[Web-SIG] Most WSGI servers close connections to early.

Marcel Hellkamp marc at gsites.de
Wed Sep 22 14:46:57 CEST 2010

I just discovered a problem that affects most WSGI server
implementations and most current web-browsers (tested with wsgiref,
paste, firefox, chrome, wget and curl):

If the server closes the connection while the client is still uploading
data via POST or PUT, the browser displays an error message ('Connection
closed') and does not display the response sent by the server.

The error occurs if an application chooses to not process a form
submissions before returning to the WSGI server. This is quite rare in
real world scenarios, but hard to debug because the server logs the
request as successfully sent to the client.

To reproduce the problem, run the following script, visit
http://localhost:8080/ and upload a big file::

from wsgiref.simple_server import make_server

def application(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/html')])
    return ["""
    <form method='post' enctype='multipart/form-data'>
      Upload bog file:
      <input type='file' name='file' />
      <input type='submit' />

server = make_server('localhost', 8080, application)

I would like to add a warning to the WSGI/web3 specification to address
this issue:

"An application should read all available data from
`environ['wsgi.input']` on POST or PUT requests, even if it does not
process that data. Otherwise, the client might fail to complete the
request and not display the response."

Mit freundlichen Grüßen
Marcel Hellkamp

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