[DEV] add v1.76.0

libs/asio/example/cpp11/timeouts/Jamfile.v2

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+#
+# Copyright (c) 2003-2021 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)
+#
+
+lib socket ; # SOLARIS
+lib nsl ; # SOLARIS
+lib ws2_32 ; # NT
+lib mswsock ; # NT
+lib ipv6 ; # HPUX
+lib network ; # HAIKU
+
+project
+  : requirements
+    <library>/boost/system//boost_system
+    <library>/boost/chrono//boost_chrono
+    <define>BOOST_ALL_NO_LIB=1
+    <threading>multi
+    <target-os>solaris:<library>socket
+    <target-os>solaris:<library>nsl
+    <target-os>windows:<define>_WIN32_WINNT=0x0501
+    <target-os>windows,<toolset>gcc:<library>ws2_32
+    <target-os>windows,<toolset>gcc:<library>mswsock
+    <target-os>windows,<toolset>gcc-cygwin:<define>__USE_W32_SOCKETS
+    <target-os>hpux,<toolset>gcc:<define>_XOPEN_SOURCE_EXTENDED
+    <target-os>hpux:<library>ipv6
+    <target-os>haiku:<library>network
+  ;
+
+exe async_tcp_client : async_tcp_client.cpp ;
+exe blocking_tcp_client : blocking_tcp_client.cpp ;
+exe blocking_token_tcp_client : blocking_token_tcp_client.cpp ;
+exe blocking_udp_client : blocking_udp_client.cpp ;
+exe server : server.cpp ;

libs/asio/example/cpp11/timeouts/async_tcp_client.cpp

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+//
+// async_tcp_client.cpp
+// ~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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)
+//
+
+#include <boost/asio/buffer.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/read_until.hpp>
+#include <boost/asio/steady_timer.hpp>
+#include <boost/asio/write.hpp>
+#include <functional>
+#include <iostream>
+#include <string>
+
+using boost::asio::steady_timer;
+using boost::asio::ip::tcp;
+using std::placeholders::_1;
+using std::placeholders::_2;
+
+//
+// This class manages socket timeouts by applying the concept of a deadline.
+// Some asynchronous operations are given deadlines by which they must complete.
+// Deadlines are enforced by an "actor" that persists for the lifetime of the
+// client object:
+//
+//  +----------------+
+//  |                |
+//  | check_deadline |<---+
+//  |                |    |
+//  +----------------+    | async_wait()
+//              |         |
+//              +---------+
+//
+// If the deadline actor determines that the deadline has expired, the socket
+// is closed and any outstanding operations are consequently cancelled.
+//
+// Connection establishment involves trying each endpoint in turn until a
+// connection is successful, or the available endpoints are exhausted. If the
+// deadline actor closes the socket, the connect actor is woken up and moves to
+// the next endpoint.
+//
+//  +---------------+
+//  |               |
+//  | start_connect |<---+
+//  |               |    |
+//  +---------------+    |
+//           |           |
+//  async_-  |    +----------------+
+// connect() |    |                |
+//           +--->| handle_connect |
+//                |                |
+//                +----------------+
+//                          :
+// Once a connection is     :
+// made, the connect        :
+// actor forks in two -     :
+//                          :
+// an actor for reading     :       and an actor for
+// inbound messages:        :       sending heartbeats:
+//                          :
+//  +------------+          :          +-------------+
+//  |            |<- - - - -+- - - - ->|             |
+//  | start_read |                     | start_write |<---+
+//  |            |<---+                |             |    |
+//  +------------+    |                +-------------+    | async_wait()
+//          |         |                        |          |
+//  async_- |    +-------------+       async_- |    +--------------+
+//   read_- |    |             |       write() |    |              |
+//  until() +--->| handle_read |               +--->| handle_write |
+//               |             |                    |              |
+//               +-------------+                    +--------------+
+//
+// The input actor reads messages from the socket, where messages are delimited
+// by the newline character. The deadline for a complete message is 30 seconds.
+//
+// The heartbeat actor sends a heartbeat (a message that consists of a single
+// newline character) every 10 seconds. In this example, no deadline is applied
+// to message sending.
+//
+class client
+{
+public:
+  client(boost::asio::io_context& io_context)
+    : socket_(io_context),
+      deadline_(io_context),
+      heartbeat_timer_(io_context)
+  {
+  }
+
+  // Called by the user of the client class to initiate the connection process.
+  // The endpoints will have been obtained using a tcp::resolver.
+  void start(tcp::resolver::results_type endpoints)
+  {
+    // Start the connect actor.
+    endpoints_ = endpoints;
+    start_connect(endpoints_.begin());
+
+    // Start the deadline actor. You will note that we're not setting any
+    // particular deadline here. Instead, the connect and input actors will
+    // update the deadline prior to each asynchronous operation.
