pub-sub (i.e., fan-out) for Twisted Deferreds

DeferredTee.py

#-*-mode: python; encoding: utf-8; test-case-name: TestDeferredTee.TestDeferredTee-*-

#=========================================================================
"""
  Copyright (c) 2014 Matt Bogosian. <https://github.com/posita>.

  Permission is hereby granted, free of charge, to any person obtaining a
  copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
"""
#=========================================================================

from __future__ import (
    absolute_import,
    division,
    print_function,
    unicode_literals,
    with_statement,
)

#---- Imports ------------------------------------------------------------

from functools import partial
from twisted.internet.defer import Deferred
from twisted.python.failure import Failure

#---- Classes ------------------------------------------------------------

#=========================================================================
class DeferredTee(object, Deferred):
    """
    Implements a kind of publish-subscribe (fan-out) model in terms of
    Twisted Deferreds. This class behaves like a normal Deferred (which
    means it can participate in chains) with one addition: it also
    propagates calls to its callback, cancel, and errback methods to each
    callable added via one of the respective tee... methods.

    Exceptions raised from any tee'd callable are silently ignored. In
    other words, if you want to capture errors on a tee, create your own
    Deferred chain and add the parent via the teeDeferred method.
    """

    #---- Constructors ---------------------------------------------------

    #=====================================================================
    def __init__(self, canceller=None):
        object.__init__(self)
        Deferred.__init__(self, canceller)
        self._t_result = DeferredTee._SENTINEL
        self._t_cbs = []
        self._t_ebs = []

    #---- Public methods -------------------------------------------------

    #=====================================================================
    def teeBoth(self, callback, *args, **kw):
        return self.teeCallbacks(callback, callback, callbackArgs=args, callbackKeywords=kw, errbackArgs=args, errbackKeywords=kw)

    #=====================================================================
    def teeCallbacks(self, callback, errback=None, callbackArgs=(), callbackKeywords={}, errbackArgs=(), errbackKeywords={}): # pylint: disable=dangerous-default-value
        if callback is not None:
            cb = partial(callback, *callbackArgs, **callbackKeywords) # pylint: disable=star-args

            if not self.called:
                self._t_cbs.append(cb)
            elif not isinstance(self._t_result, Failure):
                try:
                    cb(self._t_result)
                except Exception: # pylint: disable=broad-except
                    # Ignore failures
                    pass

        if errback is not None:
            eb = partial(errback, *errbackArgs, **errbackKeywords) # pylint: disable=star-args

            if not self.called:
                self._t_ebs.append(eb)
            elif isinstance(self._t_result, Failure):
                try:
                    eb(self._t_result)
                except Exception: # pylint: disable=broad-except
                    # Ignore failures
                    pass

        return self

    #=====================================================================
    def teeCallback(self, callback, *args, **kw):
        return self.teeCallbacks(callback, None, callbackArgs=args, callbackKeywords=kw)

    #=====================================================================
    def teeDeferred(self, d):
        d._chainedTo = self # pylint: disable=protected-access

        return self.teeCallbacks(d.callback, d.errback)

    #=====================================================================
    def teeErrback(self, errback, *args, **kw):
        return self.teeCallbacks(None, errback, errbackArgs=args, errbackKeywords=kw)

    #---- Private hook methods -------------------------------------------

    #=====================================================================
    def _runCallbacks(self):
        if self._t_result is DeferredTee._SENTINEL:
            self._t_result = self.result
            self._runTeedUp()

        Deferred._runCallbacks(self)

    #---- Private methods ------------------------------------------------

    #=====================================================================
    def _runTeedUp(self):
        if isinstance(self._t_result, Failure):
            funcs = self._t_ebs
        else:
            funcs = self._t_cbs

        self._t_cbs = None
        self._t_cbs = None

        for func in funcs:
            try:
                func(self._t_result)
            except Exception: # pylint: disable=broad-except
                # Ignore failures
                pass

    #---- Private static constants ---------------------------------------

    _SENTINEL = type('_SENTINEL', ( object, ), {})

TestDeferredTee.py

#-*-mode: python; encoding: utf-8-*-

#=========================================================================
"""
  Copyright (c) 2014 Matt Bogosian. <https://github.com/posita>.

