Merge pull request #2251 from nathanielmanistaatgoogle/links

links interface and gRPC-on-wire implementation

17 files changed, 2415 insertions, 0 deletions

diff --git a/src/python/src/grpc/_links/__init__.py b/src/python/src/grpc/_links/__init__.py
new file mode 100644
index 0000000000..7086519106
--- /dev/null
+++ b/src/python/src/grpc/_links/__init__.py
@@ -0,0 +1,30 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
diff --git a/src/python/src/grpc/_links/_lonely_invocation_link_test.py b/src/python/src/grpc/_links/_lonely_invocation_link_test.py
new file mode 100644
index 0000000000..3d629f4387
--- /dev/null
+++ b/src/python/src/grpc/_links/_lonely_invocation_link_test.py
@@ -0,0 +1,88 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""A test of invocation-side code unconnected to an RPC server."""
+
+import unittest
+
+from grpc._adapter import _intermediary_low
+from grpc._links import invocation
+from grpc.framework.common import test_constants
+from grpc.framework.interfaces.links import links
+from grpc.framework.interfaces.links import test_cases
+from grpc.framework.interfaces.links import test_utilities
+
+_NULL_BEHAVIOR = lambda unused_argument: None
+
+
+class LonelyInvocationLinkTest(unittest.TestCase):
+
+  def testUpAndDown(self):
+    channel = _intermediary_low.Channel('nonexistent:54321', None)
+    invocation_link = invocation.invocation_link(channel, 'nonexistent', {}, {})
+
+    invocation_link.start()
+    invocation_link.stop()
+
+  def _test_lonely_invocation_with_termination(self, termination):
+    test_operation_id = object()
+    test_group = 'test package.Test Service'
+    test_method = 'test method'
+    invocation_link_mate = test_utilities.RecordingLink()
+
+    channel = _intermediary_low.Channel('nonexistent:54321', None)
+    invocation_link = invocation.invocation_link(
+        channel, 'nonexistent', {(test_group, test_method): _NULL_BEHAVIOR},
+        {(test_group, test_method): _NULL_BEHAVIOR})
+    invocation_link.join_link(invocation_link_mate)
+    invocation_link.start()
+
+    ticket = links.Ticket(
+        test_operation_id, 0, test_group, test_method,
+        links.Ticket.Subscription.FULL, test_constants.SHORT_TIMEOUT, 1, None,
+        None, None, None, None, termination)
+    invocation_link.accept_ticket(ticket)
+    invocation_link_mate.block_until_tickets_satisfy(test_cases.terminated)
+
+    invocation_link.stop()
+
+    self.assertIsNot(
+        invocation_link_mate.tickets()[-1].termination,
+        links.Ticket.Termination.COMPLETION)
+
+  def testLonelyInvocationLinkWithCommencementTicket(self):
+    self._test_lonely_invocation_with_termination(None)
+
+  def testLonelyInvocationLinkWithEntireTicket(self):
+    self._test_lonely_invocation_with_termination(
+        links.Ticket.Termination.COMPLETION)
+
+
+if __name__ == '__main__':
+  unittest.main()
diff --git a/src/python/src/grpc/_links/_proto_scenarios.py b/src/python/src/grpc/_links/_proto_scenarios.py
new file mode 100644
index 0000000000..ccf3c29782
--- /dev/null
+++ b/src/python/src/grpc/_links/_proto_scenarios.py
@@ -0,0 +1,261 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Test scenarios using protocol buffers."""
+
+import abc
+import threading
+
+from grpc._junkdrawer import math_pb2
+
+
+class ProtoScenario(object):
+  """An RPC test scenario using protocol buffers."""
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod
+  def group_and_method(self):
+    """Access the test group and method.
+
+    Returns:
+      The test group and method as a pair.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def serialize_request(self, request):
+    """Serialize a request protocol buffer.
+
+    Args:
+      request: A request protocol buffer.
+
+    Returns:
+      The bytestring serialization of the given request protocol buffer.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def deserialize_request(self, request_bytestring):
+    """Deserialize a request protocol buffer.
+
+    Args:
+      request_bytestring: The bytestring serialization of a request protocol
+        buffer.
+
+    Returns:
+      The request protocol buffer deserialized from the given byte string.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def serialize_response(self, response):
+    """Serialize a response protocol buffer.
+
+    Args:
+      response: A response protocol buffer.
+
+    Returns:
+      The bytestring serialization of the given response protocol buffer.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def deserialize_response(self, response_bytestring):
+    """Deserialize a response protocol buffer.
+
+    Args:
+      response_bytestring: The bytestring serialization of a response protocol
+        buffer.
+
+    Returns:
+      The response protocol buffer deserialized from the given byte string.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def requests(self):
+    """Access the sequence of requests for this scenario.
+
+    Returns:
+      A sequence of request protocol buffers.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def response_for_request(self, request):
+    """Access the response for a particular request.
+
+    Args:
+      request: A request protocol buffer.
+
+    Returns:
+      The response protocol buffer appropriate for the given request.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def verify_requests(self, experimental_requests):
+    """Verify the requests transmitted through the system under test.
+
+    Args:
+      experimental_requests: The request protocol buffers transmitted through
+        the system under test.
+
+    Returns:
+      True if the requests satisfy this test scenario; False otherwise.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def verify_responses(self, experimental_responses):
+    """Verify the responses transmitted through the system under test.
+
+    Args:
+      experimental_responses: The response protocol buffers transmitted through
+        the system under test.
+
+    Returns:
+      True if the responses satisfy this test scenario; False otherwise.
+    """
+    raise NotImplementedError()
+
+
+class EmptyScenario(ProtoScenario):
+  """A scenario that transmits no protocol buffers in either direction."""
+
+  def group_and_method(self):
+    return 'math.Math', 'DivMany'
+
+  def serialize_request(self, request):
+    raise ValueError('This should not be necessary to call!')
+
+  def deserialize_request(self, request_bytestring):
+    raise ValueError('This should not be necessary to call!')
+
+  def serialize_response(self, response):
+    raise ValueError('This should not be necessary to call!')
+
+  def deserialize_response(self, response_bytestring):
+    raise ValueError('This should not be necessary to call!')
+
+  def requests(self):
+    return ()
+
+  def response_for_request(self, request):
+    raise ValueError('This should not be necessary to call!')
+
+  def verify_requests(self, experimental_requests):
+    return not experimental_requests
+
+  def verify_responses(self, experimental_responses):
+    return not experimental_responses
+
+
+class BidirectionallyUnaryScenario(ProtoScenario):
+  """A scenario that transmits no protocol buffers in either direction."""
