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From Greg Ames <>
Subject Re: input filter which modifies body, Content-Length
Date Fri, 24 Feb 2006 16:22:29 GMT
Jeff Trawick wrote:

> It isn't clear to me what an input filter should do about
> Content-Length when it modifies the length of the body  (assuming that
> this isn't chunked encoding).

> mod_cgi uses brigades to read the body but needs to look at
> Content-Length before spawning the CGI script, so that's problematic. 
> And there is an unexpected ordering requirement so that the input
> filter can signal to this handler that the content-length can't be
> trusted, before mod_cgi spawns the child.

so is this the current ordering?

1. mod_cgi[d] handler is dispatched
2. C-L environment variable is set for the script from the initial C-L header
3. CGI child is spawned.
4. mod_cgi[d] reads the body from input filters
5. foo_input_filter changes the body, invalidating the C-L env var + whatever local 
variables the script is using to track the length
6. CGI reads from stdin into buffer of length ?

> A filter which spools up to a configured amount of request body in
> order to calculate content-length could be of some practical benefit,
> since many request bodies are relatively small and this could
> potentially allow mod_cgi[d] to properly handle chunked request
> bodies, regardless of input filtering.  With such a filter installed,
> and no need to spool beyond a configured limit, getting a brigade
> would return bucket(s) with known length and an EOS at the end. 
> Unknown lengths or EOS?  Better punt if you're mod_cgi[d].

per offline discussions,

* the CGI spec (fwiw) is oblivious to chunking
* 1.3 and pre-filtering 2.0 used to fail CGI requests with chunked bodies.  getting them 
to work properly in common cases (i.e. < 8K bodies ) would be a step forward.
* this is analogous to proxy trying to avoid chunking to the origin server, except the 
spec is weaker for CGIs

a decent solution for CGI request body chunking would also solve some cases of input 
filters modifying the length.


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