    remove_reference_t<Stream>& next_layer_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename MutableBufferSequence, typename ReadHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::buffered_read_some_handler<MutableBufferSequence, ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::buffered_read_some_handler<
+        MutableBufferSequence, ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::buffered_read_some_handler<
+        MutableBufferSequence, ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+template <typename Stream>
+template <typename MutableBufferSequence,
+    ASIO_COMPLETION_TOKEN_FOR(void (asio::error_code,
+      std::size_t)) ReadHandler>
+inline auto buffered_read_stream<Stream>::async_read_some(
+    const MutableBufferSequence& buffers, ReadHandler&& handler)
+  -> decltype(
+    async_initiate<ReadHandler,
+      void (asio::error_code, std::size_t)>(
+        declval<detail::initiate_async_buffered_read_some<Stream>>(),
+        handler, declval<detail::buffered_stream_storage*>(), buffers))
+{
+  return async_initiate<ReadHandler,
+    void (asio::error_code, std::size_t)>(
+      detail::initiate_async_buffered_read_some<Stream>(next_layer_),
+      handler, &storage_, buffers);
+}
+
+template <typename Stream>
+template <typename MutableBufferSequence>
+std::size_t buffered_read_stream<Stream>::peek(
+    const MutableBufferSequence& buffers)
+{
+  if (storage_.empty())
+    this->fill();
+  return this->peek_copy(buffers);
+}
+
+template <typename Stream>
+template <typename MutableBufferSequence>
+std::size_t buffered_read_stream<Stream>::peek(
+    const MutableBufferSequence& buffers, asio::error_code& ec)
+{
+  ec = asio::error_code();
+  if (storage_.empty() && !this->fill(ec))
+    return 0;
+  return this->peek_copy(buffers);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_BUFFERED_READ_STREAM_HPP

include/asio/impl/buffered_write_stream.hpp

@@ -0,0 +1,384 @@
+//
+// impl/buffered_write_stream.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_BUFFERED_WRITE_STREAM_HPP
+#define ASIO_IMPL_BUFFERED_WRITE_STREAM_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/associator.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+template <typename Stream>
+std::size_t buffered_write_stream<Stream>::flush()
+{
+  std::size_t bytes_written = write(next_layer_,
+      buffer(storage_.data(), storage_.size()));
+  storage_.consume(bytes_written);
+  return bytes_written;
+}
+
+template <typename Stream>
+std::size_t buffered_write_stream<Stream>::flush(asio::error_code& ec)
+{
+  std::size_t bytes_written = write(next_layer_,
+      buffer(storage_.data(), storage_.size()),
+      transfer_all(), ec);
+  storage_.consume(bytes_written);
+  return bytes_written;
+}
+
+namespace detail
+{
+  template <typename WriteHandler>
+  class buffered_flush_handler
+  {
+  public:
+    buffered_flush_handler(detail::buffered_stream_storage& storage,
+        WriteHandler& handler)
+      : storage_(storage),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    buffered_flush_handler(const buffered_flush_handler& other)
+      : storage_(other.storage_),
+        handler_(other.handler_)
+    {
+    }
+
+    buffered_flush_handler(buffered_flush_handler&& other)
+      : storage_(other.storage_),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec,
+        const std::size_t bytes_written)
+    {
+      storage_.consume(bytes_written);
+      static_cast<WriteHandler&&>(handler_)(ec, bytes_written);
+    }
+
+  //private:
+    detail::buffered_stream_storage& storage_;
+    WriteHandler handler_;
+  };
+
+  template <typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      buffered_flush_handler<WriteHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename Stream>
+  class initiate_async_buffered_flush
+  {
+  public:
+    typedef typename remove_reference_t<
+      Stream>::lowest_layer_type::executor_type executor_type;
+
+    explicit initiate_async_buffered_flush(
+        remove_reference_t<Stream>& next_layer)
+      : next_layer_(next_layer)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return next_layer_.lowest_layer().get_executor();
+    }
+
+    template <typename WriteHandler>
+    void operator()(WriteHandler&& handler,
+        buffered_stream_storage* storage) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      non_const_lvalue<WriteHandler> handler2(handler);
+      async_write(next_layer_, buffer(storage->data(), storage->size()),
+          buffered_flush_handler<decay_t<WriteHandler>>(
+            *storage, handler2.value));
+    }
+
+  private:
+    remove_reference_t<Stream>& next_layer_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename WriteHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::buffered_flush_handler<WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::buffered_flush_handler<WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::buffered_flush_handler<WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+template <typename Stream>
+template <
+    ASIO_COMPLETION_TOKEN_FOR(void (asio::error_code,
+      std::size_t)) WriteHandler>
+inline auto buffered_write_stream<Stream>::async_flush(WriteHandler&& handler)
+  -> decltype(
+    async_initiate<WriteHandler,
+      void (asio::error_code, std::size_t)>(
+        declval<detail::initiate_async_buffered_flush<Stream>>(),
+        handler, declval<detail::buffered_stream_storage*>()))
+{
+  return async_initiate<WriteHandler,
+    void (asio::error_code, std::size_t)>(
+      detail::initiate_async_buffered_flush<Stream>(next_layer_),
+      handler, &storage_);
+}
+
+template <typename Stream>
+template <typename ConstBufferSequence>
+std::size_t buffered_write_stream<Stream>::write_some(
+    const ConstBufferSequence& buffers)
+{
+  using asio::buffer_size;
+  if (buffer_size(buffers) == 0)
+    return 0;
+
+  if (storage_.size() == storage_.capacity())
+    this->flush();
+
+  return this->copy(buffers);
+}
+
+template <typename Stream>
+template <typename ConstBufferSequence>
+std::size_t buffered_write_stream<Stream>::write_some(
+    const ConstBufferSequence& buffers, asio::error_code& ec)
+{
+  ec = asio::error_code();
+
+  using asio::buffer_size;
+  if (buffer_size(buffers) == 0)
+    return 0;
+
+  if (storage_.size() == storage_.capacity() && !flush(ec))
+    return 0;
+
+  return this->copy(buffers);
+}
+
+namespace detail
+{
+  template <typename ConstBufferSequence, typename WriteHandler>
+  class buffered_write_some_handler
+  {
+  public:
+    buffered_write_some_handler(detail::buffered_stream_storage& storage,
+        const ConstBufferSequence& buffers, WriteHandler& handler)
+      : storage_(storage),
+        buffers_(buffers),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    buffered_write_some_handler(const buffered_write_some_handler& other)
+      : storage_(other.storage_),
+        buffers_(other.buffers_),
+        handler_(other.handler_)
+    {
+    }
+
+    buffered_write_some_handler(buffered_write_some_handler&& other)
+      : storage_(other.storage_),
+        buffers_(other.buffers_),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec, std::size_t)
+    {
+      if (ec)
+      {
+        const std::size_t length = 0;
+        static_cast<WriteHandler&&>(handler_)(ec, length);
+      }
+      else
+      {
+        using asio::buffer_size;
+        std::size_t orig_size = storage_.size();
+        std::size_t space_avail = storage_.capacity() - orig_size;
+        std::size_t bytes_avail = buffer_size(buffers_);
+        std::size_t length = bytes_avail < space_avail
+          ? bytes_avail : space_avail;
+        storage_.resize(orig_size + length);
+        const std::size_t bytes_copied = asio::buffer_copy(
+            storage_.data() + orig_size, buffers_, length);
+        static_cast<WriteHandler&&>(handler_)(ec, bytes_copied);
+      }
+    }
+
+  //private:
+    detail::buffered_stream_storage& storage_;
+    ConstBufferSequence buffers_;
+    WriteHandler handler_;
+  };
+
+  template <typename ConstBufferSequence, typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      buffered_write_some_handler<
+        ConstBufferSequence, WriteHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename Stream>
+  class initiate_async_buffered_write_some
+  {
+  public:
+    typedef typename remove_reference_t<
+      Stream>::lowest_layer_type::executor_type executor_type;
+
+    explicit initiate_async_buffered_write_some(
+        remove_reference_t<Stream>& next_layer)
+      : next_layer_(next_layer)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return next_layer_.lowest_layer().get_executor();
+    }
+
+    template <typename WriteHandler, typename ConstBufferSequence>
+    void operator()(WriteHandler&& handler,
+        buffered_stream_storage* storage,
+        const ConstBufferSequence& buffers) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      using asio::buffer_size;
+      non_const_lvalue<WriteHandler> handler2(handler);
+      if (buffer_size(buffers) == 0 || storage->size() < storage->capacity())
+      {
+        next_layer_.async_write_some(const_buffer(0, 0),
+            buffered_write_some_handler<ConstBufferSequence,
+              decay_t<WriteHandler>>(
+                *storage, buffers, handler2.value));
+      }
+      else
+      {
+        initiate_async_buffered_flush<Stream>(this->next_layer_)(
+            buffered_write_some_handler<ConstBufferSequence,
+              decay_t<WriteHandler>>(
+                *storage, buffers, handler2.value),
+            storage);
+      }
+    }
+
+  private:
+    remove_reference_t<Stream>& next_layer_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename ConstBufferSequence, typename WriteHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::buffered_write_some_handler<ConstBufferSequence, WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::buffered_write_some_handler<
+        ConstBufferSequence, WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::buffered_write_some_handler<
+        ConstBufferSequence, WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+template <typename Stream>
+template <typename ConstBufferSequence,
+    ASIO_COMPLETION_TOKEN_FOR(void (asio::error_code,
+      std::size_t)) WriteHandler>
+inline auto buffered_write_stream<Stream>::async_write_some(
+    const ConstBufferSequence& buffers, WriteHandler&& handler)
+  -> decltype(
+    async_initiate<WriteHandler,
+      void (asio::error_code, std::size_t)>(
+        declval<detail::initiate_async_buffered_write_some<Stream>>(),
+        handler, declval<detail::buffered_stream_storage*>(), buffers))
+{
+  return async_initiate<WriteHandler,
+    void (asio::error_code, std::size_t)>(
+      detail::initiate_async_buffered_write_some<Stream>(next_layer_),
+      handler, &storage_, buffers);
+}
+
+template <typename Stream>
+template <typename ConstBufferSequence>
+std::size_t buffered_write_stream<Stream>::copy(
+    const ConstBufferSequence& buffers)
+{
+  using asio::buffer_size;
+  std::size_t orig_size = storage_.size();
+  std::size_t space_avail = storage_.capacity() - orig_size;
+  std::size_t bytes_avail = buffer_size(buffers);
+  std::size_t length = bytes_avail < space_avail ? bytes_avail : space_avail;
+  storage_.resize(orig_size + length);
+  return asio::buffer_copy(
+      storage_.data() + orig_size, buffers, length);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_BUFFERED_WRITE_STREAM_HPP

include/asio/impl/cancel_after.hpp

@@ -0,0 +1,268 @@
+//
+// impl/cancel_after.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CANCEL_AFTER_HPP
+#define ASIO_IMPL_CANCEL_AFTER_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associated_executor.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/timed_cancel_op.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename Initiation, typename Clock,
+    typename WaitTraits, typename... Signatures>
+struct initiate_cancel_after : initiation_base<Initiation>
+{
+  using initiation_base<Initiation>::initiation_base;
+
+  template <typename Handler, typename Rep, typename Period, typename... Args>
+  void operator()(Handler&& handler,
+      const chrono::duration<Rep, Period>& timeout,
+      cancellation_type_t cancel_type, Args&&... args) &&
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits>, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    p.p = new (p.v) op(handler2.value,
+        basic_waitable_timer<Clock, WaitTraits,
+          typename Initiation::executor_type>(this->get_executor(), timeout),
+        cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<Initiation&&>(*this), static_cast<Args&&>(args)...);
+  }
+
+  template <typename Handler, typename Rep, typename Period, typename... Args>
+  void operator()(Handler&& handler,
+      const chrono::duration<Rep, Period>& timeout,
+      cancellation_type_t cancel_type, Args&&... args) const &
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits>, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    p.p = new (p.v) op(handler2.value,
+        basic_waitable_timer<Clock, WaitTraits,
+          typename Initiation::executor_type>(this->get_executor(), timeout),
+        cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<const Initiation&>(*this),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename Initiation, typename Clock,
+    typename WaitTraits, typename Executor, typename... Signatures>
+struct initiate_cancel_after_timer : initiation_base<Initiation>
+{
+  using initiation_base<Initiation>::initiation_base;
+
+  template <typename Handler, typename Rep, typename Period, typename... Args>
+  void operator()(Handler&& handler,
+      basic_waitable_timer<Clock, WaitTraits, Executor>* timer,
+      const chrono::duration<Rep, Period>& timeout,
+      cancellation_type_t cancel_type, Args&&... args) &&
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits, Executor>&, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    timer->expires_after(timeout);
+    p.p = new (p.v) op(handler2.value, *timer, cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<Initiation&&>(*this), static_cast<Args&&>(args)...);
+  }
+
+  template <typename Handler, typename Rep, typename Period, typename... Args>
+  void operator()(Handler&& handler,
+      basic_waitable_timer<Clock, WaitTraits, Executor>* timer,
+      const chrono::duration<Rep, Period>& timeout,
+      cancellation_type_t cancel_type, Args&&... args) const &
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits, Executor>&, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    timer->expires_after(timeout);
+    p.p = new (p.v) op(handler2.value, *timer, cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<const Initiation&>(*this),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Clock,
+    typename WaitTraits, typename... Signatures>
+struct async_result<
+    cancel_after_t<CompletionToken, Clock, WaitTraits>, Signatures...>
+  : async_result<CompletionToken, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        Signatures...>(
+          declval<detail::initiate_cancel_after<
+            decay_t<Initiation>, Clock, WaitTraits, Signatures...>>(),
+          token.token_, token.timeout_, token.cancel_type_,
+          static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      Signatures...>(
+        detail::initiate_cancel_after<
+          decay_t<Initiation>, Clock, WaitTraits, Signatures...>(
+            static_cast<Initiation&&>(initiation)),
+        token.token_, token.timeout_, token.cancel_type_,
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename CompletionToken, typename Clock,
+    typename WaitTraits, typename Executor, typename... Signatures>
+struct async_result<
+    cancel_after_timer<CompletionToken, Clock, WaitTraits, Executor>,
+    Signatures...>
+  : async_result<CompletionToken, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        Signatures...>(
+          declval<detail::initiate_cancel_after_timer<
+            decay_t<Initiation>, Clock, WaitTraits, Executor, Signatures...>>(),
+          token.token_, &token.timer_, token.timeout_,
+          token.cancel_type_, static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      Signatures...>(
+        detail::initiate_cancel_after_timer<
+          decay_t<Initiation>, Clock, WaitTraits, Executor, Signatures...>(
+            static_cast<Initiation&&>(initiation)),
+        token.token_, &token.timer_, token.timeout_,
+        token.cancel_type_, static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename Clock, typename WaitTraits, typename... Signatures>
+struct async_result<partial_cancel_after<Clock, WaitTraits>, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        const cancel_after_t<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits>&,
+        Signatures...>(
+          static_cast<Initiation&&>(initiation),
+          cancel_after_t<
+            default_completion_token_t<associated_executor_t<Initiation>>,
+            Clock, WaitTraits>(
+              default_completion_token_t<associated_executor_t<Initiation>>{},
+              token.timeout_, token.cancel_type_),
+          static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      const cancel_after_t<
+        default_completion_token_t<associated_executor_t<Initiation>>,
+        Clock, WaitTraits>&,
+      Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        cancel_after_t<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.timeout_, token.cancel_type_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename Clock, typename WaitTraits,
+    typename Executor, typename... Signatures>
+struct async_result<
+    partial_cancel_after_timer<Clock, WaitTraits, Executor>, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        cancel_after_timer<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits, Executor>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.timer_, token.timeout_, token.cancel_type_),
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        cancel_after_timer<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits, Executor>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.timer_, token.timeout_, token.cancel_type_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CANCEL_AFTER_HPP

include/asio/impl/cancel_at.hpp

@@ -0,0 +1,268 @@
+//
+// impl/cancel_at.hpp
+// ~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CANCEL_AT_HPP
+#define ASIO_IMPL_CANCEL_AT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associated_executor.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/timed_cancel_op.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename Initiation, typename Clock,
+    typename WaitTraits, typename... Signatures>
+struct initiate_cancel_at : initiation_base<Initiation>
+{
+  using initiation_base<Initiation>::initiation_base;
+
+  template <typename Handler, typename Duration, typename... Args>
+  void operator()(Handler&& handler,
+      const chrono::time_point<Clock, Duration>& expiry,
+      cancellation_type_t cancel_type, Args&&... args) &&
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits>, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    p.p = new (p.v) op(handler2.value,
+        basic_waitable_timer<Clock, WaitTraits,
+          typename Initiation::executor_type>(this->get_executor(), expiry),
+        cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<Initiation&&>(*this), static_cast<Args&&>(args)...);
+  }
+
+  template <typename Handler, typename Duration, typename... Args>
+  void operator()(Handler&& handler,
+      const chrono::time_point<Clock, Duration>& expiry,
+      cancellation_type_t cancel_type, Args&&... args) const &
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits>, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    p.p = new (p.v) op(handler2.value,
+        basic_waitable_timer<Clock, WaitTraits,
+          typename Initiation::executor_type>(this->get_executor(), expiry),
+        cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<const Initiation&>(*this),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename Initiation, typename Clock,
+    typename WaitTraits, typename Executor, typename... Signatures>
+struct initiate_cancel_at_timer : initiation_base<Initiation>
+{
+  using initiation_base<Initiation>::initiation_base;
+
+  template <typename Handler, typename Duration, typename... Args>
+  void operator()(Handler&& handler,
+      basic_waitable_timer<Clock, WaitTraits, Executor>* timer,
+      const chrono::time_point<Clock, Duration>& expiry,
+      cancellation_type_t cancel_type, Args&&... args) &&
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits, Executor>&, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    timer->expires_at(expiry);
+    p.p = new (p.v) op(handler2.value, *timer, cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<Initiation&&>(*this), static_cast<Args&&>(args)...);
+  }
+
+  template <typename Handler, typename Duration, typename... Args>
+  void operator()(Handler&& handler,
+      basic_waitable_timer<Clock, WaitTraits, Executor>* timer,
+      const chrono::time_point<Clock, Duration>& expiry,
+      cancellation_type_t cancel_type, Args&&... args) const &
+  {
+    using op = detail::timed_cancel_op<decay_t<Handler>,
+        basic_waitable_timer<Clock, WaitTraits, Executor>&, Signatures...>;
+
+    non_const_lvalue<Handler> handler2(handler);
+    typename op::ptr p = { asio::detail::addressof(handler2.value),
+        op::ptr::allocate(handler2.value), 0 };
+    timer->expires_at(expiry);
+    p.p = new (p.v) op(handler2.value, *timer, cancel_type);
+
+    op* o = p.p;
+    p.v = p.p = 0;
+    o->start(static_cast<const Initiation&>(*this),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Clock,
+    typename WaitTraits, typename... Signatures>
+struct async_result<
+    cancel_at_t<CompletionToken, Clock, WaitTraits>, Signatures...>
+  : async_result<CompletionToken, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        Signatures...>(
+          declval<detail::initiate_cancel_at<
+            decay_t<Initiation>, Clock, WaitTraits, Signatures...>>(),
+          token.token_, token.expiry_, token.cancel_type_,
+          static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      Signatures...>(
+        detail::initiate_cancel_at<
+          decay_t<Initiation>, Clock, WaitTraits, Signatures...>(
+            static_cast<Initiation&&>(initiation)),
+        token.token_, token.expiry_, token.cancel_type_,
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename CompletionToken, typename Clock,
+    typename WaitTraits, typename Executor, typename... Signatures>
+struct async_result<
+    cancel_at_timer<CompletionToken, Clock, WaitTraits, Executor>,
+    Signatures...>
+  : async_result<CompletionToken, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        Signatures...>(
+          declval<detail::initiate_cancel_at_timer<
+            decay_t<Initiation>, Clock, WaitTraits, Executor, Signatures...>>(),
+          token.token_, &token.timer_, token.expiry_, token.cancel_type_,
+          static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      Signatures...>(
+        detail::initiate_cancel_at_timer<
+          decay_t<Initiation>, Clock, WaitTraits, Executor, Signatures...>(
+            static_cast<Initiation&&>(initiation)),
+        token.token_, &token.timer_, token.expiry_, token.cancel_type_,
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename Clock, typename WaitTraits, typename... Signatures>
+struct async_result<partial_cancel_at<Clock, WaitTraits>, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        const cancel_at_t<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits>&,
+        Signatures...>(
+          static_cast<Initiation&&>(initiation),
+          cancel_at_t<
+            default_completion_token_t<associated_executor_t<Initiation>>,
+            Clock, WaitTraits>(
+              default_completion_token_t<associated_executor_t<Initiation>>{},
+              token.expiry_, token.cancel_type_),
+          static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      const cancel_at_t<
+        default_completion_token_t<associated_executor_t<Initiation>>,
+        Clock, WaitTraits>&,
+      Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        cancel_at_t<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.expiry_, token.cancel_type_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <typename Clock, typename WaitTraits,
+    typename Executor, typename... Signatures>
+struct async_result<
+    partial_cancel_at_timer<Clock, WaitTraits, Executor>, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        cancel_at_timer<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits, Executor>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.timer_, token.expiry_, token.cancel_type_),
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        cancel_at_timer<
+          default_completion_token_t<associated_executor_t<Initiation>>,
+          Clock, WaitTraits, Executor>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.timer_, token.expiry_, token.cancel_type_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CANCEL_AT_HPP

include/asio/impl/cancellation_signal.ipp

@@ -0,0 +1,96 @@
+//
+// impl/cancellation_signal.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CANCELLATION_SIGNAL_IPP
+#define ASIO_IMPL_CANCELLATION_SIGNAL_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/cancellation_signal.hpp"
+#include "asio/detail/thread_context.hpp"
+#include "asio/detail/thread_info_base.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+cancellation_signal::~cancellation_signal()
+{
+  if (handler_)
+  {
+    std::pair<void*, std::size_t> mem = handler_->destroy();
+    detail::thread_info_base::deallocate(
+        detail::thread_info_base::cancellation_signal_tag(),
+        detail::thread_context::top_of_thread_call_stack(),
+        mem.first, mem.second);
+  }
+}
+
+void cancellation_slot::clear()
+{
+  if (handler_ != 0 && *handler_ != 0)
+  {
+    std::pair<void*, std::size_t> mem = (*handler_)->destroy();
+    detail::thread_info_base::deallocate(
+        detail::thread_info_base::cancellation_signal_tag(),
+        detail::thread_context::top_of_thread_call_stack(),
+        mem.first, mem.second);
+    *handler_ = 0;
+  }
+}
+
+std::pair<void*, std::size_t> cancellation_slot::prepare_memory(
+    std::size_t size, std::size_t align)
+{
+  assert(handler_);
+  std::pair<void*, std::size_t> mem;
+  if (*handler_)
+  {
+    mem = (*handler_)->destroy();
+    *handler_ = 0;
+  }
+  if (size > mem.second
+      || reinterpret_cast<std::size_t>(mem.first) % align != 0)
+  {
+    if (mem.first)
+    {
+      detail::thread_info_base::deallocate(
+          detail::thread_info_base::cancellation_signal_tag(),
+          detail::thread_context::top_of_thread_call_stack(),
+          mem.first, mem.second);
+    }
+    mem.first = detail::thread_info_base::allocate(
+        detail::thread_info_base::cancellation_signal_tag(),
+        detail::thread_context::top_of_thread_call_stack(),
+        size, align);
+    mem.second = size;
+  }
+  return mem;
+}
+
+cancellation_slot::auto_delete_helper::~auto_delete_helper()
+{
+  if (mem.first)
+  {
+    detail::thread_info_base::deallocate(
+        detail::thread_info_base::cancellation_signal_tag(),
+        detail::thread_context::top_of_thread_call_stack(),
+        mem.first, mem.second);
+  }
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CANCELLATION_SIGNAL_IPP

include/asio/impl/co_spawn.hpp

@@ -0,0 +1,455 @@
+//
+// impl/co_spawn.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CO_SPAWN_HPP
+#define ASIO_IMPL_CO_SPAWN_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associated_cancellation_slot.hpp"
+#include "asio/awaitable.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/recycling_allocator.hpp"
+#include "asio/dispatch.hpp"
+#include "asio/execution/outstanding_work.hpp"
+#include "asio/post.hpp"
+#include "asio/prefer.hpp"
+#include "asio/use_awaitable.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename Executor, typename = void>
+class co_spawn_work_guard
+{
+public:
+  typedef decay_t<
+      prefer_result_t<Executor,
+        execution::outstanding_work_t::tracked_t
+      >
+    > executor_type;
+
+  co_spawn_work_guard(const Executor& ex)
+    : executor_(asio::prefer(ex, execution::outstanding_work.tracked))
+  {
+  }
+
+  executor_type get_executor() const noexcept
+  {
+    return executor_;
+  }
+
+private:
+  executor_type executor_;
+};
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+
+template <typename Executor>
+struct co_spawn_work_guard<Executor,
+    enable_if_t<
+      !execution::is_executor<Executor>::value
+    >> : executor_work_guard<Executor>
+{
+  co_spawn_work_guard(const Executor& ex)
+    : executor_work_guard<Executor>(ex)
+  {
+  }
+};
+
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+template <typename Handler, typename Executor,
+    typename Function, typename = void>
+struct co_spawn_state
+{
+  template <typename H, typename F>
+  co_spawn_state(H&& h, const Executor& ex, F&& f)
+    : handler(std::forward<H>(h)),
+      spawn_work(ex),
+      handler_work(asio::get_associated_executor(handler, ex)),
+      function(std::forward<F>(f))
+  {
+  }
+
+  Handler handler;
+  co_spawn_work_guard<Executor> spawn_work;
+  co_spawn_work_guard<associated_executor_t<Handler, Executor>> handler_work;
+  Function function;
+};
+
+template <typename Handler, typename Executor, typename Function>
+struct co_spawn_state<Handler, Executor, Function,
+    enable_if_t<
+      is_same<
+        typename associated_executor<Handler,
+          Executor>::asio_associated_executor_is_unspecialised,
+        void
+      >::value
+    >>
+{
+  template <typename H, typename F>
+  co_spawn_state(H&& h, const Executor& ex, F&& f)
+    : handler(std::forward<H>(h)),
+      handler_work(ex),
+      function(std::forward<F>(f))
+  {
+  }
+
+  Handler handler;
+  co_spawn_work_guard<Executor> handler_work;
+  Function function;
+};
+
+struct co_spawn_dispatch
+{
+  template <typename CompletionToken>
+  auto operator()(CompletionToken&& token) const
+    -> decltype(asio::dispatch(std::forward<CompletionToken>(token)))
+  {
+    return asio::dispatch(std::forward<CompletionToken>(token));
+  }
+};
+
+struct co_spawn_post
+{
+  template <typename CompletionToken>
+  auto operator()(CompletionToken&& token) const
+    -> decltype(asio::post(std::forward<CompletionToken>(token)))
+  {
+    return asio::post(std::forward<CompletionToken>(token));
+  }
+};
+
+template <typename T, typename Handler, typename Executor, typename Function>
+awaitable<awaitable_thread_entry_point, Executor> co_spawn_entry_point(
+    awaitable<T, Executor>*, co_spawn_state<Handler, Executor, Function> s)
+{
+  (void) co_await co_spawn_dispatch{};
+
+  std::exception_ptr e = nullptr;
+  bool done = false;
+#if !defined(ASIO_NO_EXCEPTIONS)
+  try
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  {
+    T t = co_await s.function();
+
+    done = true;
+
+    bool is_launching = (co_await awaitable_thread_is_launching{});
+    if (is_launching)
+    {
+      co_await this_coro::throw_if_cancelled(false);
+      (void) co_await co_spawn_post();
+    }
+
+    (dispatch)(s.handler_work.get_executor(),
+        [handler = std::move(s.handler), t = std::move(t)]() mutable
+        {
+          std::move(handler)(std::exception_ptr(), std::move(t));
+        });
+
+    co_return;
+  }
+#if !defined(ASIO_NO_EXCEPTIONS)
+  catch (...)
+  {
+    if (done)
+      throw;
+
+    e = std::current_exception();
+  }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+
+  bool is_launching = (co_await awaitable_thread_is_launching{});
+  if (is_launching)
+  {
+    co_await this_coro::throw_if_cancelled(false);
+    (void) co_await co_spawn_post();
+  }
+
+  (dispatch)(s.handler_work.get_executor(),
+      [handler = std::move(s.handler), e]() mutable
+      {
+        std::move(handler)(e, T());
+      });
+}
+
+template <typename Handler, typename Executor, typename Function>
+awaitable<awaitable_thread_entry_point, Executor> co_spawn_entry_point(
+    awaitable<void, Executor>*, co_spawn_state<Handler, Executor, Function> s)
+{
+  (void) co_await co_spawn_dispatch{};
+
+  std::exception_ptr e = nullptr;
+#if !defined(ASIO_NO_EXCEPTIONS)
+  try
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  {
+    co_await s.function();
+  }
+#if !defined(ASIO_NO_EXCEPTIONS)
+  catch (...)
+  {
+    e = std::current_exception();
+  }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+
+  bool is_launching = (co_await awaitable_thread_is_launching{});
+  if (is_launching)
+  {
+    co_await this_coro::throw_if_cancelled(false);
+    (void) co_await co_spawn_post();
+  }
+
+  (dispatch)(s.handler_work.get_executor(),
+      [handler = std::move(s.handler), e]() mutable
+      {
+        std::move(handler)(e);
+      });
+}
+
+template <typename T, typename Executor>
+class awaitable_as_function
+{
+public:
+  explicit awaitable_as_function(awaitable<T, Executor>&& a)
+    : awaitable_(std::move(a))
+  {
+  }
+
+  awaitable<T, Executor> operator()()
+  {
+    return std::move(awaitable_);
+  }
+
+private:
+  awaitable<T, Executor> awaitable_;
+};
+
+template <typename Handler, typename Executor, typename = void>
+class co_spawn_cancellation_handler
+{
+public:
+  co_spawn_cancellation_handler(const Handler&, const Executor& ex)
+    : signal_(detail::allocate_shared<cancellation_signal>(
+          detail::recycling_allocator<cancellation_signal,
+            detail::thread_info_base::cancellation_signal_tag>())),
+      ex_(ex)
+  {
+  }
+
+  cancellation_slot slot()
+  {
+    return signal_->slot();
+  }
+
+  void operator()(cancellation_type_t type)
+  {
+    shared_ptr<cancellation_signal> sig = signal_;
+    asio::dispatch(ex_, [sig, type]{ sig->emit(type); });
+  }
+
+private:
+  shared_ptr<cancellation_signal> signal_;
+  Executor ex_;
+};
+
+template <typename Handler, typename Executor>
+class co_spawn_cancellation_handler<Handler, Executor,
+    enable_if_t<
+      is_same<
+        typename associated_executor<Handler,
+          Executor>::asio_associated_executor_is_unspecialised,
+        void
+      >::value
+    >>
+{
+public:
+  co_spawn_cancellation_handler(const Handler&, const Executor&)
+  {
+  }
+
+  cancellation_slot slot()
+  {
+    return signal_.slot();
+  }
+
+  void operator()(cancellation_type_t type)
+  {
+    signal_.emit(type);
+  }
+
+private:
+  cancellation_signal signal_;
+};
+
+template <typename Executor>
+class initiate_co_spawn
+{
+public:
+  typedef Executor executor_type;
+
+  template <typename OtherExecutor>
+  explicit initiate_co_spawn(const OtherExecutor& ex)
+    : ex_(ex)
+  {
+  }
+
+  executor_type get_executor() const noexcept
+  {
+    return ex_;
+  }
+
+  template <typename Handler, typename F>
+  void operator()(Handler&& handler, F&& f) const
+  {
+    typedef result_of_t<F()> awaitable_type;
+    typedef decay_t<Handler> handler_type;
+    typedef decay_t<F> function_type;
+    typedef co_spawn_cancellation_handler<
+      handler_type, Executor> cancel_handler_type;
+
+    auto slot = asio::get_associated_cancellation_slot(handler);
+    cancel_handler_type* cancel_handler = slot.is_connected()
+      ? &slot.template emplace<cancel_handler_type>(handler, ex_)
+      : nullptr;
+
+    cancellation_slot proxy_slot(
+        cancel_handler
+          ? cancel_handler->slot()
+          : cancellation_slot());
+
+    cancellation_state cancel_state(proxy_slot);
+
+    auto a = (co_spawn_entry_point)(static_cast<awaitable_type*>(nullptr),
+        co_spawn_state<handler_type, Executor, function_type>(
+          std::forward<Handler>(handler), ex_, std::forward<F>(f)));
+    awaitable_handler<executor_type, void>(std::move(a),
+        ex_, proxy_slot, cancel_state).launch();
+  }
+
+private:
+  Executor ex_;
+};
+
+} // namespace detail
+
+template <typename Executor, typename T, typename AwaitableExecutor,
+    ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr, T)) CompletionToken>
+inline ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr, T))
+co_spawn(const Executor& ex,
+    awaitable<T, AwaitableExecutor> a, CompletionToken&& token,
+    constraint_t<
+      (is_executor<Executor>::value || execution::is_executor<Executor>::value)
+        && is_convertible<Executor, AwaitableExecutor>::value
+    >)
+{
+  return async_initiate<CompletionToken, void(std::exception_ptr, T)>(
+      detail::initiate_co_spawn<AwaitableExecutor>(AwaitableExecutor(ex)),
+      token, detail::awaitable_as_function<T, AwaitableExecutor>(std::move(a)));
+}
+
+template <typename Executor, typename AwaitableExecutor,
+    ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr)) CompletionToken>
+inline ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr))
+co_spawn(const Executor& ex,
+    awaitable<void, AwaitableExecutor> a, CompletionToken&& token,
+    constraint_t<
+      (is_executor<Executor>::value || execution::is_executor<Executor>::value)
+        && is_convertible<Executor, AwaitableExecutor>::value
+    >)
+{
+  return async_initiate<CompletionToken, void(std::exception_ptr)>(
+      detail::initiate_co_spawn<AwaitableExecutor>(AwaitableExecutor(ex)),
+      token, detail::awaitable_as_function<
+        void, AwaitableExecutor>(std::move(a)));
+}
+
+template <typename ExecutionContext, typename T, typename AwaitableExecutor,
+    ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr, T)) CompletionToken>
+inline ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr, T))
+co_spawn(ExecutionContext& ctx,
+    awaitable<T, AwaitableExecutor> a, CompletionToken&& token,
+    constraint_t<
+      is_convertible<ExecutionContext&, execution_context&>::value
+        && is_convertible<typename ExecutionContext::executor_type,
+          AwaitableExecutor>::value
+    >)
+{
+  return (co_spawn)(ctx.get_executor(), std::move(a),
+      std::forward<CompletionToken>(token));
+}
+
+template <typename ExecutionContext, typename AwaitableExecutor,
+    ASIO_COMPLETION_TOKEN_FOR(
+      void(std::exception_ptr)) CompletionToken>
+inline ASIO_INITFN_AUTO_RESULT_TYPE(
+    CompletionToken, void(std::exception_ptr))
+co_spawn(ExecutionContext& ctx,
+    awaitable<void, AwaitableExecutor> a, CompletionToken&& token,
+    constraint_t<
+      is_convertible<ExecutionContext&, execution_context&>::value
+        && is_convertible<typename ExecutionContext::executor_type,
+          AwaitableExecutor>::value
+    >)
+{
+  return (co_spawn)(ctx.get_executor(), std::move(a),
+      std::forward<CompletionToken>(token));
+}
+
+template <typename Executor, typename F,
+    ASIO_COMPLETION_TOKEN_FOR(typename detail::awaitable_signature<
+      result_of_t<F()>>::type) CompletionToken>
+inline ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken,
+    typename detail::awaitable_signature<result_of_t<F()>>::type)
+co_spawn(const Executor& ex, F&& f, CompletionToken&& token,
+    constraint_t<
+      is_executor<Executor>::value || execution::is_executor<Executor>::value
+    >)
+{
+  return async_initiate<CompletionToken,
+    typename detail::awaitable_signature<result_of_t<F()>>::type>(
+      detail::initiate_co_spawn<
+        typename result_of_t<F()>::executor_type>(ex),
+      token, std::forward<F>(f));
+}
+
+template <typename ExecutionContext, typename F,
+    ASIO_COMPLETION_TOKEN_FOR(typename detail::awaitable_signature<
+      result_of_t<F()>>::type) CompletionToken>
+inline ASIO_INITFN_AUTO_RESULT_TYPE(CompletionToken,
+    typename detail::awaitable_signature<result_of_t<F()>>::type)
+co_spawn(ExecutionContext& ctx, F&& f, CompletionToken&& token,
+    constraint_t<
+      is_convertible<ExecutionContext&, execution_context&>::value
+    >)
+{
+  return (co_spawn)(ctx.get_executor(), std::forward<F>(f),
+      std::forward<CompletionToken>(token));
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CO_SPAWN_HPP

