Boost C++ Libraries 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.


// 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
// Official repository:

// Example: WebSocket client, coroutine

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


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>


// Sends a WebSocket message and prints the response
    std::string host,
    std::string port,
    std::string text)
    // These objects perform our I/O
    auto resolver = net::use_awaitable.as_default_on(
            tcp::resolver(co_await net::this_coro::executor));
    auto ws = net::use_awaitable.as_default_on(
            websocket::stream<beast::tcp_stream>(co_await net::this_coro::executor));

    // Look up the domain name
    auto const results = co_await resolver.async_resolve(host, port);

    // Set a timeout on the operation

    // Make the connection on the IP address we get from a lookup
    auto ep = co_await beast::get_lowest_layer(ws).async_connect(results);

    // Update the host_ string. This will provide the value of the
    // Host HTTP header during the WebSocket handshake.
    // See
    host += ':' + std::to_string(ep.port());

    // Turn off the timeout on the tcp_stream, because
    // the websocket stream has its own timeout system.

    // Set suggested timeout settings for the websocket

    // Set a decorator to change the User-Agent of the handshake
        [](websocket::request_type& req)
                std::string(BOOST_BEAST_VERSION_STRING) +
                    " websocket-client-coro");

    // Perform the websocket handshake
    co_await ws.async_handshake(host, "/");

    // Send the message
    co_await ws.async_write(net::buffer(std::string(text)));

    // This buffer will hold the incoming message
    beast::flat_buffer buffer;

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

    // Close the WebSocket connection
    co_await ws.async_close(websocket::close_code::normal);

    // If we get here then the connection is closed gracefully

    // The make_printable() function helps print a ConstBufferSequence
    std::cout << beast::make_printable( << std::endl;


int main(int argc, char** argv)
    // Check command line arguments.
    if(argc != 4)
        std::cerr <<
            "Usage: websocket-client-awaitable <host> <port> <text>\n" <<
            "Example:\n" <<
            "    websocket-client-awaitable 80 \"Hello, world!\"\n";
        return EXIT_FAILURE;
    auto const host = argv[1];
    auto const port = argv[2];
    auto const text = argv[3];

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

    // Launch the asynchronous operation
                  do_session(host, port, text),
                  [](std::exception_ptr e)
                      if (e)
                          catch(std::exception & e)
                              std::cerr << "Error: " << e.what() << "\n";

    // Run the I/O service. The call will return when
    // the socket is closed.;

    return EXIT_SUCCESS;


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