net/http: ServeContent should support dynamic files/Chunked transfer

[themihai]

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 .

[bradfitz]

We support Chunked encoding already.

ServeContent assumes the file is not actively growing.

If it's actively growing, just set the headers and stream the content to the ResponseWriter. It works.

For questions about Go, see https://golang.org/wiki/Questions.