package main

// A simple echo server. It listens on a random port, prints that port, then

// echos back anything sent to it.

import (

"errors"

"fmt"

"io"

"log"

"net"

)

func main() {

l, err := net.Listen("tcp", "127.0.0.1:0")

if err != nil {

log.Fatalf("listen error: err=%s", err)

}

defer l.Close()

tcpAddr, valid := l.Addr().(*net.TCPAddr)

if !valid {

log.Panic("address is not valid")

}

remotePort := tcpAddr.Port

_, err = fmt.Println(remotePort)

if err != nil {

log.Panicf("print error: err=%s", err)

}

for {

conn, err := l.Accept()

if err != nil {

log.Panicf("accept error, err=%s", err)

return

}

go func() {

defer conn.Close()

_, err := io.Copy(conn, conn)

if errors.Is(err, io.EOF) {

return

} else if err != nil {

log.Panicf("copy error, err=%s", err)

}

}()

}

}