XMLHttpRequest 206 Partial Content

Question

I would like to issue a partial content request from an XMLHttpRequest object in javascript. I'm loading a large binary file from the server, and I'd rather stream it from the server similar to how html5 video is handled.

I can use setRequestHeader to set the Range header. The Network inspector in Chrome shows that the Range header is set successfully. However, the Accept-Encoding header is set to "gzip,deflate", and Chrome will not let me set that header (from W3C standards).

Is there any way to force the server to respond with a 206 partial content from the XMLHttpRequest object only from javascript?

Answer 1

This range-request works fine for me: http://jsfiddle.net/QFdU4/

var xhr = new XMLHttpRequest;

xhr.onreadystatechange = function () {
  if (xhr.readyState != 4) {
    return;
  }
  alert(xhr.status);
};

xhr.open('GET', 'http://fiddle.jshell.net/img/logo.png', true);
xhr.setRequestHeader('Range', 'bytes=100-200'); // the bytes (incl.) you request
xhr.send(null);

You have to make sure that the server allows range requests, though. You can test it with curl:

$ curl -v -r 100-200 http://example.com/movie.mkv > /dev/null

Answer 2

I think I figured out why the 206 request wasn't working. With gzip compression enabled, the range header gets ignored if the outgoing data can be gzipped.

The file I was requesting was a large binary file, which nginx interpreted as having mimetype application/octet-stream. This is one of the mimetypes that gets gzipped. If I renamed the file to have a .png filetype, the image/png mimetype is not gzipped, and hence the range request works correctly.

This is also why setting the Accept-Encoding header with curl to identity also allows the range request to work fine. However, I cannot change that header from an XHR.

Solution: Change the mimetype table on the server!