Golang:multiple Http.writeheader Calls

Background: Golang HTTP service, read files, provided to the client when downloading. Multiple Http.writeheader calls error occurred.

Func DownloadFile (w http. Responsewriter, R *http. Request, Sequence UInt64, UserIDstring) {userkey:=userid FileName:= R.formvalue ("filename")    ifLen (UserKey) <=0|| Len (filename) <=0 {        //........} fp:= Fmt. Sprintf ("%s%s/%s", G_sc. RootDir, userkey, filename) fd, err:=OS. Open (FP)ifErr = =Nil {defer FD. Close () buf, err:=Ioutil. ReadAll (FD)ifErr! =Nil {//.........}Else{size:=Len (BUF) W.header (). ADD ("Content-length"Fmt. Sprintf ("%d", size)) Fmt. Fprint (W,string(BUF))} }}

The problem occurs in these lines of code:

Size: = Len (BUF)
W.header (). ADD ("Content-length", FMT. Sprintf ("%d", size))
Fmt. Fprint (W, String (BUF))

The following modifications can be made:

 buf: = new   (bytes. Buffer) buf. Write (...)  if   err { //   HTTP. Error (W, err. String, http. Statusinternalservererror)  return  }  if  err: = buf. WriteTo (w); Err!= nil {log. Printf (  writeto:%v   " , err)  //  You can not use HTTP. Error here anymore. So just log the message (e.g. "broken pipe ...") } 

or comment the two lines of codeSize: = Len (BUF)
W.header (). ADD ("Content-length", FMT. Sprintf ("%d", size))
Fmt. Fprint (W, String (BUF))

Golang:multiple Http.writeheader Calls