Good one to study

send.go

import (
	"errors"
	"log"
	"net/http"
	"time"
	"flag"
	"fmt"
)

var (
	towards = flag.String("towards", "", "the host:port of the server to send to")
)

func main() {
	flag.Parse()
	err := send()
	if err != nil {
		log.Fatal("whoops")
	}
}

// send wants 200 from the upstream service, or times out.
func send() error {
	timeout := time.After(5 * time.Second)
	ok := make(chan bool)

	go func() {
		upstream := fmt.Sprintf("http://%s/ping", *towards)
		resp, err := http.Get(upstream)
		if err != nil || resp.StatusCode != 200 {
			ok <- false
			return
		}
		ok <- true
	}()

	select {
	case <-timeout:
		return errors.New("timed out")
	case v := <-ok:
		if !v {
			return errors.New("unexpected upstream response")
		}
		break
	}

	return nil
}