include/asio/impl/config.hpp

@@ -0,0 +1,102 @@
+//
+// impl/config.hpp
+// ~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CONFIG_HPP
+#define ASIO_IMPL_CONFIG_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <cerrno>
+#include <cstdlib>
+#include <limits>
+#include <stdexcept>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename T>
+T config_get(const config_service& service, const char* section,
+    const char* key_name, T default_value, false_type /*is_bool*/)
+{
+  if (is_unsigned<T>::value)
+  {
+    char buf[std::numeric_limits<unsigned long long>::digits10
+        + 1 /* sign */ + 1 /* partial digit */ + 1 /* NUL */];
+    if (const char* str = service.get_value(
+          section, key_name, buf, sizeof(buf)))
+    {
+      char* end = nullptr;
+      errno = 0;
+      unsigned long long result = std::strtoull(str, &end, 0);
+      if (errno == ERANGE
+          || result > static_cast<unsigned long long>(
+            (std::numeric_limits<T>::max)()))
+        detail::throw_exception(std::out_of_range("config out of range"));
+      return static_cast<T>(result);
+    }
+  }
+  else
+  {
+    char buf[std::numeric_limits<unsigned long long>::digits10
+        + 1 /* sign */ + 1 /* partial digit */ + 1 /* NUL */];
+    if (const char* str = service.get_value(
+          section, key_name, buf, sizeof(buf)))
+    {
+      char* end = nullptr;
+      errno = 0;
+      long long result = std::strtoll(str, &end, 0);
+      if (errno == ERANGE || result < (std::numeric_limits<T>::min)()
+          || result > (std::numeric_limits<T>::max)())
+        detail::throw_exception(std::out_of_range("config out of range"));
+      return static_cast<T>(result);
+    }
+  }
+  return default_value;
+}
+
+template <typename T>
+T config_get(const config_service& service, const char* section,
+    const char* key_name, T default_value, true_type /*is_bool*/)
+{
+  char buf[std::numeric_limits<unsigned long long>::digits10
+      + 1 /* sign */ + 1 /* partial digit */ + 1 /* NUL */];
+  if (const char* str = service.get_value(
+        section, key_name, buf, sizeof(buf)))
+  {
+    char* end = nullptr;
+    errno = 0;
+    unsigned long long result = std::strtoll(str, &end, 0);
+    if (errno == ERANGE || (result != 0 && result != 1))
+      detail::throw_exception(std::out_of_range("config out of range"));
+    return static_cast<T>(result != 0);
+  }
+  return default_value;
+}
+
+} // namespace detail
+
+template <typename T>
+constraint_t<is_integral<T>::value, T>
+config::get(const char* section, const char* key_name, T default_value) const
+{
+  return detail::config_get(service_, section,
+      key_name, default_value, is_same<T, bool>());
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CONFIG_HPP

include/asio/impl/config.ipp

@@ -0,0 +1,345 @@
+//
+// impl/config.ipp
+// ~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CONFIG_IPP
+#define ASIO_IMPL_CONFIG_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/config.hpp"
+#include "asio/detail/concurrency_hint.hpp"
+#include <cctype>
+#include <cstdio>
+#include <cstring>
+#include <cstdlib>
+#include <vector>
+#include <utility>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+config_service::config_service(execution_context& ctx)
+  : detail::execution_context_service_base<config_service>(ctx)
+{
+}
+
+void config_service::shutdown()
+{
+}
+
+const char* config_service::get_value(const char* /*section*/,
+    const char* /*key_name*/, char* /*value*/, std::size_t /*value_len*/) const
+{
+  return nullptr;
+}
+
+namespace detail {
+
+class config_from_concurrency_hint_service : public config_service
+{
+public:
+  explicit config_from_concurrency_hint_service(
+      execution_context& ctx, int concurrency_hint)
+    : config_service(ctx),
+      concurrency_hint_(concurrency_hint)
+  {
+  }
+
+  const char* get_value(const char* section, const char* key_name,
+      char* value, std::size_t value_len) const override
+  {
+    if (std::strcmp(section, "scheduler") == 0)
+    {
+      if (std::strcmp(key_name, "concurrency_hint") == 0)
+      {
+        if (ASIO_CONCURRENCY_HINT_IS_SPECIAL(concurrency_hint_))
+        {
+          return
+            !ASIO_CONCURRENCY_HINT_IS_LOCKING(
+              SCHEDULER, concurrency_hint_) ||
+            !ASIO_CONCURRENCY_HINT_IS_LOCKING(
+                REACTOR_IO, concurrency_hint_) ? "1" : "-1";
+        }
+        else
+        {
+          std::snprintf(value, value_len, "%d", concurrency_hint_);
+          return value;
+        }
+      }
+      else if (std::strcmp(key_name, "locking") == 0)
+      {
+        return ASIO_CONCURRENCY_HINT_IS_LOCKING(
+            SCHEDULER, concurrency_hint_) ? "1" : "0";
+      }
+    }
+    else if (std::strcmp(section, "reactor") == 0)
+    {
+      if (std::strcmp(key_name, "io_locking") == 0)
+      {
+        return ASIO_CONCURRENCY_HINT_IS_LOCKING(
+            REACTOR_IO, concurrency_hint_) ? "1" : "0";
+      }
+      else if (std::strcmp(key_name, "registration_locking") == 0)
+      {
+        return ASIO_CONCURRENCY_HINT_IS_LOCKING(
+            REACTOR_REGISTRATION, concurrency_hint_) ? "1" : "0";
+      }
+    }
+    return nullptr;
+  }
+
+private:
+  int concurrency_hint_;
+};
+
+} // namespace detail
+
+config_from_concurrency_hint::config_from_concurrency_hint()
+  : concurrency_hint_(ASIO_CONCURRENCY_HINT_DEFAULT)
+{
+}
+
+void config_from_concurrency_hint::make(execution_context& ctx) const
+{
+  (void)make_service<detail::config_from_concurrency_hint_service>(ctx,
+      concurrency_hint_ == 1
+        ? ASIO_CONCURRENCY_HINT_1 : concurrency_hint_);
+}
+
+namespace detail {
+
+class config_from_string_service : public config_service
+{
+public:
+  config_from_string_service(execution_context& ctx,
+      std::string s, std::string prefix)
+    : config_service(ctx),
+      string_(static_cast<std::string&&>(s)),
+      prefix_(static_cast<std::string&&>(prefix))
+  {
+    enum
+    {
+      expecting_key_name,
+      key_name,
+      expecting_equals,
+      expecting_value,
+      value,
+      expecting_eol
+    } state = expecting_key_name;
+    std::pair<const char*, const char*> entry{};
+
+    for (char& c : string_)
+    {
+      switch (state)
+      {
+      case expecting_key_name:
+        switch (c)
+        {
+        case ' ': case '\t': case '\n':
+          break;
+        case '#':
+          state = expecting_eol;
+          break;
+        default:
+          entry.first = &c;
+          state = key_name;
+          break;
+        }
+        break;
+      case key_name:
+        switch (c)
+        {
+        case ' ': case '\t':
+          c = 0;
+          state = expecting_equals;
+          break;
+        case '=':
+          c = 0;
+          state = expecting_value;
+          break;
+        case '\n':
+          entry.first = nullptr;
+          state = expecting_key_name;
+          break;
+        case '#':
+          entry.first = nullptr;
+          state = expecting_eol;
+          break;
+        default:
+          break;
+        }
+        break;
+      case expecting_equals:
+        switch (c)
+        {
+        case ' ': case '\t':
+          break;
+        case '=':
+          state = expecting_value;
+          break;
+        case '\n':
+          entry.first = nullptr;
+          state = expecting_key_name;
+          break;
+        default:
+          entry.first = nullptr;
+          state = expecting_eol;
+          break;
+        }
+        break;
+      case expecting_value:
+        switch (c)
+        {
+        case ' ': case '\t':
+          break;
+        case '\n':
+          entry.first = nullptr;
+          state = expecting_key_name;
+          break;
+        case '#':
+          entry.first = nullptr;
+          state = expecting_eol;
+          break;
+        default:
+          entry.second = &c;
+          state = value;
+          break;
+        }
+        break;
+      case value:
+        switch (c)
+        {
+        case '\n':
+          c = 0;
+          entries_.push_back(entry);
+          entry.first = entry.second = nullptr;
+          state = expecting_key_name;
+          break;
+        case '#':
+          c = 0;
+          entries_.push_back(entry);
+          entry.first = entry.second = nullptr;
+          state = expecting_eol;
+          break;
+        default:
+          break;
+        }
+        break;
+      case expecting_eol:
+        switch (c)
+        {
+        case '\n':
+          state = expecting_key_name;
+          break;
+        default:
+          break;
+        }
+        break;
+      }
+    }
+    if (entry.first && entry.second)
+      entries_.push_back(entry);
+  }
+
+  const char* get_value(const char* section, const char* key_name,
+      char* /*value*/, std::size_t /*value_len*/) const override
+  {
+    std::string entry_key;
+    entry_key.reserve(prefix_.length() + 1
+        + std::strlen(section) + 1
+        + std::strlen(key_name) + 1);
+    entry_key.append(prefix_);
+    if (!entry_key.empty())
+      entry_key.append(".");
+    entry_key.append(section);
+    entry_key.append(".");
+    entry_key.append(key_name);
+    for (const std::pair<const char*, const char*>& entry : entries_)
+      if (entry_key == entry.first)
+        return entry.second;
+    return nullptr;
+  }
+
+private:
+  std::string string_;
+  std::string prefix_;
+  std::vector<std::pair<const char*, const char*>> entries_;
+};
+
+} // namespace detail
+
+void config_from_string::make(execution_context& ctx) const
+{
+  (void)make_service<detail::config_from_string_service>(ctx, string_, prefix_);
+}
+
+namespace detail {
+
+#if defined(ASIO_MSVC)
+# pragma warning (push)
+# pragma warning (disable:4996) // suppress unsafe warning for std::getenv
+#endif // defined(ASIO_MSVC)
+
+class config_from_env_service : public config_service
+{
+public:
+  explicit config_from_env_service(
+      execution_context& ctx, std::string prefix)
+    : config_service(ctx),
+      prefix_(static_cast<std::string&&>(prefix))
+  {
+  }
+
+  const char* get_value(const char* section, const char* key_name,
+      char* /*value*/, std::size_t /*value_len*/) const override
+  {
+    std::string env_var;
+    env_var.reserve(prefix_.length() + 1
+        + std::strlen(section) + 1
+        + std::strlen(key_name) + 1);
+    env_var.append(prefix_);
+    if (!env_var.empty())
+      env_var.append("_");
+    env_var.append(section);
+    env_var.append("_");
+    env_var.append(key_name);
+    for (char& c : env_var)
+      c = static_cast<char>(std::toupper(static_cast<unsigned char>(c)));
+    return std::getenv(env_var.c_str());
+  }
+
+private:
+  std::string prefix_;
+};
+
+#if defined(ASIO_MSVC)
+# pragma warning (pop)
+#endif // defined(ASIO_MSVC)
+
+} // namespace detail
+
+config_from_env::config_from_env()
+  : prefix_("asio")
+{
+}
+
+void config_from_env::make(execution_context& ctx) const
+{
+  (void)make_service<detail::config_from_env_service>(ctx, prefix_);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CONFIG_IPP

include/asio/impl/connect.hpp

@@ -0,0 +1,645 @@
+//
+// impl/connect.hpp
+// ~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CONNECT_HPP
+#define ASIO_IMPL_CONNECT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <algorithm>
+#include "asio/associator.hpp"
+#include "asio/detail/base_from_cancellation_state.hpp"
+#include "asio/detail/bind_handler.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_tracking.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/throw_error.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/error.hpp"
+#include "asio/post.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail
+{
+  template <typename Protocol, typename Iterator>
+  inline typename Protocol::endpoint deref_connect_result(
+      Iterator iter, asio::error_code& ec)
+  {
+    return ec ? typename Protocol::endpoint() : *iter;
+  }
+
+  template <typename ConnectCondition, typename Iterator>
+  inline Iterator call_connect_condition(ConnectCondition& connect_condition,
+      const asio::error_code& ec, Iterator next, Iterator end,
+      constraint_t<
+        is_same<
+          result_of_t<ConnectCondition(asio::error_code, Iterator)>,
+          Iterator
+        >::value
+      > = 0)
+  {
+    if (next != end)
+      return connect_condition(ec, next);
+    return end;
+  }
+
+  template <typename ConnectCondition, typename Iterator>
+  inline Iterator call_connect_condition(ConnectCondition& connect_condition,
+      const asio::error_code& ec, Iterator next, Iterator end,
+      constraint_t<
+        is_same<
+          result_of_t<ConnectCondition(asio::error_code,
+            decltype(*declval<Iterator>()))>,
+          bool
+        >::value
+      > = 0)
+  {
+    for (;next != end; ++next)
+      if (connect_condition(ec, *next))
+        return next;
+    return end;
+  }
+} // namespace detail
+
+template <typename Protocol, typename Executor, typename EndpointSequence>
+typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
+    const EndpointSequence& endpoints,
+    constraint_t<
+      is_endpoint_sequence<EndpointSequence>::value
+    >)
+{
+  asio::error_code ec;
+  typename Protocol::endpoint result = connect(s, endpoints, ec);
+  asio::detail::throw_error(ec, "connect");
+  return result;
+}
+
+template <typename Protocol, typename Executor, typename EndpointSequence>
+typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
+    const EndpointSequence& endpoints, asio::error_code& ec,
+    constraint_t<
+      is_endpoint_sequence<EndpointSequence>::value
+    >)
+{
+  return detail::deref_connect_result<Protocol>(
+      connect(s, endpoints.begin(), endpoints.end(),
+        detail::default_connect_condition(), ec), ec);
+}
+
+template <typename Protocol, typename Executor, typename Iterator>
+Iterator connect(basic_socket<Protocol, Executor>& s,
+    Iterator begin, Iterator end)
+{
+  asio::error_code ec;
+  Iterator result = connect(s, begin, end, ec);
+  asio::detail::throw_error(ec, "connect");
+  return result;
+}
+
+template <typename Protocol, typename Executor, typename Iterator>
+inline Iterator connect(basic_socket<Protocol, Executor>& s,
+    Iterator begin, Iterator end, asio::error_code& ec)
+{
+  return connect(s, begin, end, detail::default_connect_condition(), ec);
+}
+
+template <typename Protocol, typename Executor,
+    typename EndpointSequence, typename ConnectCondition>
+typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
+    const EndpointSequence& endpoints, ConnectCondition connect_condition,
+    constraint_t<
+      is_endpoint_sequence<EndpointSequence>::value
+    >,
+    constraint_t<
+      is_connect_condition<ConnectCondition,
+        decltype(declval<const EndpointSequence&>().begin())>::value
+    >)
+{
+  asio::error_code ec;
+  typename Protocol::endpoint result = connect(
+      s, endpoints, connect_condition, ec);
+  asio::detail::throw_error(ec, "connect");
+  return result;
+}
+
+template <typename Protocol, typename Executor,
+    typename EndpointSequence, typename ConnectCondition>
+typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
+    const EndpointSequence& endpoints, ConnectCondition connect_condition,
+    asio::error_code& ec,
+    constraint_t<
+      is_endpoint_sequence<EndpointSequence>::value
+    >,
+    constraint_t<
+      is_connect_condition<ConnectCondition,
+        decltype(declval<const EndpointSequence&>().begin())>::value
+    >)
+{
+  return detail::deref_connect_result<Protocol>(
+      connect(s, endpoints.begin(), endpoints.end(),
+        connect_condition, ec), ec);
+}
+
+template <typename Protocol, typename Executor,
+    typename Iterator, typename ConnectCondition>
+Iterator connect(basic_socket<Protocol, Executor>& s, Iterator begin,
+    Iterator end, ConnectCondition connect_condition,
+    constraint_t<
+      is_connect_condition<ConnectCondition, Iterator>::value
+    >)
+{
+  asio::error_code ec;
+  Iterator result = connect(s, begin, end, connect_condition, ec);
+  asio::detail::throw_error(ec, "connect");
+  return result;
+}
+
+template <typename Protocol, typename Executor,
+    typename Iterator, typename ConnectCondition>
+Iterator connect(basic_socket<Protocol, Executor>& s, Iterator begin,
+    Iterator end, ConnectCondition connect_condition,
+    asio::error_code& ec,
+    constraint_t<
+      is_connect_condition<ConnectCondition, Iterator>::value
+    >)
+{
+  ec = asio::error_code();
+
+  for (Iterator iter = begin; iter != end; ++iter)
+  {
+    iter = (detail::call_connect_condition(connect_condition, ec, iter, end));
+    if (iter != end)
+    {
+      s.close(ec);
+      s.connect(*iter, ec);
+      if (!ec)
+        return iter;
+    }
+    else
+      break;
+  }
+
+  if (!ec)
+    ec = asio::error::not_found;
+
+  return end;
+}
+
+namespace detail
+{
+  // Enable the empty base class optimisation for the connect condition.
+  template <typename ConnectCondition>
+  class base_from_connect_condition
+  {
+  protected:
+    explicit base_from_connect_condition(
+        const ConnectCondition& connect_condition)
+      : connect_condition_(connect_condition)
+    {
+    }
+
+    template <typename Iterator>
+    void check_condition(const asio::error_code& ec,
+        Iterator& iter, Iterator& end)
+    {
+      iter = detail::call_connect_condition(connect_condition_, ec, iter, end);
+    }
+
+  private:
+    ConnectCondition connect_condition_;
+  };
+
+  // The default_connect_condition implementation is essentially a no-op. This
+  // template specialisation lets us eliminate all costs associated with it.
+  template <>
+  class base_from_connect_condition<default_connect_condition>
+  {
+  protected:
+    explicit base_from_connect_condition(const default_connect_condition&)
+    {
+    }
+
+    template <typename Iterator>
+    void check_condition(const asio::error_code&, Iterator&, Iterator&)
+    {
+    }
+  };
+
+  template <typename Protocol, typename Executor, typename EndpointSequence,
+      typename ConnectCondition, typename RangeConnectHandler>
+  class range_connect_op
+    : public base_from_cancellation_state<RangeConnectHandler>,
+      base_from_connect_condition<ConnectCondition>
+  {
+  public:
+    range_connect_op(basic_socket<Protocol, Executor>& sock,
+        const EndpointSequence& endpoints,
+        const ConnectCondition& connect_condition,
+        RangeConnectHandler& handler)
+      : base_from_cancellation_state<RangeConnectHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_connect_condition<ConnectCondition>(connect_condition),
+        socket_(sock),
+        endpoints_(endpoints),
+        index_(0),
+        start_(0),
+        handler_(static_cast<RangeConnectHandler&&>(handler))
+    {
+    }
+
+    range_connect_op(const range_connect_op& other)
+      : base_from_cancellation_state<RangeConnectHandler>(other),
+        base_from_connect_condition<ConnectCondition>(other),
+        socket_(other.socket_),
+        endpoints_(other.endpoints_),
+        index_(other.index_),
+        start_(other.start_),
+        handler_(other.handler_)
+    {
+    }
+
+    range_connect_op(range_connect_op&& other)
+      : base_from_cancellation_state<RangeConnectHandler>(
+          static_cast<base_from_cancellation_state<RangeConnectHandler>&&>(
+            other)),
+        base_from_connect_condition<ConnectCondition>(other),
+        socket_(other.socket_),
+        endpoints_(other.endpoints_),
+        index_(other.index_),
+        start_(other.start_),
+        handler_(static_cast<RangeConnectHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec, int start = 0)
+    {
+      this->process(ec, start,
+          const_cast<const EndpointSequence&>(endpoints_).begin(),
+          const_cast<const EndpointSequence&>(endpoints_).end());
+    }
+
+  //private:
+    template <typename Iterator>
+    void process(asio::error_code ec,
+        int start, Iterator begin, Iterator end)
+    {
+      Iterator iter = begin;
+      std::advance(iter, index_);
+
+      switch (start_ = start)
+      {
+        case 1:
+        for (;;)
+        {
+          this->check_condition(ec, iter, end);
+          index_ = std::distance(begin, iter);
+
+          if (iter != end)
+          {
+            socket_.close(ec);
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
+            socket_.async_connect(*iter,
+                static_cast<range_connect_op&&>(*this));
+            return;
+          }
+
+          if (start)
+          {
+            ec = asio::error::not_found;
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
+            asio::post(socket_.get_executor(),
+                detail::bind_handler(
+                  static_cast<range_connect_op&&>(*this), ec));
+            return;
+          }
+
+          /* fall-through */ default:
+
+          if (iter == end)
+            break;
+
+          if (!socket_.is_open())
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+
+          if (!ec)
+            break;
+
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+
+          ++iter;
+          ++index_;
+        }
+
+        static_cast<RangeConnectHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const typename Protocol::endpoint&>(
+              ec || iter == end ? typename Protocol::endpoint() : *iter));
+      }
+    }
+
+    basic_socket<Protocol, Executor>& socket_;
+    EndpointSequence endpoints_;
+    std::size_t index_;
+    int start_;
+    RangeConnectHandler handler_;
+  };
+
+  template <typename Protocol, typename Executor, typename EndpointSequence,
+      typename ConnectCondition, typename RangeConnectHandler>
+  inline bool asio_handler_is_continuation(
+      range_connect_op<Protocol, Executor, EndpointSequence,
+        ConnectCondition, RangeConnectHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+  }
+
+  template <typename Protocol, typename Executor>
+  class initiate_async_range_connect
+  {
+  public:
+    typedef Executor executor_type;
+
+    explicit initiate_async_range_connect(basic_socket<Protocol, Executor>& s)
+      : socket_(s)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return socket_.get_executor();
+    }
+
+    template <typename RangeConnectHandler,
+        typename EndpointSequence, typename ConnectCondition>
+    void operator()(RangeConnectHandler&& handler,
+        const EndpointSequence& endpoints,
+        const ConnectCondition& connect_condition) const
+    {
+      // If you get an error on the following line it means that your
+      // handler does not meet the documented type requirements for an
+      // RangeConnectHandler.
+      ASIO_RANGE_CONNECT_HANDLER_CHECK(RangeConnectHandler,
+          handler, typename Protocol::endpoint) type_check;
+
+      non_const_lvalue<RangeConnectHandler> handler2(handler);
+      range_connect_op<Protocol, Executor, EndpointSequence, ConnectCondition,
+        decay_t<RangeConnectHandler>>(socket_, endpoints,
+          connect_condition, handler2.value)(asio::error_code(), 1);
+    }
+
+  private:
+    basic_socket<Protocol, Executor>& socket_;
+  };
+
+  template <typename Protocol, typename Executor, typename Iterator,
+      typename ConnectCondition, typename IteratorConnectHandler>
+  class iterator_connect_op
+    : public base_from_cancellation_state<IteratorConnectHandler>,
+      base_from_connect_condition<ConnectCondition>
+  {
+  public:
+    iterator_connect_op(basic_socket<Protocol, Executor>& sock,
+        const Iterator& begin, const Iterator& end,
+        const ConnectCondition& connect_condition,
+        IteratorConnectHandler& handler)
+      : base_from_cancellation_state<IteratorConnectHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_connect_condition<ConnectCondition>(connect_condition),
+        socket_(sock),
+        iter_(begin),
+        end_(end),
+        start_(0),
+        handler_(static_cast<IteratorConnectHandler&&>(handler))
+    {
+    }
+
+    iterator_connect_op(const iterator_connect_op& other)
+      : base_from_cancellation_state<IteratorConnectHandler>(other),
+        base_from_connect_condition<ConnectCondition>(other),
+        socket_(other.socket_),
+        iter_(other.iter_),
+        end_(other.end_),
+        start_(other.start_),
+        handler_(other.handler_)
+    {
+    }
+
+    iterator_connect_op(iterator_connect_op&& other)
+      : base_from_cancellation_state<IteratorConnectHandler>(
+          static_cast<base_from_cancellation_state<IteratorConnectHandler>&&>(
+            other)),
+        base_from_connect_condition<ConnectCondition>(other),
+        socket_(other.socket_),
+        iter_(other.iter_),
+        end_(other.end_),
+        start_(other.start_),
+        handler_(static_cast<IteratorConnectHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec, int start = 0)
+    {
+      switch (start_ = start)
+      {
+        case 1:
+        for (;;)
+        {
+          this->check_condition(ec, iter_, end_);
+
+          if (iter_ != end_)
+          {
+            socket_.close(ec);
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
+            socket_.async_connect(*iter_,
+                static_cast<iterator_connect_op&&>(*this));
+            return;
+          }
+
+          if (start)
+          {
+            ec = asio::error::not_found;
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_connect"));
+            asio::post(socket_.get_executor(),
+                detail::bind_handler(
+                  static_cast<iterator_connect_op&&>(*this), ec));
+            return;
+          }
+
+          /* fall-through */ default:
+
+          if (iter_ == end_)
+            break;
+
+          if (!socket_.is_open())
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+
+          if (!ec)
+            break;
+
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+
+          ++iter_;
+        }
+
+        static_cast<IteratorConnectHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const Iterator&>(iter_));
+      }
+    }
+
+  //private:
+    basic_socket<Protocol, Executor>& socket_;
+    Iterator iter_;
+    Iterator end_;
+    int start_;
+    IteratorConnectHandler handler_;
+  };
+
+  template <typename Protocol, typename Executor, typename Iterator,
+      typename ConnectCondition, typename IteratorConnectHandler>
+  inline bool asio_handler_is_continuation(
+      iterator_connect_op<Protocol, Executor, Iterator,
+        ConnectCondition, IteratorConnectHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+  }
+
+  template <typename Protocol, typename Executor>
+  class initiate_async_iterator_connect
+  {
+  public:
+    typedef Executor executor_type;
+
+    explicit initiate_async_iterator_connect(
+        basic_socket<Protocol, Executor>& s)
+      : socket_(s)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return socket_.get_executor();
+    }
+
+    template <typename IteratorConnectHandler,
+        typename Iterator, typename ConnectCondition>
+    void operator()(IteratorConnectHandler&& handler,
+        Iterator begin, Iterator end,
+        const ConnectCondition& connect_condition) const
+    {
+      // If you get an error on the following line it means that your
+      // handler does not meet the documented type requirements for an
+      // IteratorConnectHandler.
+      ASIO_ITERATOR_CONNECT_HANDLER_CHECK(
+          IteratorConnectHandler, handler, Iterator) type_check;
+
+      non_const_lvalue<IteratorConnectHandler> handler2(handler);
+      iterator_connect_op<Protocol, Executor, Iterator, ConnectCondition,
+        decay_t<IteratorConnectHandler>>(socket_, begin, end,
+          connect_condition, handler2.value)(asio::error_code(), 1);
+    }
+
+  private:
+    basic_socket<Protocol, Executor>& socket_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename Protocol, typename Executor, typename EndpointSequence,
+    typename ConnectCondition, typename RangeConnectHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::range_connect_op<Protocol, Executor,
+      EndpointSequence, ConnectCondition, RangeConnectHandler>,
+    DefaultCandidate>
+  : Associator<RangeConnectHandler, DefaultCandidate>
+{
+  static typename Associator<RangeConnectHandler, DefaultCandidate>::type get(
+      const detail::range_connect_op<Protocol, Executor, EndpointSequence,
+        ConnectCondition, RangeConnectHandler>& h) noexcept
+  {
+    return Associator<RangeConnectHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::range_connect_op<Protocol, Executor,
+        EndpointSequence, ConnectCondition, RangeConnectHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(
+      Associator<RangeConnectHandler, DefaultCandidate>::get(
+        h.handler_, c))
+  {
+    return Associator<RangeConnectHandler, DefaultCandidate>::get(
+        h.handler_, c);
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Protocol, typename Executor, typename Iterator,
+    typename ConnectCondition, typename IteratorConnectHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::iterator_connect_op<Protocol, Executor,
+      Iterator, ConnectCondition, IteratorConnectHandler>,
+    DefaultCandidate>
+  : Associator<IteratorConnectHandler, DefaultCandidate>
+{
+  static typename Associator<IteratorConnectHandler, DefaultCandidate>::type
+  get(const detail::iterator_connect_op<Protocol, Executor, Iterator,
+        ConnectCondition, IteratorConnectHandler>& h) noexcept
+  {
+    return Associator<IteratorConnectHandler, DefaultCandidate>::get(
+        h.handler_);
+  }
+
+  static auto get(
+      const detail::iterator_connect_op<Protocol, Executor,
+        Iterator, ConnectCondition, IteratorConnectHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(
+      Associator<IteratorConnectHandler, DefaultCandidate>::get(
+        h.handler_, c))
+  {
+    return Associator<IteratorConnectHandler, DefaultCandidate>::get(
+        h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CONNECT_HPP

