Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the master branch, built from commit 41e2058a8b.

libs/beast/example/websocket/server/awaitable/websocket_server_awaitable.cpp

//
// Copyright (c) 2022 Klemens D. Morgenstern (klemens dot morgenstern at gmx dot net)
//
// 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)
//
// Official repository: https://github.com/boostorg/beast
//

//------------------------------------------------------------------------------
//
// Example: WebSocket server, coroutine
//
//------------------------------------------------------------------------------

#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/asio/awaitable.hpp>
#include <boost/asio/co_spawn.hpp>
#include <boost/asio/detached.hpp>
#include <boost/asio/use_awaitable.hpp>
#include <algorithm>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <memory>
#include <string>
#include <thread>
#include <vector>

#if defined(BOOST_ASIO_HAS_CO_AWAIT)

namespace beast = boost::beast;         // from <boost/beast.hpp>
namespace http = beast::http;           // from <boost/beast/http.hpp>
namespace websocket = beast::websocket; // from <boost/beast/websocket.hpp>
namespace net = boost::asio;            // from <boost/asio.hpp>
using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>

using stream = websocket::stream<
        typename beast::tcp_stream::rebind_executor<
            typename net::use_awaitable_t<>::executor_with_default<net::any_io_executor>>::other>;

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

// Echoes back all received WebSocket messages
net::awaitable<void>
do_session(stream ws)
{
    // Set suggested timeout settings for the websocket
    ws.set_option(
        websocket::stream_base::timeout::suggested(
            beast::role_type::server));

    // Set a decorator to change the Server of the handshake
    ws.set_option(websocket::stream_base::decorator(
        [](websocket::response_type& res)
        {
            res.set(http::field::server,
                std::string(BOOST_BEAST_VERSION_STRING) +
                    " websocket-server-coro");
        }));

    // Accept the websocket handshake
    co_await ws.async_accept();

    try
    {
        for(;;)
        {
            // This buffer will hold the incoming message
            beast::flat_buffer buffer;

            // Read a message
            co_await ws.async_read(buffer);

            // Echo the message back
            ws.text(ws.got_text());
            co_await ws.async_write(buffer.data());
        }
    }
    catch(const boost::system::system_error & se)
    {
        if (se.code() != websocket::error::closed)
            throw;
    }
}

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

// Accepts incoming connections and launches the sessions
net::awaitable<void>
do_listen(
    tcp::endpoint endpoint)
{

    // Open the acceptor
    auto acceptor = net::use_awaitable.as_default_on(tcp::acceptor(co_await net::this_coro::executor));
    acceptor.open(endpoint.protocol());

    // Allow address reuse
    acceptor.set_option(net::socket_base::reuse_address(true));

    // Bind to the server address
    acceptor.bind(endpoint);

    // Start listening for connections
    acceptor.listen(net::socket_base::max_listen_connections);

    for(;;)
        boost::asio::co_spawn(
                acceptor.get_executor(),
                do_session(stream(co_await acceptor.async_accept())),
                [](std::exception_ptr e)
                {
                    if (e)
                    {
                        try
                        {
                            std::rethrow_exception(e);
                        }
                        catch (std::exception &e) {
                            std::cerr << "Error in session: " << e.what() << "\n";
                        }
                    }
                });
}

int main(int argc, char* argv[])
{
    // Check command line arguments.
    if (argc != 4)
    {
        std::cerr <<
            "Usage: websocket-server-awaitable <address> <port> <threads>\n" <<
            "Example:\n" <<
            "    websocket-server-awaitable 0.0.0.0 8080 1\n";
        return EXIT_FAILURE;
    }
    auto const address = net::ip::make_address(argv[1]);
    auto const port = static_cast<unsigned short>(std::atoi(argv[2]));
    auto const threads = std::max<int>(1, std::atoi(argv[3]));

    // The io_context is required for all I/O
    net::io_context ioc(threads);

    // Spawn a listening port
    boost::asio::co_spawn(
              ioc,
              do_listen(tcp::endpoint{address, port}),
              [](std::exception_ptr e)
              {
                  if (e)
                      try
                      {
                          std::rethrow_exception(e);
                      }
                      catch(std::exception & e)
                      {
                          std::cerr << "Error: " << e.what() << "\n";
                      }
            });

    // Run the I/O service on the requested number of threads
    std::vector<std::thread> v;
    v.reserve(threads - 1);
    for(auto i = threads - 1; i > 0; --i)
        v.emplace_back(
        [&ioc]
        {
            ioc.run();
        });
    ioc.run();

    return EXIT_SUCCESS;
}

#else

int main(int, char * [])
{
    std::printf("awaitables require C++20\n");
    return 1;
}

#endif