+
+  _DIVIDEND = 59
+  _DIVISOR = 7
+  _QUOTIENT = 8
+  _REMAINDER = 3
+
+  _REQUEST = math_pb2.DivArgs(dividend=_DIVIDEND, divisor=_DIVISOR)
+  _RESPONSE = math_pb2.DivReply(quotient=_QUOTIENT, remainder=_REMAINDER)
+
+  def group_and_method(self):
+    return 'math.Math', 'Div'
+
+  def serialize_request(self, request):
+    return request.SerializeToString()
+
+  def deserialize_request(self, request_bytestring):
+    return math_pb2.DivArgs.FromString(request_bytestring)
+
+  def serialize_response(self, response):
+    return response.SerializeToString()
+
+  def deserialize_response(self, response_bytestring):
+    return math_pb2.DivReply.FromString(response_bytestring)
+
+  def requests(self):
+    return [self._REQUEST]
+
+  def response_for_request(self, request):
+    return self._RESPONSE
+
+  def verify_requests(self, experimental_requests):
+    return tuple(experimental_requests) == (self._REQUEST,)
+
+  def verify_responses(self, experimental_responses):
+    return tuple(experimental_responses) == (self._RESPONSE,)
+
+
+class BidirectionallyStreamingScenario(ProtoScenario):
+  """A scenario that transmits no protocol buffers in either direction."""
+
+  _STREAM_LENGTH = 200
+  _REQUESTS = tuple(
+      math_pb2.DivArgs(dividend=59 + index, divisor=7 + index)
+      for index in range(_STREAM_LENGTH))
+
+  def __init__(self):
+    self._lock = threading.Lock()
+    self._responses = []
+
+  def group_and_method(self):
+    return 'math.Math', 'DivMany'
+
+  def serialize_request(self, request):
+    return request.SerializeToString()
+
+  def deserialize_request(self, request_bytestring):
+    return math_pb2.DivArgs.FromString(request_bytestring)
+
+  def serialize_response(self, response):
+    return response.SerializeToString()
+
+  def deserialize_response(self, response_bytestring):
+    return math_pb2.DivReply.FromString(response_bytestring)
+
+  def requests(self):
+    return self._REQUESTS
+
+  def response_for_request(self, request):
+    quotient, remainder = divmod(request.dividend, request.divisor)
+    response = math_pb2.DivReply(quotient=quotient, remainder=remainder)
+    with self._lock:
+      self._responses.append(response)
+    return response
+
+  def verify_requests(self, experimental_requests):
+    return tuple(experimental_requests) == self._REQUESTS
+
+  def verify_responses(self, experimental_responses):
+    with self._lock:
+      return tuple(experimental_responses) == tuple(self._responses)
diff --git a/src/python/src/grpc/_links/_transmission_test.py b/src/python/src/grpc/_links/_transmission_test.py
new file mode 100644
index 0000000000..c5ef1edb25
--- /dev/null
+++ b/src/python/src/grpc/_links/_transmission_test.py
@@ -0,0 +1,226 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Tests transmission of tickets across gRPC-on-the-wire."""
+
+import unittest
+
+from grpc._adapter import _intermediary_low
+from grpc._links import _proto_scenarios
+from grpc._links import invocation
+from grpc._links import service
+from grpc.framework.common import test_constants
+from grpc.framework.interfaces.links import links
+from grpc.framework.interfaces.links import test_cases
+from grpc.framework.interfaces.links import test_utilities
+
+_IDENTITY = lambda x: x
+
+
+class TransmissionTest(test_cases.TransmissionTest, unittest.TestCase):
+
+  def create_transmitting_links(self):
+    service_link = service.service_link(
+        {self.group_and_method(): self.deserialize_request},
+        {self.group_and_method(): self.serialize_response})
+    port = service_link.add_port(0, None)
+    service_link.start()
+    channel = _intermediary_low.Channel('localhost:%d' % port, None)
+    invocation_link = invocation.invocation_link(
+        channel, 'localhost',
+        {self.group_and_method(): self.serialize_request},
+        {self.group_and_method(): self.deserialize_response})
+    invocation_link.start()
+    return invocation_link, service_link
+
+  def destroy_transmitting_links(self, invocation_side_link, service_side_link):
+    invocation_side_link.stop()
+    service_side_link.stop_gracefully()
+
+  def create_invocation_initial_metadata(self):
+    return (
+        ('first invocation initial metadata key', 'just a string value'),
+        ('second invocation initial metadata key', '0123456789'),
+        ('third invocation initial metadata key-bin', '\x00\x57' * 100),
+    )
+
+  def create_invocation_terminal_metadata(self):
+    return None
+
+  def create_service_initial_metadata(self):
+    return (
+        ('first service initial metadata key', 'just another string value'),
+        ('second service initial metadata key', '9876543210'),
+        ('third service initial metadata key-bin', '\x00\x59\x02' * 100),
+    )
+
+  def create_service_terminal_metadata(self):
+    return (
+        ('first service terminal metadata key', 'yet another string value'),
+        ('second service terminal metadata key', 'abcdefghij'),
+        ('third service terminal metadata key-bin', '\x00\x37' * 100),
+    )
+
+  def create_invocation_completion(self):
+    return None, None
+
+  def create_service_completion(self):
+    return _intermediary_low.Code.OK, 'An exuberant test "details" message!'