include/asio/impl/connect_pipe.hpp

@@ -0,0 +1,73 @@
+//
+// impl/connect_pipe.hpp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CONNECT_PIPE_HPP
+#define ASIO_IMPL_CONNECT_PIPE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_PIPE)
+
+#include "asio/connect_pipe.hpp"
+#include "asio/detail/throw_error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+template <typename Executor1, typename Executor2>
+void connect_pipe(basic_readable_pipe<Executor1>& read_end,
+    basic_writable_pipe<Executor2>& write_end)
+{
+  asio::error_code ec;
+  asio::connect_pipe(read_end, write_end, ec);
+  asio::detail::throw_error(ec, "connect_pipe");
+}
+
+template <typename Executor1, typename Executor2>
+ASIO_SYNC_OP_VOID connect_pipe(basic_readable_pipe<Executor1>& read_end,
+    basic_writable_pipe<Executor2>& write_end, asio::error_code& ec)
+{
+  detail::native_pipe_handle p[2];
+  detail::create_pipe(p, ec);
+  if (ec)
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+
+  read_end.assign(p[0], ec);
+  if (ec)
+  {
+    detail::close_pipe(p[0]);
+    detail::close_pipe(p[1]);
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+  }
+
+  write_end.assign(p[1], ec);
+  if (ec)
+  {
+    asio::error_code temp_ec;
+    read_end.close(temp_ec);
+    detail::close_pipe(p[1]);
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+  }
+
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // defined(ASIO_HAS_PIPE)
+
+#endif // ASIO_IMPL_CONNECT_PIPE_HPP

include/asio/impl/connect_pipe.ipp

@@ -0,0 +1,150 @@
+//
+// impl/connect_pipe.ipp
+// ~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2021 Klemens D. Morgenstern
+//                    (klemens dot morgenstern at gmx dot net)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CONNECT_PIPE_IPP
+#define ASIO_IMPL_CONNECT_PIPE_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_PIPE)
+
+#include "asio/connect_pipe.hpp"
+
+#if defined(ASIO_HAS_IOCP)
+# include <cstdio>
+# if _WIN32_WINNT >= 0x601
+#  include <bcrypt.h>
+#  if !defined(ASIO_NO_DEFAULT_LINKED_LIBS)
+#   if defined(_MSC_VER)
+#    pragma comment(lib, "bcrypt.lib")
+#   endif // defined(_MSC_VER)
+#  endif // !defined(ASIO_NO_DEFAULT_LINKED_LIBS)
+# endif // _WIN32_WINNT >= 0x601
+#else // defined(ASIO_HAS_IOCP)
+# include "asio/detail/descriptor_ops.hpp"
+#endif // defined(ASIO_HAS_IOCP)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+void create_pipe(native_pipe_handle p[2], asio::error_code& ec)
+{
+#if defined(ASIO_HAS_IOCP)
+  using namespace std; // For sprintf and memcmp.
+
+  static long counter1 = 0;
+  static long counter2 = 0;
+
+  long n1 = ::InterlockedIncrement(&counter1);
+  long n2 = (static_cast<unsigned long>(n1) % 0x10000000) == 0
+    ? ::InterlockedIncrement(&counter2)
+    : ::InterlockedExchangeAdd(&counter2, 0);
+
+  wchar_t pipe_name[128];
+#if defined(ASIO_HAS_SECURE_RTL)
+  swprintf_s(
+#else // defined(ASIO_HAS_SECURE_RTL)
+  _snwprintf(
+#endif // defined(ASIO_HAS_SECURE_RTL)
+      pipe_name, 128,
+      // Include address of static to discriminate asio instances in DLLs.
+      L"\\\\.\\pipe\\asio-A0812896-741A-484D-AF23-BE51BF620E22-%u-%p-%ld-%ld",
+      static_cast<unsigned int>(::GetCurrentProcessId()), &counter1, n1, n2);
+
+  p[0] = ::CreateNamedPipeW(pipe_name,
+      PIPE_ACCESS_INBOUND | FILE_FLAG_OVERLAPPED,
+      0, 1, 8192, 8192, 0, 0);
+
+  if (p[0] == INVALID_HANDLE_VALUE)
+  {
+    DWORD last_error = ::GetLastError();
+    ec.assign(last_error, asio::error::get_system_category());
+    return;
+  }
+
+  p[1] = ::CreateFileW(pipe_name, GENERIC_WRITE, 0,
+    0, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, 0);
+
+  if (p[1] == INVALID_HANDLE_VALUE)
+  {
+    DWORD last_error = ::GetLastError();
+    ::CloseHandle(p[0]);
+    ec.assign(last_error, asio::error::get_system_category());
+    return;
+  }
+
+# if _WIN32_WINNT >= 0x601
+  unsigned char nonce[16];
+  if (::BCryptGenRandom(0, nonce, sizeof(nonce),
+        BCRYPT_USE_SYSTEM_PREFERRED_RNG) != 0)
+  {
+    ec = asio::error::connection_aborted;
+    ::CloseHandle(p[0]);
+    ::CloseHandle(p[1]);
+    return;
+  }
+
+  DWORD bytes_written = 0;
+  BOOL ok = ::WriteFile(p[1], nonce, sizeof(nonce), &bytes_written, 0);
+  if (!ok || bytes_written != sizeof(nonce))
+  {
+    ec = asio::error::connection_aborted;
+    ::CloseHandle(p[0]);
+    ::CloseHandle(p[1]);
+    return;
+  }
+
+  unsigned char nonce_check[sizeof(nonce)];
+  DWORD bytes_read = 0;
+  ok = ::ReadFile(p[0], nonce_check, sizeof(nonce), &bytes_read, 0);
+  if (!ok || bytes_read != sizeof(nonce)
+      || memcmp(nonce, nonce_check, sizeof(nonce)) != 0)
+  {
+    ec = asio::error::connection_aborted;
+    ::CloseHandle(p[0]);
+    ::CloseHandle(p[1]);
+    return;
+  }
+#endif // _WIN32_WINNT >= 0x601
+
+  asio::error::clear(ec);
+#else // defined(ASIO_HAS_IOCP)
+  int result = ::pipe(p);
+  detail::descriptor_ops::get_last_error(ec, result != 0);
+#endif // defined(ASIO_HAS_IOCP)
+}
+
+void close_pipe(native_pipe_handle p)
+{
+#if defined(ASIO_HAS_IOCP)
+  ::CloseHandle(p);
+#else // defined(ASIO_HAS_IOCP)
+  asio::error_code ignored_ec;
+  detail::descriptor_ops::state_type state = 0;
+  detail::descriptor_ops::close(p, state, ignored_ec);
+#endif // defined(ASIO_HAS_IOCP)
+}
+
+} // namespace detail
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // defined(ASIO_HAS_PIPE)
+
+#endif // ASIO_IMPL_CONNECT_PIPE_IPP

include/asio/impl/consign.hpp

@@ -0,0 +1,144 @@
+//
+// impl/consign.hpp
+// ~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_CONSIGN_HPP
+#define ASIO_IMPL_CONSIGN_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/utility.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Class to adapt a consign_t as a completion handler.
+template <typename Handler, typename... Values>
+class consign_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename H>
+  consign_handler(H&& handler, std::tuple<Values...> values)
+    : handler_(static_cast<H&&>(handler)),
+      values_(static_cast<std::tuple<Values...>&&>(values))
+  {
+  }
+
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    static_cast<Handler&&>(handler_)(static_cast<Args&&>(args)...);
+  }
+
+//private:
+  Handler handler_;
+  std::tuple<Values...> values_;
+};
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    consign_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+      this_handler->handler_);
+}
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename... Values, typename... Signatures>
+struct async_result<consign_t<CompletionToken, Values...>, Signatures...>
+  : async_result<CompletionToken, Signatures...>
+{
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        std::tuple<Values...> values, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          detail::consign_handler<decay_t<Handler>, Values...>(
+            static_cast<Handler&&>(handler),
+            static_cast<std::tuple<Values...>&&>(values)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        std::tuple<Values...> values, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          detail::consign_handler<decay_t<Handler>, Values...>(
+            static_cast<Handler&&>(handler),
+            static_cast<std::tuple<Values...>&&>(values)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<CompletionToken, Signatures...>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_, static_cast<std::tuple<Values...>&&>(token.values_),
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<CompletionToken, Signatures...>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_, static_cast<std::tuple<Values...>&&>(token.values_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename... Values, typename DefaultCandidate>
+struct associator<Associator,
+    detail::consign_handler<Handler, Values...>, DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const detail::consign_handler<Handler, Values...>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::consign_handler<Handler, Values...>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_CONSIGN_HPP

include/asio/impl/deferred.hpp

@@ -0,0 +1,147 @@
+//
+// impl/deferred.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_DEFERRED_HPP
+#define ASIO_IMPL_DEFERRED_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Signature>
+class async_result<deferred_t, Signature>
+{
+public:
+  template <typename Initiation, typename... InitArgs>
+  static deferred_async_operation<Signature, Initiation, InitArgs...>
+  initiate(Initiation&& initiation, deferred_t, InitArgs&&... args)
+  {
+    return deferred_async_operation<Signature, Initiation, InitArgs...>(
+        deferred_init_tag{},
+        static_cast<Initiation&&>(initiation),
+        static_cast<InitArgs&&>(args)...);
+  }
+};
+
+template <typename... Signatures>
+class async_result<deferred_t, Signatures...>
+{
+public:
+  template <typename Initiation, typename... InitArgs>
+  static deferred_async_operation<
+      deferred_signatures<Signatures...>, Initiation, InitArgs...>
+  initiate(Initiation&& initiation, deferred_t, InitArgs&&... args)
+  {
+    return deferred_async_operation<
+        deferred_signatures<Signatures...>, Initiation, InitArgs...>(
+          deferred_init_tag{},
+          static_cast<Initiation&&>(initiation),
+          static_cast<InitArgs&&>(args)...);
+  }
+};
+
+template <typename Function, typename Signature>
+class async_result<deferred_function<Function>, Signature>
+{
+public:
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation&& initiation,
+      deferred_function<Function> token, InitArgs&&... init_args)
+    -> decltype(
+        deferred_sequence<
+          deferred_async_operation<
+            Signature, Initiation, InitArgs...>,
+          Function>(deferred_init_tag{},
+            deferred_async_operation<
+              Signature, Initiation, InitArgs...>(
+                deferred_init_tag{},
+                static_cast<Initiation&&>(initiation),
+                static_cast<InitArgs&&>(init_args)...),
+            static_cast<Function&&>(token.function_)))
+  {
+    return deferred_sequence<
+        deferred_async_operation<
+          Signature, Initiation, InitArgs...>,
+        Function>(deferred_init_tag{},
+          deferred_async_operation<
+            Signature, Initiation, InitArgs...>(
+              deferred_init_tag{},
+              static_cast<Initiation&&>(initiation),
+              static_cast<InitArgs&&>(init_args)...),
+          static_cast<Function&&>(token.function_));
+  }
+};
+
+template <typename Function, typename... Signatures>
+class async_result<deferred_function<Function>, Signatures...>
+{
+public:
+  template <typename Initiation, typename... InitArgs>
+  static auto initiate(Initiation&& initiation,
+      deferred_function<Function> token, InitArgs&&... init_args)
+    -> decltype(
+        deferred_sequence<
+          deferred_async_operation<
+            deferred_signatures<Signatures...>, Initiation, InitArgs...>,
+          Function>(deferred_init_tag{},
+            deferred_async_operation<
+              deferred_signatures<Signatures...>, Initiation, InitArgs...>(
+                deferred_init_tag{},
+                static_cast<Initiation&&>(initiation),
+                static_cast<InitArgs&&>(init_args)...),
+            static_cast<Function&&>(token.function_)))
+  {
+    return deferred_sequence<
+        deferred_async_operation<
+          deferred_signatures<Signatures...>, Initiation, InitArgs...>,
+        Function>(deferred_init_tag{},
+          deferred_async_operation<
+            deferred_signatures<Signatures...>, Initiation, InitArgs...>(
+              deferred_init_tag{},
+              static_cast<Initiation&&>(initiation),
+              static_cast<InitArgs&&>(init_args)...),
+          static_cast<Function&&>(token.function_));
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename Tail, typename DefaultCandidate>
+struct associator<Associator,
+    detail::deferred_sequence_handler<Handler, Tail>,
+    DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const detail::deferred_sequence_handler<Handler, Tail>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::deferred_sequence_handler<Handler, Tail>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_DEFERRED_HPP

include/asio/impl/detached.hpp

@@ -0,0 +1,77 @@
+//
+// impl/detached.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_DETACHED_HPP
+#define ASIO_IMPL_DETACHED_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/async_result.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+  // Class to adapt a detached_t as a completion handler.
+  class detached_handler
+  {
+  public:
+    typedef void result_type;
+
+    detached_handler(detached_t)
+    {
+    }
+
+    template <typename... Args>
+    void operator()(Args...)
+    {
+    }
+  };
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename... Signatures>
+struct async_result<detached_t, Signatures...>
+{
+  typedef asio::detail::detached_handler completion_handler_type;
+
+  typedef void return_type;
+
+  explicit async_result(completion_handler_type&)
+  {
+  }
+
+  void get()
+  {
+  }
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static return_type initiate(Initiation&& initiation,
+      RawCompletionToken&&, Args&&... args)
+  {
+    static_cast<Initiation&&>(initiation)(
+        detail::detached_handler(detached_t()),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_DETACHED_HPP

include/asio/impl/error.ipp

@@ -0,0 +1,128 @@
+//
+// impl/error.ipp
+// ~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_ERROR_IPP
+#define ASIO_IMPL_ERROR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <string>
+#include "asio/error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace error {
+
+#if !defined(ASIO_WINDOWS) && !defined(__CYGWIN__)
+
+namespace detail {
+
+class netdb_category : public asio::error_category
+{
+public:
+  const char* name() const noexcept
+  {
+    return "asio.netdb";
+  }
+
+  std::string message(int value) const
+  {
+    if (value == error::host_not_found)
+      return "Host not found (authoritative)";
+    if (value == error::host_not_found_try_again)
+      return "Host not found (non-authoritative), try again later";
+    if (value == error::no_data)
+      return "The query is valid, but it does not have associated data";
+    if (value == error::no_recovery)
+      return "A non-recoverable error occurred during database lookup";
+    return "asio.netdb error";
+  }
+};
+
+} // namespace detail
+
+const asio::error_category& get_netdb_category()
+{
+  static detail::netdb_category instance;
+  return instance;
+}
+
+namespace detail {
+
+class addrinfo_category : public asio::error_category
+{
+public:
+  const char* name() const noexcept
+  {
+    return "asio.addrinfo";
+  }
+
+  std::string message(int value) const
+  {
+    if (value == error::service_not_found)
+      return "Service not found";
+    if (value == error::socket_type_not_supported)
+      return "Socket type not supported";
+    return "asio.addrinfo error";
+  }
+};
+
+} // namespace detail
+
+const asio::error_category& get_addrinfo_category()
+{
+  static detail::addrinfo_category instance;
+  return instance;
+}
+
+#endif // !defined(ASIO_WINDOWS) && !defined(__CYGWIN__)
+
+namespace detail {
+
+class misc_category : public asio::error_category
+{
+public:
+  const char* name() const noexcept
+  {
+    return "asio.misc";
+  }
+
+  std::string message(int value) const
+  {
+    if (value == error::already_open)
+      return "Already open";
+    if (value == error::eof)
+      return "End of file";
+    if (value == error::not_found)
+      return "Element not found";
+    if (value == error::fd_set_failure)
+      return "The descriptor does not fit into the select call's fd_set";
+    return "asio.misc error";
+  }
+};
+
+} // namespace detail
+
+const asio::error_category& get_misc_category()
+{
+  static detail::misc_category instance;
+  return instance;
+}
+
+} // namespace error
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_ERROR_IPP

include/asio/impl/error_code.ipp

@@ -0,0 +1,207 @@
+//
+// impl/error_code.ipp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_ERROR_CODE_IPP
+#define ASIO_IMPL_ERROR_CODE_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+# include <winerror.h>
+#elif defined(ASIO_WINDOWS_RUNTIME)
+# include <windows.h>
+#else
+# include <cerrno>
+# include <cstring>
+# include <string>
+#endif
+#include "asio/detail/local_free_on_block_exit.hpp"
+#include "asio/detail/socket_types.hpp"
+#include "asio/error_code.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+class system_category : public error_category
+{
+public:
+  const char* name() const noexcept
+  {
+    return "asio.system";
+  }
+
+  std::string message(int value) const
+  {
+#if defined(ASIO_WINDOWS_RUNTIME) || defined(ASIO_WINDOWS_APP)
+    std::wstring wmsg(128, wchar_t());
+    for (;;)
+    {
+      DWORD wlength = ::FormatMessageW(FORMAT_MESSAGE_FROM_SYSTEM
+          | FORMAT_MESSAGE_IGNORE_INSERTS, 0, value,
+          MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+          &wmsg[0], static_cast<DWORD>(wmsg.size()), 0);
+      if (wlength == 0 && ::GetLastError() == ERROR_INSUFFICIENT_BUFFER)
+      {
+        wmsg.resize(wmsg.size() + wmsg.size() / 2);
+        continue;
+      }
+      if (wlength && wmsg[wlength - 1] == '\n')
+        --wlength;
+      if (wlength && wmsg[wlength - 1] == '\r')
+        --wlength;
+      if (wlength)
+      {
+        std::string msg(wlength * 2, char());
+        int length = ::WideCharToMultiByte(CP_ACP, 0,
+            wmsg.c_str(), static_cast<int>(wlength),
+            &msg[0], static_cast<int>(wlength * 2), 0, 0);
+        if (length <= 0)
+          return "asio.system error";
+        msg.resize(static_cast<std::size_t>(length));
+        return msg;
+      }
+      else
+        return "asio.system error";
+    }
+#elif defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+    char* msg = 0;
+    DWORD length = ::FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER
+        | FORMAT_MESSAGE_FROM_SYSTEM
+        | FORMAT_MESSAGE_IGNORE_INSERTS, 0, value,
+        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (char*)&msg, 0, 0);
+    detail::local_free_on_block_exit local_free_obj(msg);
+    if (length && msg[length - 1] == '\n')
+      msg[--length] = '\0';
+    if (length && msg[length - 1] == '\r')
+      msg[--length] = '\0';
+    if (length)
+      return msg;
+    else
+      return "asio.system error";
+#else // defined(ASIO_WINDOWS_DESKTOP) || defined(__CYGWIN__)
+#if !defined(__sun)
+    if (value == ECANCELED)
+      return "Operation aborted.";
+#endif // !defined(__sun)
+#if defined(__sun) || defined(__QNX__) || defined(__SYMBIAN32__)
+    using namespace std;
+    return strerror(value);
+#else
+    char buf[256] = "";
+    using namespace std;
+    return strerror_result(strerror_r(value, buf, sizeof(buf)), buf);
+#endif
+#endif // defined(ASIO_WINDOWS_DESKTOP) || defined(__CYGWIN__)
+  }
+
+#if defined(ASIO_HAS_STD_ERROR_CODE)
+  std::error_condition default_error_condition(
+      int ev) const noexcept
+  {
+    switch (ev)
+    {
+    case access_denied:
+      return std::errc::permission_denied;
+    case address_family_not_supported:
+      return std::errc::address_family_not_supported;
+    case address_in_use:
+      return std::errc::address_in_use;
+    case already_connected:
+      return std::errc::already_connected;
+    case already_started:
+      return std::errc::connection_already_in_progress;
+    case broken_pipe:
+      return std::errc::broken_pipe;
+    case connection_aborted:
+      return std::errc::connection_aborted;
+    case connection_refused:
+      return std::errc::connection_refused;
+    case connection_reset:
+      return std::errc::connection_reset;
+    case bad_descriptor:
+      return std::errc::bad_file_descriptor;
+    case fault:
+      return std::errc::bad_address;
+    case host_unreachable:
+      return std::errc::host_unreachable;
+    case in_progress:
+      return std::errc::operation_in_progress;
+    case interrupted:
+      return std::errc::interrupted;
+    case invalid_argument:
+      return std::errc::invalid_argument;
+    case message_size:
+      return std::errc::message_size;
+    case name_too_long:
+      return std::errc::filename_too_long;
+    case network_down:
+      return std::errc::network_down;
+    case network_reset:
+      return std::errc::network_reset;
+    case network_unreachable:
+      return std::errc::network_unreachable;
+    case no_descriptors:
+      return std::errc::too_many_files_open;
+    case no_buffer_space:
+      return std::errc::no_buffer_space;
+    case no_memory:
+      return std::errc::not_enough_memory;
+    case no_permission:
+      return std::errc::operation_not_permitted;
+    case no_protocol_option:
+      return std::errc::no_protocol_option;
+    case no_such_device:
+      return std::errc::no_such_device;
+    case not_connected:
+      return std::errc::not_connected;
+    case not_socket:
+      return std::errc::not_a_socket;
+    case operation_aborted:
+      return std::errc::operation_canceled;
+    case operation_not_supported:
+      return std::errc::operation_not_supported;
+    case shut_down:
+      return std::make_error_condition(ev, *this);
+    case timed_out:
+      return std::errc::timed_out;
+    case try_again:
+      return std::errc::resource_unavailable_try_again;
+    case would_block:
+      return std::errc::operation_would_block;
+    default:
+      return std::make_error_condition(ev, *this);
+    }
+  }
+#endif // defined(ASIO_HAS_STD_ERROR_CODE)
+
+private:
+  // Helper function to adapt the result from glibc's variant of strerror_r.
+  static const char* strerror_result(int, const char* s) { return s; }
+  static const char* strerror_result(const char* s, const char*) { return s; }
+};
+
+} // namespace detail
+
+const error_category& system_category()
+{
+  static detail::system_category instance;
+  return instance;
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_ERROR_CODE_IPP

include/asio/impl/execution_context.hpp

@@ -0,0 +1,145 @@
+//
+// impl/execution_context.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_EXECUTION_CONTEXT_HPP
+#define ASIO_IMPL_EXECUTION_CONTEXT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <cstring>
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/service_registry.hpp"
+#include "asio/detail/throw_exception.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+template <typename Allocator>
+execution_context::execution_context(allocator_arg_t, const Allocator& a)
+  : execution_context(detail::allocate_object<allocator_impl<Allocator>>(a, a))
+{
+}
+
+template <typename Allocator>
+execution_context::execution_context(allocator_arg_t, const Allocator& a,
+    const service_maker& initial_services)
+  : execution_context(detail::allocate_object<allocator_impl<Allocator>>(a, a),
+      initial_services)
+{
+}
+
+inline execution_context::auto_allocator_ptr::~auto_allocator_ptr()
+{
+  ptr_->destroy();
+}
+
+template <typename Allocator>
+void execution_context::allocator_impl<Allocator>::destroy()
+{
+  detail::deallocate_object(allocator_, this);
+}
+
+template <typename Allocator>
+void* execution_context::allocator_impl<Allocator>::allocate(
+    std::size_t size, std::size_t align)
+{
+  typename std::allocator_traits<Allocator>::template
+    rebind_alloc<unsigned char> alloc(allocator_);
+
+  std::size_t space = size + align - 1;
+  unsigned char* base = std::allocator_traits<decltype(alloc)>::allocate(
+      alloc, space + sizeof(std::ptrdiff_t));
+
+  void* p = base;
+  if (detail::align(align, size, p, space))
+  {
+    std::ptrdiff_t off = static_cast<unsigned char*>(p) - base;
+    std::memcpy(static_cast<unsigned char*>(p) + size, &off, sizeof(off));
+    return p;
+  }
+
+  std::bad_alloc ex;
+  asio::detail::throw_exception(ex);
+  return 0;
+}
+
+template <typename Allocator>
+void execution_context::allocator_impl<Allocator>::deallocate(
+    void* ptr, std::size_t size, std::size_t align)
+{
+  if (ptr)
+  {
+    typename std::allocator_traits<Allocator>::template
+      rebind_alloc<unsigned char> alloc(allocator_);
+
+    std::ptrdiff_t off;
+    std::memcpy(&off, static_cast<unsigned char*>(ptr) + size, sizeof(off));
+    unsigned char* base = static_cast<unsigned char*>(ptr) - off;
+
+    std::allocator_traits<decltype(alloc)>::deallocate(
+        alloc, base, size + align - 1 + sizeof(std::ptrdiff_t));
+  }
+}
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Service>
+inline Service& use_service(execution_context& e)
+{
+  // Check that Service meets the necessary type requirements.
+  (void)static_cast<execution_context::service*>(static_cast<Service*>(0));
+
+  return e.service_registry_->template use_service<Service>();
+}
+
+template <typename Service, typename... Args>
+Service& make_service(execution_context& e, Args&&... args)
+{
+  // Check that Service meets the necessary type requirements.
+  (void)static_cast<execution_context::service*>(static_cast<Service*>(0));
+
+  return e.service_registry_->template make_service<Service>(
+      static_cast<Args&&>(args)...);
+}
+
+template <typename Service>
+inline void add_service(execution_context& e, Service* svc)
+{
+  // Check that Service meets the necessary type requirements.
+  (void)static_cast<execution_context::service*>(static_cast<Service*>(0));
+
+  e.service_registry_->template add_service<Service>(svc);
+}
+
+template <typename Service>
+inline bool has_service(execution_context& e)
+{
+  // Check that Service meets the necessary type requirements.
+  (void)static_cast<execution_context::service*>(static_cast<Service*>(0));
+
+  return e.service_registry_->template has_service<Service>();
+}
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+inline execution_context& execution_context::service::context()
+{
+  return owner_;
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_EXECUTION_CONTEXT_HPP

include/asio/impl/execution_context.ipp

@@ -0,0 +1,120 @@
+//
+// impl/execution_context.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_EXECUTION_CONTEXT_IPP
+#define ASIO_IMPL_EXECUTION_CONTEXT_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/execution_context.hpp"
+#include "asio/detail/service_registry.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+execution_context::execution_context()
+  : execution_context(
+      detail::allocate_object<allocator_impl<std::allocator<void>>>(
+        std::allocator<void>(), std::allocator<void>()))
+{
+}
+
+execution_context::execution_context(allocator_impl_base* alloc)
+  : allocator_{alloc},
+    service_registry_(
+        detail::allocate_object<detail::service_registry>(
+          allocator<void>(*this), *this))
+{
+}
+
+execution_context::execution_context(
+    const execution_context::service_maker& initial_services)
+  : execution_context(
+      detail::allocate_object<allocator_impl<std::allocator<void>>>(
+        std::allocator<void>(), std::allocator<void>()),
+      initial_services)
+{
+}
+
+execution_context::execution_context(allocator_impl_base* alloc,
+    const execution_context::service_maker& initial_services)
+  : allocator_{alloc},
+    service_registry_(
+        detail::allocate_object<detail::service_registry>(
+          allocator<void>(*this), *this))
+{
+  initial_services.make(*this);
+}
+
+execution_context::~execution_context()
+{
+  shutdown();
+  destroy();
+  detail::deallocate_object(allocator<void>(*this), service_registry_);
+}
+
+void execution_context::shutdown()
+{
+  service_registry_->shutdown_services();
+}
+
+void execution_context::destroy()
+{
+  service_registry_->destroy_services();
+}
+
+void execution_context::notify_fork(
+    asio::execution_context::fork_event event)
+{
+  service_registry_->notify_fork(event);
+}
+
+execution_context::allocator_impl_base::~allocator_impl_base()
+{
+}
+
+execution_context::service::service(execution_context& owner)
+  : owner_(owner),
+    next_(0),
+    destroy_(0)
+{
+}
+
+execution_context::service::~service()
+{
+}
+
+void execution_context::service::notify_fork(execution_context::fork_event)
+{
+}
+
+execution_context::service_maker::~service_maker()
+{
+}
+
+service_already_exists::service_already_exists()
+  : std::logic_error("Service already exists.")
+{
+}
+
+invalid_service_owner::invalid_service_owner()
+  : std::logic_error("Invalid service owner.")
+{
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_EXECUTION_CONTEXT_IPP

