esp-idf/examples/protocols/asio/tcp_echo_server/main/echo_server.cpp

#include "asio.hpp"
#include <string>
#include <iostream>
#include "protocol_examples_common.h"
#include "esp_event.h"
#include "tcpip_adapter.h"
#include "nvs_flash.h"

using asio::ip::tcp;

class session
  : public std::enable_shared_from_this<session>
{
public:
  session(tcp::socket socket)
    : socket_(std::move(socket))
  {
  }

  void start()
  {
    do_read();
  }

private:
  void do_read()
  {
    auto self(shared_from_this());
    socket_.async_read_some(asio::buffer(data_, max_length),
        [this, self](std::error_code ec, std::size_t length)
        {
          if (!ec)
          {
            data_[length] = 0;
            std::cout << data_ << std::endl;
            do_write(length);
          }
        });
  }

  void do_write(std::size_t length)
  {
    auto self(shared_from_this());
    asio::async_write(socket_, asio::buffer(data_, length),
        [this, self](std::error_code ec, std::size_t length)
        {
          if (!ec)
          {
            do_read();
          }
        });
  }

  tcp::socket socket_;
  enum { max_length = 1024 };
  char data_[max_length];
};

class server
{
public:
  server(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](std::error_code ec, tcp::socket socket)
        {
          if (!ec)
          {
            std::make_shared<session>(std::move(socket))->start();
          }

          do_accept();
        });
  }

  tcp::acceptor acceptor_;
};


extern "C" void app_main()
{
    ESP_ERROR_CHECK(nvs_flash_init());
    tcpip_adapter_init();
    ESP_ERROR_CHECK(esp_event_loop_create_default());

    /* This helper function configures Wi-Fi or Ethernet, as selected in menuconfig.
     * Read "Establishing Wi-Fi or Ethernet Connection" section in
     * examples/protocols/README.md for more information about this function.
     */
    ESP_ERROR_CHECK(example_connect());

    /* This helper function configures blocking UART I/O */
    ESP_ERROR_CHECK(example_configure_stdin_stdout());

    asio::io_context io_context;

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

    std::cout << "ASIO engine is up and running" << std::endl;

    io_context.run();
}