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include/asio/completion_condition.hpp

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+//
+// completion_condition.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_COMPLETION_CONDITION_HPP
+#define ASIO_COMPLETION_CONDITION_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include <cstddef>
+#include "asio/detail/type_traits.hpp"
+#include "asio/error_code.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+namespace detail {
+
+// The default maximum number of bytes to transfer in a single operation.
+enum default_max_transfer_size_t { default_max_transfer_size = 65536 };
+
+// Adapt result of old-style completion conditions (which had a bool result
+// where true indicated that the operation was complete).
+inline std::size_t adapt_completion_condition_result(bool result)
+{
+  return result ? 0 : default_max_transfer_size;
+}
+
+// Adapt result of current completion conditions (which have a size_t result
+// where 0 means the operation is complete, and otherwise the result is the
+// maximum number of bytes to transfer on the next underlying operation).
+inline std::size_t adapt_completion_condition_result(std::size_t result)
+{
+  return result;
+}
+
+class transfer_all_t
+{
+public:
+  typedef std::size_t result_type;
+
+  template <typename Error>
+  std::size_t operator()(const Error& err, std::size_t)
+  {
+    return !!err ? 0 : default_max_transfer_size;
+  }
+};
+
+class transfer_at_least_t
+{
+public:
+  typedef std::size_t result_type;
+
+  explicit transfer_at_least_t(std::size_t minimum)
+    : minimum_(minimum)
+  {
+  }
+
+  template <typename Error>
+  std::size_t operator()(const Error& err, std::size_t bytes_transferred)
+  {
+    return (!!err || bytes_transferred >= minimum_)
+      ? 0 : default_max_transfer_size;
+  }
+
+private:
+  std::size_t minimum_;
+};
+
+class transfer_exactly_t
+{
+public:
+  typedef std::size_t result_type;
+
+  explicit transfer_exactly_t(std::size_t size)
+    : size_(size)
+  {
+  }
+
+  template <typename Error>
+  std::size_t operator()(const Error& err, std::size_t bytes_transferred)
+  {
+    return (!!err || bytes_transferred >= size_) ? 0 :
+      (size_ - bytes_transferred < default_max_transfer_size
+        ? size_ - bytes_transferred : std::size_t(default_max_transfer_size));
+  }
+
+private:
+  std::size_t size_;
+};
+
+template <typename T, typename = void>
+struct is_completion_condition_helper : false_type
+{
+};
+
+template <typename T>
+struct is_completion_condition_helper<T,
+    enable_if_t<
+      is_same<
+        result_of_t<T(asio::error_code, std::size_t)>,
+        bool
+      >::value
+    >
+  > : true_type
+{
+};
+
+template <typename T>
+struct is_completion_condition_helper<T,
+    enable_if_t<
+      is_same<
+        result_of_t<T(asio::error_code, std::size_t)>,
+        std::size_t
+      >::value
+    >
+  > : true_type
+{
+};
+
+} // namespace detail
+
+#if defined(GENERATING_DOCUMENTATION)
+
+/// Trait for determining whether a function object is a completion condition.
+template <typename T>
+struct is_completion_condition
+{
+  static constexpr bool value = automatically_determined;
+};
+
+#else // defined(GENERATING_DOCUMENTATION)
+
+template <typename T>
+struct is_completion_condition : detail::is_completion_condition_helper<T>
+{
+};
+
+#endif // defined(GENERATING_DOCUMENTATION)
+
+/**
+ * @defgroup completion_condition Completion Condition Function Objects
+ *
+ * Function objects used for determining when a read or write operation should
+ * complete.
+ */
+/*@{*/
+
+/// Return a completion condition function object that indicates that a read or
+/// write operation should continue until all of the data has been transferred,
+/// or until an error occurs.
+/**
+ * This function is used to create an object, of unspecified type, that meets
+ * CompletionCondition requirements.
+ *
+ * @par Example
+ * Reading until a buffer is full:
+ * @code
+ * boost::array<char, 128> buf;
+ * asio::error_code ec;
+ * std::size_t n = asio::read(
+ *     sock, asio::buffer(buf),
+ *     asio::transfer_all(), ec);
+ * if (ec)
+ * {
+ *   // An error occurred.
+ * }
+ * else
+ * {
+ *   // n == 128
+ * }
+ * @endcode
+ */
+#if defined(GENERATING_DOCUMENTATION)
+unspecified transfer_all();
+#else
+inline detail::transfer_all_t transfer_all()
+{
+  return detail::transfer_all_t();
+}
+#endif
+
+/// Return a completion condition function object that indicates that a read or
+/// write operation should continue until a minimum number of bytes has been
+/// transferred, or until an error occurs.
+/**
+ * This function is used to create an object, of unspecified type, that meets
+ * CompletionCondition requirements.
+ *
+ * @par Example
+ * Reading until a buffer is full or contains at least 64 bytes:
+ * @code
+ * boost::array<char, 128> buf;
+ * asio::error_code ec;
+ * std::size_t n = asio::read(
+ *     sock, asio::buffer(buf),
+ *     asio::transfer_at_least(64), ec);
+ * if (ec)
+ * {
+ *   // An error occurred.
+ * }
+ * else
+ * {
+ *   // n >= 64 && n <= 128
+ * }
+ * @endcode
+ */
+#if defined(GENERATING_DOCUMENTATION)
+unspecified transfer_at_least(std::size_t minimum);
+#else
+inline detail::transfer_at_least_t transfer_at_least(std::size_t minimum)
+{
+  return detail::transfer_at_least_t(minimum);
+}
+#endif
+
+/// Return a completion condition function object that indicates that a read or
+/// write operation should continue until an exact number of bytes has been
+/// transferred, or until an error occurs.
+/**
+ * This function is used to create an object, of unspecified type, that meets
+ * CompletionCondition requirements.
+ *
+ * @par Example
+ * Reading until a buffer is full or contains exactly 64 bytes:
+ * @code
+ * boost::array<char, 128> buf;
+ * asio::error_code ec;
+ * std::size_t n = asio::read(
+ *     sock, asio::buffer(buf),
+ *     asio::transfer_exactly(64), ec);
+ * if (ec)
+ * {
+ *   // An error occurred.
+ * }
+ * else
+ * {
+ *   // n == 64
+ * }
+ * @endcode
+ */
+#if defined(GENERATING_DOCUMENTATION)
+unspecified transfer_exactly(std::size_t size);
+#else
+inline detail::transfer_exactly_t transfer_exactly(std::size_t size)
+{
+  return detail::transfer_exactly_t(size);
+}
+#endif
+
+/*@}*/
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_COMPLETION_CONDITION_HPP