include/asio/impl/executor.hpp

@@ -0,0 +1,317 @@
+//
+// impl/executor.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_EXECUTOR_HPP
+#define ASIO_IMPL_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+
+#include <new>
+#include "asio/detail/atomic_count.hpp"
+#include "asio/detail/global.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/executor.hpp"
+#include "asio/system_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+// Default polymorphic executor implementation.
+template <typename Executor, typename Allocator>
+class executor::impl
+  : public executor::impl_base
+{
+public:
+  typedef ASIO_REBIND_ALLOC(Allocator, impl) allocator_type;
+
+  static impl_base* create(const Executor& e, Allocator a = Allocator())
+  {
+    raw_mem mem(a);
+    impl* p = new (mem.ptr_) impl(e, a);
+    mem.ptr_ = 0;
+    return p;
+  }
+
+  static impl_base* create(std::nothrow_t, const Executor& e) noexcept
+  {
+    return new (std::nothrow) impl(e, std::allocator<void>());
+  }
+
+  impl(const Executor& e, const Allocator& a) noexcept
+    : impl_base(false),
+      ref_count_(1),
+      executor_(e),
+      allocator_(a)
+  {
+  }
+
+  impl_base* clone() const noexcept
+  {
+    detail::ref_count_up(ref_count_);
+    return const_cast<impl_base*>(static_cast<const impl_base*>(this));
+  }
+
+  void destroy() noexcept
+  {
+    if (detail::ref_count_down(ref_count_))
+    {
+      allocator_type alloc(allocator_);
+      impl* p = this;
+      p->~impl();
+      alloc.deallocate(p, 1);
+    }
+  }
+
+  void on_work_started() noexcept
+  {
+    executor_.on_work_started();
+  }
+
+  void on_work_finished() noexcept
+  {
+    executor_.on_work_finished();
+  }
+
+  execution_context& context() noexcept
+  {
+    return executor_.context();
+  }
+
+  void dispatch(function&& f)
+  {
+    executor_.dispatch(static_cast<function&&>(f), allocator_);
+  }
+
+  void post(function&& f)
+  {
+    executor_.post(static_cast<function&&>(f), allocator_);
+  }
+
+  void defer(function&& f)
+  {
+    executor_.defer(static_cast<function&&>(f), allocator_);
+  }
+
+  type_id_result_type target_type() const noexcept
+  {
+    return type_id<Executor>();
+  }
+
+  void* target() noexcept
+  {
+    return &executor_;
+  }
+
+  const void* target() const noexcept
+  {
+    return &executor_;
+  }
+
+  bool equals(const impl_base* e) const noexcept
+  {
+    if (this == e)
+      return true;
+    if (target_type() != e->target_type())
+      return false;
+    return executor_ == *static_cast<const Executor*>(e->target());
+  }
+
+private:
+  mutable detail::atomic_count ref_count_;
+  Executor executor_;
+  Allocator allocator_;
+
+  struct raw_mem
+  {
+    allocator_type allocator_;
+    impl* ptr_;
+
+    explicit raw_mem(const Allocator& a)
+      : allocator_(a),
+        ptr_(allocator_.allocate(1))
+    {
+    }
+
+    ~raw_mem()
+    {
+      if (ptr_)
+        allocator_.deallocate(ptr_, 1);
+    }
+
+  private:
+    // Disallow copying and assignment.
+    raw_mem(const raw_mem&);
+    raw_mem operator=(const raw_mem&);
+  };
+};
+
+// Polymorphic executor specialisation for system_executor.
+template <typename Allocator>
+class executor::impl<system_executor, Allocator>
+  : public executor::impl_base
+{
+public:
+  static impl_base* create(const system_executor&,
+      const Allocator& = Allocator())
+  {
+    return &detail::global<impl<system_executor, std::allocator<void>> >();
+  }
+
+  static impl_base* create(std::nothrow_t, const system_executor&) noexcept
+  {
+    return &detail::global<impl<system_executor, std::allocator<void>> >();
+  }
+
+  impl()
+    : impl_base(true)
+  {
+  }
+
+  impl_base* clone() const noexcept
+  {
+    return const_cast<impl_base*>(static_cast<const impl_base*>(this));
+  }
+
+  void destroy() noexcept
+  {
+  }
+
+  void on_work_started() noexcept
+  {
+    executor_.on_work_started();
+  }
+
+  void on_work_finished() noexcept
+  {
+    executor_.on_work_finished();
+  }
+
+  execution_context& context() noexcept
+  {
+    return executor_.context();
+  }
+
+  void dispatch(function&& f)
+  {
+    executor_.dispatch(static_cast<function&&>(f),
+        std::allocator<void>());
+  }
+
+  void post(function&& f)
+  {
+    executor_.post(static_cast<function&&>(f),
+        std::allocator<void>());
+  }
+
+  void defer(function&& f)
+  {
+    executor_.defer(static_cast<function&&>(f),
+        std::allocator<void>());
+  }
+
+  type_id_result_type target_type() const noexcept
+  {
+    return type_id<system_executor>();
+  }
+
+  void* target() noexcept
+  {
+    return &executor_;
+  }
+
+  const void* target() const noexcept
+  {
+    return &executor_;
+  }
+
+  bool equals(const impl_base* e) const noexcept
+  {
+    return this == e;
+  }
+
+private:
+  system_executor executor_;
+};
+
+template <typename Executor>
+executor::executor(Executor e)
+  : impl_(impl<Executor, std::allocator<void>>::create(e))
+{
+}
+
+template <typename Executor>
+executor::executor(std::nothrow_t, Executor e) noexcept
+  : impl_(impl<Executor, std::allocator<void>>::create(std::nothrow, e))
+{
+}
+
+template <typename Executor, typename Allocator>
+executor::executor(allocator_arg_t, const Allocator& a, Executor e)
+  : impl_(impl<Executor, Allocator>::create(e, a))
+{
+}
+
+template <typename Function, typename Allocator>
+void executor::dispatch(Function&& f,
+    const Allocator& a) const
+{
+  impl_base* i = get_impl();
+  if (i->fast_dispatch_)
+    system_executor().dispatch(static_cast<Function&&>(f), a);
+  else
+    i->dispatch(function(static_cast<Function&&>(f), a));
+}
+
+template <typename Function, typename Allocator>
+void executor::post(Function&& f,
+    const Allocator& a) const
+{
+  get_impl()->post(function(static_cast<Function&&>(f), a));
+}
+
+template <typename Function, typename Allocator>
+void executor::defer(Function&& f,
+    const Allocator& a) const
+{
+  get_impl()->defer(function(static_cast<Function&&>(f), a));
+}
+
+template <typename Executor>
+Executor* executor::target() noexcept
+{
+  return impl_ && impl_->target_type() == type_id<Executor>()
+    ? static_cast<Executor*>(impl_->target()) : 0;
+}
+
+template <typename Executor>
+const Executor* executor::target() const noexcept
+{
+  return impl_ && impl_->target_type() == type_id<Executor>()
+    ? static_cast<Executor*>(impl_->target()) : 0;
+}
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+#endif // ASIO_IMPL_EXECUTOR_HPP

include/asio/impl/executor.ipp

@@ -0,0 +1,43 @@
+//
+// impl/executor.ipp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_EXECUTOR_IPP
+#define ASIO_IMPL_EXECUTOR_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+
+#include "asio/executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+bad_executor::bad_executor() noexcept
+{
+}
+
+const char* bad_executor::what() const noexcept
+{
+  return "bad executor";
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+#endif // ASIO_IMPL_EXECUTOR_IPP

include/asio/impl/io_context.hpp

@@ -0,0 +1,343 @@
+//
+// impl/io_context.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_IO_CONTEXT_HPP
+#define ASIO_IMPL_IO_CONTEXT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/config.hpp"
+#include "asio/detail/completion_handler.hpp"
+#include "asio/detail/executor_op.hpp"
+#include "asio/detail/fenced_block.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/service_registry.hpp"
+#include "asio/detail/throw_error.hpp"
+#include "asio/detail/type_traits.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+template <typename Allocator>
+io_context::io_context(allocator_arg_t, const Allocator& a)
+  : execution_context(std::allocator_arg, a, config_from_concurrency_hint()),
+    impl_(asio::make_service<impl_type>(*this, false))
+{
+}
+
+template <typename Allocator>
+io_context::io_context(allocator_arg_t,
+    const Allocator& a, int concurrency_hint)
+  : execution_context(std::allocator_arg, a,
+      config_from_concurrency_hint(concurrency_hint)),
+    impl_(asio::make_service<impl_type>(*this, false))
+{
+}
+
+template <typename Allocator>
+io_context::io_context(allocator_arg_t, const Allocator& a,
+    const execution_context::service_maker& initial_services)
+  : execution_context(std::allocator_arg, a, initial_services),
+    impl_(asio::make_service<impl_type>(*this, false))
+{
+}
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Service>
+inline Service& use_service(io_context& ioc)
+{
+  // Check that Service meets the necessary type requirements.
+  (void)static_cast<execution_context::service*>(static_cast<Service*>(0));
+  (void)static_cast<const execution_context::id*>(&Service::id);
+
+  return ioc.service_registry_->template use_service<Service>(ioc);
+}
+
+template <>
+inline detail::io_context_impl& use_service<detail::io_context_impl>(
+    io_context& ioc)
+{
+  return ioc.impl_;
+}
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+inline io_context::executor_type
+io_context::get_executor() noexcept
+{
+  return executor_type(*this);
+}
+
+template <typename Rep, typename Period>
+std::size_t io_context::run_for(
+    const chrono::duration<Rep, Period>& rel_time)
+{
+  return this->run_until(chrono::steady_clock::now() + rel_time);
+}
+
+template <typename Clock, typename Duration>
+std::size_t io_context::run_until(
+    const chrono::time_point<Clock, Duration>& abs_time)
+{
+  std::size_t n = 0;
+  while (this->run_one_until(abs_time))
+    if (n != (std::numeric_limits<std::size_t>::max)())
+      ++n;
+  return n;
+}
+
+template <typename Rep, typename Period>
+std::size_t io_context::run_one_for(
+    const chrono::duration<Rep, Period>& rel_time)
+{
+  return this->run_one_until(chrono::steady_clock::now() + rel_time);
+}
+
+template <typename Clock, typename Duration>
+std::size_t io_context::run_one_until(
+    const chrono::time_point<Clock, Duration>& abs_time)
+{
+  typename Clock::time_point now = Clock::now();
+  while (now < abs_time)
+  {
+    typename Clock::duration rel_time = abs_time - now;
+    if (rel_time > chrono::seconds(1))
+      rel_time = chrono::seconds(1);
+
+    asio::error_code ec;
+    std::size_t s = impl_.wait_one(
+        static_cast<long>(chrono::duration_cast<
+          chrono::microseconds>(rel_time).count()), ec);
+    asio::detail::throw_error(ec);
+
+    if (s || impl_.stopped())
+      return s;
+
+    now = Clock::now();
+  }
+
+  return 0;
+}
+
+#if !defined(ASIO_NO_DEPRECATED)
+
+template <typename Handler>
+#if defined(GENERATING_DOCUMENTATION)
+unspecified
+#else
+inline detail::wrapped_handler<io_context&, Handler>
+#endif
+io_context::wrap(Handler handler)
+{
+  return detail::wrapped_handler<io_context&, Handler>(*this, handler);
+}
+
+#endif // !defined(ASIO_NO_DEPRECATED)
+
+template <typename Allocator, uintptr_t Bits>
+io_context::basic_executor_type<Allocator, Bits>&
+io_context::basic_executor_type<Allocator, Bits>::operator=(
+    const basic_executor_type& other) noexcept
+{
+  if (this != &other)
+  {
+    static_cast<Allocator&>(*this) = static_cast<const Allocator&>(other);
+    io_context* old_io_context = context_ptr();
+    target_ = other.target_;
+    if (Bits & outstanding_work_tracked)
+    {
+      if (context_ptr())
+        context_ptr()->impl_.work_started();
+      if (old_io_context)
+        old_io_context->impl_.work_finished();
+    }
+  }
+  return *this;
+}
+
+template <typename Allocator, uintptr_t Bits>
+io_context::basic_executor_type<Allocator, Bits>&
+io_context::basic_executor_type<Allocator, Bits>::operator=(
+    basic_executor_type&& other) noexcept
+{
+  if (this != &other)
+  {
+    static_cast<Allocator&>(*this) = static_cast<Allocator&&>(other);
+    io_context* old_io_context = context_ptr();
+    target_ = other.target_;
+    if (Bits & outstanding_work_tracked)
+    {
+      other.target_ = 0;
+      if (old_io_context)
+        old_io_context->impl_.work_finished();
+    }
+  }
+  return *this;
+}
+
+template <typename Allocator, uintptr_t Bits>
+inline bool io_context::basic_executor_type<Allocator,
+    Bits>::running_in_this_thread() const noexcept
+{
+  return context_ptr()->impl_.can_dispatch();
+}
+
+template <typename Allocator, uintptr_t Bits>
+template <typename Function>
+void io_context::basic_executor_type<Allocator, Bits>::execute(
+    Function&& f) const
+{
+  typedef decay_t<Function> function_type;
+
+  // Invoke immediately if the blocking.possibly property is enabled and we are
+  // already inside the thread pool.
+  if ((bits() & blocking_never) == 0 && context_ptr()->impl_.can_dispatch())
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(static_cast<Function&&>(f));
+
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+      detail::fenced_block b(detail::fenced_block::full);
+      static_cast<function_type&&>(tmp)();
+      return;
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      context_ptr()->impl_.capture_current_exception();
+      return;
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, Allocator, detail::operation> op;
+  typename op::ptr p = {
+      detail::addressof(static_cast<const Allocator&>(*this)),
+      op::ptr::allocate(static_cast<const Allocator&>(*this)), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f),
+      static_cast<const Allocator&>(*this));
+
+  ASIO_HANDLER_CREATION((*context_ptr(), *p.p,
+        "io_context", context_ptr(), 0, "execute"));
+
+  context_ptr()->impl_.post_immediate_completion(p.p,
+      (bits() & relationship_continuation) != 0);
+  p.v = p.p = 0;
+}
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+template <typename Allocator, uintptr_t Bits>
+inline io_context& io_context::basic_executor_type<
+    Allocator, Bits>::context() const noexcept
+{
+  return *context_ptr();
+}
+
+template <typename Allocator, uintptr_t Bits>
+inline void io_context::basic_executor_type<Allocator,
+    Bits>::on_work_started() const noexcept
+{
+  context_ptr()->impl_.work_started();
+}
+
+template <typename Allocator, uintptr_t Bits>
+inline void io_context::basic_executor_type<Allocator,
+    Bits>::on_work_finished() const noexcept
+{
+  context_ptr()->impl_.work_finished();
+}
+
+template <typename Allocator, uintptr_t Bits>
+template <typename Function, typename OtherAllocator>
+void io_context::basic_executor_type<Allocator, Bits>::dispatch(
+    Function&& f, const OtherAllocator& a) const
+{
+  typedef decay_t<Function> function_type;
+
+  // Invoke immediately if we are already inside the thread pool.
+  if (context_ptr()->impl_.can_dispatch())
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(static_cast<Function&&>(f));
+
+    detail::fenced_block b(detail::fenced_block::full);
+    static_cast<function_type&&>(tmp)();
+    return;
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type,
+      OtherAllocator, detail::operation> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((*context_ptr(), *p.p,
+        "io_context", context_ptr(), 0, "dispatch"));
+
+  context_ptr()->impl_.post_immediate_completion(p.p, false);
+  p.v = p.p = 0;
+}
+
+template <typename Allocator, uintptr_t Bits>
+template <typename Function, typename OtherAllocator>
+void io_context::basic_executor_type<Allocator, Bits>::post(
+    Function&& f, const OtherAllocator& a) const
+{
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<decay_t<Function>,
+      OtherAllocator, detail::operation> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((*context_ptr(), *p.p,
+        "io_context", context_ptr(), 0, "post"));
+
+  context_ptr()->impl_.post_immediate_completion(p.p, false);
+  p.v = p.p = 0;
+}
+
+template <typename Allocator, uintptr_t Bits>
+template <typename Function, typename OtherAllocator>
+void io_context::basic_executor_type<Allocator, Bits>::defer(
+    Function&& f, const OtherAllocator& a) const
+{
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<decay_t<Function>,
+      OtherAllocator, detail::operation> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((*context_ptr(), *p.p,
+        "io_context", context_ptr(), 0, "defer"));
+
+  context_ptr()->impl_.post_immediate_completion(p.p, true);
+  p.v = p.p = 0;
+}
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+inline asio::io_context& io_context::service::get_io_context()
+{
+  return static_cast<asio::io_context&>(context());
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_IO_CONTEXT_HPP

include/asio/impl/io_context.ipp

@@ -0,0 +1,127 @@
+//
+// impl/io_context.ipp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_IO_CONTEXT_IPP
+#define ASIO_IMPL_IO_CONTEXT_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/config.hpp"
+#include "asio/io_context.hpp"
+#include "asio/detail/concurrency_hint.hpp"
+#include "asio/detail/limits.hpp"
+#include "asio/detail/service_registry.hpp"
+#include "asio/detail/throw_error.hpp"
+
+#if defined(ASIO_HAS_IOCP)
+# include "asio/detail/win_iocp_io_context.hpp"
+#else
+# include "asio/detail/scheduler.hpp"
+#endif
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+io_context::io_context()
+  : execution_context(config_from_concurrency_hint()),
+    impl_(asio::make_service<impl_type>(*this, false))
+{
+}
+
+io_context::io_context(int concurrency_hint)
+  : execution_context(config_from_concurrency_hint(concurrency_hint)),
+    impl_(asio::make_service<impl_type>(*this, false))
+{
+}
+
+io_context::io_context(const execution_context::service_maker& initial_services)
+  : execution_context(initial_services),
+    impl_(asio::make_service<impl_type>(*this, false))
+{
+}
+
+io_context::~io_context()
+{
+  shutdown();
+}
+
+io_context::count_type io_context::run()
+{
+  asio::error_code ec;
+  count_type s = impl_.run(ec);
+  asio::detail::throw_error(ec);
+  return s;
+}
+
+io_context::count_type io_context::run_one()
+{
+  asio::error_code ec;
+  count_type s = impl_.run_one(ec);
+  asio::detail::throw_error(ec);
+  return s;
+}
+
+io_context::count_type io_context::poll()
+{
+  asio::error_code ec;
+  count_type s = impl_.poll(ec);
+  asio::detail::throw_error(ec);
+  return s;
+}
+
+io_context::count_type io_context::poll_one()
+{
+  asio::error_code ec;
+  count_type s = impl_.poll_one(ec);
+  asio::detail::throw_error(ec);
+  return s;
+}
+
+void io_context::stop()
+{
+  impl_.stop();
+}
+
+bool io_context::stopped() const
+{
+  return impl_.stopped();
+}
+
+void io_context::restart()
+{
+  impl_.restart();
+}
+
+io_context::service::service(asio::io_context& owner)
+  : execution_context::service(owner)
+{
+}
+
+io_context::service::~service()
+{
+}
+
+void io_context::service::shutdown()
+{
+}
+
+void io_context::service::notify_fork(io_context::fork_event)
+{
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_IO_CONTEXT_IPP

include/asio/impl/multiple_exceptions.ipp

@@ -0,0 +1,45 @@
+//
+// impl/multiple_exceptions.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_MULTIPLE_EXCEPTIONS_IPP
+#define ASIO_IMPL_MULTIPLE_EXCEPTIONS_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/multiple_exceptions.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+multiple_exceptions::multiple_exceptions(
+    std::exception_ptr first) noexcept
+  : first_(static_cast<std::exception_ptr&&>(first))
+{
+}
+
+const char* multiple_exceptions::what() const noexcept
+{
+  return "multiple exceptions";
+}
+
+std::exception_ptr multiple_exceptions::first_exception() const
+{
+  return first_;
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_MULTIPLE_EXCEPTIONS_IPP

include/asio/impl/prepend.hpp

@@ -0,0 +1,170 @@
+//
+// impl/prepend.hpp
+// ~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_PREPEND_HPP
+#define ASIO_IMPL_PREPEND_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/detail/utility.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Class to adapt a prepend_t as a completion handler.
+template <typename Handler, typename... Values>
+class prepend_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename H>
+  prepend_handler(H&& handler, std::tuple<Values...> values)
+    : handler_(static_cast<H&&>(handler)),
+      values_(static_cast<std::tuple<Values...>&&>(values))
+  {
+  }
+
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    this->invoke(
+        index_sequence_for<Values...>{},
+        static_cast<Args&&>(args)...);
+  }
+
+  template <std::size_t... I, typename... Args>
+  void invoke(index_sequence<I...>, Args&&... args)
+  {
+    static_cast<Handler&&>(handler_)(
+        static_cast<Values&&>(std::get<I>(values_))...,
+        static_cast<Args&&>(args)...);
+  }
+
+//private:
+  Handler handler_;
+  std::tuple<Values...> values_;
+};
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    prepend_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+}
+
+template <typename Signature, typename... Values>
+struct prepend_signature;
+
+template <typename R, typename... Args, typename... Values>
+struct prepend_signature<R(Args...), Values...>
+{
+  typedef R type(Values..., decay_t<Args>...);
+};
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename... Values, typename Signature>
+struct async_result<
+    prepend_t<CompletionToken, Values...>, Signature>
+  : async_result<CompletionToken,
+      typename detail::prepend_signature<
+        Signature, Values...>::type>
+{
+  typedef typename detail::prepend_signature<
+      Signature, Values...>::type signature;
+
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        std::tuple<Values...> values, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          detail::prepend_handler<decay_t<Handler>, Values...>(
+            static_cast<Handler&&>(handler),
+            static_cast<std::tuple<Values...>&&>(values)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        std::tuple<Values...> values, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          detail::prepend_handler<decay_t<Handler>, Values...>(
+            static_cast<Handler&&>(handler),
+            static_cast<std::tuple<Values...>&&>(values)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<CompletionToken, signature>(
+        declval<init_wrapper<decay_t<Initiation>>>(),
+        token.token_,
+        static_cast<std::tuple<Values...>&&>(token.values_),
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<CompletionToken, signature>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_,
+        static_cast<std::tuple<Values...>&&>(token.values_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename... Values, typename DefaultCandidate>
+struct associator<Associator,
+    detail::prepend_handler<Handler, Values...>, DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const detail::prepend_handler<Handler, Values...>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::prepend_handler<Handler, Values...>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_PREPEND_HPP