+
+  def assertMetadataEqual(self, original_metadata, transmitted_metadata):
+    self.assertSequenceEqual(original_metadata, transmitted_metadata)
+
+
+class RoundTripTest(unittest.TestCase):
+
+  def testZeroMessageRoundTrip(self):
+    test_operation_id = object()
+    test_group = 'test package.Test Group'
+    test_method = 'test method'
+    identity_transformation = {(test_group, test_method): _IDENTITY}
+    test_code = _intermediary_low.Code.OK
+    test_message = 'a test message'
+
+    service_link = service.service_link(
+        identity_transformation, identity_transformation)
+    service_mate = test_utilities.RecordingLink()
+    service_link.join_link(service_mate)
+    port = service_link.add_port(0, None)
+    service_link.start()
+    channel = _intermediary_low.Channel('localhost:%d' % port, None)
+    invocation_link = invocation.invocation_link(
+        channel, 'localhost', identity_transformation, identity_transformation)
+    invocation_mate = test_utilities.RecordingLink()
+    invocation_link.join_link(invocation_mate)
+    invocation_link.start()
+
+    invocation_ticket = links.Ticket(
+        test_operation_id, 0, test_group, test_method,
+        links.Ticket.Subscription.FULL, test_constants.LONG_TIMEOUT, None, None,
+        None, None, None, None, links.Ticket.Termination.COMPLETION)
+    invocation_link.accept_ticket(invocation_ticket)
+    service_mate.block_until_tickets_satisfy(test_cases.terminated)
+
+    service_ticket = links.Ticket(
+        service_mate.tickets()[-1].operation_id, 0, None, None, None, None,
+        None, None, None, None, test_code, test_message,
+        links.Ticket.Termination.COMPLETION)
+    service_link.accept_ticket(service_ticket)
+    invocation_mate.block_until_tickets_satisfy(test_cases.terminated)
+
+    invocation_link.stop()
+    service_link.stop_gracefully()
+
+    self.assertIs(
+        service_mate.tickets()[-1].termination,
+        links.Ticket.Termination.COMPLETION)
+    self.assertIs(
+        invocation_mate.tickets()[-1].termination,
+        links.Ticket.Termination.COMPLETION)
+
+  def _perform_scenario_test(self, scenario):
+    test_operation_id = object()
+    test_group, test_method = scenario.group_and_method()
+    test_code = _intermediary_low.Code.OK
+    test_message = 'a scenario test message'
+
+    service_link = service.service_link(
+        {(test_group, test_method): scenario.deserialize_request},
+        {(test_group, test_method): scenario.serialize_response})
+    service_mate = test_utilities.RecordingLink()
+    service_link.join_link(service_mate)
+    port = service_link.add_port(0, None)
+    service_link.start()
+    channel = _intermediary_low.Channel('localhost:%d' % port, None)
+    invocation_link = invocation.invocation_link(
+        channel, 'localhost',
+        {(test_group, test_method): scenario.serialize_request},
+        {(test_group, test_method): scenario.deserialize_response})
+    invocation_mate = test_utilities.RecordingLink()
+    invocation_link.join_link(invocation_mate)
+    invocation_link.start()
+
+    invocation_ticket = links.Ticket(
+        test_operation_id, 0, test_group, test_method,
+        links.Ticket.Subscription.FULL, test_constants.LONG_TIMEOUT, None, None,
+        None, None, None, None, None)
+    invocation_link.accept_ticket(invocation_ticket)
+    requests = scenario.requests()
+    for request_index, request in enumerate(requests):
+      request_ticket = links.Ticket(
+          test_operation_id, 1 + request_index, None, None, None, None, 1, None,
+          request, None, None, None, None)
+      invocation_link.accept_ticket(request_ticket)
+      service_mate.block_until_tickets_satisfy(
+          test_cases.at_least_n_payloads_received_predicate(1 + request_index))
+      response_ticket = links.Ticket(
+          service_mate.tickets()[0].operation_id, request_index, None, None,
+          None, None, 1, None, scenario.response_for_request(request), None,
+          None, None, None)
+      service_link.accept_ticket(response_ticket)
+      invocation_mate.block_until_tickets_satisfy(
+          test_cases.at_least_n_payloads_received_predicate(1 + request_index))
+    request_count = len(requests)
+    invocation_completion_ticket = links.Ticket(
+        test_operation_id, request_count + 1, None, None, None, None, None,
+        None, None, None, None, None, links.Ticket.Termination.COMPLETION)
+    invocation_link.accept_ticket(invocation_completion_ticket)
+    service_mate.block_until_tickets_satisfy(test_cases.terminated)
+    service_completion_ticket = links.Ticket(
+        service_mate.tickets()[0].operation_id, request_count, None, None, None,
+        None, None, None, None, None, test_code, test_message,
+        links.Ticket.Termination.COMPLETION)
+    service_link.accept_ticket(service_completion_ticket)
+    invocation_mate.block_until_tickets_satisfy(test_cases.terminated)
+
+    invocation_link.stop()
+    service_link.stop_gracefully()
+
+    observed_requests = tuple(
+        ticket.payload for ticket in service_mate.tickets()
+        if ticket.payload is not None)
+    observed_responses = tuple(
+        ticket.payload for ticket in invocation_mate.tickets()
+        if ticket.payload is not None)
+    self.assertTrue(scenario.verify_requests(observed_requests))
+    self.assertTrue(scenario.verify_responses(observed_responses))
+
+  def testEmptyScenario(self):
+    self._perform_scenario_test(_proto_scenarios.EmptyScenario())
+
+  def testBidirectionallyUnaryScenario(self):
+    self._perform_scenario_test(_proto_scenarios.BidirectionallyUnaryScenario())
+
+  def testBidirectionallyStreamingScenario(self):
+    self._perform_scenario_test(
+        _proto_scenarios.BidirectionallyStreamingScenario())
+
+
+if __name__ == '__main__':
+  unittest.main(verbosity=2)
diff --git a/src/python/src/grpc/_links/invocation.py b/src/python/src/grpc/_links/invocation.py
new file mode 100644
index 0000000000..0058ae91f8
--- /dev/null
+++ b/src/python/src/grpc/_links/invocation.py
@@ -0,0 +1,363 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""The RPC-invocation-side bridge between RPC Framework and GRPC-on-the-wire."""
