Exception when trying to run Flask app via CGIHandler

[homeworkprod]

I have a very simple app. It runs fine when the module (itself calling app.run()) is run.

However, when I try to run the app via CGI on Apache 2 using this .cgi script:

#!/usr/bin/env python

from wsgiref.handlers import CGIHandler
from someapp import app

CGIHandler().run(app)

it results in an exception:

Traceback (most recent call last):
  File "/usr/lib/python2.7/wsgiref/handlers.py", line 85, in run
    self.result = application(self.environ, self.start_response)
  File "/home/user/projects/SomeProject/venv/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/user/projects/SomeProject/venv/lib/python2.7/site-packages/flask/app.py", line 1812, in wsgi_app
    ctx = self.request_context(environ)
  File "/home/user/projects/SomeProject/venv/lib/python2.7/site-packages/flask/app.py", line 1773, in request_context
    return RequestContext(self, environ)
  File "/home/user/projects/SomeProject/venv/lib/python2.7/site-packages/flask/ctx.py", line 247, in __init__
    self.match_request()
  File "/home/user/projects/SomeProject/venv/lib/python2.7/site-packages/flask/ctx.py", line 286, in match_request
    self.url_adapter.match(return_rule=True)
  File "/home/user/projects/SomeProject/venv/lib/python2.7/site-packages/werkzeug/routing.py", line 1386, in match
    self.subdomain, path_info.lstrip('/'))
AttributeError: 'NoneType' object has no attribute 'lstrip'

The setup is Flask 0.10.1 with Werkzeug 0.9.4.

On first sight, the WSGI environment variables seem to be incomplete, or something like that.

[pradloff]

I too am seeing this, I'm trying to track down what is causing the problem. Here is some information I've managed to get. My .htaccess appears below and is followed by server information and the traceback. The recommended routing in the flask documentation returned 500, this was what I found to work. I'm keeping open the possibility of a server configuration problem as well. I've removed what I feel to be personal information including my username, server name, server address, and admin email.

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /USERNAME/cgi-bin/run3.cgi [L,QSA]

Error in application running
An error occured here are some diagnostics:
wsgi.multiprocess: True
REDIRECT_STATUS: 200
SERVER_SOFTWARE: Apache/2.2.15 (Red Hat) DAV/2
SCRIPT_NAME: /~USERNAME/cgi-bin/run3.cgi
SERVER_SIGNATURE:

Apache/2.2.15 (Red Hat) DAV/2 Server at SERVERNAME Port 80

REQUEST_METHOD: GET
REDIRECT_URL: /~USERNAME/hello
SERVER_PROTOCOL: HTTP/1.1
QUERY_STRING:
PATH: /usr/local/bin:/usr/bin:/bin
HTTP_USER_AGENT: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/29.0.1547.76 Safari/537.36
HTTP_CONNECTION: keep-alive
SERVER_NAME: SERVER_NAME
REMOTE_PORT: 50347
wsgi.url_scheme: http
SERVER_PORT: 80
SERVER_ADDR: SERVER_ADDR
DOCUMENT_ROOT: /var/empty
SCRIPT_FILENAME: /home1/USERNAME/public_html/cgi-bin/run3.cgi
SERVER_ADMIN: SERVER_ADMIN
SCRIPT_URI: http://SERVERNAME/USERNAME/hello
wsgi.input: <open file '', mode 'r' at 0x7f33e6e420c0>
HTTP_HOST: SERVER_NAME
SCRIPT_URL: /USERNAME/hello
wsgi.multithread: False
HTTP_CACHE_CONTROL: max-age=0
REQUEST_URI: /USERNAME/hello
HTTP_ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
wsgi.version: (1, 0)
GATEWAY_INTERFACE: CGI/1.1
wsgi.run_once: True
wsgi.errors: <open file '', mode 'w' at 0x7f33e6e421e0>
REMOTE_ADDR: 128.223.131.46
HTTP_ACCEPT_LANGUAGE: en-US,en;q=0.8
wsgi.file_wrapper: wsgiref.util.FileWrapper
HTTP_ACCEPT_ENCODING: gzip,deflate,sdch

