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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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