+
+import abc
+import enum
+import logging
+import threading
+import time
+
+from grpc._adapter import _intermediary_low
+from grpc.framework.foundation import activated
+from grpc.framework.foundation import logging_pool
+from grpc.framework.foundation import relay
+from grpc.framework.interfaces.links import links
+
+
+@enum.unique
+class _Read(enum.Enum):
+  AWAITING_METADATA = 'awaiting metadata'
+  READING = 'reading'
+  AWAITING_ALLOWANCE = 'awaiting allowance'
+  CLOSED = 'closed'
+
+
+@enum.unique
+class _HighWrite(enum.Enum):
+  OPEN = 'open'
+  CLOSED = 'closed'
+
+
+@enum.unique
+class _LowWrite(enum.Enum):
+  OPEN = 'OPEN'
+  ACTIVE = 'ACTIVE'
+  CLOSED = 'CLOSED'
+
+
+class _RPCState(object):
+
+  def __init__(
+      self, call, request_serializer, response_deserializer, sequence_number,
+      read, allowance, high_write, low_write):
+    self.call = call
+    self.request_serializer = request_serializer
+    self.response_deserializer = response_deserializer
+    self.sequence_number = sequence_number
+    self.read = read
+    self.allowance = allowance
+    self.high_write = high_write
+    self.low_write = low_write
+
+
+class _Kernel(object):
+
+  def __init__(
+      self, channel, host, request_serializers, response_deserializers,
+      ticket_relay):
+    self._lock = threading.Lock()
+    self._channel = channel
+    self._host = host
+    self._request_serializers = request_serializers
+    self._response_deserializers = response_deserializers
+    self._relay = ticket_relay
+
+    self._completion_queue = None
+    self._rpc_states = None
+    self._pool = None
+
+  def _on_write_event(self, operation_id, unused_event, rpc_state):
+    if rpc_state.high_write is _HighWrite.CLOSED:
+      rpc_state.call.complete(operation_id)
+      rpc_state.low_write = _LowWrite.CLOSED
+    else:
+      ticket = links.Ticket(
+          operation_id, rpc_state.sequence_number, None, None, None, None, 1,
+          None, None, None, None, None, None)
+      rpc_state.sequence_number += 1
+      self._relay.add_value(ticket)
+      rpc_state.low_write = _LowWrite.OPEN
+
+  def _on_read_event(self, operation_id, event, rpc_state):
+    if event.bytes is None:
+      rpc_state.read = _Read.CLOSED
+    else:
+      if 0 < rpc_state.allowance:
+        rpc_state.allowance -= 1
+        rpc_state.call.read(operation_id)
+      else:
+        rpc_state.read = _Read.AWAITING_ALLOWANCE
+      ticket = links.Ticket(
+          operation_id, rpc_state.sequence_number, None, None, None, None, None,
+          None, rpc_state.response_deserializer(event.bytes), None, None, None,
+          None)
+      rpc_state.sequence_number += 1
+      self._relay.add_value(ticket)
+
+  def _on_metadata_event(self, operation_id, event, rpc_state):
+    rpc_state.allowance -= 1
+    rpc_state.call.read(operation_id)
+    rpc_state.read = _Read.READING
+    ticket = links.Ticket(
+        operation_id, rpc_state.sequence_number, None, None,
+        links.Ticket.Subscription.FULL, None, None, event.metadata, None, None,
+        None, None, None)
+    rpc_state.sequence_number += 1
+    self._relay.add_value(ticket)
+
+  def _on_finish_event(self, operation_id, event, rpc_state):
+    self._rpc_states.pop(operation_id, None)
+    if event.status.code is _intermediary_low.Code.OK:
+      termination = links.Ticket.Termination.COMPLETION
+    elif event.status.code is _intermediary_low.Code.CANCELLED:
+      termination = links.Ticket.Termination.CANCELLATION
+    elif event.status.code is _intermediary_low.Code.DEADLINE_EXCEEDED:
+      termination = links.Ticket.Termination.EXPIRATION
+    else:
+      termination = links.Ticket.Termination.TRANSMISSION_FAILURE
+    ticket = links.Ticket(
+        operation_id, rpc_state.sequence_number, None, None, None, None, None,
+        None, None, event.metadata, event.status.code, event.status.details,
+        termination)
+    rpc_state.sequence_number += 1
+    self._relay.add_value(ticket)
+
+  def _spin(self, completion_queue):
+    while True:
+      event = completion_queue.get(None)
+      if event.kind is _intermediary_low.Event.Kind.STOP:
+        return
+      operation_id = event.tag
+      with self._lock:
+        if self._completion_queue is None:
+          continue
+        rpc_state = self._rpc_states.get(operation_id)
+        if rpc_state is not None:
+          if event.kind is _intermediary_low.Event.Kind.WRITE_ACCEPTED:
+            self._on_write_event(operation_id, event, rpc_state)
+          elif event.kind is _intermediary_low.Event.Kind.METADATA_ACCEPTED:
+            self._on_metadata_event(operation_id, event, rpc_state)
+          elif event.kind is _intermediary_low.Event.Kind.READ_ACCEPTED:
+            self._on_read_event(operation_id, event, rpc_state)
+          elif event.kind is _intermediary_low.Event.Kind.FINISH:
+            self._on_finish_event(operation_id, event, rpc_state)
+          elif event.kind is _intermediary_low.Event.Kind.COMPLETE_ACCEPTED:
+            pass
+          else:
+            logging.error('Illegal RPC event! %s', (event,))
+
+  def _invoke(
+      self, operation_id, group, method, initial_metadata, payload, termination,
+      timeout, allowance):
+    """Invoke an RPC.
+
+    Args:
+      operation_id: Any object to be used as an operation ID for the RPC.
+      group: The group to which the RPC method belongs.
+      method: The RPC method name.
+      initial_metadata: The initial metadata object for the RPC.
+      payload: A payload object for the RPC or None if no payload was given at
+        invocation-time.
+      termination: A links.Ticket.Termination value or None indicated whether or
+        not more writes will follow from this side of the RPC.
+      timeout: A duration of time in seconds to allow for the RPC.
+      allowance: The number of payloads (beyond the free first one) that the
+        local ticket exchange mate has granted permission to be read.
+    """
+    if termination is links.Ticket.Termination.COMPLETION:
+      high_write = _HighWrite.CLOSED
+    elif termination is None:
+      high_write = _HighWrite.OPEN
+    else:
+      return
+
+    request_serializer = self._request_serializers.get((group, method))
+    response_deserializer = self._response_deserializers.get((group, method))
+    if request_serializer is None or response_deserializer is None:
+      cancellation_ticket = links.Ticket(
+          operation_id, 0, None, None, None, None, None, None, None, None, None,
+          None, links.Ticket.Termination.CANCELLATION)
+      self._relay.add_value(cancellation_ticket)
+      return
+
+    call = _intermediary_low.Call(
+        self._channel, self._completion_queue, '/%s/%s' % (group, method),
+        self._host, time.time() + timeout)
+    if initial_metadata is not None:
+      for metadata_key, metadata_value in initial_metadata:
+        call.add_metadata(metadata_key, metadata_value)
+    call.invoke(self._completion_queue, operation_id, operation_id)
+    if payload is None:
+      if high_write is _HighWrite.CLOSED:
+        call.complete(operation_id)
+        low_write = _LowWrite.CLOSED
+      else:
+        low_write = _LowWrite.OPEN
+    else:
+      call.write(request_serializer(payload), operation_id)
+      low_write = _LowWrite.ACTIVE
+    self._rpc_states[operation_id] = _RPCState(
+        call, request_serializer, response_deserializer, 0,
+        _Read.AWAITING_METADATA, 1 if allowance is None else (1 + allowance),
+        high_write, low_write)
+
+  def _advance(self, operation_id, rpc_state, payload, termination, allowance):
+    if payload is not None:
+      rpc_state.call.write(rpc_state.request_serializer(payload), operation_id)
+      rpc_state.low_write = _LowWrite.ACTIVE
+
+    if allowance is not None:
+      if rpc_state.read is _Read.AWAITING_ALLOWANCE:
+        rpc_state.allowance += allowance - 1
+        rpc_state.call.read(operation_id)
+        rpc_state.read = _Read.READING
+      else:
+        rpc_state.allowance += allowance
+
+    if termination is links.Ticket.Termination.COMPLETION:
+      rpc_state.high_write = _HighWrite.CLOSED
+      if rpc_state.low_write is _LowWrite.OPEN:
+        rpc_state.call.complete(operation_id)
+        rpc_state.low_write = _LowWrite.CLOSED
+    elif termination is not None:
+      rpc_state.call.cancel()
+
+  def add_ticket(self, ticket):
+    with self._lock:
+      if self._completion_queue is None:
+        return
+      if ticket.sequence_number == 0:
+        self._invoke(
+            ticket.operation_id, ticket.group, ticket.method,
+            ticket.initial_metadata, ticket.payload, ticket.termination,
+            ticket.timeout, ticket.allowance)
+      else:
+        rpc_state = self._rpc_states.get(ticket.operation_id)
+        if rpc_state is not None:
+          self._advance(
+              ticket.operation_id, rpc_state, ticket.payload,
+              ticket.termination, ticket.allowance)
+
+  def start(self):
+    """Starts this object.
