Flask/Werkzeug how to attach HTTP content-length header to file download

Question

I am using Flask (based on Werkzeug) which uses Python.

The user can download a file, I'm using the send_from_directory-function.

However when actually downloading the file, the HTTP header content-length is not set. So the user has no idea how big the file being downloaded is.

I can use os.path.getsize(FILE_LOCATION) in Python to get the file size (in bytes), but cannot find a way to set the content-length header in Flask.

Any ideas?

Answer 1

I believe you'd do something like this (untested):

from flask import Response
response = Response()
response.headers.add('content-length', str(os.path.getsize(FILE_LOCATION)))

See: Werkzug's Headers object and Flask's Response object.

Answer 2

Since version 0.6 the canonical way to add headers to a response object is via the make_response method (see Flask docs).

def index():
    response = make_response(render_template('index.html', foo=42))
    response.headers['X-Parachutes'] = 'parachutes are cool'
    return response

Answer 3

I needed this also, but for every requests, so here's what I did (based on the doc) :

@app.after_request
def after_request(response):
    response.headers.add('Access-Control-Allow-Origin', '*')
    return response