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From Graham Leggett <minf...@sharp.fm>
Subject Re: [PATCH] mod_proxy sessions
Date Mon, 01 Feb 2010 16:48:01 GMT
On 01 Feb 2010, at 6:09 PM, yle lists wrote:

> I'd like to submit a patch (against 2.2.14) that provides mod_proxy  
> sessions handling, that is, the ability to bind backend connections  
> (resources) to a session-id.
>
> When proxy sessions are enabled, the backend connections are  
> recycled in a per-session reslist.
> The worker uses a hashmap for the acquired sessions, and recycles  
> the released ones in a reslist.
>
> One can use the sessions to limit, per-client (provided the client  
> can be identified, by IP or cookie or whatever), the number of  
> connections to the backend, or to forward statefull over-http- 
> protocols.
>
> The session-id used for a particular request is given by the "proxy- 
> session-id" note (r->notes), so that the other modules (or a Rewrite/ 
> SetEnv rule) can set it to a client identifier.
>
> Another note ("proxy-session-client", true/false) can be used to  
> bind the session to the client connection (the connection-id is the  
> session-id), like mod_proxy 2.0.
> I use it to forward client NTLM connections, since the backend  
> connections will be per-client connection.
>
> For the sessions to be enabled, one can use the worker parameter  
> SessionsCache=on, and the SessionsCache(S)Max|Min parameters control  
> the sessions reslist.
> The Session(S)Max|Min parameters control the number of connections  
> per session.
>
> Finally, the patch also includes the functions apr_reslist_create_ex  
> and apr_reslist_clear which would allow one to clear a reslist with  
> a given clearor function.
> I also included comments in the patch regarding the destructor of  
> the proxy connection which, IMHO, is broken in httpd-2.2x.

Some comments based on a quick once over.

Many small patches are easier to review than one big patch. Small  
patches are likely to be accepted quickly, leaving time for issues  
with other patches to be resolved.

Changes to APR should be packaged separately and submitted to the APR  
project, httpd and APR split from each other some time ago, and httpd  
doesn't keep it's own private changes to APR. The extensions you  
propose to reslist look interesting, and are definitely worth picking  
up there.

The patch should be to trunk rather than httpd v2.2, as all changes  
must be made to the trunk first before being considered for backport  
to v2.2.

Your changes to ap_proxy_acquire_connection() and friends changes the  
ABI of the code, and as such cannot be backported as is to v2.2 as it  
stands.

Another potential issue is that this patch extends mod_proxy instead  
of adding a new module called mod_proxy_session. mod_proxy already  
contains too much non-abstracted code, and this makes it worse.  
Ideally, the bulk of the code should be in a module of its own.

I also don't fully see why the ABI of ap_proxy_acquire_connection()  
and friends was changed, can you clarify what you were trying to do?

Regards,
Graham
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