+    deadline_.async_wait(std::bind(&client::check_deadline, this));
+  }
+
+  // This function terminates all the actors to shut down the connection. It
+  // may be called by the user of the client class, or by the class itself in
+  // response to graceful termination or an unrecoverable error.
+  void stop()
+  {
+    stopped_ = true;
+    boost::system::error_code ignored_error;
+    socket_.close(ignored_error);
+    deadline_.cancel();
+    heartbeat_timer_.cancel();
+  }
+
+private:
+  void start_connect(tcp::resolver::results_type::iterator endpoint_iter)
+  {
+    if (endpoint_iter != endpoints_.end())
+    {
+      std::cout << "Trying " << endpoint_iter->endpoint() << "...\n";
+
+      // Set a deadline for the connect operation.
+      deadline_.expires_after(std::chrono::seconds(60));
+
+      // Start the asynchronous connect operation.
+      socket_.async_connect(endpoint_iter->endpoint(),
+          std::bind(&client::handle_connect,
+            this, _1, endpoint_iter));
+    }
+    else
+    {
+      // There are no more endpoints to try. Shut down the client.
+      stop();
+    }
+  }
+
+  void handle_connect(const boost::system::error_code& error,
+      tcp::resolver::results_type::iterator endpoint_iter)
+  {
+    if (stopped_)
+      return;
+
+    // The async_connect() function automatically opens the socket at the start
+    // of the asynchronous operation. If the socket is closed at this time then
+    // the timeout handler must have run first.
+    if (!socket_.is_open())
+    {
+      std::cout << "Connect timed out\n";
+
+      // Try the next available endpoint.
+      start_connect(++endpoint_iter);
+    }
+
+    // Check if the connect operation failed before the deadline expired.
+    else if (error)
+    {
+      std::cout << "Connect error: " << error.message() << "\n";
+
+      // We need to close the socket used in the previous connection attempt
+      // before starting a new one.
+      socket_.close();
+
+      // Try the next available endpoint.
+      start_connect(++endpoint_iter);
+    }
+
+    // Otherwise we have successfully established a connection.
+    else
+    {
+      std::cout << "Connected to " << endpoint_iter->endpoint() << "\n";
+
+      // Start the input actor.
+      start_read();
+
+      // Start the heartbeat actor.
+      start_write();
+    }
+  }
+
+  void start_read()
+  {
+    // Set a deadline for the read operation.
+    deadline_.expires_after(std::chrono::seconds(30));
+
+    // Start an asynchronous operation to read a newline-delimited message.
+    boost::asio::async_read_until(socket_,
+        boost::asio::dynamic_buffer(input_buffer_), '\n',
+        std::bind(&client::handle_read, this, _1, _2));
+  }
+
+  void handle_read(const boost::system::error_code& error, std::size_t n)
+  {
+    if (stopped_)
+      return;
+
+    if (!error)
+    {
+      // Extract the newline-delimited message from the buffer.
+      std::string line(input_buffer_.substr(0, n - 1));
+      input_buffer_.erase(0, n);
+
+      // Empty messages are heartbeats and so ignored.
+      if (!line.empty())
+      {
+        std::cout << "Received: " << line << "\n";
+      }
+
+      start_read();
+    }
+    else
+    {
+      std::cout << "Error on receive: " << error.message() << "\n";
+
+      stop();
+    }
+  }
+
+  void start_write()
+  {
+    if (stopped_)
+      return;
+
+    // Start an asynchronous operation to send a heartbeat message.
+    boost::asio::async_write(socket_, boost::asio::buffer("\n", 1),
+        std::bind(&client::handle_write, this, _1));
+  }
+
+  void handle_write(const boost::system::error_code& error)
+  {
+    if (stopped_)
+      return;
+
+    if (!error)
+    {
+      // Wait 10 seconds before sending the next heartbeat.
+      heartbeat_timer_.expires_after(std::chrono::seconds(10));
+      heartbeat_timer_.async_wait(std::bind(&client::start_write, this));
+    }
+    else
+    {
+      std::cout << "Error on heartbeat: " << error.message() << "\n";
+
+      stop();
+    }
+  }
+
+  void check_deadline()
+  {
+    if (stopped_)
+      return;
+
+    // Check whether the deadline has passed. We compare the deadline against
+    // the current time since a new asynchronous operation may have moved the
+    // deadline before this actor had a chance to run.
+    if (deadline_.expiry() <= steady_timer::clock_type::now())
+    {
+      // The deadline has passed. The socket is closed so that any outstanding
+      // asynchronous operations are cancelled.
+      socket_.close();
+
+      // There is no longer an active deadline. The expiry is set to the
+      // maximum time point so that the actor takes no action until a new
+      // deadline is set.
+      deadline_.expires_at(steady_timer::time_point::max());
+    }
+
+    // Put the actor back to sleep.