include/asio/impl/read.hpp

@@ -0,0 +1,902 @@
+//
+// impl/read.hpp
+// ~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_READ_HPP
+#define ASIO_IMPL_READ_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <algorithm>
+#include "asio/associator.hpp"
+#include "asio/buffer.hpp"
+#include "asio/detail/array_fwd.hpp"
+#include "asio/detail/base_from_cancellation_state.hpp"
+#include "asio/detail/base_from_completion_cond.hpp"
+#include "asio/detail/bind_handler.hpp"
+#include "asio/detail/consuming_buffers.hpp"
+#include "asio/detail/dependent_type.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_tracking.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/throw_error.hpp"
+#include "asio/error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail
+{
+  template <typename SyncReadStream, typename MutableBufferSequence,
+      typename MutableBufferIterator, typename CompletionCondition>
+  std::size_t read_buffer_seq(SyncReadStream& s,
+      const MutableBufferSequence& buffers, const MutableBufferIterator&,
+      CompletionCondition completion_condition, asio::error_code& ec)
+  {
+    ec = asio::error_code();
+    asio::detail::consuming_buffers<mutable_buffer,
+        MutableBufferSequence, MutableBufferIterator> tmp(buffers);
+    while (!tmp.empty())
+    {
+      if (std::size_t max_size = detail::adapt_completion_condition_result(
+            completion_condition(ec, tmp.total_consumed())))
+        tmp.consume(s.read_some(tmp.prepare(max_size), ec));
+      else
+        break;
+    }
+    return tmp.total_consumed();
+  }
+} // namespace detail
+
+template <typename SyncReadStream, typename MutableBufferSequence,
+    typename CompletionCondition>
+std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_mutable_buffer_sequence<MutableBufferSequence>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return detail::read_buffer_seq(s, buffers,
+      asio::buffer_sequence_begin(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+}
+
+template <typename SyncReadStream, typename MutableBufferSequence>
+inline std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
+    constraint_t<
+      is_mutable_buffer_sequence<MutableBufferSequence>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read(s, buffers, transfer_all(), ec);
+  asio::detail::throw_error(ec, "read");
+  return bytes_transferred;
+}
+
+template <typename SyncReadStream, typename MutableBufferSequence>
+inline std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
+    asio::error_code& ec,
+    constraint_t<
+      is_mutable_buffer_sequence<MutableBufferSequence>::value
+    >)
+{
+  return read(s, buffers, transfer_all(), ec);
+}
+
+template <typename SyncReadStream, typename MutableBufferSequence,
+    typename CompletionCondition>
+inline std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_mutable_buffer_sequence<MutableBufferSequence>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read(s, buffers,
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "read");
+  return bytes_transferred;
+}
+
+#if !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+template <typename SyncReadStream, typename DynamicBuffer_v1,
+    typename CompletionCondition>
+std::size_t read(SyncReadStream& s,
+    DynamicBuffer_v1&& buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  decay_t<DynamicBuffer_v1> b(
+      static_cast<DynamicBuffer_v1&&>(buffers));
+
+  ec = asio::error_code();
+  std::size_t total_transferred = 0;
+  std::size_t max_size = detail::adapt_completion_condition_result(
+        completion_condition(ec, total_transferred));
+  std::size_t bytes_available = std::min<std::size_t>(
+        std::max<std::size_t>(512, b.capacity() - b.size()),
+        std::min<std::size_t>(max_size, b.max_size() - b.size()));
+  while (bytes_available > 0)
+  {
+    std::size_t bytes_transferred = s.read_some(b.prepare(bytes_available), ec);
+    b.commit(bytes_transferred);
+    total_transferred += bytes_transferred;
+    max_size = detail::adapt_completion_condition_result(
+          completion_condition(ec, total_transferred));
+    bytes_available = std::min<std::size_t>(
+          std::max<std::size_t>(512, b.capacity() - b.size()),
+          std::min<std::size_t>(max_size, b.max_size() - b.size()));
+  }
+  return total_transferred;
+}
+
+template <typename SyncReadStream, typename DynamicBuffer_v1>
+inline std::size_t read(SyncReadStream& s,
+    DynamicBuffer_v1&& buffers,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read(s,
+      static_cast<DynamicBuffer_v1&&>(buffers), transfer_all(), ec);
+  asio::detail::throw_error(ec, "read");
+  return bytes_transferred;
+}
+
+template <typename SyncReadStream, typename DynamicBuffer_v1>
+inline std::size_t read(SyncReadStream& s,
+    DynamicBuffer_v1&& buffers,
+    asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >)
+{
+  return read(s, static_cast<DynamicBuffer_v1&&>(buffers),
+      transfer_all(), ec);
+}
+
+template <typename SyncReadStream, typename DynamicBuffer_v1,
+    typename CompletionCondition>
+inline std::size_t read(SyncReadStream& s,
+    DynamicBuffer_v1&& buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read(s,
+      static_cast<DynamicBuffer_v1&&>(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "read");
+  return bytes_transferred;
+}
+
+#if !defined(ASIO_NO_EXTENSIONS)
+#if !defined(ASIO_NO_IOSTREAM)
+
+template <typename SyncReadStream, typename Allocator,
+    typename CompletionCondition>
+inline std::size_t read(SyncReadStream& s,
+    asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return read(s, basic_streambuf_ref<Allocator>(b),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+}
+
+template <typename SyncReadStream, typename Allocator>
+inline std::size_t read(SyncReadStream& s,
+    asio::basic_streambuf<Allocator>& b)
+{
+  return read(s, basic_streambuf_ref<Allocator>(b));
+}
+
+template <typename SyncReadStream, typename Allocator>
+inline std::size_t read(SyncReadStream& s,
+    asio::basic_streambuf<Allocator>& b,
+    asio::error_code& ec)
+{
+  return read(s, basic_streambuf_ref<Allocator>(b), ec);
+}
+
+template <typename SyncReadStream, typename Allocator,
+    typename CompletionCondition>
+inline std::size_t read(SyncReadStream& s,
+    asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return read(s, basic_streambuf_ref<Allocator>(b),
+      static_cast<CompletionCondition&&>(completion_condition));
+}
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+#endif // !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+template <typename SyncReadStream, typename DynamicBuffer_v2,
+    typename CompletionCondition>
+std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  DynamicBuffer_v2& b = buffers;
+
+  ec = asio::error_code();
+  std::size_t total_transferred = 0;
+  std::size_t max_size = detail::adapt_completion_condition_result(
+        completion_condition(ec, total_transferred));
+  std::size_t bytes_available = std::min<std::size_t>(
+        std::max<std::size_t>(512, b.capacity() - b.size()),
+        std::min<std::size_t>(max_size, b.max_size() - b.size()));
+  while (bytes_available > 0)
+  {
+    std::size_t pos = b.size();
+    b.grow(bytes_available);
+    std::size_t bytes_transferred = s.read_some(
+        b.data(pos, bytes_available), ec);
+    b.shrink(bytes_available - bytes_transferred);
+    total_transferred += bytes_transferred;
+    max_size = detail::adapt_completion_condition_result(
+          completion_condition(ec, total_transferred));
+    bytes_available = std::min<std::size_t>(
+          std::max<std::size_t>(512, b.capacity() - b.size()),
+          std::min<std::size_t>(max_size, b.max_size() - b.size()));
+  }
+  return total_transferred;
+}
+
+template <typename SyncReadStream, typename DynamicBuffer_v2>
+inline std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read(s,
+      static_cast<DynamicBuffer_v2&&>(buffers), transfer_all(), ec);
+  asio::detail::throw_error(ec, "read");
+  return bytes_transferred;
+}
+
+template <typename SyncReadStream, typename DynamicBuffer_v2>
+inline std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
+    asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >)
+{
+  return read(s, static_cast<DynamicBuffer_v2&&>(buffers),
+      transfer_all(), ec);
+}
+
+template <typename SyncReadStream, typename DynamicBuffer_v2,
+    typename CompletionCondition>
+inline std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read(s,
+      static_cast<DynamicBuffer_v2&&>(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "read");
+  return bytes_transferred;
+}
+
+namespace detail
+{
+  template <typename AsyncReadStream, typename MutableBufferSequence,
+      typename MutableBufferIterator, typename CompletionCondition,
+      typename ReadHandler>
+  class read_op
+    : public base_from_cancellation_state<ReadHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    read_op(AsyncReadStream& stream, const MutableBufferSequence& buffers,
+        CompletionCondition& completion_condition, ReadHandler& handler)
+      : base_from_cancellation_state<ReadHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        stream_(stream),
+        buffers_(buffers),
+        start_(0),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    read_op(const read_op& other)
+      : base_from_cancellation_state<ReadHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        stream_(other.stream_),
+        buffers_(other.buffers_),
+        start_(other.start_),
+        handler_(other.handler_)
+    {
+    }
+
+    read_op(read_op&& other)
+      : base_from_cancellation_state<ReadHandler>(
+          static_cast<base_from_cancellation_state<ReadHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        stream_(other.stream_),
+        buffers_(static_cast<buffers_type&&>(other.buffers_)),
+        start_(other.start_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, buffers_.total_consumed());
+        for (;;)
+        {
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read"));
+            stream_.async_read_some(buffers_.prepare(max_size),
+                static_cast<read_op&&>(*this));
+          }
+          return; default:
+          buffers_.consume(bytes_transferred);
+          if ((!ec && bytes_transferred == 0) || buffers_.empty())
+            break;
+          max_size = this->check_for_completion(ec, buffers_.total_consumed());
+          if (max_size == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<ReadHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(buffers_.total_consumed()));
+      }
+    }
+
+  //private:
+    typedef asio::detail::consuming_buffers<mutable_buffer,
+        MutableBufferSequence, MutableBufferIterator> buffers_type;
+
+    AsyncReadStream& stream_;
+    buffers_type buffers_;
+    int start_;
+    ReadHandler handler_;
+  };
+
+  template <typename AsyncReadStream, typename MutableBufferSequence,
+      typename MutableBufferIterator, typename CompletionCondition,
+      typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      read_op<AsyncReadStream, MutableBufferSequence, MutableBufferIterator,
+        CompletionCondition, ReadHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncReadStream, typename MutableBufferSequence,
+      typename MutableBufferIterator, typename CompletionCondition,
+      typename ReadHandler>
+  inline void start_read_op(AsyncReadStream& stream,
+      const MutableBufferSequence& buffers, const MutableBufferIterator&,
+      CompletionCondition& completion_condition, ReadHandler& handler)
+  {
+    read_op<AsyncReadStream, MutableBufferSequence,
+      MutableBufferIterator, CompletionCondition, ReadHandler>(
+        stream, buffers, completion_condition, handler)(
+          asio::error_code(), 0, 1);
+  }
+
+  template <typename AsyncReadStream>
+  class initiate_async_read
+  {
+  public:
+    typedef typename AsyncReadStream::executor_type executor_type;
+
+    explicit initiate_async_read(AsyncReadStream& stream)
+      : stream_(stream)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return stream_.get_executor();
+    }
+
+    template <typename ReadHandler, typename MutableBufferSequence,
+        typename CompletionCondition>
+    void operator()(ReadHandler&& handler,
+        const MutableBufferSequence& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      non_const_lvalue<ReadHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      start_read_op(stream_, buffers,
+          asio::buffer_sequence_begin(buffers),
+          completion_cond2.value, handler2.value);
+    }
+
+  private:
+    AsyncReadStream& stream_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncReadStream, typename MutableBufferSequence,
+    typename MutableBufferIterator, typename CompletionCondition,
+    typename ReadHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::read_op<AsyncReadStream, MutableBufferSequence,
+      MutableBufferIterator, CompletionCondition, ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::read_op<AsyncReadStream, MutableBufferSequence,
+        MutableBufferIterator, CompletionCondition, ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::read_op<AsyncReadStream, MutableBufferSequence,
+        MutableBufferIterator, CompletionCondition, ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#if !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+namespace detail
+{
+  template <typename AsyncReadStream, typename DynamicBuffer_v1,
+      typename CompletionCondition, typename ReadHandler>
+  class read_dynbuf_v1_op
+    : public base_from_cancellation_state<ReadHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    template <typename BufferSequence>
+    read_dynbuf_v1_op(AsyncReadStream& stream,
+        BufferSequence&& buffers,
+        CompletionCondition& completion_condition, ReadHandler& handler)
+      : base_from_cancellation_state<ReadHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        stream_(stream),
+        buffers_(static_cast<BufferSequence&&>(buffers)),
+        start_(0),
+        total_transferred_(0),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    read_dynbuf_v1_op(const read_dynbuf_v1_op& other)
+      : base_from_cancellation_state<ReadHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        stream_(other.stream_),
+        buffers_(other.buffers_),
+        start_(other.start_),
+        total_transferred_(other.total_transferred_),
+        handler_(other.handler_)
+    {
+    }
+
+    read_dynbuf_v1_op(read_dynbuf_v1_op&& other)
+      : base_from_cancellation_state<ReadHandler>(
+          static_cast<base_from_cancellation_state<ReadHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        stream_(other.stream_),
+        buffers_(static_cast<DynamicBuffer_v1&&>(other.buffers_)),
+        start_(other.start_),
+        total_transferred_(other.total_transferred_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size, bytes_available;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, total_transferred_);
+        bytes_available = std::min<std::size_t>(
+              std::max<std::size_t>(512,
+                buffers_.capacity() - buffers_.size()),
+              std::min<std::size_t>(max_size,
+                buffers_.max_size() - buffers_.size()));
+        for (;;)
+        {
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read"));
+            stream_.async_read_some(buffers_.prepare(bytes_available),
+                static_cast<read_dynbuf_v1_op&&>(*this));
+          }
+          return; default:
+          total_transferred_ += bytes_transferred;
+          buffers_.commit(bytes_transferred);
+          max_size = this->check_for_completion(ec, total_transferred_);
+          bytes_available = std::min<std::size_t>(
+                std::max<std::size_t>(512,
+                  buffers_.capacity() - buffers_.size()),
+                std::min<std::size_t>(max_size,
+                  buffers_.max_size() - buffers_.size()));
+          if ((!ec && bytes_transferred == 0) || bytes_available == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<ReadHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(total_transferred_));
+      }
+    }
+
+  //private:
+    AsyncReadStream& stream_;
+    DynamicBuffer_v1 buffers_;
+    int start_;
+    std::size_t total_transferred_;
+    ReadHandler handler_;
+  };
+
+  template <typename AsyncReadStream, typename DynamicBuffer_v1,
+      typename CompletionCondition, typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      read_dynbuf_v1_op<AsyncReadStream, DynamicBuffer_v1,
+        CompletionCondition, ReadHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncReadStream>
+  class initiate_async_read_dynbuf_v1
+  {
+  public:
+    typedef typename AsyncReadStream::executor_type executor_type;
+
+    explicit initiate_async_read_dynbuf_v1(AsyncReadStream& stream)
+      : stream_(stream)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return stream_.get_executor();
+    }
+
+    template <typename ReadHandler, typename DynamicBuffer_v1,
+        typename CompletionCondition>
+    void operator()(ReadHandler&& handler,
+        DynamicBuffer_v1&& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      non_const_lvalue<ReadHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      read_dynbuf_v1_op<AsyncReadStream, decay_t<DynamicBuffer_v1>,
+        CompletionCondition, decay_t<ReadHandler>>(
+          stream_, static_cast<DynamicBuffer_v1&&>(buffers),
+            completion_cond2.value, handler2.value)(
+              asio::error_code(), 0, 1);
+    }
+
+  private:
+    AsyncReadStream& stream_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncReadStream, typename DynamicBuffer_v1,
+    typename CompletionCondition, typename ReadHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::read_dynbuf_v1_op<AsyncReadStream,
+      DynamicBuffer_v1, CompletionCondition, ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::read_dynbuf_v1_op<AsyncReadStream, DynamicBuffer_v1,
+        CompletionCondition, ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::read_dynbuf_v1_op<AsyncReadStream,
+        DynamicBuffer_v1, CompletionCondition, ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#endif // !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+namespace detail
+{
+  template <typename AsyncReadStream, typename DynamicBuffer_v2,
+      typename CompletionCondition, typename ReadHandler>
+  class read_dynbuf_v2_op
+    : public base_from_cancellation_state<ReadHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    template <typename BufferSequence>
+    read_dynbuf_v2_op(AsyncReadStream& stream,
+        BufferSequence&& buffers,
+        CompletionCondition& completion_condition, ReadHandler& handler)
+      : base_from_cancellation_state<ReadHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        stream_(stream),
+        buffers_(static_cast<BufferSequence&&>(buffers)),
+        start_(0),
+        total_transferred_(0),
+        bytes_available_(0),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    read_dynbuf_v2_op(const read_dynbuf_v2_op& other)
+      : base_from_cancellation_state<ReadHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        stream_(other.stream_),
+        buffers_(other.buffers_),
+        start_(other.start_),
+        total_transferred_(other.total_transferred_),
+        bytes_available_(other.bytes_available_),
+        handler_(other.handler_)
+    {
+    }
+
+    read_dynbuf_v2_op(read_dynbuf_v2_op&& other)
+      : base_from_cancellation_state<ReadHandler>(
+          static_cast<base_from_cancellation_state<ReadHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        stream_(other.stream_),
+        buffers_(static_cast<DynamicBuffer_v2&&>(other.buffers_)),
+        start_(other.start_),
+        total_transferred_(other.total_transferred_),
+        bytes_available_(other.bytes_available_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size, pos;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, total_transferred_);
+        bytes_available_ = std::min<std::size_t>(
+              std::max<std::size_t>(512,
+                buffers_.capacity() - buffers_.size()),
+              std::min<std::size_t>(max_size,
+                buffers_.max_size() - buffers_.size()));
+        for (;;)
+        {
+          pos = buffers_.size();
+          buffers_.grow(bytes_available_);
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read"));
+            stream_.async_read_some(buffers_.data(pos, bytes_available_),
+                static_cast<read_dynbuf_v2_op&&>(*this));
+          }
+          return; default:
+          total_transferred_ += bytes_transferred;
+          buffers_.shrink(bytes_available_ - bytes_transferred);
+          max_size = this->check_for_completion(ec, total_transferred_);
+          bytes_available_ = std::min<std::size_t>(
+                std::max<std::size_t>(512,
+                  buffers_.capacity() - buffers_.size()),
+                std::min<std::size_t>(max_size,
+                  buffers_.max_size() - buffers_.size()));
+          if ((!ec && bytes_transferred == 0) || bytes_available_ == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<ReadHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(total_transferred_));
+      }
+    }
+
+  //private:
+    AsyncReadStream& stream_;
+    DynamicBuffer_v2 buffers_;
+    int start_;
+    std::size_t total_transferred_;
+    std::size_t bytes_available_;
+    ReadHandler handler_;
+  };
+
+  template <typename AsyncReadStream, typename DynamicBuffer_v2,
+      typename CompletionCondition, typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      read_dynbuf_v2_op<AsyncReadStream, DynamicBuffer_v2,
+        CompletionCondition, ReadHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncReadStream>
+  class initiate_async_read_dynbuf_v2
+  {
+  public:
+    typedef typename AsyncReadStream::executor_type executor_type;
+
+    explicit initiate_async_read_dynbuf_v2(AsyncReadStream& stream)
+      : stream_(stream)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return stream_.get_executor();
+    }
+
+    template <typename ReadHandler, typename DynamicBuffer_v2,
+        typename CompletionCondition>
+    void operator()(ReadHandler&& handler,
+        DynamicBuffer_v2&& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      non_const_lvalue<ReadHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      read_dynbuf_v2_op<AsyncReadStream, decay_t<DynamicBuffer_v2>,
+        CompletionCondition, decay_t<ReadHandler>>(
+          stream_, static_cast<DynamicBuffer_v2&&>(buffers),
+            completion_cond2.value, handler2.value)(
+              asio::error_code(), 0, 1);
+    }
+
+  private:
+    AsyncReadStream& stream_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncReadStream, typename DynamicBuffer_v2,
+    typename CompletionCondition, typename ReadHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::read_dynbuf_v2_op<AsyncReadStream,
+      DynamicBuffer_v2, CompletionCondition, ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::read_dynbuf_v2_op<AsyncReadStream, DynamicBuffer_v2,
+        CompletionCondition, ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::read_dynbuf_v2_op<AsyncReadStream,
+        DynamicBuffer_v2, CompletionCondition, ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_READ_HPP

include/asio/impl/read_at.hpp

@@ -0,0 +1,562 @@
+//
+// impl/read_at.hpp
+// ~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_READ_AT_HPP
+#define ASIO_IMPL_READ_AT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include <algorithm>
+#include "asio/associator.hpp"
+#include "asio/buffer.hpp"
+#include "asio/detail/array_fwd.hpp"
+#include "asio/detail/base_from_cancellation_state.hpp"
+#include "asio/detail/base_from_completion_cond.hpp"
+#include "asio/detail/bind_handler.hpp"
+#include "asio/detail/consuming_buffers.hpp"
+#include "asio/detail/dependent_type.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_tracking.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/throw_error.hpp"
+#include "asio/error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail
+{
+  template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence,
+      typename MutableBufferIterator, typename CompletionCondition>
+  std::size_t read_at_buffer_sequence(SyncRandomAccessReadDevice& d,
+      uint64_t offset, const MutableBufferSequence& buffers,
+      const MutableBufferIterator&, CompletionCondition completion_condition,
+      asio::error_code& ec)
+  {
+    ec = asio::error_code();
+    asio::detail::consuming_buffers<mutable_buffer,
+        MutableBufferSequence, MutableBufferIterator> tmp(buffers);
+    while (!tmp.empty())
+    {
+      if (std::size_t max_size = detail::adapt_completion_condition_result(
+            completion_condition(ec, tmp.total_consumed())))
+      {
+        tmp.consume(d.read_some_at(offset + tmp.total_consumed(),
+              tmp.prepare(max_size), ec));
+      }
+      else
+        break;
+    }
+    return tmp.total_consumed();
+  }
+} // namespace detail
+
+template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence,
+    typename CompletionCondition>
+std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, const MutableBufferSequence& buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return detail::read_at_buffer_sequence(d, offset, buffers,
+      asio::buffer_sequence_begin(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+}
+
+template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence>
+inline std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, const MutableBufferSequence& buffers)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read_at(
+      d, offset, buffers, transfer_all(), ec);
+  asio::detail::throw_error(ec, "read_at");
+  return bytes_transferred;
+}
+
+template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence>
+inline std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, const MutableBufferSequence& buffers,
+    asio::error_code& ec)
+{
+  return read_at(d, offset, buffers, transfer_all(), ec);
+}
+
+template <typename SyncRandomAccessReadDevice, typename MutableBufferSequence,
+    typename CompletionCondition>
+inline std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, const MutableBufferSequence& buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read_at(d, offset, buffers,
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "read_at");
+  return bytes_transferred;
+}
+
+#if !defined(ASIO_NO_EXTENSIONS)
+#if !defined(ASIO_NO_IOSTREAM)
+
+template <typename SyncRandomAccessReadDevice, typename Allocator,
+    typename CompletionCondition>
+std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  ec = asio::error_code();
+  std::size_t total_transferred = 0;
+  std::size_t max_size = detail::adapt_completion_condition_result(
+        completion_condition(ec, total_transferred));
+  std::size_t bytes_available = read_size_helper(b, max_size);
+  while (bytes_available > 0)
+  {
+    std::size_t bytes_transferred = d.read_some_at(
+        offset + total_transferred, b.prepare(bytes_available), ec);
+    b.commit(bytes_transferred);
+    total_transferred += bytes_transferred;
+    max_size = detail::adapt_completion_condition_result(
+          completion_condition(ec, total_transferred));
+    bytes_available = read_size_helper(b, max_size);
+  }
+  return total_transferred;
+}
+
+template <typename SyncRandomAccessReadDevice, typename Allocator>
+inline std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read_at(
+      d, offset, b, transfer_all(), ec);
+  asio::detail::throw_error(ec, "read_at");
+  return bytes_transferred;
+}
+
+template <typename SyncRandomAccessReadDevice, typename Allocator>
+inline std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b,
+    asio::error_code& ec)
+{
+  return read_at(d, offset, b, transfer_all(), ec);
+}
+
+template <typename SyncRandomAccessReadDevice, typename Allocator,
+    typename CompletionCondition>
+inline std::size_t read_at(SyncRandomAccessReadDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = read_at(d, offset, b,
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "read_at");
+  return bytes_transferred;
+}
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+
+namespace detail
+{
+  template <typename AsyncRandomAccessReadDevice,
+      typename MutableBufferSequence, typename MutableBufferIterator,
+      typename CompletionCondition, typename ReadHandler>
+  class read_at_op
+    : public base_from_cancellation_state<ReadHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    read_at_op(AsyncRandomAccessReadDevice& device,
+        uint64_t offset, const MutableBufferSequence& buffers,
+        CompletionCondition& completion_condition, ReadHandler& handler)
+      : base_from_cancellation_state<ReadHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        device_(device),
+        offset_(offset),
+        buffers_(buffers),
+        start_(0),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    read_at_op(const read_at_op& other)
+      : base_from_cancellation_state<ReadHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        device_(other.device_),
+        offset_(other.offset_),
+        buffers_(other.buffers_),
+        start_(other.start_),
+        handler_(other.handler_)
+    {
+    }
+
+    read_at_op(read_at_op&& other)
+      : base_from_cancellation_state<ReadHandler>(
+          static_cast<base_from_cancellation_state<ReadHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        device_(other.device_),
+        offset_(other.offset_),
+        buffers_(static_cast<buffers_type&&>(other.buffers_)),
+        start_(other.start_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, buffers_.total_consumed());
+        for (;;)
+        {
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read_at"));
+            device_.async_read_some_at(
+                offset_ + buffers_.total_consumed(), buffers_.prepare(max_size),
+                static_cast<read_at_op&&>(*this));
+          }
+          return; default:
+          buffers_.consume(bytes_transferred);
+          if ((!ec && bytes_transferred == 0) || buffers_.empty())
+            break;
+          max_size = this->check_for_completion(ec, buffers_.total_consumed());
+          if (max_size == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<ReadHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(buffers_.total_consumed()));
+      }
+    }
+
+  //private:
+    typedef asio::detail::consuming_buffers<mutable_buffer,
+        MutableBufferSequence, MutableBufferIterator> buffers_type;
+
+    AsyncRandomAccessReadDevice& device_;
+    uint64_t offset_;
+    buffers_type buffers_;
+    int start_;
+    ReadHandler handler_;
+  };
+
+  template <typename AsyncRandomAccessReadDevice,
+      typename MutableBufferSequence, typename MutableBufferIterator,
+      typename CompletionCondition, typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
+        MutableBufferIterator, CompletionCondition, ReadHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncRandomAccessReadDevice,
+      typename MutableBufferSequence, typename MutableBufferIterator,
+      typename CompletionCondition, typename ReadHandler>
+  inline void start_read_at_op(AsyncRandomAccessReadDevice& d,
+      uint64_t offset, const MutableBufferSequence& buffers,
+      const MutableBufferIterator&, CompletionCondition& completion_condition,
+      ReadHandler& handler)
+  {
+    detail::read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
+      MutableBufferIterator, CompletionCondition, ReadHandler>(
+        d, offset, buffers, completion_condition, handler)(
+          asio::error_code(), 0, 1);
+  }
+
+  template <typename AsyncRandomAccessReadDevice>
+  class initiate_async_read_at
+  {
+  public:
+    typedef typename AsyncRandomAccessReadDevice::executor_type executor_type;
+
+    explicit initiate_async_read_at(AsyncRandomAccessReadDevice& device)
+      : device_(device)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return device_.get_executor();
+    }
+
+    template <typename ReadHandler, typename MutableBufferSequence,
+        typename CompletionCondition>
+    void operator()(ReadHandler&& handler,
+        uint64_t offset, const MutableBufferSequence& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      non_const_lvalue<ReadHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      start_read_at_op(device_, offset, buffers,
+          asio::buffer_sequence_begin(buffers),
+          completion_cond2.value, handler2.value);
+    }
+
+  private:
+    AsyncRandomAccessReadDevice& device_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncRandomAccessReadDevice, typename MutableBufferSequence,
+    typename MutableBufferIterator, typename CompletionCondition,
+    typename ReadHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::read_at_op<AsyncRandomAccessReadDevice, MutableBufferSequence,
+      MutableBufferIterator, CompletionCondition, ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::read_at_op<AsyncRandomAccessReadDevice,
+        MutableBufferSequence, MutableBufferIterator,
+        CompletionCondition, ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::read_at_op<AsyncRandomAccessReadDevice,
+        MutableBufferSequence, MutableBufferIterator,
+        CompletionCondition, ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#if !defined(ASIO_NO_EXTENSIONS)
+#if !defined(ASIO_NO_IOSTREAM)
+
+namespace detail
+{
+  template <typename AsyncRandomAccessReadDevice, typename Allocator,
+      typename CompletionCondition, typename ReadHandler>
+  class read_at_streambuf_op
+    : public base_from_cancellation_state<ReadHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    read_at_streambuf_op(AsyncRandomAccessReadDevice& device,
+        uint64_t offset, basic_streambuf<Allocator>& streambuf,
+        CompletionCondition& completion_condition, ReadHandler& handler)
+      : base_from_cancellation_state<ReadHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        device_(device),
+        offset_(offset),
+        streambuf_(streambuf),
+        start_(0),
+        total_transferred_(0),
+        handler_(static_cast<ReadHandler&&>(handler))
+    {
+    }
+
+    read_at_streambuf_op(const read_at_streambuf_op& other)
+      : base_from_cancellation_state<ReadHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        device_(other.device_),
+        offset_(other.offset_),
+        streambuf_(other.streambuf_),
+        start_(other.start_),
+        total_transferred_(other.total_transferred_),
+        handler_(other.handler_)
+    {
+    }
+
+    read_at_streambuf_op(read_at_streambuf_op&& other)
+      : base_from_cancellation_state<ReadHandler>(
+          static_cast<base_from_cancellation_state<ReadHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        device_(other.device_),
+        offset_(other.offset_),
+        streambuf_(other.streambuf_),
+        start_(other.start_),
+        total_transferred_(other.total_transferred_),
+        handler_(static_cast<ReadHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size, bytes_available;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, total_transferred_);
+        bytes_available = read_size_helper(streambuf_, max_size);
+        for (;;)
+        {
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_read_at"));
+            device_.async_read_some_at(offset_ + total_transferred_,
+                streambuf_.prepare(bytes_available),
+                static_cast<read_at_streambuf_op&&>(*this));
+          }
+          return; default:
+          total_transferred_ += bytes_transferred;
+          streambuf_.commit(bytes_transferred);
+          max_size = this->check_for_completion(ec, total_transferred_);
+          bytes_available = read_size_helper(streambuf_, max_size);
+          if ((!ec && bytes_transferred == 0) || bytes_available == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<ReadHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(total_transferred_));
+      }
+    }
+
+  //private:
+    AsyncRandomAccessReadDevice& device_;
+    uint64_t offset_;
+    asio::basic_streambuf<Allocator>& streambuf_;
+    int start_;
+    std::size_t total_transferred_;
+    ReadHandler handler_;
+  };
+
+  template <typename AsyncRandomAccessReadDevice, typename Allocator,
+      typename CompletionCondition, typename ReadHandler>
+  inline bool asio_handler_is_continuation(
+      read_at_streambuf_op<AsyncRandomAccessReadDevice, Allocator,
+        CompletionCondition, ReadHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncRandomAccessReadDevice>
+  class initiate_async_read_at_streambuf
+  {
+  public:
+    typedef typename AsyncRandomAccessReadDevice::executor_type executor_type;
+
+    explicit initiate_async_read_at_streambuf(
+        AsyncRandomAccessReadDevice& device)
+      : device_(device)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return device_.get_executor();
+    }
+
+    template <typename ReadHandler,
+        typename Allocator, typename CompletionCondition>
+    void operator()(ReadHandler&& handler,
+        uint64_t offset, basic_streambuf<Allocator>* b,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a ReadHandler.
+      ASIO_READ_HANDLER_CHECK(ReadHandler, handler) type_check;
+
+      non_const_lvalue<ReadHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      read_at_streambuf_op<AsyncRandomAccessReadDevice, Allocator,
+        CompletionCondition, decay_t<ReadHandler>>(
+          device_, offset, *b, completion_cond2.value, handler2.value)(
+            asio::error_code(), 0, 1);
+    }
+
+  private:
+    AsyncRandomAccessReadDevice& device_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncRandomAccessReadDevice, typename Executor,
+    typename CompletionCondition, typename ReadHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::read_at_streambuf_op<AsyncRandomAccessReadDevice,
+      Executor, CompletionCondition, ReadHandler>,
+    DefaultCandidate>
+  : Associator<ReadHandler, DefaultCandidate>
+{
+  static typename Associator<ReadHandler, DefaultCandidate>::type get(
+      const detail::read_at_streambuf_op<AsyncRandomAccessReadDevice,
+        Executor, CompletionCondition, ReadHandler>& h) noexcept
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::read_at_streambuf_op<AsyncRandomAccessReadDevice,
+        Executor, CompletionCondition, ReadHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<ReadHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_READ_AT_HPP

include/asio/impl/redirect_error.hpp

@@ -0,0 +1,287 @@
+
+// impl/redirect_error.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_REDIRECT_ERROR_HPP
+#define ASIO_IMPL_REDIRECT_ERROR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/associated_executor.hpp"
+#include "asio/associator.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/initiation_base.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/system_error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+// Class to adapt a redirect_error_t as a completion handler.
+template <typename Handler>
+class redirect_error_handler
+{
+public:
+  typedef void result_type;
+
+  template <typename CompletionToken>
+  redirect_error_handler(redirect_error_t<CompletionToken> e)
+    : ec_(e.ec_),
+      handler_(static_cast<CompletionToken&&>(e.token_))
+  {
+  }
+
+  template <typename RedirectedHandler>
+  redirect_error_handler(asio::error_code& ec,
+      RedirectedHandler&& h)
+    : ec_(ec),
+      handler_(static_cast<RedirectedHandler&&>(h))
+  {
+  }
+
+  void operator()()
+  {
+    static_cast<Handler&&>(handler_)();
+  }
+
+  template <typename Arg, typename... Args>
+  enable_if_t<
+    !is_same<decay_t<Arg>, asio::error_code>::value
+  >
+  operator()(Arg&& arg, Args&&... args)
+  {
+    static_cast<Handler&&>(handler_)(
+        static_cast<Arg&&>(arg),
+        static_cast<Args&&>(args)...);
+  }
+
+  template <typename... Args>
+  void operator()(const asio::error_code& ec, Args&&... args)
+  {
+    ec_ = ec;
+    static_cast<Handler&&>(handler_)(static_cast<Args&&>(args)...);
+  }
+
+//private:
+  asio::error_code& ec_;
+  Handler handler_;
+};
+
+template <typename Handler>
+inline bool asio_handler_is_continuation(
+    redirect_error_handler<Handler>* this_handler)
+{
+  return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+}
+
+template <typename Signature>
+struct redirect_error_signature
+{
+  typedef Signature type;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<R(asio::error_code, Args...)>
+{
+  typedef R type(Args...);
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<R(const asio::error_code&, Args...)>
+{
+  typedef R type(Args...);
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<R(asio::error_code, Args...) &>
+{
+  typedef R type(Args...) &;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<R(const asio::error_code&, Args...) &>
+{
+  typedef R type(Args...) &;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<R(asio::error_code, Args...) &&>
+{
+  typedef R type(Args...) &&;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<R(const asio::error_code&, Args...) &&>
+{
+  typedef R type(Args...) &&;
+};
+
+#if defined(ASIO_HAS_NOEXCEPT_FUNCTION_TYPE)
+
+template <typename R, typename... Args>
+struct redirect_error_signature<
+  R(asio::error_code, Args...) noexcept>
+{
+  typedef R type(Args...) & noexcept;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<
+  R(const asio::error_code&, Args...) noexcept>
+{
+  typedef R type(Args...) & noexcept;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<
+  R(asio::error_code, Args...) & noexcept>
+{
+  typedef R type(Args...) & noexcept;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<
+  R(const asio::error_code&, Args...) & noexcept>
+{
+  typedef R type(Args...) & noexcept;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<
+  R(asio::error_code, Args...) && noexcept>
+{
+  typedef R type(Args...) && noexcept;
+};
+
+template <typename R, typename... Args>
+struct redirect_error_signature<
+  R(const asio::error_code&, Args...) && noexcept>
+{
+  typedef R type(Args...) && noexcept;
+};
+
+#endif // defined(ASIO_HAS_NOEXCEPT_FUNCTION_TYPE)
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename CompletionToken, typename Signature>
+struct async_result<redirect_error_t<CompletionToken>, Signature>
+  : async_result<CompletionToken,
+      typename detail::redirect_error_signature<Signature>::type>
+{
+  template <typename Initiation>
+  struct init_wrapper : detail::initiation_base<Initiation>
+  {
+    using detail::initiation_base<Initiation>::initiation_base;
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        asio::error_code* ec, Args&&... args) &&
+    {
+      static_cast<Initiation&&>(*this)(
+          detail::redirect_error_handler<decay_t<Handler>>(
+            *ec, static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+
+    template <typename Handler, typename... Args>
+    void operator()(Handler&& handler,
+        asio::error_code* ec, Args&&... args) const &
+    {
+      static_cast<const Initiation&>(*this)(
+          detail::redirect_error_handler<decay_t<Handler>>(
+            *ec, static_cast<Handler&&>(handler)),
+          static_cast<Args&&>(args)...);
+    }
+  };
+
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<
+        conditional_t<
+          is_const<remove_reference_t<RawCompletionToken>>::value,
+            const CompletionToken, CompletionToken>,
+        typename detail::redirect_error_signature<Signature>::type>(
+          declval<init_wrapper<decay_t<Initiation>>>(),
+          token.token_, &token.ec_, static_cast<Args&&>(args)...))
+  {
+    return async_initiate<
+      conditional_t<
+        is_const<remove_reference_t<RawCompletionToken>>::value,
+          const CompletionToken, CompletionToken>,
+      typename detail::redirect_error_signature<Signature>::type>(
+        init_wrapper<decay_t<Initiation>>(
+          static_cast<Initiation&&>(initiation)),
+        token.token_, &token.ec_, static_cast<Args&&>(args)...);
+  }
+};
+
+template <template <typename, typename> class Associator,
+    typename Handler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::redirect_error_handler<Handler>, DefaultCandidate>
+  : Associator<Handler, DefaultCandidate>
+{
+  static typename Associator<Handler, DefaultCandidate>::type get(
+      const detail::redirect_error_handler<Handler>& h) noexcept
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(const detail::redirect_error_handler<Handler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<Handler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<Handler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+template <typename... Signatures>
+struct async_result<partial_redirect_error, Signatures...>
+{
+  template <typename Initiation, typename RawCompletionToken, typename... Args>
+  static auto initiate(Initiation&& initiation,
+      RawCompletionToken&& token, Args&&... args)
+    -> decltype(
+      async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        redirect_error_t<
+          default_completion_token_t<associated_executor_t<Initiation>>>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.ec_),
+        static_cast<Args&&>(args)...))
+  {
+    return async_initiate<Signatures...>(
+        static_cast<Initiation&&>(initiation),
+        redirect_error_t<
+          default_completion_token_t<associated_executor_t<Initiation>>>(
+            default_completion_token_t<associated_executor_t<Initiation>>{},
+            token.ec_),
+        static_cast<Args&&>(args)...);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_REDIRECT_ERROR_HPP