+
+    This method must be called before attempting to exchange tickets with this
+    object.
+    """
+    with self._lock:
+      self._completion_queue = _intermediary_low.CompletionQueue()
+      self._rpc_states = {}
+      self._pool = logging_pool.pool(1)
+      self._pool.submit(self._spin, self._completion_queue)
+
+  def stop(self):
+    """Stops this object.
+
+    This method must be called for proper termination of this object, and no
+    attempts to exchange tickets with this object may be made after this method
+    has been called.
+    """
+    with self._lock:
+      self._completion_queue.stop()
+      self._completion_queue = None
+      pool = self._pool
+      self._pool = None
+      self._rpc_states = None
+    pool.shutdown(wait=True)
+
+
+class InvocationLink(links.Link, activated.Activated):
+  """A links.Link for use on the invocation-side of a gRPC connection.
+
+  Implementations of this interface are only valid for use when activated.
+  """
+  __metaclass__ = abc.ABCMeta
+
+
+class _InvocationLink(InvocationLink):
+
+  def __init__(
+      self, channel, host, request_serializers, response_deserializers):
+    self._relay = relay.relay(None)
+    self._kernel = _Kernel(
+        channel, host, request_serializers, response_deserializers, self._relay)
+
+  def _start(self):
+    self._relay.start()
+    self._kernel.start()
+    return self
+
+  def _stop(self):
+    self._kernel.stop()
+    self._relay.stop()
+
+  def accept_ticket(self, ticket):
+    """See links.Link.accept_ticket for specification."""
+    self._kernel.add_ticket(ticket)
+
+  def join_link(self, link):
+    """See links.Link.join_link for specification."""
+    self._relay.set_behavior(link.accept_ticket)
+
+  def __enter__(self):
+    """See activated.Activated.__enter__ for specification."""
+    return self._start()
+
+  def __exit__(self, exc_type, exc_val, exc_tb):
+    """See activated.Activated.__exit__ for specification."""
+    self._stop()
+    return False
+
+  def start(self):
+    """See activated.Activated.start for specification."""
+    return self._start()
+
+  def stop(self):
+    """See activated.Activated.stop for specification."""
+    self._stop()
+
+
+def invocation_link(channel, host, request_serializers, response_deserializers):
+  """Creates an InvocationLink.
+
+  Args:
+    channel: A channel for use by the link.
+    host: The host to specify when invoking RPCs.
+    request_serializers: A dict from group-method pair to request object
+      serialization behavior.
+    response_deserializers: A dict from group-method pair to response object
+      deserialization behavior.
+
+  Returns:
+    An InvocationLink.
+  """
+  return _InvocationLink(
+      channel, host, request_serializers, response_deserializers)
diff --git a/src/python/src/grpc/_links/service.py b/src/python/src/grpc/_links/service.py
new file mode 100644
index 0000000000..7783e91824
--- /dev/null
+++ b/src/python/src/grpc/_links/service.py
@@ -0,0 +1,402 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""The RPC-service-side bridge between RPC Framework and GRPC-on-the-wire."""
+
+import abc
+import enum
+import logging
+import threading
+import time
+
+from grpc._adapter import _intermediary_low
+from grpc.framework.foundation import logging_pool
+from grpc.framework.foundation import relay
+from grpc.framework.interfaces.links import links
+
+
+@enum.unique
+class _Read(enum.Enum):
+  READING = 'reading'
+  AWAITING_ALLOWANCE = 'awaiting allowance'
+  CLOSED = 'closed'
+
+
+@enum.unique
+class _HighWrite(enum.Enum):
+  OPEN = 'open'
+  CLOSED = 'closed'
+
+
+@enum.unique
+class _LowWrite(enum.Enum):
+  """The possible categories of low-level write state."""
+
+  OPEN = 'OPEN'
+  ACTIVE = 'ACTIVE'
+  CLOSED = 'CLOSED'
+
+
+class _RPCState(object):
+
+  def __init__(
+      self, request_deserializer, response_serializer, sequence_number, read,
+      allowance, high_write, low_write, premetadataed, terminal_metadata, code,
+      message):
+    self.request_deserializer = request_deserializer
+    self.response_serializer = response_serializer
+    self.sequence_number = sequence_number
+    self.read = read
+    self.allowance = allowance
+    self.high_write = high_write
+    self.low_write = low_write
+    self.premetadataed = premetadataed
+    self.terminal_metadata = terminal_metadata
+    self.code = code
+    self.message = message
+
+
+def _metadatafy(call, metadata):
+  for metadata_key, metadata_value in metadata:
+    call.add_metadata(metadata_key, metadata_value)
+
+
+class _Kernel(object):
+
+  def __init__(self, request_deserializers, response_serializers, ticket_relay):
+    self._lock = threading.Lock()
+    self._request_deserializers = request_deserializers
+    self._response_serializers = response_serializers
+    self._relay = ticket_relay
+
+    self._completion_queue = None
+    self._server = None
+    self._rpc_states = {}
+    self._pool = None
+
+  def _on_service_acceptance_event(self, event, server):
+    server.service(None)
+
+    service_acceptance = event.service_acceptance
+    call = service_acceptance.call
+    call.accept(self._completion_queue, call)
+    try:
+      group, method = service_acceptance.method.split('/')[1:3]
+    except ValueError:
+      logging.info('Illegal path "%s"!', service_acceptance.method)
+      return
+    request_deserializer = self._request_deserializers.get((group, method))
+    response_serializer = self._response_serializers.get((group, method))
+    if request_deserializer is None or response_serializer is None:
+      # TODO(nathaniel): Terminate the RPC with code NOT_FOUND.
