434 lines
13 KiB
C++
434 lines
13 KiB
C++
//
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// server.cpp
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// ~~~~~~~~~~
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//
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// Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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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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//
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#include <algorithm>
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#include <cstdlib>
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#include <deque>
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#include <iostream>
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#include <memory>
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#include <set>
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#include <string>
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#include <boost/asio/buffer.hpp>
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#include <boost/asio/io_context.hpp>
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#include <boost/asio/ip/tcp.hpp>
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#include <boost/asio/ip/udp.hpp>
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#include <boost/asio/read_until.hpp>
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#include <boost/asio/steady_timer.hpp>
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#include <boost/asio/write.hpp>
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using boost::asio::steady_timer;
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using boost::asio::ip::tcp;
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using boost::asio::ip::udp;
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//----------------------------------------------------------------------
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class subscriber
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{
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public:
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virtual ~subscriber() = default;
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virtual void deliver(const std::string& msg) = 0;
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};
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typedef std::shared_ptr<subscriber> subscriber_ptr;
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//----------------------------------------------------------------------
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class channel
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{
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public:
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void join(subscriber_ptr subscriber)
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{
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subscribers_.insert(subscriber);
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}
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void leave(subscriber_ptr subscriber)
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{
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subscribers_.erase(subscriber);
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}
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void deliver(const std::string& msg)
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{
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for (const auto& s : subscribers_)
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{
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s->deliver(msg);
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}
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}
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private:
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std::set<subscriber_ptr> subscribers_;
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};
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//----------------------------------------------------------------------
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//
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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 two "actors" that persist for the lifetime of the
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// session object, one for input and one for output:
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//
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// +----------------+ +----------------+
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// | | | |
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// | check_deadline |<-------+ | check_deadline |<-------+
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// | | | | | |
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// +----------------+ | +----------------+ |
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// | | | |
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// async_wait() | +----------------+ async_wait() | +----------------+
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// on input | | lambda | on output | | lambda |
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// deadline +--->| in | deadline +--->| in |
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// | check_deadline | | check_deadline |
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// +----------------+ +----------------+
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//
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// If either deadline actor determines that the corresponding deadline has
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// expired, the socket is closed and any outstanding operations are cancelled.
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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:
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//
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// +-------------+
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// | |
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// | read_line |<----+
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// | | |
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// +-------------+ |
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// | |
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// async_- | +-------------+
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// read_- | | lambda |
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// until() +--->| in |
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// | read_line |
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// +-------------+
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//
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// The deadline for receiving a complete message is 30 seconds. If a non-empty
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// message is received, it is delivered to all subscribers. If a heartbeat (a
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// message that consists of a single newline character) is received, a heartbeat
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// is enqueued for the client, provided there are no other messages waiting to
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// be sent.
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//
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// The output actor is responsible for sending messages to the client:
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//
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// +----------------+
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// | |<---------------------+
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// | await_output | |
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// | |<-------+ |
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// +----------------+ | |
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// | | | |
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// | async_- | +----------------+ |
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// | wait() | | lambda | |
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// | +->| in | |
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// | | await_output | |
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// | +----------------+ |
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// V |
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// +--------------+ +--------------+
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// | | async_write() | lambda |
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// | write_line |-------------->| in |
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// | | | write_line |
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// +--------------+ +--------------+
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//
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// The output actor first waits for an output message to be enqueued. It does
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// this by using a steady_timer as an asynchronous condition variable. The
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// steady_timer will be signalled whenever the output queue is non-empty.
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//
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// Once a message is available, it is sent to the client. The deadline for
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// sending a complete message is 30 seconds. After the message is successfully
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// sent, the output actor again waits for the output queue to become non-empty.
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//
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class tcp_session
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: public subscriber,
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public std::enable_shared_from_this<tcp_session>
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{
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public:
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tcp_session(tcp::socket socket, channel& ch)
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: channel_(ch),
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socket_(std::move(socket))
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{
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input_deadline_.expires_at(steady_timer::time_point::max());
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output_deadline_.expires_at(steady_timer::time_point::max());
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// The non_empty_output_queue_ steady_timer is set to the maximum time
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// point whenever the output queue is empty. This ensures that the output
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// actor stays asleep until a message is put into the queue.
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non_empty_output_queue_.expires_at(steady_timer::time_point::max());
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}
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// Called by the server object to initiate the four actors.
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void start()
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{
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channel_.join(shared_from_this());
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read_line();
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check_deadline(input_deadline_);
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await_output();
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check_deadline(output_deadline_);
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}
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private:
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void stop()
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{
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channel_.leave(shared_from_this());
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boost::system::error_code ignored_error;
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socket_.close(ignored_error);
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input_deadline_.cancel();
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non_empty_output_queue_.cancel();
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output_deadline_.cancel();
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}
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bool stopped() const
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{
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return !socket_.is_open();
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}
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void deliver(const std::string& msg) override
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{
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output_queue_.push_back(msg + "\n");
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// Signal that the output queue contains messages. Modifying the expiry
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// will wake the output actor, if it is waiting on the timer.
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non_empty_output_queue_.expires_at(steady_timer::time_point::min());
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}
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void read_line()
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{
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// Set a deadline for the read operation.
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input_deadline_.expires_after(std::chrono::seconds(30));
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// Start an asynchronous operation to read a newline-delimited message.
