Cancel on timeout

timeout.py

from twisted.internet import defer, reactor
from twisted.python import log
from twisted.trial.unittest import TestCase

def foo(timeout):
    """
    Actual code returning deferred than cancels its DelayedCalls.
    """
    def canceller(d):
        dc.cancel()

    d = defer.Deferred(canceller)
    dc = reactor.callLater(timeout, d.callback, None)
    return d

def timeouter(result, d):
    """
    Trap timeout to cancel given deferred.
    """
    result.trap(defer.TimeoutError)
    d.cancel()
    return result

def chainIgnoreCancel(d, d2):
    """
    Chain d to d2, ignoring d being cancelled.
    """
    def cb(result):
        d2.callback(result)

    def eb(result):
        if not result.check(defer.CancelledError):
            d2.errback(result)

    d.addCallbacks(cb, eb)


class Tests(TestCase):
    timeout = 2

    def tearDown(self):
        log.msg("hi")

    def test_timeout(self):
        d = defer.Deferred()
        dReal = foo(self.timeout + 1)
        d.addErrback(timeouter, dReal)
        chainIgnoreCancel(dReal, d)
        return d