[Web-SIG] Internal redirect using Location with absolute path and status of 200.

Graham Dumpleton graham.dumpleton at gmail.com
Thu May 24 08:49:11 CEST 2007

On 24/05/07, Ian Bicking <ianb at colorstudy.com> wrote:
> Graham Dumpleton wrote:
> > Does anyone think this would be nice extension for a WSGI adapter
> > written against current specification to implement even if not
> > necessarily portable?
> Eh.  In the context of mod_wsgi, I think it would be more interesting to
> provide a WSGI application that called back into Apache (basically
> wrapping Apache's normal subrequest machinery in a WSGI exterior).

I was trying to avoid as much as possible having mod_wsgi provide any
sort of hooks which would allow one to perform actions against
internals of Apache. I had two reasons for this.

The first reason is that it would only be available when using
mod_wsgi and thus an application written to that interface would not
then be a portable WSGI application.

The second reason is that I can't provide that feature for both modes
that mod_wsgi operates in. The first mode I speak of here is
'embedded' mode, which is where everything runs in the Apache child
processes just like mod_python and thus has access to all the
redirection machinery. The second mode and one for which I wouldn't be
able to provide this feature for is 'daemon' mode, which is similar to
FASTCGI/SCGI solutions, where the WSGI request handling is done within
the context of a separate process. Although this daemon process is
forked from the main Apache process and managed by Apache, it is only
capable of handling the specific WSGI request handed off to it from
the Apache child process that received the request, it cant do
internal redirects or other complicated stuff involving internal
Apache APIs.

Because in 'daemon' mode an application can run as a distinct user and
not the Apache user, and because it moves the memory bloat of a WSGI
application out of the Apache child processes, this mode is likely to
be the preferred way of using mod_wsgi. If the feature weren't to be
available in this mode it is sort of questionable whether one should
provide it for 'embedded' mode. The 'Location' header based redirect I
can though do in both modes no problem, as the 'Location' header
redirect would be handled in Apache child process when handling
response from daemon process. It can only redirect to a GET request as
POST data would have already been consumed as necessary to send that
through to the daemon process in case it was required just like if it
was a CGI script.

In the longer term I am looking at doing an alternate Apache module
for using Python similar to mod_python which gives full Apache API
access using SWIG rather than hand crafted API like mod_python. This
Apache module may be a better vehicle for hosting WSGI application
where you want to hook into Apache internals. Thus, mod_wsgi might be
seen as average users solution and suitable (safe) for commodity web
hosting, whereas this other Apache module I speak of might be seen as
more for power users who dedicate Apache instance to the application.


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