+    deadline_.async_wait(std::bind(&client::check_deadline, this));
+  }
+
+private:
+  bool stopped_ = false;
+  tcp::resolver::results_type endpoints_;
+  tcp::socket socket_;
+  std::string input_buffer_;
+  steady_timer deadline_;
+  steady_timer heartbeat_timer_;
+};
+
+int main(int argc, char* argv[])
+{
+  try
+  {
+    if (argc != 3)
+    {
+      std::cerr << "Usage: client <host> <port>\n";
+      return 1;
+    }
+
+    boost::asio::io_context io_context;
+    tcp::resolver r(io_context);
+    client c(io_context);
+
+    c.start(r.resolve(argv[1], argv[2]));
+
+    io_context.run();
+  }
+  catch (std::exception& e)
+  {
+    std::cerr << "Exception: " << e.what() << "\n";
+  }
+
+  return 0;
+}

libs/asio/example/cpp11/timeouts/blocking_tcp_client.cpp

@@ -0,0 +1,192 @@
+//
+// blocking_tcp_client.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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)
+//
+
+#include <boost/asio/buffer.hpp>
+#include <boost/asio/connect.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/read_until.hpp>
+#include <boost/system/system_error.hpp>
+#include <boost/asio/write.hpp>
+#include <cstdlib>
+#include <iostream>
+#include <string>
+
+using boost::asio::ip::tcp;
+
+//----------------------------------------------------------------------
+
+//
+// This class manages socket timeouts by running the io_context using the timed
+// io_context::run_for() member function. Each asynchronous operation is given
+// a timeout within which it must complete. The socket operations themselves
+// use lambdas as completion handlers. For a given socket operation, the client
+// object runs the io_context to block thread execution until the operation
+// completes or the timeout is reached. If the io_context::run_for() function
+// times out, the socket is closed and the outstanding asynchronous operation
+// is cancelled.
+//
+class client
+{
+public:
+  void connect(const std::string& host, const std::string& service,
+      std::chrono::steady_clock::duration timeout)
+  {
+    // Resolve the host name and service to a list of endpoints.
+    auto endpoints = tcp::resolver(io_context_).resolve(host, service);
+
+    // Start the asynchronous operation itself. The lambda that is used as a
+    // callback will update the error variable when the operation completes.
+    // The blocking_udp_client.cpp example shows how you can use std::bind
+    // rather than a lambda.
+    boost::system::error_code error;
+    boost::asio::async_connect(socket_, endpoints,
+        [&](const boost::system::error_code& result_error,
+            const tcp::endpoint& /*result_endpoint*/)
+        {
+          error = result_error;
+        });
+
+    // Run the operation until it completes, or until the timeout.
+    run(timeout);
+
+    // Determine whether a connection was successfully established.
+    if (error)
+      throw std::system_error(error);
+  }
+
+  std::string read_line(std::chrono::steady_clock::duration timeout)
+  {
+    // Start the asynchronous operation. The lambda that is used as a callback
+    // will update the error and n variables when the operation completes. The
+    // blocking_udp_client.cpp example shows how you can use std::bind rather
+    // than a lambda.
+    boost::system::error_code error;
+    std::size_t n = 0;
+    boost::asio::async_read_until(socket_,
+        boost::asio::dynamic_buffer(input_buffer_), '\n',
+        [&](const boost::system::error_code& result_error,
+            std::size_t result_n)
+        {
+          error = result_error;
+          n = result_n;
+        });
+
+    // Run the operation until it completes, or until the timeout.
+    run(timeout);
+
+    // Determine whether the read completed successfully.
+    if (error)
+      throw std::system_error(error);
+
+    std::string line(input_buffer_.substr(0, n - 1));
+    input_buffer_.erase(0, n);
+    return line;
+  }
+
+  void write_line(const std::string& line,
+      std::chrono::steady_clock::duration timeout)
+  {
+    std::string data = line + "\n";
+
+    // Start the asynchronous operation itself. The lambda that is used as a
+    // callback will update the error variable when the operation completes.
+    // The blocking_udp_client.cpp example shows how you can use std::bind
+    // rather than a lambda.
+    boost::system::error_code error;
+    boost::asio::async_write(socket_, boost::asio::buffer(data),
+        [&](const boost::system::error_code& result_error,
+            std::size_t /*result_n*/)
+        {
+          error = result_error;
+        });
+
+    // Run the operation until it completes, or until the timeout.
+    run(timeout);
+
+    // Determine whether the read completed successfully.
+    if (error)
+      throw std::system_error(error);
+  }
+
+private:
+  void run(std::chrono::steady_clock::duration timeout)
+  {
+    // Restart the io_context, as it may have been left in the "stopped" state
+    // by a previous operation.
+    io_context_.restart();
+
+    // Block until the asynchronous operation has completed, or timed out. If
+    // the pending asynchronous operation is a composed operation, the deadline
+    // applies to the entire operation, rather than individual operations on
+    // the socket.