+      call.cancel()
+      return
+
+    call.read(call)
+    self._rpc_states[call] = _RPCState(
+        request_deserializer, response_serializer, 1, _Read.READING, 0,
+        _HighWrite.OPEN, _LowWrite.OPEN, False, None, None, None)
+    ticket = links.Ticket(
+        call, 0, group, method, links.Ticket.Subscription.FULL,
+        service_acceptance.deadline - time.time(), None, event.metadata, None,
+        None, None, None, None)
+    self._relay.add_value(ticket)
+
+  def _on_read_event(self, event):
+    call = event.tag
+    rpc_state = self._rpc_states.get(call, None)
+    if rpc_state is None:
+      return
+
+    if event.bytes is None:
+      rpc_state.read = _Read.CLOSED
+      payload = None
+      termination = links.Ticket.Termination.COMPLETION
+    else:
+      if 0 < rpc_state.allowance:
+        rpc_state.allowance -= 1
+        call.read(call)
+      else:
+        rpc_state.read = _Read.AWAITING_ALLOWANCE
+      payload = rpc_state.request_deserializer(event.bytes)
+      termination = None
+    ticket = links.Ticket(
+        call, rpc_state.sequence_number, None, None, None, None, None, None,
+        payload, None, None, None, termination)
+    rpc_state.sequence_number += 1
+    self._relay.add_value(ticket)
+
+  def _on_write_event(self, event):
+    call = event.tag
+    rpc_state = self._rpc_states.get(call, None)
+    if rpc_state is None:
+      return
+
+    if rpc_state.high_write is _HighWrite.CLOSED:
+      if rpc_state.terminal_metadata is not None:
+        _metadatafy(call, rpc_state.terminal_metadata)
+      call.status(
+          _intermediary_low.Status(rpc_state.code, rpc_state.message), call)
+      rpc_state.low_write = _LowWrite.CLOSED
+    else:
+      ticket = links.Ticket(
+          call, rpc_state.sequence_number, None, None, None, None, 1, None,
+          None, None, None, None, None)
+      rpc_state.sequence_number += 1
+      self._relay.add_value(ticket)
+      rpc_state.low_write = _LowWrite.OPEN
+
+  def _on_finish_event(self, event):
+    call = event.tag
+    rpc_state = self._rpc_states.pop(call, None)
+    if rpc_state is None:
+      return
+    code = event.status.code
+    if code is _intermediary_low.Code.OK:
+      return
+
+    if code is _intermediary_low.Code.CANCELLED:
+      termination = links.Ticket.Termination.CANCELLATION
+    elif code is _intermediary_low.Code.DEADLINE_EXCEEDED:
+      termination = links.Ticket.Termination.EXPIRATION
+    else:
+      termination = links.Ticket.Termination.TRANSMISSION_FAILURE
+    ticket = links.Ticket(
+        call, rpc_state.sequence_number, None, None, None, None, None, None,
+        None, None, None, None, termination)
+    rpc_state.sequence_number += 1
+    self._relay.add_value(ticket)
+
+  def _spin(self, completion_queue, server):
+    while True:
+      event = completion_queue.get(None)
+      if event.kind is _intermediary_low.Event.Kind.STOP:
+        return
+      with self._lock:
+        if self._server is None:
+          continue
+        elif event.kind is _intermediary_low.Event.Kind.SERVICE_ACCEPTED:
+          self._on_service_acceptance_event(event, server)
+        elif event.kind is _intermediary_low.Event.Kind.READ_ACCEPTED:
+          self._on_read_event(event)
+        elif event.kind is _intermediary_low.Event.Kind.WRITE_ACCEPTED:
+          self._on_write_event(event)
+        elif event.kind is _intermediary_low.Event.Kind.COMPLETE_ACCEPTED:
+          pass
+        elif event.kind is _intermediary_low.Event.Kind.FINISH:
+          self._on_finish_event(event)
+        else:
+          logging.error('Illegal event! %s', (event,))
+
+  def add_ticket(self, ticket):
+    with self._lock:
+      if self._server is None:
+        return
+      call = ticket.operation_id
+      rpc_state = self._rpc_states.get(call)
+      if rpc_state is None:
+        return
+
+      if ticket.initial_metadata is not None:
+        _metadatafy(call, ticket.initial_metadata)
+        call.premetadata()
+        rpc_state.premetadataed = True
+      elif not rpc_state.premetadataed:
+        if (ticket.terminal_metadata is not None or
+            ticket.payload is not None or
+            ticket.termination is links.Ticket.Termination.COMPLETION or
+            ticket.code is not None or
+            ticket.message is not None):
+          call.premetadata()
+          rpc_state.premetadataed = True
+
+      if ticket.allowance is not None:
+        if rpc_state.read is _Read.AWAITING_ALLOWANCE:
+          rpc_state.allowance += ticket.allowance - 1
+          call.read(call)
+          rpc_state.read = _Read.READING
+        else:
+          rpc_state.allowance += ticket.allowance
+
+      if ticket.payload is not None:
+        call.write(rpc_state.response_serializer(ticket.payload), call)
+        rpc_state.low_write = _LowWrite.ACTIVE
+
+      if ticket.terminal_metadata is not None:
+        rpc_state.terminal_metadata = ticket.terminal_metadata
+      if ticket.code is not None:
+        rpc_state.code = ticket.code
+      if ticket.message is not None:
+        rpc_state.message = ticket.message
+
+      if ticket.termination is links.Ticket.Termination.COMPLETION:
+        rpc_state.high_write = _HighWrite.CLOSED
+        if rpc_state.low_write is _LowWrite.OPEN:
+          if rpc_state.terminal_metadata is not None:
+            _metadatafy(call, rpc_state.terminal_metadata)
+          status = _intermediary_low.Status(
+              _intermediary_low.Code.OK
+              if rpc_state.code is None else rpc_state.code,
+              '' if rpc_state.message is None else rpc_state.message)
+          call.status(status, call)
+          rpc_state.low_write = _LowWrite.CLOSED
+      elif ticket.termination is not None:
+        call.cancel()
+        self._rpc_states.pop(call, None)
+
+  def add_port(self, port, server_credentials):
+    with self._lock:
+      address = '[::]:%d' % port
+      if self._server is None:
+        self._completion_queue = _intermediary_low.CompletionQueue()
+        self._server = _intermediary_low.Server(self._completion_queue)
+      if server_credentials is None:
+        return self._server.add_http2_addr(address)
+      else:
+        return self._server.add_secure_http2_addr(address, server_credentials)
+
+  def start(self):
+    with self._lock:
+      if self._server is None:
+        self._completion_queue = _intermediary_low.CompletionQueue()
+        self._server = _intermediary_low.Server(self._completion_queue)
+      self._pool = logging_pool.pool(1)
+      self._pool.submit(self._spin, self._completion_queue, self._server)
+      self._server.start()
+      self._server.service(None)
+
+  def graceful_stop(self):
+    with self._lock:
+      self._server.stop()
+      self._server = None
+      self._completion_queue.stop()
+      self._completion_queue = None
+      pool = self._pool
+      self._pool = None
+      self._rpc_states = None
+    pool.shutdown(wait=True)
+
+  def immediate_stop(self):
+    # TODO(nathaniel): Implementation.
