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Date: Tue, 05 Jun 2012 09:29:59 +0200
From: Sorin Manolache <sorinm@gmail.com>
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To: modules-dev@httpd.apache.org
Subject: Re: Protocol converter module
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On 2012-06-04 18:40, Robert Mitschke wrote:
> Hi everybody,
>
> I am attempting to write a module that implements a binary protocol that is
> not http and is not fully request and response based using apache. I have
> looked at mode echo and some others and I have Nick Kew's book.
>
> I want my module to convert incoming messages into http requests so that
> Apache is going to serve them using normal application server
> infrastructure. This is what I, based on the info I have can easily do
> using an input and output filter.
>
> What I also need the protocol to be able to do is to send messages to the
> client with no incoming data from the client. This may be based on a
> timeout or based on a request coming from somewhere else (a tier-2
> application server sending me a request on a totally different connection).
>
>> From what I have read so far, I could not find a hook that allows me to do
> so. The only way that I could figure out how to do that is to modify
> http_core.c and in ap_process_http_sync_connection query for either the
> timeout or the separate even to have occured using some shared memory
> technique. This however does not feel right to me. I would ideally like to
> keep using http_core as it is without touching it.
>
> Is there a way for me to wake up trigger the input filter chain even when
> there is no data on the actual connection? I could then create a request
> from the context of my persistent connection for a handler that I have
> written that triggers the output filter chain to send the correct message.
> Or even better is there a way I can trigger the output filter chain? Are
> there hooks for this purpose?
>
> I would very much appreciate a hint in the right direction.
>

Hello,

As your protocol is not http, I think that you should not execute 
ap_process_http_*_connection. ap_process_http_*_connection is a callback 
placed on the process_connection hook. I would suggest that you place 
your own protocol-specific callback on the process_connection hook. In 
your callback you get the socket descriptor and you perform "select" 
syscalls with timeout on the descriptor in a loop to get the timeout 
behaviour.

If you want to push data upon an incoming http request from a 
third-party, I think you cannot avoid the shared memory approach. The 
process that handles your http request has somehow to communicate with 
the process in which you handle the non-http connection to your client.

I've written something similar for SMPP and I remember I considered the 
filter implementation alternative but ultimately I did it without filters.

Sorin

> Best regards,
> Robert
>