1 //
2 // daytime_client.cpp
3 // ~~~~~~~~~~~~~~~~~~
4 //
5 // Copyright (c) 2003-2015 Christopher M. Kohlhoff (chris at kohlhoff dot com)
6 //
7 // Distributed under the Boost Software License, Version 1.0. (See accompanying
8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
9 //
10
11 #include <array>
12 #include <future>
13 #include <iostream>
14 #include <thread>
15 #include <boost/asio/io_service.hpp>
16 #include <boost/asio/ip/udp.hpp>
17 #include <boost/asio/use_future.hpp>
18
19 using boost::asio::ip::udp;
20
get_daytime(boost::asio::io_service & io_service,const char * hostname)21 void get_daytime(boost::asio::io_service& io_service, const char* hostname)
22 {
23 try
24 {
25 udp::resolver resolver(io_service);
26
27 std::future<udp::resolver::iterator> iter =
28 resolver.async_resolve(
29 {udp::v4(), hostname, "daytime"},
30 boost::asio::use_future);
31
32 // The async_resolve operation above returns the endpoint iterator as a
33 // future value that is not retrieved ...
34
35 udp::socket socket(io_service, udp::v4());
36
37 std::array<char, 1> send_buf = {{ 0 }};
38 std::future<std::size_t> send_length =
39 socket.async_send_to(boost::asio::buffer(send_buf),
40 *iter.get(), // ... until here. This call may block.
41 boost::asio::use_future);
42
43 // Do other things here while the send completes.
44
45 send_length.get(); // Blocks until the send is complete. Throws any errors.
46
47 std::array<char, 128> recv_buf;
48 udp::endpoint sender_endpoint;
49 std::future<std::size_t> recv_length =
50 socket.async_receive_from(
51 boost::asio::buffer(recv_buf),
52 sender_endpoint,
53 boost::asio::use_future);
54
55 // Do other things here while the receive completes.
56
57 std::cout.write(
58 recv_buf.data(),
59 recv_length.get()); // Blocks until receive is complete.
60 }
61 catch (std::system_error& e)
62 {
63 std::cerr << e.what() << std::endl;
64 }
65 }
66
main(int argc,char * argv[])67 int main(int argc, char* argv[])
68 {
69 try
70 {
71 if (argc != 2)
72 {
73 std::cerr << "Usage: daytime_client <host>" << std::endl;
74 return 1;
75 }
76
77 // We run the io_service off in its own thread so that it operates
78 // completely asynchronously with respect to the rest of the program.
79 boost::asio::io_service io_service;
80 boost::asio::io_service::work work(io_service);
81 std::thread thread([&io_service](){ io_service.run(); });
82
83 get_daytime(io_service, argv[1]);
84
85 io_service.stop();
86 thread.join();
87 }
88 catch (std::exception& e)
89 {
90 std::cerr << e.what() << std::endl;
91 }
92
93 return 0;
94 }
95