+    io_context_.run_for(timeout);
+
+    // If the asynchronous operation completed successfully then the io_context
+    // would have been stopped due to running out of work. If it was not
+    // stopped, then the io_context::run_for call must have timed out.
+    if (!io_context_.stopped())
+    {
+      // Close the socket to cancel the outstanding asynchronous operation.
+      socket_.close();
+
+      // Run the io_context again until the operation completes.
+      io_context_.run();
+    }
+  }
+
+  boost::asio::io_context io_context_;
+  tcp::socket socket_{io_context_};
+  std::string input_buffer_;
+};
+
+//----------------------------------------------------------------------
+
+int main(int argc, char* argv[])
+{
+  try
+  {
+    if (argc != 4)
+    {
+      std::cerr << "Usage: blocking_tcp_client <host> <port> <message>\n";
+      return 1;
+    }
+
+    client c;
+    c.connect(argv[1], argv[2], std::chrono::seconds(10));
+
+    auto time_sent = std::chrono::steady_clock::now();
+
+    c.write_line(argv[3], std::chrono::seconds(10));
+
+    for (;;)
+    {
+      std::string line = c.read_line(std::chrono::seconds(10));
+
+      // Keep going until we get back the line that was sent.
+      if (line == argv[3])
+        break;
+    }
+
+    auto time_received = std::chrono::steady_clock::now();
+
+    std::cout << "Round trip time: ";
+    std::cout << std::chrono::duration_cast<
+      std::chrono::microseconds>(
+        time_received - time_sent).count();
+    std::cout << " microseconds\n";
+  }
+  catch (std::exception& e)
+  {
+    std::cerr << "Exception: " << e.what() << "\n";
+  }
+
+  return 0;
+}

libs/asio/example/cpp11/timeouts/blocking_token_tcp_client.cpp

@@ -0,0 +1,200 @@
+//
+// blocking_token_tcp_client.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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)
+//
+
+#include <boost/asio/connect.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/read_until.hpp>
+#include <boost/asio/streambuf.hpp>
+#include <boost/system/system_error.hpp>
+#include <boost/asio/write.hpp>
+#include <cstdlib>
+#include <iostream>
+#include <memory>
+#include <string>
+
+using boost::asio::ip::tcp;
+
+// We will use our sockets only with an io_context.
+using tcp_socket = boost::asio::basic_stream_socket<
+    tcp, boost::asio::io_context::executor_type>;
+
+//----------------------------------------------------------------------
+
+// A custom completion token that makes asynchronous operations behave as
+// though they are blocking calls with a timeout.
+struct close_after
+{
+  close_after(std::chrono::steady_clock::duration t, tcp_socket& s)
+    : timeout_(t), socket_(s)
+  {
+  }
+
+  // The maximum time to wait for an asynchronous operation to complete.
+  std::chrono::steady_clock::duration timeout_;
+
+  // The socket to be closed if the operation does not complete in time.
+  tcp_socket& socket_;
+};
+
+namespace boost {
+namespace asio {
+
+// The async_result template is specialised to allow the close_after token to
+// be used with asynchronous operations that have a completion signature of
+// void(error_code, T). Generalising this for all completion signature forms is
+// left as an exercise for the reader.
+template <typename T>
+class async_result<close_after, void(boost::system::error_code, T)>
+{
+public:
+  // An asynchronous operation's initiating function automatically creates an
+  // completion_handler_type object from the token. This function object is
+  // then called on completion of the asynchronous operation.
+  class completion_handler_type
+  {
+  public:
+    completion_handler_type(const close_after& token)
+      : token_(token)
+    {
+    }
+
+    void operator()(const boost::system::error_code& error, T t)
+    {
+      *error_ = error;
+      *t_ = t;
+    }
+
+  private:
+    friend class async_result;
+    close_after token_;
+    boost::system::error_code* error_;
+    T* t_;
+  };
+
+  // The async_result constructor associates the completion handler object with
+  // the result of the initiating function.
+  explicit async_result(completion_handler_type& h)
+    : timeout_(h.token_.timeout_),
+      socket_(h.token_.socket_)
+  {
+    h.error_ = &error_;
+    h.t_ = &t_;
+  }
+
+  // The return_type typedef determines the result type of the asynchronous
+  // operation's initiating function.
+  typedef T return_type;
+
+  // The get() function is used to obtain the result of the asynchronous
+  // operation's initiating function. For the close_after completion token, we
+  // use this function to run the io_context until the operation is complete.
+  return_type get()
+  {
+    boost::asio::io_context& io_context = boost::asio::query(
+        socket_.get_executor(), boost::asio::execution::context);
+
+    // Restart the io_context, as it may have been left in the "stopped" state
+    // by a previous operation.