include/asio/impl/serial_port_base.hpp

@@ -0,0 +1,59 @@
+//
+// impl/serial_port_base.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2008 Rep Invariant Systems, Inc. (info@repinvariant.com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_SERIAL_PORT_BASE_HPP
+#define ASIO_IMPL_SERIAL_PORT_BASE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+inline serial_port_base::baud_rate::baud_rate(unsigned int rate)
+  : value_(rate)
+{
+}
+
+inline unsigned int serial_port_base::baud_rate::value() const
+{
+  return value_;
+}
+
+inline serial_port_base::flow_control::type
+serial_port_base::flow_control::value() const
+{
+  return value_;
+}
+
+inline serial_port_base::parity::type serial_port_base::parity::value() const
+{
+  return value_;
+}
+
+inline serial_port_base::stop_bits::type
+serial_port_base::stop_bits::value() const
+{
+  return value_;
+}
+
+inline unsigned int serial_port_base::character_size::value() const
+{
+  return value_;
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_SERIAL_PORT_BASE_HPP

include/asio/impl/serial_port_base.ipp

@@ -0,0 +1,554 @@
+//
+// impl/serial_port_base.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+// Copyright (c) 2008 Rep Invariant Systems, Inc. (info@repinvariant.com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_SERIAL_PORT_BASE_IPP
+#define ASIO_IMPL_SERIAL_PORT_BASE_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HAS_SERIAL_PORT)
+
+#include <stdexcept>
+#include "asio/error.hpp"
+#include "asio/serial_port_base.hpp"
+#include "asio/detail/throw_exception.hpp"
+
+#if defined(GENERATING_DOCUMENTATION)
+# define ASIO_OPTION_STORAGE implementation_defined
+#elif defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+# define ASIO_OPTION_STORAGE DCB
+#else
+# define ASIO_OPTION_STORAGE termios
+#endif
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+ASIO_SYNC_OP_VOID serial_port_base::baud_rate::store(
+    ASIO_OPTION_STORAGE& storage, asio::error_code& ec) const
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  storage.BaudRate = value_;
+#else
+  speed_t baud;
+  switch (value_)
+  {
+  // Do POSIX-specified rates first.
+  case 0: baud = B0; break;
+  case 50: baud = B50; break;
+  case 75: baud = B75; break;
+  case 110: baud = B110; break;
+  case 134: baud = B134; break;
+  case 150: baud = B150; break;
+  case 200: baud = B200; break;
+  case 300: baud = B300; break;
+  case 600: baud = B600; break;
+  case 1200: baud = B1200; break;
+  case 1800: baud = B1800; break;
+  case 2400: baud = B2400; break;
+  case 4800: baud = B4800; break;
+  case 9600: baud = B9600; break;
+  case 19200: baud = B19200; break;
+  case 38400: baud = B38400; break;
+  // And now the extended ones conditionally.
+# ifdef B7200
+  case 7200: baud = B7200; break;
+# endif
+# ifdef B14400
+  case 14400: baud = B14400; break;
+# endif
+# ifdef B57600
+  case 57600: baud = B57600; break;
+# endif
+# ifdef B115200
+  case 115200: baud = B115200; break;
+# endif
+# ifdef B230400
+  case 230400: baud = B230400; break;
+# endif
+# ifdef B460800
+  case 460800: baud = B460800; break;
+# endif
+# ifdef B500000
+  case 500000: baud = B500000; break;
+# endif
+# ifdef B576000
+  case 576000: baud = B576000; break;
+# endif
+# ifdef B921600
+  case 921600: baud = B921600; break;
+# endif
+# ifdef B1000000
+  case 1000000: baud = B1000000; break;
+# endif
+# ifdef B1152000
+  case 1152000: baud = B1152000; break;
+# endif
+# ifdef B2000000
+  case 2000000: baud = B2000000; break;
+# endif
+# ifdef B3000000
+  case 3000000: baud = B3000000; break;
+# endif
+# ifdef B3500000
+  case 3500000: baud = B3500000; break;
+# endif
+# ifdef B4000000
+  case 4000000: baud = B4000000; break;
+# endif
+  default:
+    ec = asio::error::invalid_argument;
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+  }
+# if defined(_BSD_SOURCE) || defined(_DEFAULT_SOURCE)
+  ::cfsetspeed(&storage, baud);
+# else
+  ::cfsetispeed(&storage, baud);
+  ::cfsetospeed(&storage, baud);
+# endif
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::baud_rate::load(
+    const ASIO_OPTION_STORAGE& storage, asio::error_code& ec)
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  value_ = storage.BaudRate;
+#else
+  speed_t baud = ::cfgetospeed(&storage);
+  switch (baud)
+  {
+  // First do those specified by POSIX.
+  case B0: value_ = 0; break;
+  case B50: value_ = 50; break;
+  case B75: value_ = 75; break;
+  case B110: value_ = 110; break;
+  case B134: value_ = 134; break;
+  case B150: value_ = 150; break;
+  case B200: value_ = 200; break;
+  case B300: value_ = 300; break;
+  case B600: value_ = 600; break;
+  case B1200: value_ = 1200; break;
+  case B1800: value_ = 1800; break;
+  case B2400: value_ = 2400; break;
+  case B4800: value_ = 4800; break;
+  case B9600: value_ = 9600; break;
+  case B19200: value_ = 19200; break;
+  case B38400: value_ = 38400; break;
+  // Now conditionally handle a bunch of extended rates.
+# ifdef B7200
+  case B7200: value_ = 7200; break;
+# endif
+# ifdef B14400
+  case B14400: value_ = 14400; break;
+# endif
+# ifdef B57600
+  case B57600: value_ = 57600; break;
+# endif
+# ifdef B115200
+  case B115200: value_ = 115200; break;
+# endif
+# ifdef B230400
+  case B230400: value_ = 230400; break;
+# endif
+# ifdef B460800
+  case B460800: value_ = 460800; break;
+# endif
+# ifdef B500000
+  case B500000: value_ = 500000; break;
+# endif
+# ifdef B576000
+  case B576000: value_ = 576000; break;
+# endif
+# ifdef B921600
+  case B921600: value_ = 921600; break;
+# endif
+# ifdef B1000000
+  case B1000000: value_ = 1000000; break;
+# endif
+# ifdef B1152000
+  case B1152000: value_ = 1152000; break;
+# endif
+# ifdef B2000000
+  case B2000000: value_ = 2000000; break;
+# endif
+# ifdef B3000000
+  case B3000000: value_ = 3000000; break;
+# endif
+# ifdef B3500000
+  case B3500000: value_ = 3500000; break;
+# endif
+# ifdef B4000000
+  case B4000000: value_ = 4000000; break;
+# endif
+  default:
+    value_ = 0;
+    ec = asio::error::invalid_argument;
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+serial_port_base::flow_control::flow_control(
+    serial_port_base::flow_control::type t)
+  : value_(t)
+{
+  if (t != none && t != software && t != hardware)
+  {
+    std::out_of_range ex("invalid flow_control value");
+    asio::detail::throw_exception(ex);
+  }
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::flow_control::store(
+    ASIO_OPTION_STORAGE& storage, asio::error_code& ec) const
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  storage.fOutxCtsFlow = FALSE;
+  storage.fOutxDsrFlow = FALSE;
+  storage.fTXContinueOnXoff = TRUE;
+  storage.fDtrControl = DTR_CONTROL_ENABLE;
+  storage.fDsrSensitivity = FALSE;
+  storage.fOutX = FALSE;
+  storage.fInX = FALSE;
+  storage.fRtsControl = RTS_CONTROL_ENABLE;
+  switch (value_)
+  {
+  case none:
+    break;
+  case software:
+    storage.fOutX = TRUE;
+    storage.fInX = TRUE;
+    break;
+  case hardware:
+    storage.fOutxCtsFlow = TRUE;
+    storage.fRtsControl = RTS_CONTROL_HANDSHAKE;
+    break;
+  default:
+    break;
+  }
+#else
+  switch (value_)
+  {
+  case none:
+    storage.c_iflag &= ~(IXOFF | IXON);
+# if defined(_BSD_SOURCE) || defined(_DEFAULT_SOURCE)
+    storage.c_cflag &= ~CRTSCTS;
+# elif defined(__QNXNTO__)
+    storage.c_cflag &= ~(IHFLOW | OHFLOW);
+# endif
+    break;
+  case software:
+    storage.c_iflag |= IXOFF | IXON;
+# if defined(_BSD_SOURCE) || defined(_DEFAULT_SOURCE)
+    storage.c_cflag &= ~CRTSCTS;
+# elif defined(__QNXNTO__)
+    storage.c_cflag &= ~(IHFLOW | OHFLOW);
+# endif
+    break;
+  case hardware:
+# if defined(_BSD_SOURCE) || defined(_DEFAULT_SOURCE)
+    storage.c_iflag &= ~(IXOFF | IXON);
+    storage.c_cflag |= CRTSCTS;
+    break;
+# elif defined(__QNXNTO__)
+    storage.c_iflag &= ~(IXOFF | IXON);
+    storage.c_cflag |= (IHFLOW | OHFLOW);
+    break;
+# else
+    ec = asio::error::operation_not_supported;
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+# endif
+  default:
+    break;
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::flow_control::load(
+    const ASIO_OPTION_STORAGE& storage, asio::error_code& ec)
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  if (storage.fOutX && storage.fInX)
+  {
+    value_ = software;
+  }
+  else if (storage.fOutxCtsFlow && storage.fRtsControl == RTS_CONTROL_HANDSHAKE)
+  {
+    value_ = hardware;
+  }
+  else
+  {
+    value_ = none;
+  }
+#else
+  if (storage.c_iflag & (IXOFF | IXON))
+  {
+    value_ = software;
+  }
+# if defined(_BSD_SOURCE) || defined(_DEFAULT_SOURCE)
+  else if (storage.c_cflag & CRTSCTS)
+  {
+    value_ = hardware;
+  }
+# elif defined(__QNXNTO__)
+  else if (storage.c_cflag & IHFLOW && storage.c_cflag & OHFLOW)
+  {
+    value_ = hardware;
+  }
+# endif
+  else
+  {
+    value_ = none;
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+serial_port_base::parity::parity(serial_port_base::parity::type t)
+  : value_(t)
+{
+  if (t != none && t != odd && t != even)
+  {
+    std::out_of_range ex("invalid parity value");
+    asio::detail::throw_exception(ex);
+  }
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::parity::store(
+    ASIO_OPTION_STORAGE& storage, asio::error_code& ec) const
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  switch (value_)
+  {
+  case none:
+    storage.fParity = FALSE;
+    storage.Parity = NOPARITY;
+    break;
+  case odd:
+    storage.fParity = TRUE;
+    storage.Parity = ODDPARITY;
+    break;
+  case even:
+    storage.fParity = TRUE;
+    storage.Parity = EVENPARITY;
+    break;
+  default:
+    break;
+  }
+#else
+  switch (value_)
+  {
+  case none:
+    storage.c_iflag |= IGNPAR;
+    storage.c_cflag &= ~(PARENB | PARODD);
+    break;
+  case even:
+    storage.c_iflag &= ~(IGNPAR | PARMRK);
+    storage.c_iflag |= INPCK;
+    storage.c_cflag |= PARENB;
+    storage.c_cflag &= ~PARODD;
+    break;
+  case odd:
+    storage.c_iflag &= ~(IGNPAR | PARMRK);
+    storage.c_iflag |= INPCK;
+    storage.c_cflag |= (PARENB | PARODD);
+    break;
+  default:
+    break;
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::parity::load(
+    const ASIO_OPTION_STORAGE& storage, asio::error_code& ec)
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  if (storage.Parity == EVENPARITY)
+  {
+    value_ = even;
+  }
+  else if (storage.Parity == ODDPARITY)
+  {
+    value_ = odd;
+  }
+  else
+  {
+    value_ = none;
+  }
+#else
+  if (storage.c_cflag & PARENB)
+  {
+    if (storage.c_cflag & PARODD)
+    {
+      value_ = odd;
+    }
+    else
+    {
+      value_ = even;
+    }
+  }
+  else
+  {
+    value_ = none;
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+serial_port_base::stop_bits::stop_bits(
+    serial_port_base::stop_bits::type t)
+  : value_(t)
+{
+  if (t != one && t != onepointfive && t != two)
+  {
+    std::out_of_range ex("invalid stop_bits value");
+    asio::detail::throw_exception(ex);
+  }
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::stop_bits::store(
+    ASIO_OPTION_STORAGE& storage, asio::error_code& ec) const
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  switch (value_)
+  {
+  case one:
+    storage.StopBits = ONESTOPBIT;
+    break;
+  case onepointfive:
+    storage.StopBits = ONE5STOPBITS;
+    break;
+  case two:
+    storage.StopBits = TWOSTOPBITS;
+    break;
+  default:
+    break;
+  }
+#else
+  switch (value_)
+  {
+  case one:
+    storage.c_cflag &= ~CSTOPB;
+    break;
+  case two:
+    storage.c_cflag |= CSTOPB;
+    break;
+  default:
+    ec = asio::error::operation_not_supported;
+    ASIO_SYNC_OP_VOID_RETURN(ec);
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::stop_bits::load(
+    const ASIO_OPTION_STORAGE& storage, asio::error_code& ec)
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  if (storage.StopBits == ONESTOPBIT)
+  {
+    value_ = one;
+  }
+  else if (storage.StopBits == ONE5STOPBITS)
+  {
+    value_ = onepointfive;
+  }
+  else if (storage.StopBits == TWOSTOPBITS)
+  {
+    value_ = two;
+  }
+  else
+  {
+    value_ = one;
+  }
+#else
+  value_ = (storage.c_cflag & CSTOPB) ? two : one;
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+serial_port_base::character_size::character_size(unsigned int t)
+  : value_(t)
+{
+  if (t < 5 || t > 8)
+  {
+    std::out_of_range ex("invalid character_size value");
+    asio::detail::throw_exception(ex);
+  }
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::character_size::store(
+    ASIO_OPTION_STORAGE& storage, asio::error_code& ec) const
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  storage.ByteSize = value_;
+#else
+  storage.c_cflag &= ~CSIZE;
+  switch (value_)
+  {
+  case 5: storage.c_cflag |= CS5; break;
+  case 6: storage.c_cflag |= CS6; break;
+  case 7: storage.c_cflag |= CS7; break;
+  case 8: storage.c_cflag |= CS8; break;
+  default: break;
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+ASIO_SYNC_OP_VOID serial_port_base::character_size::load(
+    const ASIO_OPTION_STORAGE& storage, asio::error_code& ec)
+{
+#if defined(ASIO_WINDOWS) || defined(__CYGWIN__)
+  value_ = storage.ByteSize;
+#else
+  if ((storage.c_cflag & CSIZE) == CS5) { value_ = 5; }
+  else if ((storage.c_cflag & CSIZE) == CS6) { value_ = 6; }
+  else if ((storage.c_cflag & CSIZE) == CS7) { value_ = 7; }
+  else if ((storage.c_cflag & CSIZE) == CS8) { value_ = 8; }
+  else
+  {
+    // Hmmm, use 8 for now.
+    value_ = 8;
+  }
+#endif
+  ec = asio::error_code();
+  ASIO_SYNC_OP_VOID_RETURN(ec);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#undef ASIO_OPTION_STORAGE
+
+#endif // defined(ASIO_HAS_SERIAL_PORT)
+
+#endif // ASIO_IMPL_SERIAL_PORT_BASE_IPP

include/asio/impl/src.hpp

@@ -0,0 +1,96 @@
+//
+// impl/src.hpp
+// ~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_SRC_HPP
+#define ASIO_IMPL_SRC_HPP
+
+#define ASIO_SOURCE
+
+#include "asio/detail/config.hpp"
+
+#if defined(ASIO_HEADER_ONLY)
+# error Do not compile Asio library source with ASIO_HEADER_ONLY defined
+#endif
+
+#include "asio/impl/any_completion_executor.ipp"
+#include "asio/impl/any_io_executor.ipp"
+#include "asio/impl/awaitable.ipp"
+#include "asio/impl/cancellation_signal.ipp"
+#include "asio/impl/config.ipp"
+#include "asio/impl/connect_pipe.ipp"
+#include "asio/impl/error.ipp"
+#include "asio/impl/error_code.ipp"
+#include "asio/impl/execution_context.ipp"
+#include "asio/impl/executor.ipp"
+#include "asio/impl/io_context.ipp"
+#include "asio/impl/multiple_exceptions.ipp"
+#include "asio/impl/serial_port_base.ipp"
+#include "asio/impl/system_context.ipp"
+#include "asio/impl/thread_pool.ipp"
+#include "asio/detail/impl/buffer_sequence_adapter.ipp"
+#include "asio/detail/impl/descriptor_ops.ipp"
+#include "asio/detail/impl/dev_poll_reactor.ipp"
+#include "asio/detail/impl/epoll_reactor.ipp"
+#include "asio/detail/impl/eventfd_select_interrupter.ipp"
+#include "asio/detail/impl/handler_tracking.ipp"
+#include "asio/detail/impl/io_uring_descriptor_service.ipp"
+#include "asio/detail/impl/io_uring_file_service.ipp"
+#include "asio/detail/impl/io_uring_socket_service_base.ipp"
+#include "asio/detail/impl/io_uring_service.ipp"
+#include "asio/detail/impl/kqueue_reactor.ipp"
+#include "asio/detail/impl/null_event.ipp"
+#include "asio/detail/impl/pipe_select_interrupter.ipp"
+#include "asio/detail/impl/posix_event.ipp"
+#include "asio/detail/impl/posix_mutex.ipp"
+#include "asio/detail/impl/posix_serial_port_service.ipp"
+#include "asio/detail/impl/posix_thread.ipp"
+#include "asio/detail/impl/posix_tss_ptr.ipp"
+#include "asio/detail/impl/reactive_descriptor_service.ipp"
+#include "asio/detail/impl/reactive_socket_service_base.ipp"
+#include "asio/detail/impl/resolver_service_base.ipp"
+#include "asio/detail/impl/resolver_thread_pool.ipp"
+#include "asio/detail/impl/scheduler.ipp"
+#include "asio/detail/impl/select_reactor.ipp"
+#include "asio/detail/impl/service_registry.ipp"
+#include "asio/detail/impl/signal_set_service.ipp"
+#include "asio/detail/impl/socket_ops.ipp"
+#include "asio/detail/impl/socket_select_interrupter.ipp"
+#include "asio/detail/impl/strand_executor_service.ipp"
+#include "asio/detail/impl/strand_service.ipp"
+#include "asio/detail/impl/thread_context.ipp"
+#include "asio/detail/impl/throw_error.ipp"
+#include "asio/detail/impl/timer_queue_set.ipp"
+#include "asio/detail/impl/win_iocp_file_service.ipp"
+#include "asio/detail/impl/win_iocp_handle_service.ipp"
+#include "asio/detail/impl/win_iocp_io_context.ipp"
+#include "asio/detail/impl/win_iocp_serial_port_service.ipp"
+#include "asio/detail/impl/win_iocp_socket_service_base.ipp"
+#include "asio/detail/impl/win_event.ipp"
+#include "asio/detail/impl/win_mutex.ipp"
+#include "asio/detail/impl/win_object_handle_service.ipp"
+#include "asio/detail/impl/win_static_mutex.ipp"
+#include "asio/detail/impl/win_thread.ipp"
+#include "asio/detail/impl/win_tss_ptr.ipp"
+#include "asio/detail/impl/winrt_ssocket_service_base.ipp"
+#include "asio/detail/impl/winrt_timer_scheduler.ipp"
+#include "asio/detail/impl/winsock_init.ipp"
+#include "asio/execution/impl/bad_executor.ipp"
+#include "asio/experimental/impl/channel_error.ipp"
+#include "asio/generic/detail/impl/endpoint.ipp"
+#include "asio/ip/impl/address.ipp"
+#include "asio/ip/impl/address_v4.ipp"
+#include "asio/ip/impl/address_v6.ipp"
+#include "asio/ip/impl/host_name.ipp"
+#include "asio/ip/impl/network_v4.ipp"
+#include "asio/ip/impl/network_v6.ipp"
+#include "asio/ip/detail/impl/endpoint.ipp"
+#include "asio/local/detail/impl/endpoint.ipp"
+
+#endif // ASIO_IMPL_SRC_HPP

include/asio/impl/system_context.hpp

@@ -0,0 +1,34 @@
+//
+// impl/system_context.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_SYSTEM_CONTEXT_HPP
+#define ASIO_IMPL_SYSTEM_CONTEXT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/system_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+inline system_context::executor_type
+system_context::get_executor() noexcept
+{
+  return system_executor();
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_SYSTEM_CONTEXT_HPP

include/asio/impl/system_context.ipp

@@ -0,0 +1,93 @@
+//
+// impl/system_context.ipp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_SYSTEM_CONTEXT_IPP
+#define ASIO_IMPL_SYSTEM_CONTEXT_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/system_context.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+struct system_context::thread_function
+{
+  detail::scheduler* scheduler_;
+
+  void operator()()
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+      asio::error_code ec;
+      scheduler_->run(ec);
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      std::terminate();
+    }
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+  }
+};
+
+system_context::system_context()
+  : scheduler_(add_scheduler(new detail::scheduler(*this, false))),
+    threads_(std::allocator<void>())
+{
+  scheduler_.work_started();
+
+  thread_function f = { &scheduler_ };
+  num_threads_ = detail::thread::hardware_concurrency() * 2;
+  num_threads_ = num_threads_ ? num_threads_ : 2;
+  threads_.create_threads(f, num_threads_);
+}
+
+system_context::~system_context()
+{
+  scheduler_.work_finished();
+  scheduler_.stop();
+  threads_.join();
+}
+
+void system_context::stop()
+{
+  scheduler_.stop();
+}
+
+bool system_context::stopped() const noexcept
+{
+  return scheduler_.stopped();
+}
+
+void system_context::join()
+{
+  scheduler_.work_finished();
+  threads_.join();
+}
+
+detail::scheduler& system_context::add_scheduler(detail::scheduler* s)
+{
+  detail::scoped_ptr<detail::scheduler> scoped_impl(s);
+  asio::add_service<detail::scheduler>(*this, scoped_impl.get());
+  return *scoped_impl.release();
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_SYSTEM_CONTEXT_IPP

include/asio/impl/system_executor.hpp

@@ -0,0 +1,179 @@
+//
+// impl/system_executor.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_SYSTEM_EXECUTOR_HPP
+#define ASIO_IMPL_SYSTEM_EXECUTOR_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/executor_op.hpp"
+#include "asio/detail/global.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/system_context.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+template <typename Blocking, typename Relationship, typename Allocator>
+inline system_context&
+basic_system_executor<Blocking, Relationship, Allocator>::query(
+    execution::context_t) noexcept
+{
+  return detail::global<system_context>();
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+inline std::size_t
+basic_system_executor<Blocking, Relationship, Allocator>::query(
+    execution::occupancy_t) const noexcept
+{
+  return detail::global<system_context>().num_threads_;
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function>
+inline void
+basic_system_executor<Blocking, Relationship, Allocator>::do_execute(
+    Function&& f, execution::blocking_t::possibly_t) const
+{
+  // Obtain a non-const instance of the function.
+  detail::non_const_lvalue<Function> f2(f);
+
+#if !defined(ASIO_NO_EXCEPTIONS)
+  try
+  {
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+    detail::fenced_block b(detail::fenced_block::full);
+    static_cast<decay_t<Function>&&>(f2.value)();
+#if !defined(ASIO_NO_EXCEPTIONS)
+  }
+  catch (...)
+  {
+    std::terminate();
+  }
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function>
+inline void
+basic_system_executor<Blocking, Relationship, Allocator>::do_execute(
+    Function&& f, execution::blocking_t::always_t) const
+{
+  // Obtain a non-const instance of the function.
+  detail::non_const_lvalue<Function> f2(f);
+
+#if !defined(ASIO_NO_EXCEPTIONS)
+  try
+  {
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+    detail::fenced_block b(detail::fenced_block::full);
+    static_cast<decay_t<Function>&&>(f2.value)();
+#if !defined(ASIO_NO_EXCEPTIONS)
+  }
+  catch (...)
+  {
+    std::terminate();
+  }
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function>
+void basic_system_executor<Blocking, Relationship, Allocator>::do_execute(
+    Function&& f, execution::blocking_t::never_t) const
+{
+  system_context& ctx = detail::global<system_context>();
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<decay_t<Function>, Allocator> op;
+  typename op::ptr p = { detail::addressof(allocator_),
+      op::ptr::allocate(allocator_), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), allocator_);
+
+  if (is_same<Relationship, execution::relationship_t::continuation_t>::value)
+  {
+    ASIO_HANDLER_CREATION((ctx, *p.p,
+          "system_executor", &ctx, 0, "execute(blk=never,rel=cont)"));
+  }
+  else
+  {
+    ASIO_HANDLER_CREATION((ctx, *p.p,
+          "system_executor", &ctx, 0, "execute(blk=never,rel=fork)"));
+  }
+
+  ctx.scheduler_.post_immediate_completion(p.p,
+      is_same<Relationship, execution::relationship_t::continuation_t>::value);
+  p.v = p.p = 0;
+}
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+template <typename Blocking, typename Relationship, typename Allocator>
+inline system_context& basic_system_executor<
+    Blocking, Relationship, Allocator>::context() const noexcept
+{
+  return detail::global<system_context>();
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function, typename OtherAllocator>
+void basic_system_executor<Blocking, Relationship, Allocator>::dispatch(
+    Function&& f, const OtherAllocator&) const
+{
+  decay_t<Function>(static_cast<Function&&>(f))();
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function, typename OtherAllocator>
+void basic_system_executor<Blocking, Relationship, Allocator>::post(
+    Function&& f, const OtherAllocator& a) const
+{
+  system_context& ctx = detail::global<system_context>();
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<decay_t<Function>, OtherAllocator> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((ctx, *p.p,
+        "system_executor", &this->context(), 0, "post"));
+
+  ctx.scheduler_.post_immediate_completion(p.p, false);
+  p.v = p.p = 0;
+}
+
+template <typename Blocking, typename Relationship, typename Allocator>
+template <typename Function, typename OtherAllocator>
+void basic_system_executor<Blocking, Relationship, Allocator>::defer(
+    Function&& f, const OtherAllocator& a) const
+{
+  system_context& ctx = detail::global<system_context>();
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<decay_t<Function>, OtherAllocator> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((ctx, *p.p,
+        "system_executor", &this->context(), 0, "defer"));
+
+  ctx.scheduler_.post_immediate_completion(p.p, true);
+  p.v = p.p = 0;
+}
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_SYSTEM_EXECUTOR_HPP

