main.go

package main

import (
	"flag"
	"log"
	"net"
)

const (
	defaultAddr     = ":1234"
	defaultNumTries = 4
)

var (
	addr     string
	numTries int
)

func main() {

	// use flags
	flag.StringVar(&addr, "addr", defaultAddr, "address on which to listen")
	flag.IntVar(&numTries, "n", defaultNumTries, "number of consecutive tries")
	flag.Parse()
	log.Printf("Using address=`%v`\n", addr)
	log.Printf("Will try %v times\n", numTries)

	// listen and close numTries times binding to addr
	for i := 0; i < numTries; i++ {
		listenAndClose(i)
	}

	// sweet, no issues.
	log.Printf("PASS\n")
}

// listenAndClose creates a tcp listener on addr and closes it, logging its
// actions to and exiting the program in the event of an error.
func listenAndClose(i int) {
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		log.Fatalf("creating ln %v failed: %v\n", i, err)
	}
	log.Printf("%3d: listener created on %v\n", i, ln.Addr())
	if err := ln.Close(); err != nil {
		log.Fatalf("closing ln %v failed: %v\n", i, err)
	}
	log.Printf("%3d: listener closed\n", i)
}

(master=)$ go version
go version go1.5 darwin/amd64
(master=)$ go run main.go
2015/11/14 13:32:41 Using address=`:1234`
2015/11/14 13:32:41 Will try 4 times
2015/11/14 13:32:41   0: listener created on [::]:1234
2015/11/14 13:32:41   0: listener closed
2015/11/14 13:32:41   1: listener created on [::]:1234
2015/11/14 13:32:41   1: listener closed
2015/11/14 13:32:41   2: listener created on [::]:1234
2015/11/14 13:32:41   2: listener closed
2015/11/14 13:32:41   3: listener created on [::]:1234
2015/11/14 13:32:41   3: listener closed
2015/11/14 13:32:41 PASS
(master=)$ go run main.go -addr=""
2015/11/14 13:32:46 Using address=``
2015/11/14 13:32:46 Will try 4 times
2015/11/14 13:32:46   0: listener created on [::]:65349
2015/11/14 13:32:46   0: listener closed
2015/11/14 13:32:46   1: listener created on [::]:65350
2015/11/14 13:32:46   1: listener closed
2015/11/14 13:32:46   2: listener created on [::]:65351
2015/11/14 13:32:46   2: listener closed
2015/11/14 13:32:46   3: listener created on [::]:65352
2015/11/14 13:32:46   3: listener closed
2015/11/14 13:32:46 PASS