+    io_context.restart();
+
+    // Block until the asynchronous operation has completed, or timed out. If
+    // the pending asynchronous operation is a composed operation, the deadline
+    // applies to the entire operation, rather than individual operations on
+    // the socket.
+    io_context.run_for(timeout_);
+
+    // If the asynchronous operation completed successfully then the io_context
+    // would have been stopped due to running out of work. If it was not
+    // stopped, then the io_context::run_for call must have timed out and the
+    // operation is still incomplete.
+    if (!io_context.stopped())
+    {
+      // Close the socket to cancel the outstanding asynchronous operation.
+      socket_.close();
+
+      // Run the io_context again until the operation completes.
+      io_context.run();
+    }
+
+    // If the operation failed, throw an exception. Otherwise return the result.
+    return error_ ? throw std::system_error(error_) : t_;
+  }
+
+private:
+  std::chrono::steady_clock::duration timeout_;
+  tcp_socket& socket_;
+  boost::system::error_code error_;
+  T t_;
+};
+
+} // namespace asio
+} // namespace boost
+
+//----------------------------------------------------------------------
+
+int main(int argc, char* argv[])
+{
+  try
+  {
+    if (argc != 4)
+    {
+      std::cerr << "Usage: blocking_tcp_client <host> <port> <message>\n";
+      return 1;
+    }
+
+    boost::asio::io_context io_context;
+
+    // Resolve the host name and service to a list of endpoints.
+    auto endpoints = tcp::resolver(io_context).resolve(argv[1], argv[2]);
+
+    tcp_socket socket(io_context);
+
+    // Run an asynchronous connect operation with a timeout.
+    boost::asio::async_connect(socket, endpoints,
+        close_after(std::chrono::seconds(10), socket));
+
+    auto time_sent = std::chrono::steady_clock::now();
+
+    // Run an asynchronous write operation with a timeout.
+    std::string msg = argv[3] + std::string("\n");
+    boost::asio::async_write(socket, boost::asio::buffer(msg),
+        close_after(std::chrono::seconds(10), socket));
+
+    for (std::string input_buffer;;)
+    {
+      // Run an asynchronous read operation with a timeout.
+      std::size_t n = boost::asio::async_read_until(socket,
+          boost::asio::dynamic_buffer(input_buffer), '\n',
+          close_after(std::chrono::seconds(10), socket));
+
+      std::string line(input_buffer.substr(0, n - 1));
+      input_buffer.erase(0, n);
+
+      // Keep going until we get back the line that was sent.
+      if (line == argv[3])
+        break;
+    }
+
+    auto time_received = std::chrono::steady_clock::now();
+
+    std::cout << "Round trip time: ";
+    std::cout << std::chrono::duration_cast<
+      std::chrono::microseconds>(
+        time_received - time_sent).count();
+    std::cout << " microseconds\n";
+  }
+  catch (std::exception& e)
+  {
+    std::cerr << "Exception: " << e.what() << "\n";
+  }
+
+  return 0;
+}

libs/asio/example/cpp11/timeouts/blocking_udp_client.cpp

@@ -0,0 +1,155 @@
+//
+// blocking_udp_client.cpp
+// ~~~~~~~~~~~~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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)
+//
+
+#include <boost/asio/buffer.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/udp.hpp>
+#include <cstdlib>
+#include <functional>
+#include <iostream>
+
+using boost::asio::ip::udp;
+using std::placeholders::_1;
+using std::placeholders::_2;
+
+//----------------------------------------------------------------------
+
+//
+// This class manages socket timeouts by running the io_context using the timed
+// io_context::run_for() member function. Each asynchronous operation is given
+// a timeout within which it must complete. The socket operations themselves
+// use std::bind to specify the completion handler:
+//
+//   +---------------+
+//   |               |
+//   |    receive    |
+//   |               |
+//   +---------------+
+//           |
+//  async_-  |    +----------------+
+// receive() |    |                |
+//           +--->| handle_receive |
+//                |                |
+//                +----------------+
+//
+// For a given socket operation, the client object runs the io_context to block
+// thread execution until the operation completes or the timeout is reached. If
+// the io_context::run_for() function times out, the socket is closed and the
+// outstanding asynchronous operation is cancelled.
+//
+class client
+{
+public:
+  client(const udp::endpoint& listen_endpoint)
+    : socket_(io_context_, listen_endpoint)
+  {
+  }
+
+  std::size_t receive(const boost::asio::mutable_buffer& buffer,
+      std::chrono::steady_clock::duration timeout,
+      boost::system::error_code& error)
+  {
+    // Start the asynchronous operation. The handle_receive function used as a
+    // callback will update the error and length variables.
+    std::size_t length = 0;
+    socket_.async_receive(boost::asio::buffer(buffer),
+        std::bind(&client::handle_receive, _1, _2, &error, &length));
+
+    // Run the operation until it completes, or until the timeout.
