SID-01935: mod_perl sometimes returns - did not send an HTTP header

Status:	Asked	TWiki version:	6.0.0	Perl version:	5.10
Category:	CategoryAPI	Server OS:	RHEL6	Last update:	10 years ago

With mod_perl enabled for view and viewauth we see big improvement in the time to load a page. However sometimes the page returns just the page source and the apache error log shows messages like:

[warn] /twiki/bin/viewauth/TWiki/TWikiVariables did not send an HTTP header [error] malformed header from script. Bad header=i/TWikiVariables: viewauth

This is reproducable on pages that use the SEARCH variable and the TWikiVariables page always fails.

Anyone had similar experiences?

What is the solution?

Thanks in advance Pete

-- Peter Jones - 2014-06-18

Discussion and Answer

I have no TWiki site running under mod_perl so I do not know. FYI, Hideyo-san likes to run TWiki under Fast CGI, and he runs a very large TWiki.

-- Peter Thoeny - 2014-06-18

Pure guess: Maybe the content length is not correct on the pages that fail? Docs: http://perl.apache.org/docs/general/correct_headers/correct_headers.html

-- Peter Thoeny - 2014-06-18

Maybe this helps in debugging: http://www.rexswain.com/httpview.html

-- Peter Thoeny - 2014-06-18

I am running TWiki 6.0.0 under mod_perl, but no such problem so far. The symptoms suggest that "something" spits out some text, maybe a warning or an error message, before the headers (in particular the Content-Type) are built. So, the first line(s) of the output might contain a hint what's going wrong.

Things I'd investigate in such a situation are:

• The mod_perl startup script. "Harmless" warnings in that script may become fatal later.
• The grep related settings in /bin/configure. SEARCH greps explicitly, and TWikiVariables greps under the hood.

-- Harald Jörg - 2014-06-28

mod_perl sometimes does this if the code sending the headers is not a separate print statement from the code that sends the body.

eg:

works:-

print $headers; print $body;

fails:-

print $headers . $body;

Some apache magic takes place intercepting the "print" stuff to figure out headers, which gets confused if it's all coming at once...

-- TWiki Guest - 2014-08-25

That is interesting info. Can you provide a source for this?

-- Peter Thoeny - 2014-08-25

No, that's not "Apache magic" or anything like that... It's called "bad programming", and happened to me too. If you put them separated in the code, there's a probability that you're sending one part to the browser and not the other, what generates this error.

-- TWiki Guest - 2015-11-14

Thanks for the feedback TWikiGuest.

On another note, you can help the community with a patch, or even with pointers to more details.

-- Peter Thoeny - 2015-11-14

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