how to use beast::http::async_read

Question

I'm trying to write a simple http server. while beast::http::read is working as respected, The async version does not call the handler at all (when trying to get http://localhost:8080/)

#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <boost/beast.hpp>

namespace asio = boost::asio;
namespace beast = boost::beast;
using tcp = asio::ip::tcp;

int main()
{
    asio::io_context m_io_context;
    tcp::acceptor m_acceptor(m_io_context, {tcp::v4(), 8080});
    tcp::socket m_socket(m_io_context);
    beast::flat_buffer buffer;
    beast::http::request<beast::http::string_body> request;

    m_acceptor.accept(m_socket);

    while (true)
    {
        // Do something...
        //beast::http::read(m_socket, buffer, request);  // This works well
        beast::http::async_read(
            m_socket, buffer, request,
            [](const beast::error_code& ec, std::size_t bytes_transferred)
            {
                // This function is never being called!!
                // ...
            });
    }
}

Answer 1

Take a look on boost documentation on async_read, the function call always returns immediately. So your callback won't be processed, to make it work, you need to execute run of the m_io_context object. Take a look on boost documentation example.

#include <iostream>
#include <string>
#include <boost/asio.hpp>
#include <boost/beast.hpp>

namespace asio = boost::asio;
namespace beast = boost::beast;
using tcp = asio::ip::tcp;

int main()
{
    asio::io_context m_io_context;
    tcp::acceptor m_acceptor(m_io_context, {tcp::v4(), 8080});
    tcp::socket m_socket(m_io_context);
    beast::flat_buffer buffer;
    beast::http::request<beast::http::string_body> request;

    m_acceptor.accept(m_socket);

    beast::http::async_read(
        m_socket, buffer, request,
        [](const beast::error_code& ec, std::size_t bytes_transferred)
        {
            // start the next async read here
        });

    m_io_context.run();
}