+    run(timeout);
+
+    return length;
+  }
+
+private:
+  void run(std::chrono::steady_clock::duration timeout)
+  {
+    // Restart the io_context, as it may have been left in the "stopped" state
+    // by a previous operation.
+    io_context_.restart();
+
+    // Block until the asynchronous operation has completed, or timed out. If
+    // the pending asynchronous operation is a composed operation, the deadline
+    // applies to the entire operation, rather than individual operations on
+    // the socket.
+    io_context_.run_for(timeout);
+
+    // If the asynchronous operation completed successfully then the io_context
+    // would have been stopped due to running out of work. If it was not
+    // stopped, then the io_context::run_for call must have timed out.
+    if (!io_context_.stopped())
+    {
+      // Cancel the outstanding asynchronous operation.
+      socket_.cancel();
+
+      // Run the io_context again until the operation completes.
+      io_context_.run();
+    }
+  }
+
+  static void handle_receive(
+      const boost::system::error_code& error, std::size_t length,
+      boost::system::error_code* out_error, std::size_t* out_length)
+  {
+    *out_error = error;
+    *out_length = length;
+  }
+
+private:
+  boost::asio::io_context io_context_;
+  udp::socket socket_;
+};
+
+//----------------------------------------------------------------------
+
+int main(int argc, char* argv[])
+{
+  try
+  {
+    using namespace std; // For atoi.
+
+    if (argc != 3)
+    {
+      std::cerr << "Usage: blocking_udp_client <listen_addr> <listen_port>\n";
+      return 1;
+    }
+
+    udp::endpoint listen_endpoint(
+        boost::asio::ip::make_address(argv[1]),
+        std::atoi(argv[2]));
+
+    client c(listen_endpoint);
+
+    for (;;)
+    {
+      char data[1024];
+      boost::system::error_code error;
+      std::size_t n = c.receive(boost::asio::buffer(data),
+          std::chrono::seconds(10), error);
+
+      if (error)
+      {
+        std::cout << "Receive error: " << error.message() << "\n"; 
+      }
+      else
+      {
+        std::cout << "Received: ";
+        std::cout.write(data, n);
+        std::cout << "\n";
+      }
+    }
+  }
+  catch (std::exception& e)
+  {
+    std::cerr << "Exception: " << e.what() << "\n";
+  }
+
+  return 0;
+}

libs/asio/example/cpp11/timeouts/server.cpp

@@ -0,0 +1,433 @@
+//
+// server.cpp
+// ~~~~~~~~~~
+//
+// Copyright (c) 2003-2021 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)
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <deque>
+#include <iostream>
+#include <memory>
+#include <set>
+#include <string>
+#include <boost/asio/buffer.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/ip/udp.hpp>
+#include <boost/asio/read_until.hpp>
+#include <boost/asio/steady_timer.hpp>
+#include <boost/asio/write.hpp>
+
+using boost::asio::steady_timer;
+using boost::asio::ip::tcp;
+using boost::asio::ip::udp;
+
+//----------------------------------------------------------------------
+
+class subscriber
+{
+public:
+  virtual ~subscriber() = default;
+  virtual void deliver(const std::string& msg) = 0;
+};
+
+typedef std::shared_ptr<subscriber> subscriber_ptr;
+
+//----------------------------------------------------------------------
+
+class channel
+{
+public:
+  void join(subscriber_ptr subscriber)
+  {
+    subscribers_.insert(subscriber);
+  }
+
+  void leave(subscriber_ptr subscriber)
+  {
+    subscribers_.erase(subscriber);
+  }
+
+  void deliver(const std::string& msg)
+  {
+    for (const auto& s : subscribers_)
+    {
+      s->deliver(msg);
+    }
+  }
+
+private:
+  std::set<subscriber_ptr> subscribers_;
+};
+
+//----------------------------------------------------------------------
+
+//
+// This class manages socket timeouts by applying the concept of a deadline.
+// Some asynchronous operations are given deadlines by which they must complete.
+// Deadlines are enforced by two "actors" that persist for the lifetime of the
+// session object, one for input and one for output:
+//
+//  +----------------+                      +----------------+
+//  |                |                      |                |
+//  | check_deadline |<-------+             | check_deadline |<-------+
+//  |                |        |             |                |        |
+//  +----------------+        |             +----------------+        |
+//               |            |                          |            |
+//  async_wait() |    +----------------+    async_wait() |    +----------------+
+//   on input    |    |     lambda     |     on output   |    |     lambda     |
+//   deadline    +--->|       in       |     deadline    +--->|       in       |
+//                    | check_deadline |                      | check_deadline |
+//                    +----------------+                      +----------------+
+//
+// If either deadline actor determines that the corresponding deadline has
+// expired, the socket is closed and any outstanding operations are cancelled.
