Golang Progress Download file

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An afternoon that didn't find a job. Code//Very unattractive temporary works package mainimport ("Net/http" "FMT" "OS" "Errors" "IO" "StrConv") func main () { DownloadFile ("Http://localhost:8089/ThunderSpeed1.0.35.366.exe", func (length, Downlen Int64) {FMT. Println (length, Downlen, float32 (downlen)/float32 (length))})}func DownloadFile (URL string, fb func (length, Downlen int   ) Error {var (fsize int64 buf = make ([]byte, 32*1024) written int64)//create an HTTP client Client: = new (http. Client)//get method gets the resource resp, err: = client. Get (URL) if err! = Nil {return ERR}//Read server returns the file size fsize, err = StrConv. parseint (resp. Header.get ("Content-length"), ten, +) if err! = Nil {fmt. PRINTLN (ERR)}//Create file, err: = OS. Create ("Test.exe") if err! = Nil {return err} defer file. Close () If Resp. Body = = Nil {return errors. New ("body is null")} Defer resp. Body.close ()///Below is a simplified version of Io.copybuffer () for {//Read bytes nr, er: = resp. Body.read (bUF) if nr > 0 {//write bytes NW, ew: = file.         Write (BUF[0:NR])//data length greater than 0 if NW > 0 {written + = Int64 (NW)}//write error            If ew! = Nil {err = ew break}//Read is data length not equal to write data length if nr! = NW { Err = io. Errshortwrite break}} if er! = nil {if er! = io. EOF {err = er} break}//No errors soon use callback fb (Fsize, written)} return err }