include/asio/impl/thread_pool.hpp

@@ -0,0 +1,319 @@
+//
+// impl/thread_pool.hpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_THREAD_POOL_HPP
+#define ASIO_IMPL_THREAD_POOL_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/config.hpp"
+#include "asio/detail/blocking_executor_op.hpp"
+#include "asio/detail/executor_op.hpp"
+#include "asio/detail/fenced_block.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution_context.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+
+template <typename Allocator>
+thread_pool::thread_pool(allocator_arg_t, const Allocator& a)
+  : execution_context(std::allocator_arg, a),
+    scheduler_(asio::make_service<detail::scheduler>(*this, false)),
+    threads_(allocator<void>(*this)),
+    num_threads_(default_thread_pool_size()),
+    joinable_(true)
+{
+  start();
+}
+
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+template <typename Allocator>
+thread_pool::thread_pool(allocator_arg_t,
+    const Allocator& a, std::size_t num_threads)
+  : execution_context(std::allocator_arg, a,
+      config_from_concurrency_hint(num_threads == 1 ? 1 : 0)),
+    scheduler_(asio::make_service<detail::scheduler>(*this, false)),
+    threads_(allocator<void>(*this)),
+    num_threads_(clamp_thread_pool_size(num_threads)),
+    joinable_(true)
+{
+  start();
+}
+
+template <typename Allocator>
+thread_pool::thread_pool(allocator_arg_t,
+    const Allocator& a, std::size_t num_threads,
+    const execution_context::service_maker& initial_services)
+  : execution_context(std::allocator_arg, a, initial_services),
+    scheduler_(asio::make_service<detail::scheduler>(*this, false)),
+    threads_(allocator<void>(*this)),
+    num_threads_(clamp_thread_pool_size(num_threads)),
+    joinable_(true)
+{
+  start();
+}
+
+inline thread_pool::executor_type
+thread_pool::get_executor() noexcept
+{
+  return executor_type(*this);
+}
+
+inline thread_pool::executor_type
+thread_pool::executor() noexcept
+{
+  return executor_type(*this);
+}
+
+template <typename Allocator, unsigned int Bits>
+thread_pool::basic_executor_type<Allocator, Bits>&
+thread_pool::basic_executor_type<Allocator, Bits>::operator=(
+    const basic_executor_type& other) noexcept
+{
+  if (this != &other)
+  {
+    thread_pool* old_thread_pool = pool_;
+    pool_ = other.pool_;
+    allocator_ = other.allocator_;
+    bits_ = other.bits_;
+    if (Bits & outstanding_work_tracked)
+    {
+      if (pool_)
+        pool_->scheduler_.work_started();
+      if (old_thread_pool)
+        old_thread_pool->scheduler_.work_finished();
+    }
+  }
+  return *this;
+}
+
+template <typename Allocator, unsigned int Bits>
+thread_pool::basic_executor_type<Allocator, Bits>&
+thread_pool::basic_executor_type<Allocator, Bits>::operator=(
+    basic_executor_type&& other) noexcept
+{
+  if (this != &other)
+  {
+    thread_pool* old_thread_pool = pool_;
+    pool_ = other.pool_;
+    allocator_ = std::move(other.allocator_);
+    bits_ = other.bits_;
+    if (Bits & outstanding_work_tracked)
+    {
+      other.pool_ = 0;
+      if (old_thread_pool)
+        old_thread_pool->scheduler_.work_finished();
+    }
+  }
+  return *this;
+}
+
+template <typename Allocator, unsigned int Bits>
+inline bool thread_pool::basic_executor_type<Allocator,
+    Bits>::running_in_this_thread() const noexcept
+{
+  return pool_->scheduler_.can_dispatch();
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function>
+void thread_pool::basic_executor_type<Allocator,
+    Bits>::do_execute(Function&& f, false_type) const
+{
+  typedef decay_t<Function> function_type;
+
+  // Invoke immediately if the blocking.possibly property is enabled and we are
+  // already inside the thread pool.
+  if ((bits_ & blocking_never) == 0 && pool_->scheduler_.can_dispatch())
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(static_cast<Function&&>(f));
+
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+      detail::fenced_block b(detail::fenced_block::full);
+      static_cast<function_type&&>(tmp)();
+      return;
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      pool_->scheduler_.capture_current_exception();
+      return;
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, Allocator> op;
+  typename op::ptr p = { detail::addressof(allocator_),
+      op::ptr::allocate(allocator_), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), allocator_);
+
+  if ((bits_ & relationship_continuation) != 0)
+  {
+    ASIO_HANDLER_CREATION((*pool_, *p.p,
+          "thread_pool", pool_, 0, "execute(blk=never,rel=cont)"));
+  }
+  else
+  {
+    ASIO_HANDLER_CREATION((*pool_, *p.p,
+          "thread_pool", pool_, 0, "execute(blk=never,rel=fork)"));
+  }
+
+  pool_->scheduler_.post_immediate_completion(p.p,
+      (bits_ & relationship_continuation) != 0);
+  p.v = p.p = 0;
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function>
+void thread_pool::basic_executor_type<Allocator,
+    Bits>::do_execute(Function&& f, true_type) const
+{
+  // Obtain a non-const instance of the function.
+  detail::non_const_lvalue<Function> f2(f);
+
+  // Invoke immediately if we are already inside the thread pool.
+  if (pool_->scheduler_.can_dispatch())
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+      detail::fenced_block b(detail::fenced_block::full);
+      static_cast<decay_t<Function>&&>(f2.value)();
+      return;
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      std::terminate();
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+
+  // Construct an operation to wrap the function.
+  typedef decay_t<Function> function_type;
+  detail::blocking_executor_op<function_type> op(f2.value);
+
+  ASIO_HANDLER_CREATION((*pool_, op,
+        "thread_pool", pool_, 0, "execute(blk=always)"));
+
+  pool_->scheduler_.post_immediate_completion(&op, false);
+  op.wait();
+}
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+template <typename Allocator, unsigned int Bits>
+inline thread_pool& thread_pool::basic_executor_type<
+    Allocator, Bits>::context() const noexcept
+{
+  return *pool_;
+}
+
+template <typename Allocator, unsigned int Bits>
+inline void thread_pool::basic_executor_type<Allocator,
+    Bits>::on_work_started() const noexcept
+{
+  pool_->scheduler_.work_started();
+}
+
+template <typename Allocator, unsigned int Bits>
+inline void thread_pool::basic_executor_type<Allocator,
+    Bits>::on_work_finished() const noexcept
+{
+  pool_->scheduler_.work_finished();
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void thread_pool::basic_executor_type<Allocator, Bits>::dispatch(
+    Function&& f, const OtherAllocator& a) const
+{
+  typedef decay_t<Function> function_type;
+
+  // Invoke immediately if we are already inside the thread pool.
+  if (pool_->scheduler_.can_dispatch())
+  {
+    // Make a local, non-const copy of the function.
+    function_type tmp(static_cast<Function&&>(f));
+
+    detail::fenced_block b(detail::fenced_block::full);
+    static_cast<function_type&&>(tmp)();
+    return;
+  }
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, OtherAllocator> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((*pool_, *p.p,
+        "thread_pool", pool_, 0, "dispatch"));
+
+  pool_->scheduler_.post_immediate_completion(p.p, false);
+  p.v = p.p = 0;
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void thread_pool::basic_executor_type<Allocator, Bits>::post(
+    Function&& f, const OtherAllocator& a) const
+{
+  typedef decay_t<Function> function_type;
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, OtherAllocator> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((*pool_, *p.p,
+        "thread_pool", pool_, 0, "post"));
+
+  pool_->scheduler_.post_immediate_completion(p.p, false);
+  p.v = p.p = 0;
+}
+
+template <typename Allocator, unsigned int Bits>
+template <typename Function, typename OtherAllocator>
+void thread_pool::basic_executor_type<Allocator, Bits>::defer(
+    Function&& f, const OtherAllocator& a) const
+{
+  typedef decay_t<Function> function_type;
+
+  // Allocate and construct an operation to wrap the function.
+  typedef detail::executor_op<function_type, OtherAllocator> op;
+  typename op::ptr p = { detail::addressof(a), op::ptr::allocate(a), 0 };
+  p.p = new (p.v) op(static_cast<Function&&>(f), a);
+
+  ASIO_HANDLER_CREATION((*pool_, *p.p,
+        "thread_pool", pool_, 0, "defer"));
+
+  pool_->scheduler_.post_immediate_completion(p.p, true);
+  p.v = p.p = 0;
+}
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_THREAD_POOL_HPP

include/asio/impl/thread_pool.ipp

@@ -0,0 +1,145 @@
+//
+// impl/thread_pool.ipp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_THREAD_POOL_IPP
+#define ASIO_IMPL_THREAD_POOL_IPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <stdexcept>
+#include "asio/thread_pool.hpp"
+#include "asio/detail/throw_exception.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+struct thread_pool::thread_function
+{
+  detail::scheduler* scheduler_;
+
+  void operator()()
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+    {
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+      asio::error_code ec;
+      scheduler_->run(ec);
+#if !defined(ASIO_NO_EXCEPTIONS)
+    }
+    catch (...)
+    {
+      std::terminate();
+    }
+#endif// !defined(ASIO_NO_EXCEPTIONS)
+  }
+};
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+
+long thread_pool::default_thread_pool_size()
+{
+  std::size_t num_threads = detail::thread::hardware_concurrency() * 2;
+  num_threads = num_threads == 0 ? 2 : num_threads;
+  return static_cast<long>(num_threads);
+}
+
+thread_pool::thread_pool()
+  : scheduler_(asio::make_service<detail::scheduler>(*this, false)),
+    threads_(allocator<void>(*this)),
+    num_threads_(default_thread_pool_size()),
+    joinable_(true)
+{
+  start();
+}
+
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+long thread_pool::clamp_thread_pool_size(std::size_t n)
+{
+  if (n > 0x7FFFFFFF)
+  {
+    std::out_of_range ex("thread pool size");
+    asio::detail::throw_exception(ex);
+  }
+  return static_cast<long>(n & 0x7FFFFFFF);
+}
+
+thread_pool::thread_pool(std::size_t num_threads)
+  : execution_context(config_from_concurrency_hint(num_threads == 1 ? 1 : 0)),
+    scheduler_(asio::make_service<detail::scheduler>(*this, false)),
+    threads_(allocator<void>(*this)),
+    num_threads_(clamp_thread_pool_size(num_threads)),
+    joinable_(true)
+{
+  start();
+}
+
+thread_pool::thread_pool(std::size_t num_threads,
+    const execution_context::service_maker& initial_services)
+  : execution_context(initial_services),
+    scheduler_(asio::make_service<detail::scheduler>(*this, false)),
+    threads_(allocator<void>(*this)),
+    num_threads_(clamp_thread_pool_size(num_threads)),
+    joinable_(true)
+{
+  start();
+}
+
+thread_pool::~thread_pool()
+{
+  stop();
+  join();
+  shutdown();
+}
+
+void thread_pool::start()
+{
+  scheduler_.work_started();
+  thread_function f = { &scheduler_ };
+  threads_.create_threads(f, static_cast<std::size_t>(num_threads_));
+}
+
+void thread_pool::stop()
+{
+  scheduler_.stop();
+}
+
+void thread_pool::attach()
+{
+  ++num_threads_;
+  thread_function f = { &scheduler_ };
+  f();
+}
+
+void thread_pool::join()
+{
+  if (joinable_)
+  {
+    joinable_ = false;
+    scheduler_.work_finished();
+    threads_.join();
+  }
+}
+
+void thread_pool::wait()
+{
+  join();
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_THREAD_POOL_IPP

include/asio/impl/use_awaitable.hpp

@@ -0,0 +1,234 @@
+//
+// impl/use_awaitable.hpp
+// ~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_USE_AWAITABLE_HPP
+#define ASIO_IMPL_USE_AWAITABLE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/async_result.hpp"
+#include "asio/cancellation_signal.hpp"
+#include "asio/disposition.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename Executor, typename T>
+class awaitable_handler_base
+  : public awaitable_thread<Executor>
+{
+public:
+  typedef void result_type;
+  typedef awaitable<T, Executor> awaitable_type;
+
+  // Construct from the entry point of a new thread of execution.
+  awaitable_handler_base(awaitable<awaitable_thread_entry_point, Executor> a,
+      const Executor& ex, cancellation_slot pcs, cancellation_state cs)
+    : awaitable_thread<Executor>(std::move(a), ex, pcs, cs)
+  {
+  }
+
+  // Transfer ownership from another awaitable_thread.
+  explicit awaitable_handler_base(awaitable_thread<Executor>* h)
+    : awaitable_thread<Executor>(std::move(*h))
+  {
+  }
+
+protected:
+  awaitable_frame<T, Executor>* frame() noexcept
+  {
+    return static_cast<awaitable_frame<T, Executor>*>(
+        this->entry_point()->top_of_stack_);
+  }
+};
+
+template <typename, typename...>
+class awaitable_handler;
+
+template <typename Executor>
+class awaitable_handler<Executor>
+  : public awaitable_handler_base<Executor, void>
+{
+public:
+  using awaitable_handler_base<Executor, void>::awaitable_handler_base;
+
+  void operator()()
+  {
+    this->frame()->attach_thread(this);
+    this->frame()->return_void();
+    this->frame()->clear_cancellation_slot();
+    this->frame()->pop_frame();
+    this->pump();
+  }
+};
+
+template <typename Executor, typename T>
+class awaitable_handler<Executor, T>
+  : public awaitable_handler_base<Executor,
+      conditional_t<is_disposition<T>::value, void, T>>
+{
+public:
+  using awaitable_handler_base<Executor,
+    conditional_t<is_disposition<T>::value, void, T>>
+      ::awaitable_handler_base;
+
+  template <typename Arg>
+  void operator()(Arg&& arg)
+  {
+    this->frame()->attach_thread(this);
+    if constexpr (is_disposition<T>::value)
+    {
+      if (arg == no_error)
+        this->frame()->return_void();
+      else
+        this->frame()->set_disposition(arg);
+    }
+    else
+      this->frame()->return_value(std::forward<Arg>(arg));
+    this->frame()->clear_cancellation_slot();
+    this->frame()->pop_frame();
+    this->pump();
+  }
+};
+
+template <typename Executor, typename T0, typename T1>
+class awaitable_handler<Executor, T0, T1>
+  : public awaitable_handler_base<Executor,
+      conditional_t<is_disposition<T0>::value, T1, std::tuple<T0, T1>>>
+{
+public:
+  using awaitable_handler_base<Executor,
+    conditional_t<is_disposition<T0>::value, T1, std::tuple<T0, T1>>>
+      ::awaitable_handler_base;
+
+  template <typename Arg0, typename Arg1>
+  void operator()(Arg0&& arg0, Arg1&& arg1)
+  {
+    this->frame()->attach_thread(this);
+    if constexpr (is_disposition<T0>::value)
+    {
+      if (arg0 == no_error)
+        this->frame()->return_value(std::forward<Arg1>(arg1));
+      else
+        this->frame()->set_disposition(std::forward<Arg0>(arg0));
+    }
+    else
+    {
+      this->frame()->return_values(std::forward<Arg0>(arg0),
+          std::forward<Arg1>(arg1));
+    }
+    this->frame()->clear_cancellation_slot();
+    this->frame()->pop_frame();
+    this->pump();
+  }
+};
+
+template <typename Executor, typename T0, typename... Ts>
+class awaitable_handler<Executor, T0, Ts...>
+  : public awaitable_handler_base<Executor,
+      conditional_t<is_disposition<T0>::value,
+        std::tuple<Ts...>, std::tuple<T0, Ts...>>>
+{
+public:
+  using awaitable_handler_base<Executor,
+      conditional_t<is_disposition<T0>::value,
+        std::tuple<Ts...>, std::tuple<T0, Ts...>>>
+          ::awaitable_handler_base;
+
+  template <typename Arg0, typename... Args>
+  void operator()(Arg0&& arg0, Args&&... args)
+  {
+    this->frame()->attach_thread(this);
+    if constexpr (is_disposition<T0>::value)
+    {
+      if (arg0 == no_error)
+        this->frame()->return_values(std::forward<Args>(args)...);
+      else
+        this->frame()->set_disposition(std::forward<Arg0>(arg0));
+    }
+    else
+    {
+      this->frame()->return_values(std::forward<Arg0>(arg0),
+          std::forward<Args>(args)...);
+    }
+    this->frame()->clear_cancellation_slot();
+    this->frame()->pop_frame();
+    this->pump();
+  }
+};
+
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+#if defined(_MSC_VER)
+template <typename T>
+T dummy_return()
+{
+  return std::move(*static_cast<T*>(nullptr));
+}
+
+template <>
+inline void dummy_return()
+{
+}
+#endif // defined(_MSC_VER)
+
+template <typename Executor, typename R, typename... Args>
+class async_result<use_awaitable_t<Executor>, R(Args...)>
+{
+public:
+  typedef typename detail::awaitable_handler<
+      Executor, decay_t<Args>...> handler_type;
+  typedef typename handler_type::awaitable_type return_type;
+
+  template <typename Initiation, typename... InitArgs>
+#if defined(__APPLE_CC__) && (__clang_major__ == 13)
+  __attribute__((noinline))
+#endif // defined(__APPLE_CC__) && (__clang_major__ == 13)
+  static handler_type* do_init(
+      detail::awaitable_frame_base<Executor>* frame, Initiation& initiation,
+      use_awaitable_t<Executor> u, InitArgs&... args)
+  {
+    (void)u;
+    ASIO_HANDLER_LOCATION((u.file_name_, u.line_, u.function_name_));
+    handler_type handler(frame->detach_thread());
+    std::move(initiation)(std::move(handler), std::move(args)...);
+    return nullptr;
+  }
+
+  template <typename Initiation, typename... InitArgs>
+  static return_type initiate(Initiation initiation,
+      use_awaitable_t<Executor> u, InitArgs... args)
+  {
+    co_await [&] (auto* frame)
+      {
+        return do_init(frame, initiation, u, args...);
+      };
+
+    for (;;) {} // Never reached.
+#if defined(_MSC_VER) && !defined(__clang__)
+    co_return dummy_return<typename return_type::value_type>();
+#endif // defined(_MSC_VER) && !defined(__clang__)
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_USE_AWAITABLE_HPP

include/asio/impl/use_future.hpp

@@ -0,0 +1,642 @@
+//
+// impl/use_future.hpp
+// ~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_USE_FUTURE_HPP
+#define ASIO_IMPL_USE_FUTURE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <tuple>
+#include "asio/async_result.hpp"
+#include "asio/detail/memory.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/dispatch.hpp"
+#include "asio/disposition.hpp"
+#include "asio/execution.hpp"
+#include "asio/packaged_task.hpp"
+#include "asio/system_error.hpp"
+#include "asio/system_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+namespace detail {
+
+template <typename T, typename F, typename... Args>
+inline void promise_invoke_and_set(std::promise<T>& p,
+    F& f, Args&&... args)
+{
+#if !defined(ASIO_NO_EXCEPTIONS)
+  try
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  {
+    p.set_value(f(static_cast<Args&&>(args)...));
+  }
+#if !defined(ASIO_NO_EXCEPTIONS)
+  catch (...)
+  {
+    p.set_exception(std::current_exception());
+  }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+}
+
+template <typename F, typename... Args>
+inline void promise_invoke_and_set(std::promise<void>& p,
+    F& f, Args&&... args)
+{
+#if !defined(ASIO_NO_EXCEPTIONS)
+  try
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  {
+    f(static_cast<Args&&>(args)...);
+    p.set_value();
+  }
+#if !defined(ASIO_NO_EXCEPTIONS)
+  catch (...)
+  {
+    p.set_exception(std::current_exception());
+  }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+}
+
+// A function object adapter to invoke a nullary function object and capture
+// any exception thrown into a promise.
+template <typename T, typename F>
+class promise_invoker
+{
+public:
+  promise_invoker(const shared_ptr<std::promise<T>>& p,
+      F&& f)
+    : p_(p), f_(static_cast<F&&>(f))
+  {
+  }
+
+  void operator()()
+  {
+#if !defined(ASIO_NO_EXCEPTIONS)
+    try
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+    {
+      f_();
+    }
+#if !defined(ASIO_NO_EXCEPTIONS)
+    catch (...)
+    {
+      p_->set_exception(std::current_exception());
+    }
+#endif // !defined(ASIO_NO_EXCEPTIONS)
+  }
+
+private:
+  shared_ptr<std::promise<T>> p_;
+  decay_t<F> f_;
+};
+
+// An executor that adapts the system_executor to capture any exception thrown
+// by a submitted function object and save it into a promise.
+template <typename T, typename Blocking = execution::blocking_t::possibly_t>
+class promise_executor
+{
+public:
+  explicit promise_executor(const shared_ptr<std::promise<T>>& p)
+    : p_(p)
+  {
+  }
+
+  execution_context& query(execution::context_t) const noexcept
+  {
+    return asio::query(system_executor(), execution::context);
+  }
+
+  static constexpr Blocking query(execution::blocking_t)
+  {
+    return Blocking();
+  }
+
+  promise_executor<T, execution::blocking_t::possibly_t>
+  require(execution::blocking_t::possibly_t) const
+  {
+    return promise_executor<T, execution::blocking_t::possibly_t>(p_);
+  }
+
+  promise_executor<T, execution::blocking_t::never_t>
+  require(execution::blocking_t::never_t) const
+  {
+    return promise_executor<T, execution::blocking_t::never_t>(p_);
+  }
+
+  template <typename F>
+  void execute(F&& f) const
+  {
+    asio::require(system_executor(), Blocking()).execute(
+        promise_invoker<T, F>(p_, static_cast<F&&>(f)));
+  }
+
+#if !defined(ASIO_NO_TS_EXECUTORS)
+  execution_context& context() const noexcept
+  {
+    return system_executor().context();
+  }
+
+  void on_work_started() const noexcept {}
+  void on_work_finished() const noexcept {}
+
+  template <typename F, typename A>
+  void dispatch(F&& f, const A&) const
+  {
+    promise_invoker<T, F>(p_, static_cast<F&&>(f))();
+  }
+
+  template <typename F, typename A>
+  void post(F&& f, const A& a) const
+  {
+    system_executor().post(
+        promise_invoker<T, F>(p_, static_cast<F&&>(f)), a);
+  }
+
+  template <typename F, typename A>
+  void defer(F&& f, const A& a) const
+  {
+    system_executor().defer(
+        promise_invoker<T, F>(p_, static_cast<F&&>(f)), a);
+  }
+#endif // !defined(ASIO_NO_TS_EXECUTORS)
+
+  friend bool operator==(const promise_executor& a,
+      const promise_executor& b) noexcept
+  {
+    return a.p_ == b.p_;
+  }
+
+  friend bool operator!=(const promise_executor& a,
+      const promise_executor& b) noexcept
+  {
+    return a.p_ != b.p_;
+  }
+
+private:
+  shared_ptr<std::promise<T>> p_;
+};
+
+// The base class for all completion handlers that create promises.
+template <typename T>
+class promise_creator
+{
+public:
+  typedef promise_executor<T> executor_type;
+
+  executor_type get_executor() const noexcept
+  {
+    return executor_type(p_);
+  }
+
+  typedef std::future<T> future_type;
+
+  future_type get_future()
+  {
+    return p_->get_future();
+  }
+
+protected:
+  template <typename Allocator>
+  void create_promise(const Allocator& a)
+  {
+    ASIO_REBIND_ALLOC(Allocator, char) b(a);
+    p_ = std::allocate_shared<std::promise<T>>(b, std::allocator_arg, b);
+  }
+
+  shared_ptr<std::promise<T>> p_;
+};
+
+// For completion signature void().
+class promise_handler_0
+  : public promise_creator<void>
+{
+public:
+  void operator()()
+  {
+    this->p_->set_value();
+  }
+};
+
+// For completion signature void(disposition auto).
+template <typename Disposition>
+class promise_handler_d_0
+  : public promise_creator<void>
+{
+public:
+  void operator()(Disposition d)
+  {
+    if (d != no_error)
+    {
+      this->p_->set_exception(
+          (to_exception_ptr)(static_cast<Disposition&&>(d)));
+    }
+    else
+    {
+      this->p_->set_value();
+    }
+  }
+};
+
+// For completion signature void(T).
+template <typename T>
+class promise_handler_1
+  : public promise_creator<T>
+{
+public:
+  template <typename Arg>
+  void operator()(Arg&& arg)
+  {
+    this->p_->set_value(static_cast<Arg&&>(arg));
+  }
+};
+
+// For completion signature void(disposition auto, T).
+template <typename Disposition, typename T>
+class promise_handler_d_1
+  : public promise_creator<T>
+{
+public:
+  template <typename Arg>
+  void operator()(Disposition d, Arg&& arg)
+  {
+    if (d != no_error)
+    {
+      this->p_->set_exception(
+          (to_exception_ptr)(static_cast<Disposition&&>(d)));
+    }
+    else
+      this->p_->set_value(static_cast<Arg&&>(arg));
+  }
+};
+
+// For completion signature void(T1, ..., Tn);
+template <typename T>
+class promise_handler_n
+  : public promise_creator<T>
+{
+public:
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    this->p_->set_value(
+        std::forward_as_tuple(
+          static_cast<Args&&>(args)...));
+  }
+};
+
+// For completion signature void(error_code, T1, ..., Tn);
+template <typename Disposition, typename T>
+class promise_handler_d_n
+  : public promise_creator<T>
+{
+public:
+  template <typename... Args>
+  void operator()(Disposition d, Args&&... args)
+  {
+    if (d != no_error)
+    {
+      this->p_->set_exception(
+          (to_exception_ptr)(static_cast<Disposition&&>(d)));
+    }
+    else
+    {
+      this->p_->set_value(
+          std::forward_as_tuple(
+            static_cast<Args&&>(args)...));
+    }
+  }
+};
+
+// Helper template to choose the appropriate concrete promise handler
+// implementation based on the supplied completion signature.
+template <typename, typename = void> class promise_handler_selector;
+
+template <>
+class promise_handler_selector<void()>
+  : public promise_handler_0 {};
+
+template <typename Arg>
+class promise_handler_selector<void(Arg),
+  enable_if_t<is_disposition<Arg>::value>>
+    : public promise_handler_d_0<Arg> {};
+
+template <typename Arg>
+class promise_handler_selector<void(Arg),
+  enable_if_t<!is_disposition<Arg>::value>>
+    : public promise_handler_1<Arg> {};
+
+template <typename Arg0, typename Arg1>
+class promise_handler_selector<void(Arg0, Arg1),
+  enable_if_t<is_disposition<Arg0>::value>>
+    : public promise_handler_d_1<Arg0, Arg1> {};
+
+template <typename Arg0, typename... ArgN>
+class promise_handler_selector<void(Arg0, ArgN...),
+  enable_if_t<!is_disposition<Arg0>::value>>
+    : public promise_handler_n<std::tuple<Arg0, ArgN...>> {};
+
+template <typename Arg0, typename... ArgN>
+class promise_handler_selector<void(Arg0, ArgN...),
+  enable_if_t<is_disposition<Arg0>::value>>
+    : public promise_handler_d_n<Arg0, std::tuple<ArgN...>> {};
+
+// Completion handlers produced from the use_future completion token, when not
+// using use_future::operator().
+template <typename Signature, typename Allocator>
+class promise_handler
+  : public promise_handler_selector<Signature>
+{
+public:
+  typedef Allocator allocator_type;
+  typedef void result_type;
+
+  promise_handler(use_future_t<Allocator> u)
+    : allocator_(u.get_allocator())
+  {
+    this->create_promise(allocator_);
+  }
+
+  allocator_type get_allocator() const noexcept
+  {
+    return allocator_;
+  }
+
+private:
+  Allocator allocator_;
+};
+
+template <typename Function>
+struct promise_function_wrapper
+{
+  explicit promise_function_wrapper(Function& f)
+    : function_(static_cast<Function&&>(f))
+  {
+  }
+
+  explicit promise_function_wrapper(const Function& f)
+    : function_(f)
+  {
+  }
+
+  void operator()()
+  {
+    function_();
+  }
+
+  Function function_;
+};
+
+// Helper base class for async_result specialisation.
+template <typename Signature, typename Allocator>
+class promise_async_result
+{
+public:
+  typedef promise_handler<Signature, Allocator> completion_handler_type;
+  typedef typename completion_handler_type::future_type return_type;
+
+  explicit promise_async_result(completion_handler_type& h)
+    : future_(h.get_future())
+  {
+  }
+
+  return_type get()
+  {
+    return static_cast<return_type&&>(future_);
+  }
+
+private:
+  return_type future_;
+};
+
+// Return value from use_future::operator().
+template <typename Function, typename Allocator>
+class packaged_token
+{
+public:
+  packaged_token(Function f, const Allocator& a)
+    : function_(static_cast<Function&&>(f)),
+      allocator_(a)
+  {
+  }
+
+//private:
+  Function function_;
+  Allocator allocator_;
+};
+
+// Completion handlers produced from the use_future completion token, when
+// using use_future::operator().
+template <typename Function, typename Allocator, typename Result>
+class packaged_handler
+  : public promise_creator<Result>
+{
+public:
+  typedef Allocator allocator_type;
+  typedef void result_type;
+
+  packaged_handler(packaged_token<Function, Allocator> t)
+    : function_(static_cast<Function&&>(t.function_)),
+      allocator_(t.allocator_)
+  {
+    this->create_promise(allocator_);
+  }
+
+  allocator_type get_allocator() const noexcept
+  {
+    return allocator_;
+  }
+
+  template <typename... Args>
+  void operator()(Args&&... args)
+  {
+    (promise_invoke_and_set)(*this->p_,
+        function_, static_cast<Args&&>(args)...);
+  }
+
+private:
+  Function function_;
+  Allocator allocator_;
+};
+
+// Helper base class for async_result specialisation.
+template <typename Function, typename Allocator, typename Result>
+class packaged_async_result
+{
+public:
+  typedef packaged_handler<Function, Allocator, Result> completion_handler_type;
+  typedef typename completion_handler_type::future_type return_type;
+
+  explicit packaged_async_result(completion_handler_type& h)
+    : future_(h.get_future())
+  {
+  }
+
+  return_type get()
+  {
+    return static_cast<return_type&&>(future_);
+  }
+
+private:
+  return_type future_;
+};
+
+} // namespace detail
+
+template <typename Allocator> template <typename Function>
+inline detail::packaged_token<decay_t<Function>, Allocator>
+use_future_t<Allocator>::operator()(Function&& f) const
+{
+  return detail::packaged_token<decay_t<Function>, Allocator>(
+      static_cast<Function&&>(f), allocator_);
+}
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <typename Allocator, typename Result, typename... Args>
+class async_result<use_future_t<Allocator>, Result(Args...)>
+  : public detail::promise_async_result<
+      void(decay_t<Args>...), Allocator>
+{
+public:
+  explicit async_result(
+    typename detail::promise_async_result<void(decay_t<Args>...),
+      Allocator>::completion_handler_type& h)
+    : detail::promise_async_result<
+        void(decay_t<Args>...), Allocator>(h)
+  {
+  }
+};
+
+template <typename Function, typename Allocator,
+    typename Result, typename... Args>
+class async_result<detail::packaged_token<Function, Allocator>, Result(Args...)>
+  : public detail::packaged_async_result<Function, Allocator,
+      result_of_t<Function(Args...)>>
+{
+public:
+  explicit async_result(
+    typename detail::packaged_async_result<Function, Allocator,
+      result_of_t<Function(Args...)>>::completion_handler_type& h)
+    : detail::packaged_async_result<Function, Allocator,
+        result_of_t<Function(Args...)>>(h)
+  {
+  }
+};
+
+namespace traits {
+
+#if !defined(ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+template <typename T, typename Blocking>
+struct equality_comparable<
+    asio::detail::promise_executor<T, Blocking>>
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+template <typename T, typename Blocking, typename Function>
+struct execute_member<
+    asio::detail::promise_executor<T, Blocking>, Function>
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = false;
+  typedef void result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+template <typename T, typename Blocking, typename Property>
+struct query_static_constexpr_member<
+    asio::detail::promise_executor<T, Blocking>,
+    Property,
+    typename asio::enable_if<
+      asio::is_convertible<
+        Property,
+        asio::execution::blocking_t
+      >::value
+    >::type
+  >
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef Blocking result_type;
+
+  static constexpr result_type value() noexcept
+  {
+    return Blocking();
+  }
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+template <typename T, typename Blocking>
+struct query_member<
+    asio::detail::promise_executor<T, Blocking>,
+    execution::context_t
+  >
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef asio::system_context& result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)
+
+#if !defined(ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+template <typename T, typename Blocking>
+struct require_member<
+    asio::detail::promise_executor<T, Blocking>,
+    execution::blocking_t::possibly_t
+  >
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef asio::detail::promise_executor<T,
+      execution::blocking_t::possibly_t> result_type;
+};
+
+template <typename T, typename Blocking>
+struct require_member<
+    asio::detail::promise_executor<T, Blocking>,
+    execution::blocking_t::never_t
+  >
+{
+  static constexpr bool is_valid = true;
+  static constexpr bool is_noexcept = true;
+  typedef asio::detail::promise_executor<T,
+      execution::blocking_t::never_t> result_type;
+};
+
+#endif // !defined(ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)
+
+} // namespace traits
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_USE_FUTURE_HPP

