`request.body` blocks when there is no POST body

[ryanpetrello]

I have a very simple WSGI application. When the request has no POST body, request.body blocks:

from wsgiref.simple_server import make_server
from webob import Request, Response


class MyApp(object):

    def __call__(self, environ, start_response):
        request = Request(environ)
        response = Response()
        print request.body # blocks here
        response.body = 'Hello, World!'
        return response(environ, start_response)

httpd = make_server('localhost', 8080, MyApp())
try:
    httpd.serve_forever()
except KeyboardInterrupt:
    print '^C'

Making a request via curl:

curl -X POST http://localhost:8080/

[alfredodeza]

This is something I've hit and is terrible to deal with, as in, there is no workaround.

As soon as you attempt to inspect the request object you block for ever.

Is there any information I could provide to allow this to be fixed?

[mcdonc]

Short of pdb-stepping through it and seeing why it's blocking, you mean?

[alfredodeza]

I have stepped through, but as soon as I even attempt to try to get that attribute it completely halts.

Unless you are referring to actually step through in WebOb, which I did not attempt :(

[mcdonc]

Yeah, that's what someone will have to do eventually.

[alfredodeza]

I have some findings, hopefully this info might make it a bit clear.

The part of webob that hangs is in webob/request.py in the BaseRequest class on the copy_body method.

The method does a few checks on the body (is it readable?, is the content_length None?, etc...) and on the check for content_length being None, it assumes the body is chunked or FakeCGIBody (described in a comment).

Then it goes to read the body file with this call:

self.body = self.body_file.raw.read()

That is exactly where it hangs. Stepping through that takes me to webob/descriptors.py to the environ_getter function that gets the wsgi.input key from the environ. When that returns it goes to the socket module to execute the read() call.

The read() call blocks when it gets to this section:

> /System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/socket.py(350)read()
     349             while True:
 --> 350                 try:
     351                     data = self._sock.recv(rbufsize)

rbufsize in this case is 8192.

I am not sure how to attempt to fix this, but I hope that walk through the process might make sense to someone more familiar with how the request should be handled by webob.

[ryanpetrello]

This seems like a potential denial of service. Has any progress been made on this?

[RishiRamraj]

That's a problem with the wsgiref server, which you shouldn't use in production. Here's a non-blocking Python 3 example that works with uwsgi:

from webob import Request

def application(environ, start_response):
    # Read the request.
    request = Request(environ)
    print(request.body)
    print(len(request.body))

    # Send the response.
    start_response('200 OK', [('Content-Type','text/html')])
    return [b'Hello World']

Run uwsgi using:

uwsgi --http :8080 --wsgi-file app.py

Issue the same curl request:

curl -X POST http://localhost:8080/

You should get the following from uwsgi on stdout:

b''
0

And the following from curl:

Hello World

[ryanpetrello]

Yep, you're right. Thanks!

[RishiRamraj]

Be sure to report the bug to:
http://bugs.python.org/

There may be others struggling with this problem, particularly if they use wsgiref for testing.