[Twisted-Python] Implementing Postfix Inet Policy Check Client

[Tom Boland]

Greetings all.

This may be a very basic question.  I'm hoping to implement a postfix
policy check client in twisted.  It's a simple protocol.  You send
newline separated key value pairs like:

recipient=email at ddr.ess
sender=another at ddr.ess
size=1024
helo_name=mail.server
etc..

you terminate the request with an additional newline.  The response
comes back like

action=OK

You can send mutliple requests in the same connection.  What I'm
envisaging is a module that can be used to provide a deferred
request/response pairing to my calling application.  The module class
will manage the single connection to the postfix policy daemon (I'm
actually going to have persistent connections to a few daemons), and
reconnect when necessary etc.  Any requests will return a deferred that
I can add callbacks to.  How would you design this with twisted?  I can
easily envisage a way of using a clientfactory to instantiate separate
connections for each request/response, but actually being able to simply
send a request and receive the single response for that request is
something I'm struggling to do within a LineReceiver instance (for
instance).  Would the twisted.protocols.amp module help given that I
can't change the server-side protocol?

Any advice much appreciated!

Thanks.  Tom.