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/http/client/awaitable/http_client_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: HTTP client, coroutine
//
//------------------------------------------------------------------------------



#include <boost/beast/core.hpp>
#include <boost/beast/http.hpp>
#include <boost/beast/version.hpp>
#include <boost/asio/awaitable.hpp>
#include <boost/asio/co_spawn.hpp>
#include <boost/asio/detached.hpp>
#include <boost/asio/use_awaitable.hpp>

#if defined(BOOST_ASIO_HAS_CO_AWAIT)

#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>

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

// Performs an HTTP GET and prints the response
net::awaitable<void>
do_session(
    std::string host,
    std::string port,
    std::string target,
    int version)
{
    // These objects perform our I/O
    // They use an executor with a default completion token of use_awaitable
    // This makes our code easy, but will use exceptions as the default error handling,
    // i.e. if the connection drops, we might see an exception.
    auto resolver = net::use_awaitable.as_default_on(tcp::resolver(co_await net::this_coro::executor));
    auto stream = net::use_awaitable.as_default_on(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 the timeout.
    stream.expires_after(std::chrono::seconds(30));

    // Make the connection on the IP address we get from a lookup
    co_await stream.async_connect(results);

    // 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.
    stream.expires_after(std::chrono::seconds(30));

    // Send the HTTP request to the remote host
    co_await http::async_write(stream, req);

    // 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
    co_await http::async_read(stream, b, res);

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

    // Gracefully close the socket
    beast::error_code ec;
    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)
        throw boost::system::system_error(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-awaitable <host> <port> <target> [<HTTP version: 1.0 or 1.1(default)>]\n" <<
            "Example:\n" <<
            "    http-client-awaitable www.example.com 80 /\n" <<
            "    http-client-awaitable www.example.com 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
    net::co_spawn(
        ioc,
        do_session(host, port, target, version),
        // If the awaitable exists with an exception, it gets delivered here as `e`.
        // This can happen for regular errors, such as connection drops.
        [](std::exception_ptr e)
        {
          if (e)
          try
          {
              std::rethrow_exception(e);
          }
          catch(std::exception & ex)
          {
              std::cerr << "Error: " << ex.what() << "\n";
          }
        });

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

    return EXIT_SUCCESS;
}

#else

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

#endif