[Moin-user] Odd bug related to If-Modified-Since using moin 1.5.4 with CGI on apache

Eamon Nerbonne eamon at nerbonne.org
Tue Jul 18 07:46:43 EDT 2006

There doesn't seem to be a stack trace generated.  errors caused by faulty
skins or similar generate stack traces (Therefore I don't think I've turned
them off); but this error does not.  The apache error log doesn't contain
anything other than 500 Internal server error either (yes, it's odd and not
informative).   Instead of the usual colored box informing you of the error,
this generates a Bland white page with a standard Apache 500 error.

I have however narrowed the cause of the error:

The affected moin instances aren't returning Cache-control:no-cache,
Pragma:no-cache and Expires:-1.

Adding 'Cache-Control: must-revalidate' fixes that.

Also, it seems newer moinmoin instances are now returning Last-Modified,
which they previously didn't, this would mask any bug regarding
If-Modified-Since: that would never even be sent.

In summary:
- it chokes on If-Modified-Since
- a python stack trace doesn't seem to be generated (but is generated on
other faults)
- some caching related headers seem to missing from the response
- I can't find another moinmoin wiki on the web suffering from the same
problem, so it's probably(?) local - then again I can't find that many
moinmoin 1.5.4's ;-)
-it might be a config error, however to my knowledge with the exception of
the .htaccess hacks I use to fix up the situation nothing caching-wise, or
header-wise for that matter is different from the default.
-it might be a moinmoin bug, but then almost certainly CGI only; as there
are quite a few non-CGI wikis online and none of them seem to be affected
(but almost all of those I tested do obviously custom things with headers).
It would make sense for header errors to be different on different platforms
as it doesn't surprise me that a CGI served wiki deals with those
differently than a twisted or standalone or mod_python or whatnot server
version would.

If none of this rings any bells I'll just wait until 1.6 and investigate
more thoroughly then.


On 7/17/06, Thomas Waldmann < tw-public at gmx.de> wrote:
> > On my machine, any request to moinmoin containing the HTTP header
> > If-Modified-Since results in an Internal Server Error without python
> > stacktrace.
> We need the html of that stacktrace as attachment: backtrace.html in a
> bug report on the moinmoin wiki.
> Please also copy this text there and add the requested details. Just
> subscribe to the page so you get notified when someone
> >   Generally, this header is generated when you refresh the page,
> > or when you return to a previously generated page.  All instances on
> this
> > machine using the system-wide moinmoin installation (gentoo) exhibit
> this
> > error, and a few initial moinmoin-playground I set up in a
> self-contained
> > directory (which hasn't been updated to 1.5.4), don't.  Moin is
> > running as a
> > CGI script in user directories and served by apache 2.0.58. Stripping
> the
> > header with an .htaccess command "RequestHeader unset If-Modified-Since"
> > resolves the problem, but not in the way I'ld like to...  The error
> > occurs
> > with multiple skins, and I can't seem to find the real cause (though,
> > beyond
> > a little python hacking to make quick macro, I've never used python,
> > so I'm
> > not an expert in this).  Does this error seem familiar to anyone, and is
> > there a real solution?
> I recently fixed some header related problems in 1.6 development branch.
> But it was rather about missing headers than about stuff causing
> backtraces.
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eamon at nerbonne.org - 06-15142163
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