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From Gary Benson <>
Subject Re: Wierd problem with apache/post test
Date Fri, 16 Nov 2001 22:30:23 GMT

On Fri, 16 Nov 2001, Cliff Woolley wrote:

> On Fri, 16 Nov 2001, Gary Benson wrote:
> > Anyone have any objections to my rewriting mod_echo_post to dump
> > everything to a temporary file and then read it back?
> I wish I understood exactly why this was happening... it seems almost
> indicative of some problem in Apache or APR.  The module shouldn't have to
> buffer all this stuff... it should be able to do a read from the input
> filter chain, process it, and send some output down the output filter
> chain, and that ought to be it.  Buffering the whole thing either in RAM
> or on disk in a production environment would open a huge DoS hole.

The problem isn't in Apache: what is happening is that the way mod_echo_post
works is exposing a weakness in the client code, in this case libwwwperl.
The clients should really read and write simultaneously, but this isn't
normally a problem since what happens with the vast majority of requests
is that the handler reads the request in its entirity, chews it over a bit
and then returns something. This behaviour doesn't saturate the buffers.

Of course, I say it is the clients' fault, but perhaps it is the OS: the
problem seems to affect only some OSes and not others -- perhaps these
OSes have fixed size socket buffers? A 100k mod_echo_post request is
enough to cause problems and none of the machines we use are _that_ short
on memory ;)


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