package main

import (
	"fmt"
	"log"
	"net"
	"strings"
)

// UDP sever
func main() {
	conn, err := net.ListenUDP("udp", &net.UDPAddr{
		IP:   net.IPv4(127, 0, 0, 1),
		Port: 40000,
	})
	if err != nil {
		log.Fatal("listen udp failed:", err)
		return
	}
	defer conn.Close()
	//不需要建立链接，直接收发数据
	data := make([]byte, 1024)
	for {
		n, addr, err := conn.ReadFromUDP(data)
		if err != nil {
			log.Println("read from udp failed:", err)
		}
		fmt.Printf("%s\n", data[:n])
		reply := string(data[:n])
		reply = strings.ToUpper(reply)
		//发送数据
		conn.WriteToUDP([]byte(reply), addr)
	}
}