[Twisted-Python] Implementing Postfix Inet Policy Check Client

[exvito here]

On Wed, Nov 18, 2015 at 9:28 AM, Tom Boland <tom at t0mb.net> wrote:

> I think what you've provided me with is useful for me, but I think it's
> backwards for my purposes, as I need to be connecting to the policy daemon
> rather than being the policy daemon!
>
> I wanted to do this with deferred calls in case one of the policy daemons
> becomes unreachable and blocks my application.  Do you think I should do
> something differently in that regard?  My SQL lookups are done
> synchronously.  If the database server goes away, I've got bigger problems
> anyway!
>

So maybe something like this is more likely to be useful:

#!/usr/bin/env python

from __future__ import print_function

from twisted.internet import reactor, protocol, endpoints, defer
from twisted.protocols import basic


class PostfixProtocol(basic.LineReceiver):

    # Assuming Postfix uses '\r\n' line breaks (does it?)
    delimiter = '\r\n'

    def __init__(self):
        self.action = None
        self.action_deferred = None

    def lineReceived(self, line):
        if '=' in line:
            self.action = line.split('=')[1]
        elif line == '':
            self.action_deferred.callback(self.action)
            self.action_deferred = None
        else:
            # oops, bad input
            pass

    def sendPostfixRequest(self, request_dict):
        if not self.action_deferred is None:
            raise Exception('transaction pending')
        for k, v in request_dict.items():
            self.sendLine('{}={}'.format(k,v))
        # Empty line signals we're done
        self.sendLine('')
        self.action_deferred = defer.Deferred()
        return self.action_deferred

@defer.inlineCallbacks
def checkPostfixPolicy(request_dict):
    ep = endpoints.clientFromString(reactor, 'tcp:host=127.0.0.1:
port=10000')
    p = yield endpoints.connectProtocol(ep, PostfixProtocol())
    action = yield p.sendPostfixRequest(request_dict)
    print('got: {}'.format(action))
    reactor.stop()


if __name__ == '__main__':

    request_dict = {
        'recipient': 'email at ddr.ess',
        'sender': 'email at ddr.ess',
    }
    reactor.callWhenRunning(checkPostfixPolicy, request_dict)
    reactor.run()

Highlights:
- This is not the same protocol as before, in particular it uses a
different delimiter.
- It assumes the response is also terminated with an empty line (does it?).
- It more than one outstanding response: a different exception should be
used.
- The input processing is very rudimentary and failure-prone.
- checkPostfixPolicy could, of course, return instead of printing. :)

Cheers,
--
  exvito
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