[mod_python] Help with mod_python, mod_proxy & cookies

Marc Boorshtein wrote ..
> All,
> 
> I am trying to figure out a way to use mod python to change the Cookie
> header of a request and then pass the request off to mod_proxy.  When
> the response comes I wish to be able to adjust any Set-Cookie headers
> in the response back to the client.  I did something similar in
> mod_perl using filters and am assuming it would be a similar process.
> I wrote a quick input filter to trace the data going through the
> filter and found a few issues:
> 
> 1.  When I have a ProxyPass in my httpd config, apache doesn't fire my
> filter
> 2.  When I remove the ProxyPass rule my filter fires, but no data
> seems to be going through it
> 3.  When I specify AddInputFilter, is there anyway to have it apply
> globally (as opposed to for a particular file extension)?

Use SetInputFilter. This should be mentioned in Apache documentation
where AddInputFilter is described.

> Here's my code:
> 
> from mod_python import apache
> 
> def inputfilter(filter):
>     apache.log_error('in filter');
>     s = filter.read()
>     apache.log_error('begin data');
>     while s:
>         apache.log_error('data : ' + s);
>         filter.write(s.upper())
>         s = filter.read()
>     apache.log_error('end data');
> 
>     if s is None:
>         filter.close()
> 
> Here's my apache config:
> <VirtualHost *>
>   PythonDebug On
>   PythonPath "sys.path + ['/home/mlb/workspace/Python\ CookieFilter/src']"
>   PythonInputFilter CookieFilterInbound COOKIEINBOUND
>   AddInputFilter COOKIEINBOUND .html
>    ProxyPass / http://localhost:8080/
> </VirtualHost>
> 
> Here's my log:
> 
> [Wed Jan 24 16:28:25 2007] [notice] Apache/2.2.3 (Fedora) configured
> -- resuming normal operations
> [Wed Jan 24 16:28:28 2007] [notice] mod_python: (Re)importing module
> 'CookieFilterInbound'
> [Wed Jan 24 16:28:28 2007] [error] in filter
> [Wed Jan 24 16:28:28 2007] [error] begin data
> [Wed Jan 24 16:28:28 2007] [error] end data
> [Wed Jan 24 16:28:28 2007] [error] [client 127.0.0.1] File does not
> exist: /var/www/html/showcookie.html
> [Wed Jan 24 16:28:28 2007] [error] in filter
> [Wed Jan 24 16:28:28 2007] [error] begin data
> [Wed Jan 24 16:28:28 2007] [error] end data
> [Wed Jan 24 16:29:23 2007] [notice] caught SIGTERM, shutting down
> 
> Any help would be greatly appreciated.

I don't believe you need to use an input filter, you could instead use a
fixup handler to do everything, including enabling of the proxy itself.

 <VirtualHost *>
   PythonDebug On
   PythonPath "sys.path + ['/home/mlb/workspace/Python CookieFilter/src']"
   PythonFixupHandler myredirectandcookiefixup
 </VirtualHost>

For starters, below (myredirectandcookiefixup.py) is how you initiate proxying.

import posixpath

from mod_python import apache

def fixuphandler(req):

  if req.proxyreq:
    return apache.DECLINED

  normalised_uri = posixpath.normpath(req.uri)

  if normalised_uri:
    if normalised_uri != '/' and req.uri[-1] == '/':
      normalised_uri += '/'

  length = len(req.filename)
  length -= len(req.hlist.directory) - 1
  length += len(req.path_info or '')

  baseurl = normalised_uri[:-length]
  path = normalised_uri[len(baseurl):]

  req.proxyreq = apache.PROXYREQ_REVERSE
  req.uri = 'http://localhost:8080' + path
  req.filename = 'proxy:%s' % req.uri
  req.handler = 'proxy-server'

  return apache.OK

All you then need to do is incorporate into this some code which uses
req.headers_in to get to the cookie headers, strip them apart, change
them as needed and then reassign them back into req.headers_in.
When the "proxy-server" handler is run, it will take the headers from
req.headers_in and use them when passing data through to backend.

You will need to have mod_python 3.3.0b for this to work though.

For more on enabling proxying in this way, see:

  http://issues.apache.org/jira/browse/MODPYTHON-141

and the mailing list discussion linked to it.

Graham