Fix time_bound_deferred to throw the right exception

Due to a failure to instantiate DeferredTimedOutError, time_bound_deferred
would throw a CancelledError when the deferred timed out, which was rather
confusing.

synapse/util/__init__.py

@@ -26,7 +26,7 @@ logger = logging.getLogger(__name__)
 
 class DeferredTimedOutError(SynapseError):
     def __init__(self):
-        super(SynapseError).__init__(504, "Timed out")
+        super(SynapseError, self).__init__(504, "Timed out")
 
 
 def unwrapFirstError(failure):
@@ -93,8 +93,10 @@ class Clock(object):
         ret_deferred = defer.Deferred()
 
         def timed_out_fn():
+            e = DeferredTimedOutError()
+
             try:
-                ret_deferred.errback(DeferredTimedOutError())
+                ret_deferred.errback(e)
             except:
                 pass
 
@@ -114,7 +116,7 @@ class Clock(object):
 
         ret_deferred.addBoth(cancel)
 
-        def sucess(res):
+        def success(res):
             try:
                 ret_deferred.callback(res)
             except:
@@ -128,7 +130,7 @@ class Clock(object):
             except:
                 pass
 
-        given_deferred.addCallbacks(callback=sucess, errback=err)
+        given_deferred.addCallbacks(callback=success, errback=err)
 
         timer = self.call_later(time_out, timed_out_fn)
 

tests/util/test_clock.py

@@ -0,0 +1,33 @@
+# -*- coding: utf-8 -*-
+# Copyright 2017 Vector Creations Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from synapse import util
+from twisted.internet import defer
+from tests import unittest
+
+
+class ClockTestCase(unittest.TestCase):
+    @defer.inlineCallbacks
+    def test_time_bound_deferred(self):
+        # just a deferred which never resolves
+        slow_deferred = defer.Deferred()
+
+        clock = util.Clock()
+        time_bound = clock.time_bound_deferred(slow_deferred, 0.001)
+
+        try:
+            yield time_bound
+            self.fail("Expected timedout error, but got nothing")
+        except util.DeferredTimedOutError:
+            pass