Concurrency in golang

concurrency.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"sync"
)

const TMP_FILE = "/tmp/urlSink.txt"

var URLS = []string{
	"http://google.com",
	"http://duckduckgo.com",
	"http://search.yahoo.com",
}

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func fetch(url string, wait *sync.WaitGroup, sink chan<- []byte) {
	defer wait.Done()

	log.Println("Fetching URL", url)
	resp, err := http.Get(url)
	if err != nil {
		check(err)
	}

	defer resp.Body.Close()

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		check(err)
	}

	sink <- body
}

func urlSink(sink <-chan []byte, destFile string) {
	var wg sync.WaitGroup

	_ = os.Remove(destFile)
	f, err := os.Create(destFile)
	check(err)

	defer f.Close()

	for v := range sink {
		wg.Add(1)

		func(arr []byte) {
                        log.Println("received value in SInk")
			defer wg.Done()

			bytes, _ := f.Write(arr)
			fmt.Printf("wrote %d bytes\n", bytes)
			check(err)
		}(v)
	}

	f.Sync()
	wg.Wait()
}

func main() {
	destFile := TMP_FILE

	//Lock group.
	var results sync.WaitGroup

	//Prepare a channel where values would be received
	dataSink := make(chan []byte)

	go func() {
		log.Println("Waiting for Values")
		urlSink(dataSink, destFile)
	}()

	for _, url := range URLS {
		results.Add(1)
		go fetch(url, &results, dataSink)
	}

	results.Wait()
	close(dataSink)

	log.Println("All Done")
}