+//
+// The input actor reads messages from the socket, where messages are delimited
+// by the newline character:
+//
+//  +-------------+
+//  |             |
+//  |  read_line  |<----+
+//  |             |     |
+//  +-------------+     |
+//          |           |
+//  async_- |    +-------------+
+//   read_- |    |   lambda    |
+//  until() +--->|     in      |
+//               |  read_line  |
+//               +-------------+
+//
+// The deadline for receiving a complete message is 30 seconds. If a non-empty
+// message is received, it is delivered to all subscribers. If a heartbeat (a
+// message that consists of a single newline character) is received, a heartbeat
+// is enqueued for the client, provided there are no other messages waiting to
+// be sent.
+//
+// The output actor is responsible for sending messages to the client:
+//
+//  +----------------+
+//  |                |<---------------------+
+//  |  await_output  |                      |
+//  |                |<-------+             |
+//  +----------------+        |             |
+//    |            |          |             |
+//    |    async_- |  +----------------+    |
+//    |     wait() |  |     lambda     |    |
+//    |            +->|       in       |    |
+//    |               |  await_output  |    |
+//    |               +----------------+    |
+//    V                                     |
+//  +--------------+               +--------------+
+//  |              | async_write() |    lambda    |
+//  |  write_line  |-------------->|      in      |
+//  |              |               |  write_line  |
+//  +--------------+               +--------------+
+//
+// The output actor first waits for an output message to be enqueued. It does
+// this by using a steady_timer as an asynchronous condition variable. The
+// steady_timer will be signalled whenever the output queue is non-empty.
+//
+// Once a message is available, it is sent to the client. The deadline for
+// sending a complete message is 30 seconds. After the message is successfully
+// sent, the output actor again waits for the output queue to become non-empty.
+//
+class tcp_session
+  : public subscriber,
+    public std::enable_shared_from_this<tcp_session>
+{
+public:
+  tcp_session(tcp::socket socket, channel& ch)
+    : channel_(ch),
+      socket_(std::move(socket))
+  {
+    input_deadline_.expires_at(steady_timer::time_point::max());
+    output_deadline_.expires_at(steady_timer::time_point::max());
+
+    // The non_empty_output_queue_ steady_timer is set to the maximum time
+    // point whenever the output queue is empty. This ensures that the output
+    // actor stays asleep until a message is put into the queue.
+    non_empty_output_queue_.expires_at(steady_timer::time_point::max());
+  }
+
+  // Called by the server object to initiate the four actors.
+  void start()
+  {
+    channel_.join(shared_from_this());
+
+    read_line();
+    check_deadline(input_deadline_);
+
+    await_output();
+    check_deadline(output_deadline_);
+  }
+
+private:
+  void stop()
+  {
+    channel_.leave(shared_from_this());
+
+    boost::system::error_code ignored_error;
+    socket_.close(ignored_error);
+    input_deadline_.cancel();
+    non_empty_output_queue_.cancel();
+    output_deadline_.cancel();
+  }
+
+  bool stopped() const
+  {
+    return !socket_.is_open();
+  }
+
+  void deliver(const std::string& msg) override
+  {
+    output_queue_.push_back(msg + "\n");
+
+    // Signal that the output queue contains messages. Modifying the expiry
+    // will wake the output actor, if it is waiting on the timer.
+    non_empty_output_queue_.expires_at(steady_timer::time_point::min());
+  }
+
+  void read_line()
+  {
+    // Set a deadline for the read operation.
+    input_deadline_.expires_after(std::chrono::seconds(30));
+
+    // Start an asynchronous operation to read a newline-delimited message.
+    auto self(shared_from_this());
+    boost::asio::async_read_until(socket_,
+        boost::asio::dynamic_buffer(input_buffer_), '\n',
+        [this, self](const boost::system::error_code& error, std::size_t n)
+        {
+          // Check if the session was stopped while the operation was pending.
+          if (stopped())
+            return;
+
+          if (!error)
+          {
+            // Extract the newline-delimited message from the buffer.
+            std::string msg(input_buffer_.substr(0, n - 1));
+            input_buffer_.erase(0, n);
+
+            if (!msg.empty())
+            {
+              channel_.deliver(msg);
+            }
+            else
+            {
+
+              // We received a heartbeat message from the client. If there's
+              // nothing else being sent or ready to be sent, send a heartbeat
+              // right back.
+              if (output_queue_.empty())
+              {
+                output_queue_.push_back("\n");
+
+                // Signal that the output queue contains messages. Modifying
+                // the expiry will wake the output actor, if it is waiting on
+                // the timer.
+                non_empty_output_queue_.expires_at(
+                    steady_timer::time_point::min());
+              }
+            }
+
+            read_line();
+          }
+          else
+          {
+            stop();
+          }
+        });
+  }
+
+  void await_output()
+  {
+    auto self(shared_from_this());
+    non_empty_output_queue_.async_wait(
+        [this, self](const boost::system::error_code& /*error*/)
+        {
+          // Check if the session was stopped while the operation was pending.
