esp-idf/examples/protocols/asio/udp_echo_server/main/udp_echo_server.cpp

//
// async_udp_echo_server.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// 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)
//

#include <cstdlib>
#include <iostream>

#include "asio.hpp"

using asio::ip::udp;

class server
{
public:
  server(asio::io_context& io_context, short port)
    : socket_(io_context, udp::endpoint(udp::v4(), port))
  {
    do_receive();
  }

  void do_receive()
  {
    socket_.async_receive_from(
        asio::buffer(data_, max_length), sender_endpoint_,
        [this](std::error_code ec, std::size_t bytes_recvd)
        {
          if (!ec && bytes_recvd > 0)
          {
            std::cout << data_ << std::endl;
            do_send(bytes_recvd);
          }
          else
          {
            do_receive();
          }
        });
  }

  void do_send(std::size_t length)
  {
    socket_.async_send_to(
        asio::buffer(data_, length), sender_endpoint_,
        [this](std::error_code /*ec*/, std::size_t  bytes /*bytes_sent*/)
        {
          do_receive();
        });
  }

private:
  udp::socket socket_;
  udp::endpoint sender_endpoint_;
  enum { max_length = 1024 };
  char data_[max_length];
};

void asio_main()
{
    asio::io_context io_context;

    server s(io_context, std::atoi(CONFIG_EXAMPLE_PORT));

    io_context.run();
}