Initial Commit

include/asio/config.hpp

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+//
+// 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_CONFIG_HPP
+#define ASIO_CONFIG_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/detail/throw_exception.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution_context.hpp"
+#include <cstddef>
+#include <string>
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// Base class for configuration implementations.
+class config_service :
+#if defined(GENERATING_DOCUMENTATION)
+  public execution_context::service
+#else // defined(GENERATING_DOCUMENTATION)
+  public detail::execution_context_service_base<config_service>
+#endif // defined(GENERATING_DOCUMENTATION)
+{
+public:
+#if defined(GENERATING_DOCUMENTATION)
+  typedef config_service key_type;
+#endif // defined(GENERATING_DOCUMENTATION)
+
+  /// Constructor.
+  ASIO_DECL explicit config_service(execution_context& ctx);
+
+  /// Shutdown the service.
+  ASIO_DECL void shutdown() override;
+
+  /// Retrieve a configuration value.
+  ASIO_DECL virtual const char* get_value(const char* section,
+      const char* key_name, char* value, std::size_t value_len) const;
+};
+
+/// Provides access to the configuration values associated with an execution
+/// context.
+class config
+{
+public:
+  /// Constructor.
+  /**
+   * This constructor initialises a @c config object to retrieve configuration
+   * values associated with the specified execution context.
+   */
+  explicit config(execution_context& context)
+    : service_(use_service<config_service>(context))
+  {
+  }
+
+  /// Copy constructor.
+  config(const config& other) noexcept
+    : service_(other.service_)
+  {
+  }
+
+  /// Retrieve an integral configuration value.
+  template <typename T>
+  constraint_t<is_integral<T>::value, T>
+  get(const char* section, const char* key_name, T default_value) const;
+
+private:
+  config_service& service_;
+};
+
+/// Configures an execution context based on a concurrency hint.
+/**
+ * This configuration service is provided for backwards compatibility with
+ * the existing concurrency hint mechanism.
+ *
+ * @par Example
+ * @code asio::io_context my_io_context{
+ *     asio::config_from_concurrency_hint{1}}; @endcode
+ */
+class config_from_concurrency_hint : public execution_context::service_maker
+{
+public:
+  /// Construct with a default concurrency hint.
+  ASIO_DECL config_from_concurrency_hint();
+
+  /// Construct with a specified concurrency hint.
+  explicit config_from_concurrency_hint(int concurrency_hint)
+    : concurrency_hint_(concurrency_hint)
+  {
+  }
+
+  /// Add a concrete service to the specified execution context.
+  ASIO_DECL void make(execution_context& ctx) const override;
+
+private:
+  int concurrency_hint_;
+};
+
+/// Configures an execution context by reading variables from a string.
+/**
+ * Each variable must be on a line of its own, and of the form:
+ *
+ * <tt>section.key=value</tt>
+ *
+ * or, if an optional prefix is specified:
+ *
+ * <tt>prefix.section.key=value</tt>
+ *
+ * Blank lines and lines starting with <tt>#</tt> are ignored. It is also
+ * permitted to include a comment starting with <tt>#</tt> after the value.
+ *
+ * @par Example
+ * @code asio::io_context my_io_context{
+ *     asio::config_from_string{
+ *       "scheduler.concurrency_hint=10\n"
+ *       "scheduler.locking=1"}}; @endcode
+ */
+class config_from_string : public execution_context::service_maker
+{
+public:
+  /// Construct with the default prefix "asio".
+  explicit config_from_string(std::string s)
+    : string_(static_cast<std::string&&>(s)),
+      prefix_()
+  {
+  }
+
+  /// Construct with a specified prefix.
+  config_from_string(std::string s, std::string prefix)
+    : string_(static_cast<std::string&&>(s)),
+      prefix_(static_cast<std::string&&>(prefix))
+  {
+  }
+
+  /// Add a concrete service to the specified execution context.
+  ASIO_DECL void make(execution_context& ctx) const override;
+
+private:
+  std::string string_;
+  std::string prefix_;
+};
+
+/// Configures an execution context by reading environment variables.
+/**
+ * The environment variable names are formed by concatenating the prefix,
+ * section, and key, with underscore as delimiter, and then converting the
+ * resulting string to upper case.
+ *
+ * @par Example
+ * @code asio::io_context my_io_context{
+ *     asio::config_from_env{"my_app"}}; @endcode
+ */
+class config_from_env : public execution_context::service_maker
+{
+public:
+  /// Construct with the default prefix "asio".
+  ASIO_DECL config_from_env();
+
+  /// Construct with a specified prefix.
+  explicit config_from_env(std::string prefix)
+    : prefix_(static_cast<std::string&&>(prefix))
+  {
+  }
+
+  /// Add a concrete service to the specified execution context.
+  ASIO_DECL void make(execution_context& ctx) const override;
+
+private:
+  std::string prefix_;
+};
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#include "asio/impl/config.hpp"
+#if defined(ASIO_HEADER_ONLY)
+# include "asio/impl/config.ipp"
+#endif // defined(ASIO_HEADER_ONLY)
+
+#endif // ASIO_CONFIG_HPP