keep-lookup

main.go

package main

import (
	"context"
	"fmt"
	"net"
	"os"
	"os/signal"
	"time"
)

func main() {
	// listen signal interrupt
	ctx, cancel := context.WithCancel(context.Background())
	go func() {
		// wait for signal interrupt
		sigChan := make(chan os.Signal, 1)
		signal.Notify(sigChan, os.Interrupt)
		<-sigChan
		cancel()
	}()
	// domain is the first command line argument
	if len(os.Args) < 2 {
		fmt.Fprintf(os.Stderr, "Usage: %s <domain>", os.Args[0])
	}
	domain := os.Args[1]
	lookupLoop(ctx, domain)
	os.Exit(0)
}

func lookupLoop(ctx context.Context, doamin string) {
	canceled := false
	go func() {
		for !canceled {
			// lookup
			ips, err := net.LookupIP(doamin)
			if err != nil {
				fmt.Fprintf(os.Stderr, "lookup %s failed: %v\n", doamin, err)
			}
			fmt.Printf("lookup %s: %v\n", doamin, ips)
			// sleep 5s
			time.Sleep(3 * time.Second)
		}

	}()
	<-ctx.Done()
}