Why is the boost server class throwing runtime error

Question

I am getting a compile error in the following code:

 boost::asio::io_context io_context;
 server server1(io_context, 1980);
 boost::thread t(boost::bind(&boost::asio::io_context::run, &io_context));

Where the definition of the server class is:

using boost::asio::ip::tcp;
class server
{
public:
    server(boost::asio::io_context& io_context, short port)
        : acceptor_(io_context, tcp::endpoint(tcp::v4(), port))
    {
        do_accept();
    }

private:
    void do_accept()
    {
        acceptor_.async_accept(
            [this](boost::system::error_code ec, tcp::socket socket)
            {
                if (!ec)
                {
                    std::make_shared<session>(std::move(socket))->start();
                }

                do_accept();
            });
    }

    tcp::acceptor acceptor_;
};

The error is at the point:

server(boost::asio::io_context& io_context, short port)
        : acceptor_(io_context, tcp::endpoint(tcp::v4(), port))

Exception thrown at 0x00007FFE9D804F69 in Everest.exe: Microsoft C++ exception: boost::wrapexceptboost::system::system_error at memory location 0x0000003AA613BDB0.

Answer 1

It seems your code is missing a listen. On my Linux box this simply doesn't do anything, but perhaps on Win32 it throws an error due to invalid state of the acceptor when doing async_accept ?

Here's a simple tester that does what is expected on linux:

#include <boost/asio.hpp>
#include <iostream>
using boost::asio::ip::tcp;

struct session : std::enable_shared_from_this<session> {
    tcp::socket _socket;

    session(tcp::socket&& s) : _socket(std::move(s)) {
        std::cerr << "new session " << _socket.remote_endpoint() << std::endl;
    }
    void start() {}
};

class server {
  public:
    server(boost::asio::io_context& io_context, short port)
        : acceptor_(io_context, tcp::endpoint(tcp::v4(), port))
    {
        acceptor_.listen();
        do_accept();
    }

  private:
    void do_accept()
    {
        acceptor_.async_accept(
            [this](boost::system::error_code ec, tcp::socket socket) {
                std::cerr << "accept " << ec.message() << std::endl;
                if (!ec) {
                    std::make_shared<session>(std::move(socket))->start();
                    do_accept();
                }
            });
    }

    tcp::acceptor acceptor_;
};

int main()
{
    boost::asio::io_context io_context;
    server                  server1(io_context, 1980);

    io_context.run();
}