一、server 端

1. 创建udp::socket，用于收发数据
   1）需要创建一个io_context对象，初始化socket对象
   2）创建一个udp::endpoint对象，指定协议版本（v4，v6）和端口号，初始化socket对象

2. 执行收发动作，socket.receive_from和socket.send_to
   1）收发都需要一个asio::buffer缓存。
   2）receive_from可以获取到client的endpoint，也可以用这个对象给client发送数据（send_to）

二、client 端

1. 创建一个udp::socket对象，用于收发数据。
2. 使用socket对象收发数据，socket.send_to和receive_from
   1）创建一个udp::endpoint对象，指定server端地址、端口。

#include <iostream>
#include <thread>
#include <boost/asio.hpp>

using namespace std;
using namespace boost;
using namespace boost::asio;
using asio::ip::udp;

void server_func() {
    io_context io;

    udp::socket server_socket(io, udp::endpoint(udp::v4(), 22333));

    int count = 1;
    while(true) {
        char buf[128] = {0};
        udp::endpoint client_endpoint;
        server_socket.receive_from(asio::buffer(buf), client_endpoint);

        printf("server -> [%d]: %s\n", count++, buf);
        cout << "server -> client info: " << client_endpoint.address() << ":" << client_endpoint.port() << endl;

        server_socket.send_to(asio::buffer("received from server"), client_endpoint);
    }
}

void client_func() {
    io_context io;
    udp::socket client_socket(io, udp::v4());

    udp::endpoint server_endpoint(ip::address::from_string("127.0.0.1"), 22333);

    while(true) {
        char buf[128] = {0};
        cout << "client -> input:\n";
        cin >> buf;

        client_socket.send_to(asio::buffer(buf), server_endpoint);

//        cout << "client -> get feedback from server: " << server_endpoint.address() << ":" << server_endpoint.port() << endl;
//        bzero(buf, 128);
        client_socket.receive_from(asio::buffer(buf), server_endpoint);
//        cout << "client -> " << buf << endl;
    }
}

int main() {
    jthread server(server_func);
    cout << "start server\n";

    jthread client(client_func);
    cout << "start client\n";

    return 0;
}