+          if (stopped())
+            return;
+
+          if (output_queue_.empty())
+          {
+            // There are no messages that are ready to be sent. The actor goes
+            // to sleep by waiting on the non_empty_output_queue_ timer. When a
+            // new message is added, the timer will be modified and the actor
+            // will wake.
+            non_empty_output_queue_.expires_at(steady_timer::time_point::max());
+            await_output();
+          }
+          else
+          {
+            write_line();
+          }
+        });
+  }
+
+  void write_line()
+  {
+    // Set a deadline for the write operation.
+    output_deadline_.expires_after(std::chrono::seconds(30));
+
+    // Start an asynchronous operation to send a message.
+    auto self(shared_from_this());
+    boost::asio::async_write(socket_,
+        boost::asio::buffer(output_queue_.front()),
+        [this, self](const boost::system::error_code& error, std::size_t /*n*/)
+        {
+          // Check if the session was stopped while the operation was pending.
+          if (stopped())
+            return;
+
+          if (!error)
+          {
+            output_queue_.pop_front();
+
+            await_output();
+          }
+          else
+          {
+            stop();
+          }
+        });
+  }
+
+  void check_deadline(steady_timer& deadline)
+  {
+    auto self(shared_from_this());
+    deadline.async_wait(
+        [this, self, &deadline](const boost::system::error_code& /*error*/)
+        {
+          // Check if the session was stopped while the operation was pending.
+          if (stopped())
+            return;
+
+          // Check whether the deadline has passed. We compare the deadline
+          // against the current time since a new asynchronous operation may
+          // have moved the deadline before this actor had a chance to run.
+          if (deadline.expiry() <= steady_timer::clock_type::now())
+          {
+            // The deadline has passed. Stop the session. The other actors will
+            // terminate as soon as possible.
+            stop();
+          }
+          else
+          {
+            // Put the actor back to sleep.
+            check_deadline(deadline);
+          }
+        });
+  }
+
+  channel& channel_;
+  tcp::socket socket_;
+  std::string input_buffer_;
+  steady_timer input_deadline_{socket_.get_executor()};
+  std::deque<std::string> output_queue_;
+  steady_timer non_empty_output_queue_{socket_.get_executor()};
+  steady_timer output_deadline_{socket_.get_executor()};
+};
+
+typedef std::shared_ptr<tcp_session> tcp_session_ptr;
+
+//----------------------------------------------------------------------
+
+class udp_broadcaster
+  : public subscriber
+{
+public:
+  udp_broadcaster(boost::asio::io_context& io_context,
+      const udp::endpoint& broadcast_endpoint)
+    : socket_(io_context)
+  {
+    socket_.connect(broadcast_endpoint);
+    socket_.set_option(udp::socket::broadcast(true));
+  }
+
+private:
+  void deliver(const std::string& msg)
+  {
+    boost::system::error_code ignored_error;
+    socket_.send(boost::asio::buffer(msg), 0, ignored_error);
+  }
+
+  udp::socket socket_;
+};
+
+//----------------------------------------------------------------------
+
+class server
+{
+public:
+  server(boost::asio::io_context& io_context,
+      const tcp::endpoint& listen_endpoint,
+      const udp::endpoint& broadcast_endpoint)
+    : io_context_(io_context),
+      acceptor_(io_context, listen_endpoint)
+  {
+    channel_.join(
+        std::make_shared<udp_broadcaster>(
+          io_context_, broadcast_endpoint));
+
+    accept();
+  }
+
+private:
+  void accept()
+  {
+    acceptor_.async_accept(
+        [this](const boost::system::error_code& error, tcp::socket socket)
+        {
+          if (!error)
+          {
+            std::make_shared<tcp_session>(std::move(socket), channel_)->start();
+          }
+
+          accept();
+        });
+  }
+
+  boost::asio::io_context& io_context_;
+  tcp::acceptor acceptor_;
+  channel channel_;
+};
+
+//----------------------------------------------------------------------
+
+int main(int argc, char* argv[])
+{
+  try
+  {
+    using namespace std; // For atoi.
+
+    if (argc != 4)
+    {
+      std::cerr << "Usage: server <listen_port> <bcast_address> <bcast_port>\n";
+      return 1;
+    }
+
+    boost::asio::io_context io_context;
+
+    tcp::endpoint listen_endpoint(tcp::v4(), atoi(argv[1]));
+
+    udp::endpoint broadcast_endpoint(
+        boost::asio::ip::make_address(argv[2]), atoi(argv[3]));
+
+    server s(io_context, listen_endpoint, broadcast_endpoint);
+
+    io_context.run();
+  }
+  catch (std::exception& e)
+  {
+    std::cerr << "Exception: " << e.what() << "\n";
+  }
+
+  return 0;
+}