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Re: [PATCH] add FAQ section about "bad request" errors

From: Pavel Lyalyakin <pavel.lyalyakin_at_visualsvn.com>
Date: Mon, 23 May 2016 19:58:47 +0300

Hello,

On Fri, May 20, 2016 at 10:50 PM, Stefan <luke1410_at_posteo.de> wrote:
>
> On 5/15/2016 02:00, Stefan wrote:
> > Hi,
> >
> >
> > following patch adds a new entry to the FAQ's trouble shooting
> > section, documenting the known problem with large headers, exceeding
> > Apache httpd's LimitRequestFieldSize setting.
> >
> > [[[
> > Document known issue about long header sections causing problems with
> > Apache httpd.
> >
> > * docs/faq.html
> > (Table of Contents): add link to new http-400 section
> > (http-400): new trouble shooting section about http-400-error
> > ]]]
> Anybody feels like approving the change? Or is there anything I should
> improve in the patch before committing it?

This error can have different causes and that's why you should not put
an emphasis on some of them, while omitting other causes. And I don't
think that the entry on troubleshooting 400 'Bad Request' errors fits
FAQ format. There can be too many answers to the question "How can I
resolve it?". This error does not give enough information to provide a
reader with instructions on how to resolve it.

I mean that it is possible to get 400 'Bad request' error in numerous
other cases and pointing out just some of them on the FAQ page is not
the best idea. IMO, such FAQ entry can distract a reader from
identifying the real root cause of the problem. Just to name a couple
of additional examples when you can get 400 'Bad request' error:

* Unlocking a file with a stolen lock will result in 400 'Bad request'
  error. This problem is described in SVN-4372[1].

* Authenticating to the server using Negotiate/Kerberos when the
  particular user who's accessing the repository is a member of too
  many groups or has enormous SID history will result in 400
  'Bad request' error. This problem is described in the article
  "HTTP status 400 Bad Request error when a user connects to VisualSVN
  Server"[2].

And don't forget that an antivirus, active firewall or proxy server
can be the root cause as well[3].

BTW, the request field size limit should usually be between 8-16KB and
configuring it to be less can lead to getting 400 'Bad Headers' errors
too. On the other hand, configuring it to be larger than 16KB can be
bad from security and performance point of view. Therefore, you should
avoid telling the reader to change the limit without considering his
particular case.

That said, I think that this FAQ entry will confuse the reader rather
than help him to identify the root cause and resolve it. It'd be
better to mention that the problem can have a lot of various causes
and the reader has to check the server logs for clues. As always, it
makes sense to recommend using the latest Subversion version and
advise searching the Apache Subversion bug tracker for "Bad request"
errors. Checking antivirus, firewall and proxy is also recommended. If
nothing of this helped, contact users@ Subversion for help.

But these basic recommendations can be applied to the troubleshooting
of practically any generic error. That's why I don't think that 400
'Bad Request' needs a special entry in the FAQ.

[1]: https://issues.apache.org/jira/browse/SVN-4372
[2]: https://www.visualsvn.com/support/topic/00098/
[3]: https://mail-archives.apache.org/mod_mbox/subversion-users/201108.mbox/%3CCALb=wn=wuWkR392eyoLP0F5E8b-k2vnE1bTU5LGVtUOEGoD8Og@mail.gmail.com%3E

--
With best regards,
Pavel Lyalyakin
VisualSVN Team
Received on 2016-05-23 18:59:34 CEST

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