Go download file

package mainimport ("fmt""io""net/http""os""strings""github.com/dustin/go-humanize")// WriteCounter counts the number of bytes written to it. By implementing the Write method,// it is of the io.Writer interface and we can pass this into io.TeeReader()// Every write to this writer, will print the progress of the file write.typeWriteCounterstruct {Totaluint64}func (wc*WriteCounter) Write(p []byte) (int, error) {n:=len(p)wc.Total+=uint64(n)wc.PrintProgress()returnn, nil}// PrintProgress prints the progress of a file writefunc (wcWriteCounter) PrintProgress() {// Clear the line by using a character return to go back to the start and remove// the remaining characters by filling it with spacesfmt.Printf("\r%s", strings.Repeat(" ", 50))// Return again and print current status of download// We use the humanize package to print the bytes in a meaningful way (e.g. 10 MB)fmt.Printf("\rDownloading... %s complete", humanize.Bytes(wc.Total))}funcmain() {iflen(os.Args) !=3 {fmt.Println("usage: download url filename")os.Exit(1) }fmt.Println("Download Started")url:=os.Args[1]filename:=os.Args[2]err:=DownloadFile(url, filename)iferr!=nil {panic(err) }fmt.Println("Download Finished")}// DownloadFile will download a url and store it in local filepath.// It writes to the destination file as it downloads it, without// loading the entire file into memory.// We pass an io.TeeReader into Copy() to report progress on the download.funcDownloadFile(urlstring, filepathstring) error {// Create the file with .tmp extension, so that we won't overwrite a// file until it's downloaded fullyout, err:=os.Create(filepath+".tmp")iferr!=nil {returnerr }deferout.Close()// Get the dataresp, err:=http.Get(url)iferr!=nil {returnerr }deferresp.Body.Close()// Create our bytes counter and pass it to be used alongside our writercounter:=&WriteCounter{}_, err=io.Copy(out, io.TeeReader(resp.Body, counter))iferr!=nil {returnerr }// The progress use the same line so print a new line once it's finished downloadingfmt.Println()// Rename the tmp file back to the original fileerr=os.Rename(filepath+".tmp", filepath)iferr!=nil {returnerr }returnnil}