doc/html/boost_asio/example/porthopper/client.cpp
// // client.cpp // ~~~~~~~~~~ // // Copyright (c) 2003-2011 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.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> #include <boost/lambda/if.hpp> #include <boost/shared_ptr.hpp> #include <algorithm> #include <cstdlib> #include <exception> #include <iostream> #include <string> #include "protocol.hpp" using namespace boost; using boost::asio::ip::tcp; using boost::asio::ip::udp; int main(int argc, char* argv[]) { try { if (argc != 3) { std::cerr << "Usage: client <host> <port>\n"; return 1; } using namespace std; // For atoi. std::string host_name = argv[1]; std::string port = argv[2]; boost::asio::io_service io_service; // Determine the location of the server. tcp::resolver resolver(io_service); tcp::resolver::query query(host_name, port); tcp::endpoint remote_endpoint = *resolver.resolve(query); // Establish the control connection to the server. tcp::socket control_socket(io_service); control_socket.connect(remote_endpoint); // Create a datagram socket to receive data from the server. boost::shared_ptr<udp::socket> data_socket( new udp::socket(io_service, udp::endpoint(udp::v4(), 0))); // Determine what port we will receive data on. udp::endpoint data_endpoint = data_socket->local_endpoint(); // Ask the server to start sending us data. control_request start = control_request::start(data_endpoint.port()); boost::asio::write(control_socket, start.to_buffers()); unsigned long last_frame_number = 0; for (;;) { // Receive 50 messages on the current data socket. for (int i = 0; i < 50; ++i) { // Receive a frame from the server. frame f; data_socket->receive(f.to_buffers(), 0); if (f.number() > last_frame_number) { last_frame_number = f.number(); std::cout << "\n" << f.payload(); } } // Time to switch to a new socket. To ensure seamless handover we will // continue to receive packets using the old socket until data arrives on // the new one. std::cout << " Starting renegotiation"; // Create the new data socket. boost::shared_ptr<udp::socket> new_data_socket( new udp::socket(io_service, udp::endpoint(udp::v4(), 0))); // Determine the new port we will use to receive data. udp::endpoint new_data_endpoint = new_data_socket->local_endpoint(); // Ask the server to switch over to the new port. control_request change = control_request::change( data_endpoint.port(), new_data_endpoint.port()); boost::system::error_code control_result; boost::asio::async_write(control_socket, change.to_buffers(), ( lambda::var(control_result) = lambda::_1 )); // Try to receive a frame from the server on the new data socket. If we // successfully receive a frame on this new data socket we can consider // the renegotation complete. In that case we will close the old data // socket, which will cause any outstanding receive operation on it to be // cancelled. frame f1; boost::system::error_code new_data_socket_result; new_data_socket->async_receive(f1.to_buffers(), ( // Note: lambda::_1 is the first argument to the callback handler, // which in this case is the error code for the operation. lambda::var(new_data_socket_result) = lambda::_1, lambda::if_(!lambda::_1) [ // We have successfully received a frame on the new data socket, // so we can close the old data socket. This will cancel any // outstanding receive operation on the old data socket. lambda::var(data_socket) = boost::shared_ptr<udp::socket>() ] )); // This loop will continue until we have successfully completed the // renegotiation (i.e. received a frame on the new data socket), or some // unrecoverable error occurs. bool done = false; while (!done) { // Even though we're performing a renegotation, we want to continue // receiving data as smoothly as possible. Therefore we will continue to // try to receive a frame from the server on the old data socket. If we // receive a frame on this socket we will interrupt the io_service, // print the frame, and resume waiting for the other operations to // complete. frame f2; done = true; // Let's be optimistic. if (data_socket) // Might have been closed by new_data_socket's handler. { data_socket->async_receive(f2.to_buffers(), 0, ( lambda::if_(!lambda::_1) [ // We have successfully received a frame on the old data // socket. Stop the io_service so that we can print it. lambda::bind(&boost::asio::io_service::stop, &io_service), lambda::var(done) = false ] )); } // Run the operations in parallel. This will block until all operations // have finished, or until the io_service is interrupted. (No threads!) io_service.reset(); io_service.run(); // If the io_service.run() was interrupted then we have received a frame // on the old data socket. We need to keep waiting for the renegotation // operations to complete. if (!done) { if (f2.number() > last_frame_number) { last_frame_number = f2.number(); std::cout << "\n" << f2.payload(); } } } // Since the loop has finished, we have either successfully completed // the renegotation, or an error has occurred. First we'll check for // errors. if (control_result) throw boost::system::system_error(control_result); if (new_data_socket_result) throw boost::system::system_error(new_data_socket_result); // If we get here it means we have successfully started receiving data on // the new data socket. This new data socket will be used from now on // (until the next time we renegotiate). std::cout << " Renegotiation complete"; data_socket = new_data_socket; data_endpoint = new_data_endpoint; if (f1.number() > last_frame_number) { last_frame_number = f1.number(); std::cout << "\n" << f1.payload(); } } } catch (std::exception& e) { std::cerr << "Exception: " << e.what() << std::endl; } return 0; }