boost/libs/asio/example/cpp03/timeouts/blocking_udp_client.cpp

//
// blocking_udp_client.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2017 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_context.hpp>
#include <boost/asio/ip/udp.hpp>
#include <cstdlib>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <iostream>

using boost::asio::deadline_timer;
using boost::asio::ip::udp;

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

//
// 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, any outstanding
// socket operations are cancelled. The socket operations themselves are
// implemented as transient actors:
//
//   +---------------+
//   |               |
//   |    receive    |
//   |               |
//   +---------------+
//           |
//  async_-  |    +----------------+
// receive() |    |                |
//           +--->| handle_receive |
//                |                |
//                +----------------+
//
// The client object runs the io_context to block thread execution until the
// actor completes.
//
class client
{
public:
  client(const udp::endpoint& listen_endpoint)
    : socket_(io_context_, listen_endpoint),
      deadline_(io_context_)
  {
    // 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();
  }

  std::size_t receive(const boost::asio::mutable_buffer& buffer,
      boost::posix_time::time_duration timeout, boost::system::error_code& ec)
  {
    // Set a deadline for the asynchronous operation.
    deadline_.expires_from_now(timeout);

    // Set up the variables that receive 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;
    std::size_t length = 0;

    // Start the asynchronous operation itself. The handle_receive function
    // used as a callback will update the ec and length variables.
    socket_.async_receive(boost::asio::buffer(buffer),
        boost::bind(&client::handle_receive, _1, _2, &ec, &length));

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

    return length;
  }

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 outstanding asynchronous operation needs
      // to be cancelled so that the blocked receive() function will return.
      //
      // Please note that cancel() has portability issues on some versions of
      // Microsoft Windows, and it may be necessary to use close() instead.
      // Consult the documentation for cancel() for further information.
      socket_.cancel();

      // 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(boost::bind(&client::check_deadline, this));
  }

  static void handle_receive(
      const boost::system::error_code& ec, std::size_t length,
      boost::system::error_code* out_ec, std::size_t* out_length)
  {
    *out_ec = ec;
    *out_length = length;
  }

private:
  boost::asio::io_context io_context_;
  udp::socket socket_;
  deadline_timer deadline_;
};

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

int main(int argc, char* argv[])
{
  try
  {
    using namespace std; // For atoi.

    if (argc != 3)
    {
      std::cerr << "Usage: blocking_udp_timeout <listen_addr> <listen_port>\n";
      return 1;
    }

    udp::endpoint listen_endpoint(
        boost::asio::ip::make_address(argv[1]),
        std::atoi(argv[2]));

    client c(listen_endpoint);

    for (;;)
    {
      char data[1024];
      boost::system::error_code ec;
      std::size_t n = c.receive(boost::asio::buffer(data),
          boost::posix_time::seconds(10), ec);

      if (ec)
      {
        std::cout << "Receive error: " << ec.message() << "\n"; 
      }
      else
      {
        std::cout << "Received: ";
        std::cout.write(data, n);
        std::cout << "\n";
      }
    }
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}