UDP is failing when the remote address goes down.

udp_fail.go

package main

import (
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net"
)

func main() {
	addr := net.UDPAddr{
		Port: 0,
		IP:   net.ParseIP("127.0.0.1"),
	}

	// create a UDP listener
	listener, err := net.ListenUDP("udp", &addr)
	if err != nil {
		log.Fatal(err)
	}

	// listen on that udp channel
	waitForCloseChan := make(chan struct{})
	go func() {
		_, err := io.Copy(ioutil.Discard, listener)
		if err != nil {
			close(waitForCloseChan)
		}
	}()

	// Dial to whatever UDP server was created
	conn, err := net.Dial("udp", listener.LocalAddr().String())
	if err != nil {
		log.Fatal(err)
	}

	_, err = fmt.Fprintf(conn, "hello udp....")
	if err != nil {
		log.Fatal("error on initial writing to udp", err)
	}

	listener.Close()

	<-waitForCloseChan

	// do this in a loop because it does not consistently fail
	for i := 0; i < 100; i++ {
		_, err = fmt.Fprintf(conn, "hello udp....")
		if err != nil {
			log.Fatal("this should not fail:", err)
		}
	}
}