include/asio/impl/write.hpp

@@ -0,0 +1,780 @@
+//
+// impl/write.hpp
+// ~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_WRITE_HPP
+#define ASIO_IMPL_WRITE_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/associator.hpp"
+#include "asio/buffer.hpp"
+#include "asio/detail/array_fwd.hpp"
+#include "asio/detail/base_from_cancellation_state.hpp"
+#include "asio/detail/base_from_completion_cond.hpp"
+#include "asio/detail/bind_handler.hpp"
+#include "asio/detail/consuming_buffers.hpp"
+#include "asio/detail/dependent_type.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_tracking.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/throw_error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail
+{
+  template <typename SyncWriteStream, typename ConstBufferSequence,
+      typename ConstBufferIterator, typename CompletionCondition>
+  std::size_t write(SyncWriteStream& s,
+      const ConstBufferSequence& buffers, const ConstBufferIterator&,
+      CompletionCondition completion_condition, asio::error_code& ec)
+  {
+    ec = asio::error_code();
+    asio::detail::consuming_buffers<const_buffer,
+        ConstBufferSequence, ConstBufferIterator> tmp(buffers);
+    while (!tmp.empty())
+    {
+      if (std::size_t max_size = detail::adapt_completion_condition_result(
+            completion_condition(ec, tmp.total_consumed())))
+        tmp.consume(s.write_some(tmp.prepare(max_size), ec));
+      else
+        break;
+    }
+    return tmp.total_consumed();
+  }
+} // namespace detail
+
+template <typename SyncWriteStream, typename ConstBufferSequence,
+    typename CompletionCondition>
+inline std::size_t write(SyncWriteStream& s, const ConstBufferSequence& buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_const_buffer_sequence<ConstBufferSequence>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return detail::write(s, buffers,
+      asio::buffer_sequence_begin(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+}
+
+template <typename SyncWriteStream, typename ConstBufferSequence>
+inline std::size_t write(SyncWriteStream& s, const ConstBufferSequence& buffers,
+    constraint_t<
+      is_const_buffer_sequence<ConstBufferSequence>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write(s, buffers, transfer_all(), ec);
+  asio::detail::throw_error(ec, "write");
+  return bytes_transferred;
+}
+
+template <typename SyncWriteStream, typename ConstBufferSequence>
+inline std::size_t write(SyncWriteStream& s, const ConstBufferSequence& buffers,
+    asio::error_code& ec,
+    constraint_t<
+      is_const_buffer_sequence<ConstBufferSequence>::value
+    >)
+{
+  return write(s, buffers, transfer_all(), ec);
+}
+
+template <typename SyncWriteStream, typename ConstBufferSequence,
+    typename CompletionCondition>
+inline std::size_t write(SyncWriteStream& s, const ConstBufferSequence& buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_const_buffer_sequence<ConstBufferSequence>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write(s, buffers,
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "write");
+  return bytes_transferred;
+}
+
+#if !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+template <typename SyncWriteStream, typename DynamicBuffer_v1,
+    typename CompletionCondition>
+std::size_t write(SyncWriteStream& s,
+    DynamicBuffer_v1&& buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  decay_t<DynamicBuffer_v1> b(
+      static_cast<DynamicBuffer_v1&&>(buffers));
+
+  std::size_t bytes_transferred = write(s, b.data(),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  b.consume(bytes_transferred);
+  return bytes_transferred;
+}
+
+template <typename SyncWriteStream, typename DynamicBuffer_v1>
+inline std::size_t write(SyncWriteStream& s,
+    DynamicBuffer_v1&& buffers,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write(s,
+      static_cast<DynamicBuffer_v1&&>(buffers),
+      transfer_all(), ec);
+  asio::detail::throw_error(ec, "write");
+  return bytes_transferred;
+}
+
+template <typename SyncWriteStream, typename DynamicBuffer_v1>
+inline std::size_t write(SyncWriteStream& s,
+    DynamicBuffer_v1&& buffers,
+    asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >)
+{
+  return write(s, static_cast<DynamicBuffer_v1&&>(buffers),
+      transfer_all(), ec);
+}
+
+template <typename SyncWriteStream, typename DynamicBuffer_v1,
+    typename CompletionCondition>
+inline std::size_t write(SyncWriteStream& s,
+    DynamicBuffer_v1&& buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write(s,
+      static_cast<DynamicBuffer_v1&&>(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "write");
+  return bytes_transferred;
+}
+
+#if !defined(ASIO_NO_EXTENSIONS)
+#if !defined(ASIO_NO_IOSTREAM)
+
+template <typename SyncWriteStream, typename Allocator,
+    typename CompletionCondition>
+inline std::size_t write(SyncWriteStream& s,
+    asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return write(s, basic_streambuf_ref<Allocator>(b),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+}
+
+template <typename SyncWriteStream, typename Allocator>
+inline std::size_t write(SyncWriteStream& s,
+    asio::basic_streambuf<Allocator>& b)
+{
+  return write(s, basic_streambuf_ref<Allocator>(b));
+}
+
+template <typename SyncWriteStream, typename Allocator>
+inline std::size_t write(SyncWriteStream& s,
+    asio::basic_streambuf<Allocator>& b,
+    asio::error_code& ec)
+{
+  return write(s, basic_streambuf_ref<Allocator>(b), ec);
+}
+
+template <typename SyncWriteStream, typename Allocator,
+    typename CompletionCondition>
+inline std::size_t write(SyncWriteStream& s,
+    asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return write(s, basic_streambuf_ref<Allocator>(b),
+      static_cast<CompletionCondition&&>(completion_condition));
+}
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+#endif // !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+template <typename SyncWriteStream, typename DynamicBuffer_v2,
+    typename CompletionCondition>
+std::size_t write(SyncWriteStream& s, DynamicBuffer_v2 buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  std::size_t bytes_transferred = write(s, buffers.data(0, buffers.size()),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  buffers.consume(bytes_transferred);
+  return bytes_transferred;
+}
+
+template <typename SyncWriteStream, typename DynamicBuffer_v2>
+inline std::size_t write(SyncWriteStream& s, DynamicBuffer_v2 buffers,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write(s,
+      static_cast<DynamicBuffer_v2&&>(buffers),
+      transfer_all(), ec);
+  asio::detail::throw_error(ec, "write");
+  return bytes_transferred;
+}
+
+template <typename SyncWriteStream, typename DynamicBuffer_v2>
+inline std::size_t write(SyncWriteStream& s, DynamicBuffer_v2 buffers,
+    asio::error_code& ec,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >)
+{
+  return write(s, static_cast<DynamicBuffer_v2&&>(buffers),
+      transfer_all(), ec);
+}
+
+template <typename SyncWriteStream, typename DynamicBuffer_v2,
+    typename CompletionCondition>
+inline std::size_t write(SyncWriteStream& s, DynamicBuffer_v2 buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_dynamic_buffer_v2<DynamicBuffer_v2>::value
+    >,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write(s,
+      static_cast<DynamicBuffer_v2&&>(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "write");
+  return bytes_transferred;
+}
+
+namespace detail
+{
+  template <typename AsyncWriteStream, typename ConstBufferSequence,
+      typename ConstBufferIterator, typename CompletionCondition,
+      typename WriteHandler>
+  class write_op
+    : public base_from_cancellation_state<WriteHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    write_op(AsyncWriteStream& stream, const ConstBufferSequence& buffers,
+        CompletionCondition& completion_condition, WriteHandler& handler)
+      : base_from_cancellation_state<WriteHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        stream_(stream),
+        buffers_(buffers),
+        start_(0),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    write_op(const write_op& other)
+      : base_from_cancellation_state<WriteHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        stream_(other.stream_),
+        buffers_(other.buffers_),
+        start_(other.start_),
+        handler_(other.handler_)
+    {
+    }
+
+    write_op(write_op&& other)
+      : base_from_cancellation_state<WriteHandler>(
+          static_cast<base_from_cancellation_state<WriteHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        stream_(other.stream_),
+        buffers_(static_cast<buffers_type&&>(other.buffers_)),
+        start_(other.start_),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, buffers_.total_consumed());
+        for (;;)
+        {
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_write"));
+            stream_.async_write_some(buffers_.prepare(max_size),
+                static_cast<write_op&&>(*this));
+          }
+          return; default:
+          buffers_.consume(bytes_transferred);
+          if ((!ec && bytes_transferred == 0) || buffers_.empty())
+            break;
+          max_size = this->check_for_completion(ec, buffers_.total_consumed());
+          if (max_size == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<WriteHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(buffers_.total_consumed()));
+      }
+    }
+
+  //private:
+    typedef asio::detail::consuming_buffers<const_buffer,
+        ConstBufferSequence, ConstBufferIterator> buffers_type;
+
+    AsyncWriteStream& stream_;
+    buffers_type buffers_;
+    int start_;
+    WriteHandler handler_;
+  };
+
+  template <typename AsyncWriteStream, typename ConstBufferSequence,
+      typename ConstBufferIterator, typename CompletionCondition,
+      typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      write_op<AsyncWriteStream, ConstBufferSequence, ConstBufferIterator,
+        CompletionCondition, WriteHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncWriteStream, typename ConstBufferSequence,
+      typename ConstBufferIterator, typename CompletionCondition,
+      typename WriteHandler>
+  inline void start_write_op(AsyncWriteStream& stream,
+      const ConstBufferSequence& buffers, const ConstBufferIterator&,
+      CompletionCondition& completion_condition, WriteHandler& handler)
+  {
+    detail::write_op<AsyncWriteStream, ConstBufferSequence,
+      ConstBufferIterator, CompletionCondition, WriteHandler>(
+        stream, buffers, completion_condition, handler)(
+          asio::error_code(), 0, 1);
+  }
+
+  template <typename AsyncWriteStream>
+  class initiate_async_write
+  {
+  public:
+    typedef typename AsyncWriteStream::executor_type executor_type;
+
+    explicit initiate_async_write(AsyncWriteStream& stream)
+      : stream_(stream)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return stream_.get_executor();
+    }
+
+    template <typename WriteHandler, typename ConstBufferSequence,
+        typename CompletionCondition>
+    void operator()(WriteHandler&& handler,
+        const ConstBufferSequence& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      non_const_lvalue<WriteHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      start_write_op(stream_, buffers,
+          asio::buffer_sequence_begin(buffers),
+          completion_cond2.value, handler2.value);
+    }
+
+  private:
+    AsyncWriteStream& stream_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncWriteStream, typename ConstBufferSequence,
+    typename ConstBufferIterator, typename CompletionCondition,
+    typename WriteHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::write_op<AsyncWriteStream, ConstBufferSequence,
+      ConstBufferIterator, CompletionCondition, WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::write_op<AsyncWriteStream, ConstBufferSequence,
+        ConstBufferIterator, CompletionCondition, WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::write_op<AsyncWriteStream, ConstBufferSequence,
+        ConstBufferIterator, CompletionCondition, WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#if !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+namespace detail
+{
+  template <typename AsyncWriteStream, typename DynamicBuffer_v1,
+      typename CompletionCondition, typename WriteHandler>
+  class write_dynbuf_v1_op
+  {
+  public:
+    template <typename BufferSequence>
+    write_dynbuf_v1_op(AsyncWriteStream& stream,
+        BufferSequence&& buffers,
+        CompletionCondition& completion_condition, WriteHandler& handler)
+      : stream_(stream),
+        buffers_(static_cast<BufferSequence&&>(buffers)),
+        completion_condition_(
+          static_cast<CompletionCondition&&>(completion_condition)),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    write_dynbuf_v1_op(const write_dynbuf_v1_op& other)
+      : stream_(other.stream_),
+        buffers_(other.buffers_),
+        completion_condition_(other.completion_condition_),
+        handler_(other.handler_)
+    {
+    }
+
+    write_dynbuf_v1_op(write_dynbuf_v1_op&& other)
+      : stream_(other.stream_),
+        buffers_(static_cast<DynamicBuffer_v1&&>(other.buffers_)),
+        completion_condition_(
+          static_cast<CompletionCondition&&>(
+            other.completion_condition_)),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      switch (start)
+      {
+        case 1:
+        async_write(stream_, buffers_.data(),
+            static_cast<CompletionCondition&&>(completion_condition_),
+            static_cast<write_dynbuf_v1_op&&>(*this));
+        return; default:
+        buffers_.consume(bytes_transferred);
+        static_cast<WriteHandler&&>(handler_)(ec,
+            static_cast<const std::size_t&>(bytes_transferred));
+      }
+    }
+
+  //private:
+    AsyncWriteStream& stream_;
+    DynamicBuffer_v1 buffers_;
+    CompletionCondition completion_condition_;
+    WriteHandler handler_;
+  };
+
+  template <typename AsyncWriteStream, typename DynamicBuffer_v1,
+      typename CompletionCondition, typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      write_dynbuf_v1_op<AsyncWriteStream, DynamicBuffer_v1,
+        CompletionCondition, WriteHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+  }
+
+  template <typename AsyncWriteStream>
+  class initiate_async_write_dynbuf_v1
+  {
+  public:
+    typedef typename AsyncWriteStream::executor_type executor_type;
+
+    explicit initiate_async_write_dynbuf_v1(AsyncWriteStream& stream)
+      : stream_(stream)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return stream_.get_executor();
+    }
+
+    template <typename WriteHandler, typename DynamicBuffer_v1,
+        typename CompletionCondition>
+    void operator()(WriteHandler&& handler,
+        DynamicBuffer_v1&& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      non_const_lvalue<WriteHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      write_dynbuf_v1_op<AsyncWriteStream,
+        decay_t<DynamicBuffer_v1>,
+          CompletionCondition, decay_t<WriteHandler>>(
+            stream_, static_cast<DynamicBuffer_v1&&>(buffers),
+              completion_cond2.value, handler2.value)(
+                asio::error_code(), 0, 1);
+    }
+
+  private:
+    AsyncWriteStream& stream_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncWriteStream, typename DynamicBuffer_v1,
+    typename CompletionCondition, typename WriteHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::write_dynbuf_v1_op<AsyncWriteStream,
+      DynamicBuffer_v1, CompletionCondition, WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::write_dynbuf_v1_op<AsyncWriteStream, DynamicBuffer_v1,
+        CompletionCondition, WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::write_dynbuf_v1_op<AsyncWriteStream,
+        DynamicBuffer_v1, CompletionCondition, WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#endif // !defined(ASIO_NO_DYNAMIC_BUFFER_V1)
+
+namespace detail
+{
+  template <typename AsyncWriteStream, typename DynamicBuffer_v2,
+      typename CompletionCondition, typename WriteHandler>
+  class write_dynbuf_v2_op
+  {
+  public:
+    template <typename BufferSequence>
+    write_dynbuf_v2_op(AsyncWriteStream& stream,
+        BufferSequence&& buffers,
+        CompletionCondition& completion_condition, WriteHandler& handler)
+      : stream_(stream),
+        buffers_(static_cast<BufferSequence&&>(buffers)),
+        completion_condition_(
+          static_cast<CompletionCondition&&>(completion_condition)),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    write_dynbuf_v2_op(const write_dynbuf_v2_op& other)
+      : stream_(other.stream_),
+        buffers_(other.buffers_),
+        completion_condition_(other.completion_condition_),
+        handler_(other.handler_)
+    {
+    }
+
+    write_dynbuf_v2_op(write_dynbuf_v2_op&& other)
+      : stream_(other.stream_),
+        buffers_(static_cast<DynamicBuffer_v2&&>(other.buffers_)),
+        completion_condition_(
+          static_cast<CompletionCondition&&>(
+            other.completion_condition_)),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      switch (start)
+      {
+        case 1:
+        async_write(stream_, buffers_.data(0, buffers_.size()),
+            static_cast<CompletionCondition&&>(completion_condition_),
+            static_cast<write_dynbuf_v2_op&&>(*this));
+        return; default:
+        buffers_.consume(bytes_transferred);
+        static_cast<WriteHandler&&>(handler_)(ec,
+            static_cast<const std::size_t&>(bytes_transferred));
+      }
+    }
+
+  //private:
+    AsyncWriteStream& stream_;
+    DynamicBuffer_v2 buffers_;
+    CompletionCondition completion_condition_;
+    WriteHandler handler_;
+  };
+
+  template <typename AsyncWriteStream, typename DynamicBuffer_v2,
+      typename CompletionCondition, typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      write_dynbuf_v2_op<AsyncWriteStream, DynamicBuffer_v2,
+        CompletionCondition, WriteHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+  }
+
+  template <typename AsyncWriteStream>
+  class initiate_async_write_dynbuf_v2
+  {
+  public:
+    typedef typename AsyncWriteStream::executor_type executor_type;
+
+    explicit initiate_async_write_dynbuf_v2(AsyncWriteStream& stream)
+      : stream_(stream)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return stream_.get_executor();
+    }
+
+    template <typename WriteHandler, typename DynamicBuffer_v2,
+        typename CompletionCondition>
+    void operator()(WriteHandler&& handler,
+        DynamicBuffer_v2&& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      non_const_lvalue<WriteHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      write_dynbuf_v2_op<AsyncWriteStream, decay_t<DynamicBuffer_v2>,
+        CompletionCondition, decay_t<WriteHandler>>(
+          stream_, static_cast<DynamicBuffer_v2&&>(buffers),
+            completion_cond2.value, handler2.value)(
+              asio::error_code(), 0, 1);
+    }
+
+  private:
+    AsyncWriteStream& stream_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncWriteStream, typename DynamicBuffer_v2,
+    typename CompletionCondition, typename WriteHandler,
+    typename DefaultCandidate>
+struct associator<Associator,
+    detail::write_dynbuf_v2_op<AsyncWriteStream,
+      DynamicBuffer_v2, CompletionCondition, WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::write_dynbuf_v2_op<AsyncWriteStream, DynamicBuffer_v2,
+        CompletionCondition, WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::write_dynbuf_v2_op<AsyncWriteStream,
+        DynamicBuffer_v2, CompletionCondition, WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_WRITE_HPP

include/asio/impl/write_at.hpp

@@ -0,0 +1,480 @@
+//
+// impl/write_at.hpp
+// ~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_IMPL_WRITE_AT_HPP
+#define ASIO_IMPL_WRITE_AT_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/associator.hpp"
+#include "asio/buffer.hpp"
+#include "asio/detail/array_fwd.hpp"
+#include "asio/detail/base_from_cancellation_state.hpp"
+#include "asio/detail/base_from_completion_cond.hpp"
+#include "asio/detail/bind_handler.hpp"
+#include "asio/detail/consuming_buffers.hpp"
+#include "asio/detail/dependent_type.hpp"
+#include "asio/detail/handler_cont_helpers.hpp"
+#include "asio/detail/handler_tracking.hpp"
+#include "asio/detail/handler_type_requirements.hpp"
+#include "asio/detail/non_const_lvalue.hpp"
+#include "asio/detail/throw_error.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail
+{
+  template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
+      typename ConstBufferIterator, typename CompletionCondition>
+  std::size_t write_at_buffer_sequence(SyncRandomAccessWriteDevice& d,
+      uint64_t offset, const ConstBufferSequence& buffers,
+      const ConstBufferIterator&, CompletionCondition completion_condition,
+      asio::error_code& ec)
+  {
+    ec = asio::error_code();
+    asio::detail::consuming_buffers<const_buffer,
+        ConstBufferSequence, ConstBufferIterator> tmp(buffers);
+    while (!tmp.empty())
+    {
+      if (std::size_t max_size = detail::adapt_completion_condition_result(
+            completion_condition(ec, tmp.total_consumed())))
+      {
+        tmp.consume(d.write_some_at(offset + tmp.total_consumed(),
+              tmp.prepare(max_size), ec));
+      }
+      else
+        break;
+    }
+    return tmp.total_consumed();
+  }
+} // namespace detail
+
+template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
+    typename CompletionCondition>
+std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, const ConstBufferSequence& buffers,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  return detail::write_at_buffer_sequence(d, offset, buffers,
+      asio::buffer_sequence_begin(buffers),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+}
+
+template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence>
+inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, const ConstBufferSequence& buffers)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write_at(
+      d, offset, buffers, transfer_all(), ec);
+  asio::detail::throw_error(ec, "write_at");
+  return bytes_transferred;
+}
+
+template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence>
+inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, const ConstBufferSequence& buffers,
+    asio::error_code& ec)
+{
+  return write_at(d, offset, buffers, transfer_all(), ec);
+}
+
+template <typename SyncRandomAccessWriteDevice, typename ConstBufferSequence,
+    typename CompletionCondition>
+inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, const ConstBufferSequence& buffers,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write_at(d, offset, buffers,
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "write_at");
+  return bytes_transferred;
+}
+
+#if !defined(ASIO_NO_EXTENSIONS)
+#if !defined(ASIO_NO_IOSTREAM)
+
+template <typename SyncRandomAccessWriteDevice, typename Allocator,
+    typename CompletionCondition>
+std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition, asio::error_code& ec,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  std::size_t bytes_transferred = write_at(d, offset, b.data(),
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  b.consume(bytes_transferred);
+  return bytes_transferred;
+}
+
+template <typename SyncRandomAccessWriteDevice, typename Allocator>
+inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write_at(d, offset, b, transfer_all(), ec);
+  asio::detail::throw_error(ec, "write_at");
+  return bytes_transferred;
+}
+
+template <typename SyncRandomAccessWriteDevice, typename Allocator>
+inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b,
+    asio::error_code& ec)
+{
+  return write_at(d, offset, b, transfer_all(), ec);
+}
+
+template <typename SyncRandomAccessWriteDevice, typename Allocator,
+    typename CompletionCondition>
+inline std::size_t write_at(SyncRandomAccessWriteDevice& d,
+    uint64_t offset, asio::basic_streambuf<Allocator>& b,
+    CompletionCondition completion_condition,
+    constraint_t<
+      is_completion_condition<CompletionCondition>::value
+    >)
+{
+  asio::error_code ec;
+  std::size_t bytes_transferred = write_at(d, offset, b,
+      static_cast<CompletionCondition&&>(completion_condition), ec);
+  asio::detail::throw_error(ec, "write_at");
+  return bytes_transferred;
+}
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+
+namespace detail
+{
+  template <typename AsyncRandomAccessWriteDevice,
+      typename ConstBufferSequence, typename ConstBufferIterator,
+      typename CompletionCondition, typename WriteHandler>
+  class write_at_op
+    : public base_from_cancellation_state<WriteHandler>,
+      base_from_completion_cond<CompletionCondition>
+  {
+  public:
+    write_at_op(AsyncRandomAccessWriteDevice& device,
+        uint64_t offset, const ConstBufferSequence& buffers,
+        CompletionCondition& completion_condition, WriteHandler& handler)
+      : base_from_cancellation_state<WriteHandler>(
+          handler, enable_partial_cancellation()),
+        base_from_completion_cond<CompletionCondition>(completion_condition),
+        device_(device),
+        offset_(offset),
+        buffers_(buffers),
+        start_(0),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    write_at_op(const write_at_op& other)
+      : base_from_cancellation_state<WriteHandler>(other),
+        base_from_completion_cond<CompletionCondition>(other),
+        device_(other.device_),
+        offset_(other.offset_),
+        buffers_(other.buffers_),
+        start_(other.start_),
+        handler_(other.handler_)
+    {
+    }
+
+    write_at_op(write_at_op&& other)
+      : base_from_cancellation_state<WriteHandler>(
+          static_cast<base_from_cancellation_state<WriteHandler>&&>(other)),
+        base_from_completion_cond<CompletionCondition>(
+          static_cast<base_from_completion_cond<CompletionCondition>&&>(other)),
+        device_(other.device_),
+        offset_(other.offset_),
+        buffers_(static_cast<buffers_type&&>(other.buffers_)),
+        start_(other.start_),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(asio::error_code ec,
+        std::size_t bytes_transferred, int start = 0)
+    {
+      std::size_t max_size;
+      switch (start_ = start)
+      {
+        case 1:
+        max_size = this->check_for_completion(ec, buffers_.total_consumed());
+        for (;;)
+        {
+          {
+            ASIO_HANDLER_LOCATION((__FILE__, __LINE__, "async_write_at"));
+            device_.async_write_some_at(
+                offset_ + buffers_.total_consumed(), buffers_.prepare(max_size),
+                static_cast<write_at_op&&>(*this));
+          }
+          return; default:
+          buffers_.consume(bytes_transferred);
+          if ((!ec && bytes_transferred == 0) || buffers_.empty())
+            break;
+          max_size = this->check_for_completion(ec, buffers_.total_consumed());
+          if (max_size == 0)
+            break;
+          if (this->cancelled() != cancellation_type::none)
+          {
+            ec = asio::error::operation_aborted;
+            break;
+          }
+        }
+
+        static_cast<WriteHandler&&>(handler_)(
+            static_cast<const asio::error_code&>(ec),
+            static_cast<const std::size_t&>(buffers_.total_consumed()));
+      }
+    }
+
+  //private:
+    typedef asio::detail::consuming_buffers<const_buffer,
+        ConstBufferSequence, ConstBufferIterator> buffers_type;
+
+    AsyncRandomAccessWriteDevice& device_;
+    uint64_t offset_;
+    buffers_type buffers_;
+    int start_;
+    WriteHandler handler_;
+  };
+
+  template <typename AsyncRandomAccessWriteDevice,
+      typename ConstBufferSequence, typename ConstBufferIterator,
+      typename CompletionCondition, typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
+        ConstBufferIterator, CompletionCondition, WriteHandler>* this_handler)
+  {
+    return this_handler->start_ == 0 ? true
+      : asio_handler_cont_helpers::is_continuation(
+          this_handler->handler_);
+  }
+
+  template <typename AsyncRandomAccessWriteDevice,
+      typename ConstBufferSequence, typename ConstBufferIterator,
+      typename CompletionCondition, typename WriteHandler>
+  inline void start_write_at_op(AsyncRandomAccessWriteDevice& d,
+      uint64_t offset, const ConstBufferSequence& buffers,
+      const ConstBufferIterator&, CompletionCondition& completion_condition,
+      WriteHandler& handler)
+  {
+    detail::write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
+      ConstBufferIterator, CompletionCondition, WriteHandler>(
+        d, offset, buffers, completion_condition, handler)(
+          asio::error_code(), 0, 1);
+  }
+
+  template <typename AsyncRandomAccessWriteDevice>
+  class initiate_async_write_at
+  {
+  public:
+    typedef typename AsyncRandomAccessWriteDevice::executor_type executor_type;
+
+    explicit initiate_async_write_at(AsyncRandomAccessWriteDevice& device)
+      : device_(device)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return device_.get_executor();
+    }
+
+    template <typename WriteHandler, typename ConstBufferSequence,
+        typename CompletionCondition>
+    void operator()(WriteHandler&& handler,
+        uint64_t offset, const ConstBufferSequence& buffers,
+        CompletionCondition&& completion_cond) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      non_const_lvalue<WriteHandler> handler2(handler);
+      non_const_lvalue<CompletionCondition> completion_cond2(completion_cond);
+      start_write_at_op(device_, offset, buffers,
+          asio::buffer_sequence_begin(buffers),
+          completion_cond2.value, handler2.value);
+    }
+
+  private:
+    AsyncRandomAccessWriteDevice& device_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename AsyncRandomAccessWriteDevice, typename ConstBufferSequence,
+    typename ConstBufferIterator, typename CompletionCondition,
+    typename WriteHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::write_at_op<AsyncRandomAccessWriteDevice, ConstBufferSequence,
+      ConstBufferIterator, CompletionCondition, WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::write_at_op<AsyncRandomAccessWriteDevice,
+        ConstBufferSequence, ConstBufferIterator,
+        CompletionCondition, WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::write_at_op<AsyncRandomAccessWriteDevice,
+        ConstBufferSequence, ConstBufferIterator,
+        CompletionCondition, WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#if !defined(ASIO_NO_EXTENSIONS)
+#if !defined(ASIO_NO_IOSTREAM)
+
+namespace detail
+{
+  template <typename Allocator, typename WriteHandler>
+  class write_at_streambuf_op
+  {
+  public:
+    write_at_streambuf_op(
+        asio::basic_streambuf<Allocator>& streambuf,
+        WriteHandler& handler)
+      : streambuf_(streambuf),
+        handler_(static_cast<WriteHandler&&>(handler))
+    {
+    }
+
+    write_at_streambuf_op(const write_at_streambuf_op& other)
+      : streambuf_(other.streambuf_),
+        handler_(other.handler_)
+    {
+    }
+
+    write_at_streambuf_op(write_at_streambuf_op&& other)
+      : streambuf_(other.streambuf_),
+        handler_(static_cast<WriteHandler&&>(other.handler_))
+    {
+    }
+
+    void operator()(const asio::error_code& ec,
+        const std::size_t bytes_transferred)
+    {
+      streambuf_.consume(bytes_transferred);
+      static_cast<WriteHandler&&>(handler_)(ec, bytes_transferred);
+    }
+
+  //private:
+    asio::basic_streambuf<Allocator>& streambuf_;
+    WriteHandler handler_;
+  };
+
+  template <typename Allocator, typename WriteHandler>
+  inline bool asio_handler_is_continuation(
+      write_at_streambuf_op<Allocator, WriteHandler>* this_handler)
+  {
+    return asio_handler_cont_helpers::is_continuation(
+        this_handler->handler_);
+  }
+
+  template <typename AsyncRandomAccessWriteDevice>
+  class initiate_async_write_at_streambuf
+  {
+  public:
+    typedef typename AsyncRandomAccessWriteDevice::executor_type executor_type;
+
+    explicit initiate_async_write_at_streambuf(
+        AsyncRandomAccessWriteDevice& device)
+      : device_(device)
+    {
+    }
+
+    executor_type get_executor() const noexcept
+    {
+      return device_.get_executor();
+    }
+
+    template <typename WriteHandler,
+        typename Allocator, typename CompletionCondition>
+    void operator()(WriteHandler&& handler,
+        uint64_t offset, basic_streambuf<Allocator>* b,
+        CompletionCondition&& completion_condition) const
+    {
+      // If you get an error on the following line it means that your handler
+      // does not meet the documented type requirements for a WriteHandler.
+      ASIO_WRITE_HANDLER_CHECK(WriteHandler, handler) type_check;
+
+      non_const_lvalue<WriteHandler> handler2(handler);
+      async_write_at(device_, offset, b->data(),
+          static_cast<CompletionCondition&&>(completion_condition),
+          write_at_streambuf_op<Allocator, decay_t<WriteHandler>>(
+            *b, handler2.value));
+    }
+
+  private:
+    AsyncRandomAccessWriteDevice& device_;
+  };
+} // namespace detail
+
+#if !defined(GENERATING_DOCUMENTATION)
+
+template <template <typename, typename> class Associator,
+    typename Executor, typename WriteHandler, typename DefaultCandidate>
+struct associator<Associator,
+    detail::write_at_streambuf_op<Executor, WriteHandler>,
+    DefaultCandidate>
+  : Associator<WriteHandler, DefaultCandidate>
+{
+  static typename Associator<WriteHandler, DefaultCandidate>::type get(
+      const detail::write_at_streambuf_op<Executor, WriteHandler>& h) noexcept
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_);
+  }
+
+  static auto get(
+      const detail::write_at_streambuf_op<Executor, WriteHandler>& h,
+      const DefaultCandidate& c) noexcept
+    -> decltype(Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c))
+  {
+    return Associator<WriteHandler, DefaultCandidate>::get(h.handler_, c);
+  }
+};
+
+#endif // !defined(GENERATING_DOCUMENTATION)
+
+#endif // !defined(ASIO_NO_IOSTREAM)
+#endif // !defined(ASIO_NO_EXTENSIONS)
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_IMPL_WRITE_AT_HPP