5 // Copyright (c) 2003-2014 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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)
11 #include <boost/asio/io_service.hpp>
12 #include <boost/asio/ip/udp.hpp>
13 #include <boost/asio/signal_set.hpp>
14 #include <boost/array.hpp>
15 #include <boost/bind.hpp>
21 using boost::asio::ip::udp;
23 class udp_daytime_server
26 udp_daytime_server(boost::asio::io_service& io_service)
27 : socket_(io_service, udp::endpoint(udp::v4(), 13))
35 socket_.async_receive_from(
36 boost::asio::buffer(recv_buffer_), remote_endpoint_,
37 boost::bind(&udp_daytime_server::handle_receive, this, _1));
40 void handle_receive(const boost::system::error_code& ec)
42 if (!ec || ec == boost::asio::error::message_size)
44 using namespace std; // For time_t, time and ctime;
46 std::string message = ctime(&now);
48 boost::system::error_code ignored_ec;
49 socket_.send_to(boost::asio::buffer(message),
50 remote_endpoint_, 0, ignored_ec);
57 udp::endpoint remote_endpoint_;
58 boost::array<char, 1> recv_buffer_;
65 boost::asio::io_service io_service;
67 // Initialise the server before becoming a daemon. If the process is
68 // started from a shell, this means any errors will be reported back to the
70 udp_daytime_server server(io_service);
72 // Register signal handlers so that the daemon may be shut down. You may
73 // also want to register for other signals, such as SIGHUP to trigger a
74 // re-read of a configuration file.
75 boost::asio::signal_set signals(io_service, SIGINT, SIGTERM);
77 boost::bind(&boost::asio::io_service::stop, &io_service));
79 // Inform the io_service that we are about to become a daemon. The
80 // io_service cleans up any internal resources, such as threads, that may
81 // interfere with forking.
82 io_service.notify_fork(boost::asio::io_service::fork_prepare);
84 // Fork the process and have the parent exit. If the process was started
85 // from a shell, this returns control to the user. Forking a new process is
86 // also a prerequisite for the subsequent call to setsid().
87 if (pid_t pid = fork())
91 // We're in the parent process and need to exit.
93 // When the exit() function is used, the program terminates without
94 // invoking local variables' destructors. Only global variables are
95 // destroyed. As the io_service object is a local variable, this means
96 // we do not have to call:
98 // io_service.notify_fork(boost::asio::io_service::fork_parent);
100 // However, this line should be added before each call to exit() if
101 // using a global io_service object. An additional call:
103 // io_service.notify_fork(boost::asio::io_service::fork_prepare);
105 // should also precede the second fork().
110 syslog(LOG_ERR | LOG_USER, "First fork failed: %m");
115 // Make the process a new session leader. This detaches it from the
119 // A process inherits its working directory from its parent. This could be
120 // on a mounted filesystem, which means that the running daemon would
121 // prevent this filesystem from being unmounted. Changing to the root
122 // directory avoids this problem.
125 // The file mode creation mask is also inherited from the parent process.
126 // We don't want to restrict the permissions on files created by the
127 // daemon, so the mask is cleared.
130 // A second fork ensures the process cannot acquire a controlling terminal.
131 if (pid_t pid = fork())
139 syslog(LOG_ERR | LOG_USER, "Second fork failed: %m");
144 // Close the standard streams. This decouples the daemon from the terminal
150 // We don't want the daemon to have any standard input.
151 if (open("/dev/null", O_RDONLY) < 0)
153 syslog(LOG_ERR | LOG_USER, "Unable to open /dev/null: %m");
157 // Send standard output to a log file.
158 const char* output = "/tmp/asio.daemon.out";
159 const int flags = O_WRONLY | O_CREAT | O_APPEND;
160 const mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
161 if (open(output, flags, mode) < 0)
163 syslog(LOG_ERR | LOG_USER, "Unable to open output file %s: %m", output);
167 // Also send standard error to the same log file.
170 syslog(LOG_ERR | LOG_USER, "Unable to dup output descriptor: %m");
174 // Inform the io_service that we have finished becoming a daemon. The
175 // io_service uses this opportunity to create any internal file descriptors
176 // that need to be private to the new process.
177 io_service.notify_fork(boost::asio::io_service::fork_child);
179 // The io_service can now be used normally.
180 syslog(LOG_INFO | LOG_USER, "Daemon started");
182 syslog(LOG_INFO | LOG_USER, "Daemon stopped");
184 catch (std::exception& e)
186 syslog(LOG_ERR | LOG_USER, "Exception: %s", e.what());
187 std::cerr << "Exception: " << e.what() << std::endl;