Exception occured:
File "run3.cgi", line 22, in run
cgihandler.result = application(cgihandler.environ, cgihandler.start_response)
File "/home1/USERNAME/.local/lib/python2.6/site-packages/Flask-0.10.1-py2.6.egg/flask/app.py", line 1836, in call
return self.wsgi_app(environ, start_response)
File "/home1/USERNAME/.local/lib/python2.6/site-packages/Flask-0.10.1-py2.6.egg/flask/app.py", line 1812, in wsgi_app
ctx = self.request_context(environ)
File "/home1/USERNAME/.local/lib/python2.6/site-packages/Flask-0.10.1-py2.6.egg/flask/app.py", line 1773, in request_context
return RequestContext(self, environ)
File "/home1/USERNAME/.local/lib/python2.6/site-packages/Flask-0.10.1-py2.6.egg/flask/ctx.py", line 247, in init
self.match_request()
File "/home1/USERNAME/.local/lib/python2.6/site-packages/Flask-0.10.1-py2.6.egg/flask/ctx.py", line 286, in match_request
self.url_adapter.match(return_rule=True)
File "/home1/USERNAME/.local/lib/python2.6/site-packages/Werkzeug-0.9.4-py2.6.egg/werkzeug/routing.py", line 1386, in match
self.subdomain, path_info.lstrip('/'))

AttributeError: 'NoneType' object has no attribute 'lstrip'

[pradloff]

Well, I've played around some more and seem to have got a working configuration.

My .htaccess file looks like:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f                                   
RewriteRule ^(.*)$ /USERNAME/cgi-bin/run3.cgi/$1 [L]

This is the same as the flask recommendation http://flask.pocoo.org/docs/deploying/cgi/, except I've removed the comment on the second line. I'm not sure if that was the intention of the documentation to have an actual comment in the .htaccess file. It appears the sketchy workaround I found was causing the actual problem with flask.

I cannot tell you if the initiator of this bug followed a similar path to cause the bug.

Cheers,

prad

[ThiefMaster]

(You know that using CGI is a bad idea, right?)

[pradloff]

I'm aware that it is very limited, but it is the only option on the server we are provided.

[homeworkprod]

pradloff: I'll fiddle around with my Apache config and see what happens. But I definitely had no line in it with a trailing line comment.

ThiefMaster: I disagree. It's often the only way to run Python on common PHP/MySQL-class hostings, and it's a good choice for self-hosting many tiny, seldomly accessed apps for which one doesn't want to have processes lurking around and supervisors to be configured.
If you want to discuss this further, I'm happy to do that on IRC; let's get back to the topic here.

[homeworkprod]

OK, just a bit more background: I wrote a bunch of CGI scripts and want to make them WSGI-compatible so they can be served "in a modern fashion". But not being able to actually run the new versions with CGI (via WSGI) would keep the existing users that want/need CGI from updating.

In this state, i. e. ported to Flask, but unable to be run via GCI, I'm kept from releasing the new versions.

[untitaker]

Bug introduced in pallets/werkzeug@daad951#L0L1231

[johanneskoester]

If you add a trailing slash to the url, it works for me.
What about the pull request? Did it solve the issue, and why was it rejected?

Thanks a lot for your help,
Johannes

[untitaker]

No idea. I pinged @mitsuhiko about this in IRC.

[johanneskoester]

I tested it myself. It seems to be sufficient to use the first part of your pull request.

[untitaker]

Yes, the second part are just tests that fail unless the first part is applied.

[mitsuhiko]

This is a bug in the CGI handler. PATH_INFO must not be None.

[mitsuhiko]

To fix this use a middleware that fixes up the issue. See pallets/werkzeug#440