HTTP 206 (Partial Content) For Flask/Python

Serving media files with HTTP 200 seems to make browsers act a bit strangely. Chrome refuses to fire onended events, and neither Chrome nor Firefox seems happy seeking through them. I am Not entirely sure for the reasons for this; I guess that they try to play the media before receiving all of it and can't guarantee they'll have downloaded the right chunk for seeking, while having no way of requesting it specifically. Who knows.

Here's a simple replacement to Flask's send_file that supports 206 partial content via byte ranges (and a function that adds the appropriate headers to all responses). It doesn't fully wrap send_file, if you care about all the other arguments and mirroring the exact behaviour, it needs a bit more work, but should suffice for 99% of uses.

[update 31/8: sorry there was a bug in this which caused strange things with certain Chrome versions, it's now been fixed]

import mimetypes
import os
import re

from flask import request, send_file, Response

@app.after_request
def after_request(response):
    response.headers.add('Accept-Ranges', 'bytes')
    return response


def send_file_partial(path):
    """ 
        Simple wrapper around send_file which handles HTTP 206 Partial Content
        (byte ranges)
        TODO: handle all send_file args, mirror send_file's error handling
        (if it has any)
    """
    range_header = request.headers.get('Range', None)
    if not range_header: return send_file(path)
    
    size = os.path.getsize(path)    
    byte1, byte2 = 0, None
    
    m = re.search('(\d+)-(\d*)', range_header)
    g = m.groups()
    
    if g[0]: byte1 = int(g[0])
    if g[1]: byte2 = int(g[1])

    length = size - byte1
    if byte2 is not None:
        length = byte2 - byte1
    
    data = None
    with open(path, 'rb') as f:
        f.seek(byte1)
        data = f.read(length)

    rv = Response(data, 
        206,
        mimetype=mimetypes.guess_type(path)[0], 
        direct_passthrough=True)
    rv.headers.add('Content-Range', 'bytes {0}-{1}/{2}'.format(byte1, byte1 + length - 1, size))

    return rv