just for fun ;), i'm "www.alash3al.xyz"

file-downloader-sample.go

package main

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

func request(method, url string, headers map[string]string) (*http.Response, error) {
	client := &http.Client{}
	defer func(){client = nil}()
	req, err := http.NewRequest(method, url, nil)
	if err != nil {return nil, err}
	for k, v := range headers {req.Header.Set(k, v)}
	return client.Do(req)
}

func main() {
	url := `https://storage.googleapis.com/golang/go1.5.1.windows-386.msi`
	//end := make(chan bool)
	done := uint64(0)
	max := 61
	info, _ := request("HEAD", url, nil)
	chunk := uint64(info.ContentLength)/uint64(max)
	wg := &sync.WaitGroup{}

	wg.Add(max)

	for i := 0; i < max; i++ {
		go (func(i int, done uint64, wg *sync.WaitGroup){

			from := uint64(i) * chunk
			to := (from + chunk) - uint64(1)
			fd, _ := os.OpenFile(fmt.Sprintf(`./tmp/tmp-%d.tmp`, i), os.O_WRONLY|os.O_CREATE, 0777)
			data, err := request("GET", url, map[string]string{
				`Range`: fmt.Sprintf(`bytes=%d-%d`, from, to),
			})

			if err != nil {
				return
			}

			fmt.Printf(`Worker(%d) Downloading from %d to %d` + "\n", i, from, to)

			defer fd.Close()
			defer data.Body.Close()
			defer wg.Done()
			defer (func(){
				*&done += uint64(data.ContentLength)
				fmt.Printf(`Worker(%d) Finished` + "\n", i)
			})()

			io.Copy(fd, data.Body)

		})(i, done, wg)
	}

	wg.Wait()
}