Boost beast使用例

最近Boost beastに触れましたが、ここに記録しておきます.
 
Introduction
Beast is a C++ header-only library serving as a foundation for writing interoperable networking libraries by providing low-level HTTP/1, WebSocket, and networking protocol vocabulary types and algorithms using the consistent asynchronous model of Boost.Asio.
This library is designed for:

Symmetry: Algorithms are role-agnostic; build clients, servers, or both.

Ease of Use: Boost.Asio users will immediately understand Beast.

Flexibility: Users make the important decisions such as buffer or thread management.

Performance: Build applications handling thousands of connections or more.

Basis for Further Abstraction. Components are well-suited for building upon.

 
Requirements
This library is for programmers familiar with Boost.Asio. Users who wish to use asynchronous interfaces should already know how to create concurrent network programs using callbacks or coroutines.

C++11: Robust support for most language features.

Boost: Boost.Asio and some other parts of Boost.

OpenSSL: Required for using TLS/Secure sockets and examples/tests

When using Microsoft Visual C++, Visual Studio 2017 or later is required.
One of these components is required in order to build the tests and examples:

Properly configured bjam/b2

CMake 3.5.1 or later (Windows only)

 
httpクライアントの例:

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

namespace beast = boost::beast;     // from 
namespace http = beast::http;       // from 
namespace net = boost::asio;        // from 
using tcp = net::ip::tcp;           // from 

// Performs an HTTP GET and prints the response
int main(int argc, char** argv)
{
    try
    {
        // Check command line arguments.
        if(argc != 4 && argc != 5)
        {
            std::cerr <<
                "Usage: http-client-sync    []
" <<
                "Example:
" <<
                "    http-client-sync www.example.com 80 /
" <<
                "    http-client-sync www.example.com 80 / 1.0
";
            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;

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

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

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

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

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

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

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

        // Receive the HTTP response
        http::read(stream, buffer, 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 beast::system_error{ec};

        // If we get here then the connection is closed gracefully
    }
    catch(std::exception const& e)
    {
        std::cerr << "Error: " << e.what() << std::endl;
        return EXIT_FAILURE;
    }
    return EXIT_SUCCESS;
}

例からわかるように、使いやすいです.
 
https://www.boost.org/doc/libs/1_68_0/libs/beast/doc/html/index.html
https://github.com/boostorg/beast