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 develop branch, built from commit 9a0a11e85a.


// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at
// Official repository:

// Example: HTTP client, coroutine

#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio/spawn.hpp>
#include <cstdlib>
#include <functional>
#include <iostream>
#include <string>

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


// Report a failure
fail(beast::error_code ec, char const* what)
    std::cerr << what << ": " << ec.message() << "\n";

// Performs an HTTP GET and prints the response
    std::string const& host,
    std::string const& port,
    std::string const& target,
    int version,
    net::io_context& ioc,
    net::yield_context yield)
    beast::error_code ec;

    // These objects perform our I/O
    tcp::resolver resolver(ioc);
    beast::tcp_stream stream(ioc);

    // Look up the domain name
    auto const results = resolver.async_resolve(host, port, yield[ec]);
        return fail(ec, "resolve");

    // Set the timeout.

    // Make the connection on the IP address we get from a lookup
    stream.async_connect(results, yield[ec]);
        return fail(ec, "connect");

    // Set up an HTTP GET request message
    http::request<http::string_body> req{http::verb::get, target, version};
    req.set(http::field::host, host);
    req.set(http::field::user_agent, BOOST_BEAST_VERSION_STRING);

    // Set the timeout.

    // Send the HTTP request to the remote host
    http::async_write(stream, req, yield[ec]);
        return fail(ec, "write");

    // This buffer is used for reading and must be persisted
    beast::flat_buffer b;

    // Declare a container to hold the response
    http::response<http::dynamic_body> res;

    // Receive the HTTP response
    http::async_read(stream, b, res, yield[ec]);
        return fail(ec, "read");

    // Write the message to standard out
    std::cout << res << std::endl;

    // Gracefully close the socket
    stream.socket().shutdown(tcp::socket::shutdown_both, ec);

    // not_connected happens sometimes
    // so don't bother reporting it.
    if(ec && ec != beast::errc::not_connected)
        return fail(ec, "shutdown");

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


int main(int argc, char** argv)
    // Check command line arguments.
    if(argc != 4 && argc != 5)
        std::cerr <<
            "Usage: http-client-coro <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]\n" <<
            "Example:\n" <<
            "    http-client-coro 80 /\n" <<
            "    http-client-coro 80 / 1.0\n";
        return EXIT_FAILURE;
    auto const host = argv[1];
    auto const port = argv[2];
    auto const target = argv[3];
    int version = argc == 5 && !std::strcmp("1.0", argv[4]) ? 10 : 11;

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

    // Launch the asynchronous operation
    boost::asio::spawn(ioc, std::bind(

    // Run the I/O service. The call will return when
    // the get operation is complete.;

    return EXIT_SUCCESS;