What version of Go are you using (go version)?

go version go1.8 darwin/amd64

What did you do?

I've tried to transcode and serve/stream a video file in the same time. Below is some pseudo code.

      go func(){
            // convert the video file in a format supported by the browser
            transcode(fromFilePath, toFilePath)
      ()
        // serve the content while transcoding takes place. 
        f, _ := os.OpenFile(toFilePath, os.O_RDONLY, 0666)
	http.ServeContent(w, r, toFilePath, time.Now(), f)

What did you expect to see?

Serve the file in chunks as the file grows/is transcoded.

What did you see instead?

ServeContent writes several headers such Content-Length even we don't know the length of the file when transcoding is complete and serves/writes only the content already transcoded at the time the request is made is served.

The solution could be to use Chunked transfer encoding .