+    raise NotImplementedError(
+        'TODO(nathaniel): after merge of rewritten lower layers')
+
+
+class ServiceLink(links.Link):
+  """A links.Link for use on the service-side of a gRPC connection.
+
+  Implementations of this interface are only valid for use between calls to
+  their start method and one of their stop methods.
+  """
+
+  @abc.abstractmethod
+  def add_port(self, port, server_credentials):
+    """Adds a port on which to service RPCs after this link has been started.
+
+    Args:
+      port: The port on which to service RPCs, or zero to request that a port be
+        automatically selected and used.
+      server_credentials: A ServerCredentials object, or None for insecure
+        service.
+
+    Returns:
+      A port on which RPCs will be serviced after this link has been started.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def start(self):
+    """Starts this object.
+
+    This method must be called before attempting to use this Link in ticket
+    exchange.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def stop_gracefully(self):
+    """Stops this link.
+
+    New RPCs will be rejected as soon as this method is called, but ongoing RPCs
+    will be allowed to continue until they terminate. This method blocks until
+    all RPCs have terminated.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def stop_immediately(self):
+    """Stops this link.
+
+    All in-progress RPCs will be terminated immediately.
+    """
+    raise NotImplementedError()
+
+
+class _ServiceLink(ServiceLink):
+
+  def __init__(self, request_deserializers, response_serializers):
+    self._relay = relay.relay(None)
+    self._kernel = _Kernel(
+        request_deserializers, response_serializers, self._relay)
+
+  def accept_ticket(self, ticket):
+    self._kernel.add_ticket(ticket)
+
+  def join_link(self, link):
+    self._relay.set_behavior(link.accept_ticket)
+
+  def add_port(self, port, server_credentials):
+    return self._kernel.add_port(port, server_credentials)
+
+  def start(self):
+    self._relay.start()
+    return self._kernel.start()
+
+  def stop_gracefully(self):
+    self._kernel.graceful_stop()
+    self._relay.stop()
+
+  def stop_immediately(self):
+    self._kernel.immediate_stop()
+    self._relay.stop()
+
+
+def service_link(request_deserializers, response_serializers):
+  """Creates a ServiceLink.
+
+  Args:
+    request_deserializers: A dict from group-method pair to request object
+      deserialization behavior.
+    response_serializers: A dict from group-method pair to response ojbect
+      serialization behavior.
+
+  Returns:
+    A ServiceLink.
+  """
+  return _ServiceLink(request_deserializers, response_serializers)
diff --git a/src/python/src/grpc/framework/common/test_constants.py b/src/python/src/grpc/framework/common/test_constants.py
new file mode 100644
index 0000000000..237b8754ed
--- /dev/null
+++ b/src/python/src/grpc/framework/common/test_constants.py
@@ -0,0 +1,37 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Constants shared among tests throughout RPC Framework."""
+
+# Value for maximum duration in seconds of RPCs that may time out as part of a
+# test.
+SHORT_TIMEOUT = 4
+# Absurdly large value for maximum duration in seconds for should-not-time-out
+# RPCs made during tests.
+LONG_TIMEOUT = 3000
diff --git a/src/python/src/grpc/framework/common/test_control.py b/src/python/src/grpc/framework/common/test_control.py
new file mode 100644
index 0000000000..3960c4e649
--- /dev/null
+++ b/src/python/src/grpc/framework/common/test_control.py
@@ -0,0 +1,87 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Code for instructing systems under test to block or fail."""
+
+import abc
+import contextlib
+import threading
+
+
+class Control(object):
+  """An object that accepts program control from a system under test.
+
+  Systems under test passed a Control should call its control() method
+  frequently during execution. The control() method may block, raise an
+  exception, or do nothing, all according to the enclosing test's desire for
+  the system under test to simulate hanging, failing, or functioning.
+  """
+
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod
+  def control(self):
+    """Potentially does anything."""
+    raise NotImplementedError()
+
+
+class PauseFailControl(Control):
+  """A Control that can be used to pause or fail code under control."""
+
+  def __init__(self):
+    self._condition = threading.Condition()
+    self._paused = False
+    self._fail = False
+
+  def control(self):
+    with self._condition:
+      if self._fail:
+        raise ValueError()
+
+      while self._paused:
+        self._condition.wait()
+
+  @contextlib.contextmanager
+  def pause(self):
+    """Pauses code under control while controlling code is in context."""
+    with self._condition:
+      self._paused = True
+    yield
+    with self._condition:
+      self._paused = False
+      self._condition.notify_all()
+
+  @contextlib.contextmanager
+  def fail(self):
+    """Fails code under control while controlling code is in context."""
+    with self._condition:
+      self._fail = True
+    yield
+    with self._condition:
+      self._fail = False
diff --git a/src/python/src/grpc/framework/common/test_coverage.py b/src/python/src/grpc/framework/common/test_coverage.py
new file mode 100644
index 0000000000..a7ed3582c4
--- /dev/null
+++ b/src/python/src/grpc/framework/common/test_coverage.py
@@ -0,0 +1,116 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Governs coverage for tests of RPCs throughout RPC Framework."""
+
+import abc
+
+# This code is designed for use with the unittest module.
+# pylint: disable=invalid-name
+
+
+class Coverage(object):
+  """Specification of test coverage."""
