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- //
- // blocking_token_tcp_client.cpp
- // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- //
- // Copyright (c) 2003-2019 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 = socket_.get_executor().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;
- }
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