How to construct a boost::beast::http::message from std::string?

Question

Is that possible to construct a boost::beast::http::message (specifically I have to construct a boost::beast::http::response<bb_http::string_body>) from std::string, std::string_view or other raw buffer?

Maybe there is some kind of parser? From what I see in Boost.Beast samples, we can either:

1. receive a response from boost::beast::read* functions. In that case the first argument should be a SyncReadStream, which has to comply with contracts of SyncReadStream from boost/beast/core/type_traits.hpp:

struct is_sync_read_stream<T, detail::void_t<decltype(
    std::declval<std::size_t&>() = std::declval<T>().read_some(
        std::declval<detail::MutableBufferSequence>()),
    std::declval<std::size_t&>() = std::declval<T>().read_some(
        std::declval<detail::MutableBufferSequence>(),
        std::declval<boost::system::error_code&>()),
            (void)0)>> : std::true_type {};

2. or construct it by hand like http::request<http::string_body> req{http::verb::get, target, version};

Answer 1

You can manually invoke the parser, e.g. with this simple skeleton function:

http::response<http::string_body> do_parse(std::string_view input)
{
    beast::error_code ec;
    http::response_parser<http::string_body> p;

    // read headers
    auto buf = boost::asio::buffer(sample);
    auto n = p.put(buf, ec);
    assert(p.is_header_done());

    // read body
    if (!ec) {
        buf += n;
        n = p.put(buf, ec);
        p.put_eof(ec);
    }
    if (ec)
        throw boost::system::system_error(ec);
    assert(p.is_done());

    return p.release();
}

This assumes that input is a sinlge complete request.

Live Demo

Live On Coliru

#include <boost/beast.hpp>
#include <boost/beast/http.hpp>
#include <string_view>
#include <iostream>
#include <iomanip>
namespace beast = boost::beast;
namespace http = beast::http;

http::response<http::string_body> do_parse(std::string_view input)
{
    beast::error_code ec;
    http::response_parser<http::string_body> p;

    // read headers
    auto buf = boost::asio::buffer(input);
    auto n   = p.put(buf, ec);
    assert(p.is_header_done());

    // read body
    if (!ec) {
        buf += n;
        n = p.put(buf, ec);
        p.put_eof(ec);
    }
    if (ec)
        throw boost::system::system_error(ec);
    assert(p.is_done());

    return p.release();
}

int main() {
    auto res = do_parse(
        "HTTP/1.1 200 OK\r\n"
        "Date: Sun, 10 Oct 2010 23:26:07 GMT\r\n"
        "Server: Apache/2.2.8 (Ubuntu) mod_ssl/2.2.8 OpenSSL/0.9.8g\r\n"
        "Last-Modified: Sun, 26 Sep 2010 22:04:35 GMT\r\n"
        "ETag: 45b6-834-49130cc1182c0\r\n"
        "Accept-Ranges: bytes\r\n"
        "Content-Length: 12\r\n"
        "Connection: close\r\n"
        "Content-Type: text/html\r\n"
        "\r\n"
        "Hello world!");
    std::cout << res << '\n';
    std::cout << "====== body:\n" << std::quoted(res.body()) << "\n";
}

Prints

HTTP/1.1 200 OK
Date: Sun, 10 Oct 2010 23:26:07 GMT
Server: Apache/2.2.8 (Ubuntu) mod_ssl/2.2.8 OpenSSL/0.9.8g
Last-Modified: Sun, 26 Sep 2010 22:04:35 GMT
ETag: 45b6-834-49130cc1182c0
Accept-Ranges: bytes
Content-Length: 12
Connection: close
Content-Type: text/html
Hello world!
====== body:
"Hello world!"