Boost C++ Libraries

doc/html/boost_asio/example/timeouts/blocking_tcp_client.cpp

//
// blocking_tcp_client.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2010 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/deadline_timer.hpp>
#include <boost/asio/io_service.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 <string>
#include <boost/lambda/bind.hpp>
#include <boost/lambda/lambda.hpp>

using boost::asio::deadline_timer;
using boost::asio::ip::tcp;
using boost::lambda::bind;
using boost::lambda::var;
using boost::lambda::_1;

//----------------------------------------------------------------------

//
// This class manages socket timeouts by applying the concept of a deadline.
// Each asynchronous operation is given a deadline by which it must complete.
// Deadlines are enforced by an "actor" that persists for the lifetime of the
// client object:
//
//  +----------------+
//  |                |     
//  | check_deadline |<---+
//  |                |    |
//  +----------------+    | async_wait()
//              |         |
//              +---------+
//
// If the actor determines that the deadline has expired, the socket is closed
// and any outstanding operations are consequently cancelled. The socket
// operations themselves use boost::lambda function objects as completion
// handlers. For a given socket operation, the client object runs the
// io_service to block thread execution until the actor completes.
//
class client
{
public:
  client()
    : socket_(io_service_),
      deadline_(io_service_)
  {
    // No deadline is required until the first socket operation is started. We
    // set the deadline to positive infinity so that the actor takes no action
    // until a specific deadline is set.
    deadline_.expires_at(boost::posix_time::pos_infin);

    // Start the persistent actor that checks for deadline expiry.
    check_deadline();
  }

  void connect(const std::string& host, const std::string& service,
      boost::posix_time::time_duration timeout)
  {
    // Resolve the host name and service to a list of endpoints.
    tcp::resolver::query query(host, service);
    tcp::resolver::iterator iter = tcp::resolver(io_service_).resolve(query);

    // Set a deadline for the asynchronous operation. The host name may resolve
    // to multiple endpoints, and this function tries to connect to each one in
    // turn. Setting the deadline here means it applies to the entire sequence.
    deadline_.expires_from_now(timeout);

    boost::system::error_code ec;

    for (; iter != tcp::resolver::iterator(); ++iter)
    {
      // We may have an open socket from a previous connection attempt. This
      // socket cannot be reused, so we must close it before trying to connect
      // again.
      socket_.close();

      // Set up the variable that receives the result of the asynchronous
      // operation. The error code is set to would_block to signal that the
      // operation is incomplete. Asio guarantees that its asynchronous
      // operations will never fail with would_block, so any other value in
      // ec indicates completion.
      ec = boost::asio::error::would_block;

      // Start the asynchronous operation itself. The boost::lambda function
      // object is used as a callback and will update the ec variable when the
      // operation completes. The blocking_udp_client.cpp example shows how you
      // can use boost::bind rather than boost::lambda.
      socket_.async_connect(iter->endpoint(), var(ec) = _1);

      // Block until the asynchronous operation has completed.
      do io_service_.run_one(); while (ec == boost::asio::error::would_block);

      // Determine whether a connection was successfully established. The
      // deadline actor may have had a chance to run and close our socket, even
      // though the connect operation notionally succeeded. Therefore we must
      // check whether the socket is still open before deciding that the we
      // were successful.
      if (!ec && socket_.is_open())
        return;
    }

    throw boost::system::system_error(
        ec ? ec : boost::asio::error::host_not_found);
  }

  std::string read_line(boost::posix_time::time_duration timeout)
  {
    // Set a deadline for the asynchronous operation. Since this function uses
    // a composed operation (async_read_until), the deadline applies to the
    // entire operation, rather than individual reads from the socket.
    deadline_.expires_from_now(timeout);

    // Set up the variable that receives the result of the asynchronous
    // operation. The error code is set to would_block to signal that the
    // operation is incomplete. Asio guarantees that its asynchronous
    // operations will never fail with would_block, so any other value in
    // ec indicates completion.
    boost::system::error_code ec = boost::asio::error::would_block;

    // Start the asynchronous operation itself. The boost::lambda function
    // object is used as a callback and will update the ec variable when the
    // operation completes. The blocking_udp_client.cpp example shows how you
    // can use boost::bind rather than boost::lambda.
    boost::asio::async_read_until(socket_, input_buffer_, '\n', var(ec) = _1);

    // Block until the asynchronous operation has completed.
    do io_service_.run_one(); while (ec == boost::asio::error::would_block);

    if (ec)
      throw boost::system::system_error(ec);

    std::string line;
    std::istream is(&input_buffer_);
    std::getline(is, line);
    return line;
  }

  void write_line(const std::string& line,
      boost::posix_time::time_duration timeout)
  {
    std::string data = line + "\n";

    // Set a deadline for the asynchronous operation. Since this function uses
    // a composed operation (async_write), the deadline applies to the entire
    // operation, rather than individual writes to the socket.
    deadline_.expires_from_now(timeout);

    // Set up the variable that receives the result of the asynchronous
    // operation. The error code is set to would_block to signal that the
    // operation is incomplete. Asio guarantees that its asynchronous
    // operations will never fail with would_block, so any other value in
    // ec indicates completion.
    boost::system::error_code ec = boost::asio::error::would_block;

    // Start the asynchronous operation itself. The boost::lambda function
    // object is used as a callback and will update the ec variable when the
    // operation completes. The blocking_udp_client.cpp example shows how you
    // can use boost::bind rather than boost::lambda.
    boost::asio::async_write(socket_, boost::asio::buffer(data), var(ec) = _1);

    // Block until the asynchronous operation has completed.
    do io_service_.run_one(); while (ec == boost::asio::error::would_block);

    if (ec)
      throw boost::system::system_error(ec);
  }

private:
  void check_deadline()
  {
    // 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_.expires_at() <= deadline_timer::traits_type::now())
    {
      // The deadline has passed. The socket is closed so that any outstanding
      // asynchronous operations are cancelled. This allows the blocked
      // connect(), read_line() or write_line() functions to return.
      socket_.close();

      // There is no longer an active deadline. The expiry is set to positive
      // infinity so that the actor takes no action until a new deadline is set.
      deadline_.expires_at(boost::posix_time::pos_infin);
    }

    // Put the actor back to sleep.
    deadline_.async_wait(bind(&client::check_deadline, this));
  }

  boost::asio::io_service io_service_;
  tcp::socket socket_;
  deadline_timer deadline_;
  boost::asio::streambuf input_buffer_;
};

//----------------------------------------------------------------------

int main(int argc, char* argv[])
{
  try
  {
    if (argc != 4)
    {
      std::cerr << "Usage: blocking_tcp <host> <port> <message>\n";
      return 1;
    }

    client c;
    c.connect(argv[1], argv[2], boost::posix_time::seconds(10));

    boost::posix_time::ptime time_sent =
      boost::posix_time::microsec_clock::universal_time();

    c.write_line(argv[3], boost::posix_time::seconds(10));

    for (;;)
    {
      std::string line = c.read_line(boost::posix_time::seconds(10));

      // Keep going until we get back the line that was sent.
      if (line == argv[3])
        break;
    }

    boost::posix_time::ptime time_received =
      boost::posix_time::microsec_clock::universal_time();

    std::cout << "Round trip time: ";
    std::cout << (time_received - time_sent).total_microseconds();
    std::cout << " microseconds\n";
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}