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// async_tcp_client.cpp
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// ~~~~~~~~~~~~~~~~~~~~
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// Copyright (c) 2003-2012 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#include <boost/asio/deadline_timer.hpp>
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#include <boost/asio/io_service.hpp>
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#include <boost/asio/ip/tcp.hpp>
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#include <boost/asio/read_until.hpp>
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#include <boost/asio/streambuf.hpp>
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#include <boost/asio/write.hpp>
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#include <boost/bind.hpp>
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using boost::asio::deadline_timer;
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using boost::asio::ip::tcp;
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// This class manages socket timeouts by applying the concept of a deadline.
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// Some asynchronous operations are given deadlines by which they must complete.
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// Deadlines are enforced by an "actor" that persists for the lifetime of the
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// | check_deadline |<---+
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// +----------------+ | async_wait()
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// If the deadline actor determines that the deadline has expired, the socket
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// is closed and any outstanding operations are consequently cancelled.
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// Connection establishment involves trying each endpoint in turn until a
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// connection is successful, or the available endpoints are exhausted. If the
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// deadline actor closes the socket, the connect actor is woken up and moves to
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// | start_connect |<---+
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// +---------------+ |
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// async_- | +----------------+
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// +--->| handle_connect |
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// Once a connection is :
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// made, the connect :
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// actor forks in two - :
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// an actor for reading : and an actor for
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// inbound messages: : sending heartbeats:
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// +------------+ : +-------------+
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// | |<- - - - -+- - - - ->| |
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// | start_read | | start_write |<---+
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// +------------+ | +-------------+ | async_wait()
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// async_- | +-------------+ async_- | +--------------+
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// read_- | | | write() | | |
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// until() +--->| handle_read | +--->| handle_write |
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// +-------------+ +--------------+
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// The input actor reads messages from the socket, where messages are delimited
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// by the newline character. The deadline for a complete message is 30 seconds.
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// The heartbeat actor sends a heartbeat (a message that consists of a single
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// newline character) every 10 seconds. In this example, no deadline is applied
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client(boost::asio::io_service& io_service)
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deadline_(io_service),
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heartbeat_timer_(io_service)
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// Called by the user of the client class to initiate the connection process.
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// The endpoint iterator will have been obtained using a tcp::resolver.
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void start(tcp::resolver::iterator endpoint_iter)
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// Start the connect actor.
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start_connect(endpoint_iter);
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// Start the deadline actor. You will note that we're not setting any
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// particular deadline here. Instead, the connect and input actors will
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// update the deadline prior to each asynchronous operation.
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deadline_.async_wait(boost::bind(&client::check_deadline, this));
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// This function terminates all the actors to shut down the connection. It
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// may be called by the user of the client class, or by the class itself in
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// response to graceful termination or an unrecoverable error.
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boost::system::error_code ignored_ec;
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socket_.close(ignored_ec);
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heartbeat_timer_.cancel();
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void start_connect(tcp::resolver::iterator endpoint_iter)
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if (endpoint_iter != tcp::resolver::iterator())
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std::cout << "Trying " << endpoint_iter->endpoint() << "...\n";
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// Set a deadline for the connect operation.
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deadline_.expires_from_now(boost::posix_time::seconds(60));
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// Start the asynchronous connect operation.
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socket_.async_connect(endpoint_iter->endpoint(),
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boost::bind(&client::handle_connect,
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this, _1, endpoint_iter));
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// There are no more endpoints to try. Shut down the client.
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void handle_connect(const boost::system::error_code& ec,
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tcp::resolver::iterator endpoint_iter)
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// The async_connect() function automatically opens the socket at the start
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// of the asynchronous operation. If the socket is closed at this time then
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// the timeout handler must have run first.
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if (!socket_.is_open())
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std::cout << "Connect timed out\n";
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// Try the next available endpoint.
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start_connect(++endpoint_iter);
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// Check if the connect operation failed before the deadline expired.
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std::cout << "Connect error: " << ec.message() << "\n";
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// We need to close the socket used in the previous connection attempt
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// before starting a new one.
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// Try the next available endpoint.
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start_connect(++endpoint_iter);
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// Otherwise we have successfully established a connection.
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std::cout << "Connected to " << endpoint_iter->endpoint() << "\n";
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// Start the input actor.
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// Start the heartbeat actor.
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// Set a deadline for the read operation.
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deadline_.expires_from_now(boost::posix_time::seconds(30));
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// Start an asynchronous operation to read a newline-delimited message.
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boost::asio::async_read_until(socket_, input_buffer_, '\n',
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boost::bind(&client::handle_read, this, _1));
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void handle_read(const boost::system::error_code& ec)
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// Extract the newline-delimited message from the buffer.
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std::istream is(&input_buffer_);
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std::getline(is, line);
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// Empty messages are heartbeats and so ignored.
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std::cout << "Received: " << line << "\n";
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std::cout << "Error on receive: " << ec.message() << "\n";
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// Start an asynchronous operation to send a heartbeat message.
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boost::asio::async_write(socket_, boost::asio::buffer("\n", 1),
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boost::bind(&client::handle_write, this, _1));
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void handle_write(const boost::system::error_code& ec)
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// Wait 10 seconds before sending the next heartbeat.
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heartbeat_timer_.expires_from_now(boost::posix_time::seconds(10));
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heartbeat_timer_.async_wait(boost::bind(&client::start_write, this));
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std::cout << "Error on heartbeat: " << ec.message() << "\n";
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void check_deadline()
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// Check whether the deadline has passed. We compare the deadline against
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// the current time since a new asynchronous operation may have moved the
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// deadline before this actor had a chance to run.
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if (deadline_.expires_at() <= deadline_timer::traits_type::now())
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// The deadline has passed. The socket is closed so that any outstanding
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// asynchronous operations are cancelled.
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// There is no longer an active deadline. The expiry is set to positive
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// infinity so that the actor takes no action until a new deadline is set.
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deadline_.expires_at(boost::posix_time::pos_infin);
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// Put the actor back to sleep.
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deadline_.async_wait(boost::bind(&client::check_deadline, this));
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boost::asio::streambuf input_buffer_;
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deadline_timer deadline_;
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deadline_timer heartbeat_timer_;
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int main(int argc, char* argv[])
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std::cerr << "Usage: client <host> <port>\n";
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boost::asio::io_service io_service;
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tcp::resolver r(io_service);
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client c(io_service);
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c.start(r.resolve(tcp::resolver::query(argv[1], argv[2])));
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catch (std::exception& e)
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std::cerr << "Exception: " << e.what() << "\n";