  Permission is hereby granted, free of charge, to any person obtaining a
  copy of this software and associated documentation files (the
  "Software"), to deal in the Software without restriction, including
  without limitation the rights to use, copy, modify, merge, publish,
  distribute, sublicense, and/or sell copies of the Software, and to
  permit persons to whom the Software is furnished to do so, subject to
  the following conditions:

  The above copyright notice and this permission notice shall be included
  in all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
  OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
"""
#=========================================================================

from __future__ import (
    absolute_import,
    division,
    print_function,
    unicode_literals,
    with_statement,
)

#---- Imports ------------------------------------------------------------

from functools import partial
from unittest import TestCase
from DeferredTee import DeferredTee

#---- Classes ------------------------------------------------------------

#=========================================================================
class TestDeferredTee(TestCase):

    #---- Public hook methods --------------------------------------------

    #=====================================================================
    def test_teeBoth(self):
        results = {}
        seta = partial(results.__setitem__, 'a')
        setb = partial(results.__setitem__, 'b')
        setc = partial(results.__setitem__, 'c')
        setd = partial(results.__setitem__, 'd')
        addbar = lambda x: x + 'bar'

        results.clear()
        d = DeferredTee()
        d.teeBoth(seta)
        d.teeBoth(setb)
        d.teeBoth(setc)
        d.addCallback(addbar)
        d.addCallback(setd)
        result = 'foo'
        d.callback(result)
        self.assertEqual(results, { 'a': result, 'b': result, 'c': result, 'd': result + 'bar' })

        results.clear()
        d = DeferredTee()
        d.teeBoth(seta)
        d.teeBoth(setb)
        d.teeBoth(setc)
        d.addCallback(addbar)
        d.addCallback(setd)
        result = ValueError('foo')
        d.errback(result)
        self.assertEqual(result, results['a'].value)
        self.assertEqual(result, results['b'].value)
        self.assertEqual(result, results['c'].value)
        self.assertEqual([ 'a', 'b', 'c' ], sorted(results.keys()))

    #=====================================================================
    def test_teeCallbackErrback(self):
        results = {}
        seta = partial(results.__setitem__, 'a')
        setb = partial(results.__setitem__, 'b')
        setc = partial(results.__setitem__, 'c')
        setd = partial(results.__setitem__, 'd')
        sete = partial(results.__setitem__, 'e')
        setf = partial(results.__setitem__, 'f')
        setg = partial(results.__setitem__, 'g')

        def raisesValueError(*a_args, **a_kwargs): # pylint: disable=unused-argument
            raise ValueError('baz')

        addbar = lambda x: str(x) + 'bar'

        results.clear()
        d = DeferredTee()
        d.teeCallback(seta)
        d.teeCallback(setb)
        d.teeCallback(raisesValueError)
        d.teeErrback(setd)
        d.teeErrback(sete)
        d.addCallback(addbar)
        result = 'foo'
        d.callback(result)
        self.assertEqual(results, { 'a': result, 'b': result })
        d.teeCallback(setc)
        d.teeCallback(raisesValueError)
        d.teeErrback(setf)
        d.addCallback(setg)
        self.assertEqual(results, { 'a': result, 'b': result, 'c': result, 'g': result + 'bar' })

        results.clear()
        d = DeferredTee()
        d.teeCallback(seta)
        d.teeCallback(setb)
        d.teeErrback(setd)
        d.teeErrback(sete)
        d.teeErrback(raisesValueError)
        d.addCallback(addbar)
        d.addCallback(setg)
        result = ValueError('foo')
        d.errback(result)
        self.assertEqual(result, results['d'].value)
        self.assertEqual(result, results['e'].value)
        self.assertEqual([ 'd', 'e' ], sorted(results.keys()))
        d.teeCallback(setc)
        d.teeCallback(raisesValueError)
        d.teeErrback(setf)
        self.assertEqual(result, results['d'].value)
        self.assertEqual(result, results['e'].value)
        self.assertEqual(result, results['f'].value)
        self.assertEqual([ 'd', 'e', 'f' ], sorted(results.keys()))