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auto self(shared_from_this());
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boost::asio::async_read_until(socket_,
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boost::asio::dynamic_buffer(input_buffer_), '\n',
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[this, self](const boost::system::error_code& error, std::size_t n)
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{
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// Check if the session was stopped while the operation was pending.
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if (stopped())
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return;
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if (!error)
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{
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// Extract the newline-delimited message from the buffer.
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std::string msg(input_buffer_.substr(0, n - 1));
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input_buffer_.erase(0, n);
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if (!msg.empty())
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{
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channel_.deliver(msg);
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}
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else
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{
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// We received a heartbeat message from the client. If there's
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// nothing else being sent or ready to be sent, send a heartbeat
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// right back.
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if (output_queue_.empty())
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{
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output_queue_.push_back("\n");
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// Signal that the output queue contains messages. Modifying
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// the expiry will wake the output actor, if it is waiting on
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// the timer.
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non_empty_output_queue_.expires_at(
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steady_timer::time_point::min());
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}
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}
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read_line();
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}
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else
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{
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stop();
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}
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});
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}
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void await_output()
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{
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auto self(shared_from_this());
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non_empty_output_queue_.async_wait(
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[this, self](const boost::system::error_code& /*error*/)
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{
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// Check if the session was stopped while the operation was pending.
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if (stopped())
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return;
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if (output_queue_.empty())
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{
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// There are no messages that are ready to be sent. The actor goes
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// to sleep by waiting on the non_empty_output_queue_ timer. When a
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// new message is added, the timer will be modified and the actor
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// will wake.
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non_empty_output_queue_.expires_at(steady_timer::time_point::max());
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await_output();
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}
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else
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{
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write_line();
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}
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});
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}
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void write_line()
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{
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// Set a deadline for the write operation.
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output_deadline_.expires_after(std::chrono::seconds(30));
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// Start an asynchronous operation to send a message.
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auto self(shared_from_this());
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boost::asio::async_write(socket_,
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boost::asio::buffer(output_queue_.front()),
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[this, self](const boost::system::error_code& error, std::size_t /*n*/)
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{
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// Check if the session was stopped while the operation was pending.
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if (stopped())
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return;
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if (!error)
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{
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output_queue_.pop_front();
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await_output();
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}
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else
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{
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stop();
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}
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});
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}
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void check_deadline(steady_timer& deadline)
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{
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auto self(shared_from_this());
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deadline.async_wait(
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[this, self, &deadline](const boost::system::error_code& /*error*/)
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{
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// Check if the session was stopped while the operation was pending.
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if (stopped())
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return;
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// Check whether the deadline has passed. We compare the deadline
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// against the current time since a new asynchronous operation may
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// have moved the deadline before this actor had a chance to run.
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if (deadline.expiry() <= steady_timer::clock_type::now())
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{
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// The deadline has passed. Stop the session. The other actors will
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// terminate as soon as possible.
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stop();
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}
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else
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{
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// Put the actor back to sleep.
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check_deadline(deadline);
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}
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});
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}
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channel& channel_;
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tcp::socket socket_;
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std::string input_buffer_;
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steady_timer input_deadline_{socket_.get_executor()};
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std::deque<std::string> output_queue_;
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steady_timer non_empty_output_queue_{socket_.get_executor()};
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steady_timer output_deadline_{socket_.get_executor()};
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};
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typedef std::shared_ptr<tcp_session> tcp_session_ptr;
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//----------------------------------------------------------------------
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class udp_broadcaster
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: public subscriber
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{
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public:
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udp_broadcaster(boost::asio::io_context& io_context,
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const udp::endpoint& broadcast_endpoint)
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: socket_(io_context)
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{
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socket_.connect(broadcast_endpoint);
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socket_.set_option(udp::socket::broadcast(true));
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}
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private:
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void deliver(const std::string& msg)
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{
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boost::system::error_code ignored_error;
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socket_.send(boost::asio::buffer(msg), 0, ignored_error);
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}
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udp::socket socket_;
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};
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//----------------------------------------------------------------------
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class server
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{
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public:
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server(boost::asio::io_context& io_context,
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const tcp::endpoint& listen_endpoint,
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const udp::endpoint& broadcast_endpoint)
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: io_context_(io_context),
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acceptor_(io_context, listen_endpoint)
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{
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channel_.join(
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std::make_shared<udp_broadcaster>(
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io_context_, broadcast_endpoint));
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accept();
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}
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private:
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void accept()
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{
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acceptor_.async_accept(
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[this](const boost::system::error_code& error, tcp::socket socket)
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{
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if (!error)
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{
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std::make_shared<tcp_session>(std::move(socket), channel_)->start();
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}
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accept();
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});
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}
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boost::asio::io_context& io_context_;
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tcp::acceptor acceptor_;
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channel channel_;
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};
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//----------------------------------------------------------------------
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int main(int argc, char* argv[])
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{
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try
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{
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using namespace std; // For atoi.
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if (argc != 4)
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{
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std::cerr << "Usage: server <listen_port> <bcast_address> <bcast_port>\n";
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return 1;
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}
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boost::asio::io_context io_context;
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tcp::endpoint listen_endpoint(tcp::v4(), atoi(argv[1]));
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udp::endpoint broadcast_endpoint(
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boost::asio::ip::make_address(argv[2]), atoi(argv[3]));
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server s(io_context, listen_endpoint, broadcast_endpoint);
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io_context.run();
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}
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catch (std::exception& e)
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{
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std::cerr << "Exception: " << e.what() << "\n";
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}
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return 0;
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}
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