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod
+  def testSuccessfulUnaryRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testSuccessfulUnaryRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testSuccessfulStreamRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testSuccessfulStreamRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testSequentialInvocations(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testParallelInvocations(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testWaitingForSomeButNotAllParallelInvocations(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testCancelledUnaryRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testCancelledUnaryRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testCancelledStreamRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testCancelledStreamRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testExpiredUnaryRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testExpiredUnaryRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testExpiredStreamRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testExpiredStreamRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testFailedUnaryRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testFailedUnaryRequestStreamResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testFailedStreamRequestUnaryResponse(self):
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def testFailedStreamRequestStreamResponse(self):
+    raise NotImplementedError()
diff --git a/src/python/src/grpc/framework/foundation/relay.py b/src/python/src/grpc/framework/foundation/relay.py
new file mode 100644
index 0000000000..9c23946552
--- /dev/null
+++ b/src/python/src/grpc/framework/foundation/relay.py
@@ -0,0 +1,175 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Implementations of in-order work deference."""
+
+import abc
+import enum
+import threading
+
+from grpc.framework.foundation import activated
+from grpc.framework.foundation import logging_pool
+
+_NULL_BEHAVIOR = lambda unused_value: None
+
+
+class Relay(object):
+  """Performs work submitted to it in another thread.
+
+  Performs work in the order in which work was submitted to it; otherwise there
+  would be no reason to use an implementation of this interface instead of a
+  thread pool.
+  """
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod
+  def add_value(self, value):
+    """Adds a value to be passed to the behavior registered with this Relay.
+
+    Args:
+      value: A value that will be passed to a call made in another thread to the
+        behavior registered with this Relay.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def set_behavior(self, behavior):
+    """Sets the behavior that this Relay should call when passed values.
+
+    Args:
+      behavior: The behavior that this Relay should call in another thread when
+        passed a value, or None to have passed values ignored.
+    """
+    raise NotImplementedError()
+
+
+class _PoolRelay(activated.Activated, Relay):
+
+  @enum.unique
+  class _State(enum.Enum):
+    INACTIVE = 'inactive'
+    IDLE = 'idle'
+    SPINNING = 'spinning'
+
+  def __init__(self, pool, behavior):
+    self._condition = threading.Condition()
+    self._pool = pool
+    self._own_pool = pool is None
+    self._state = _PoolRelay._State.INACTIVE
+    self._activated = False
+    self._spinning = False
+    self._values = []
+    self._behavior = _NULL_BEHAVIOR if behavior is None else behavior
+
+  def _spin(self, behavior, value):
+    while True:
+      behavior(value)
+      with self._condition:
+        if self._values:
+          value = self._values.pop(0)
+          behavior = self._behavior
+        else:
+          self._state = _PoolRelay._State.IDLE
+          self._condition.notify_all()
+          break
+
+  def add_value(self, value):
+    with self._condition:
+      if self._state is _PoolRelay._State.INACTIVE:
+        raise ValueError('add_value not valid on inactive Relay!')
+      elif self._state is _PoolRelay._State.IDLE:
+        self._pool.submit(self._spin, self._behavior, value)
+        self._state = _PoolRelay._State.SPINNING
+      else:
+        self._values.append(value)
+
+  def set_behavior(self, behavior):
+    with self._condition:
+      self._behavior = _NULL_BEHAVIOR if behavior is None else behavior
+
+  def _start(self):
+    with self._condition:
+      self._state = _PoolRelay._State.IDLE
+      if self._own_pool:
+        self._pool = logging_pool.pool(1)
+      return self
+
+  def _stop(self):
+    with self._condition:
+      while self._state is _PoolRelay._State.SPINNING:
+        self._condition.wait()
+      if self._own_pool:
+        self._pool.shutdown(wait=True)
+      self._state = _PoolRelay._State.INACTIVE
+
+  def __enter__(self):
+    return self._start()
+
+  def __exit__(self, exc_type, exc_val, exc_tb):
+    self._stop()
+    return False
+
+  def start(self):
+    return self._start()
+
+  def stop(self):
+    self._stop()
+
+
+def relay(behavior):
+  """Creates a Relay.
+
+  Args:
+    behavior: The behavior to be called by the created Relay, or None to have
+      passed values dropped until a different behavior is given to the returned
+      Relay later.
+
+  Returns:
+    An object that is both an activated.Activated and a Relay. The object is
+      only valid for use as a Relay when activated.
+  """
+  return _PoolRelay(None, behavior)
+
+
+def pool_relay(pool, behavior):
+  """Creates a Relay that uses a given thread pool.
+
+  This object will make use of at most one thread in the given pool.
+
+  Args:
+    pool: A futures.ThreadPoolExecutor for use by the created Relay.
+    behavior: The behavior to be called by the created Relay, or None to have
+      passed values dropped until a different behavior is given to the returned
+      Relay later.
+
+  Returns:
+    An object that is both an activated.Activated and a Relay. The object is
+      only valid for use as a Relay when activated.
+  """
+  return _PoolRelay(pool, behavior)
diff --git a/src/python/src/grpc/framework/interfaces/__init__.py b/src/python/src/grpc/framework/interfaces/__init__.py
new file mode 100644
index 0000000000..7086519106
--- /dev/null
+++ b/src/python/src/grpc/framework/interfaces/__init__.py
@@ -0,0 +1,30 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
diff --git a/src/python/src/grpc/framework/interfaces/links/__init__.py b/src/python/src/grpc/framework/interfaces/links/__init__.py
new file mode 100644
index 0000000000..7086519106
--- /dev/null
+++ b/src/python/src/grpc/framework/interfaces/links/__init__.py
@@ -0,0 +1,30 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+
diff --git a/src/python/src/grpc/framework/interfaces/links/links.py b/src/python/src/grpc/framework/interfaces/links/links.py
new file mode 100644
index 0000000000..5ebbac8a6f
--- /dev/null
+++ b/src/python/src/grpc/framework/interfaces/links/links.py
@@ -0,0 +1,124 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""The low-level ticket-exchanging-links interface of RPC Framework."""
+
+import abc
+import collections
+import enum
+
+
+class Ticket(
+    collections.namedtuple(
+        'Ticket',
+        ['operation_id', 'sequence_number', 'group', 'method', 'subscription',
+         'timeout', 'allowance', 'initial_metadata', 'payload',
+         'terminal_metadata', 'code', 'message', 'termination'])):
+  """A sum type for all values sent from a front to a back.
+
+  Attributes:
+    operation_id: A unique-with-respect-to-equality hashable object identifying
+      a particular operation.
+    sequence_number: A zero-indexed integer sequence number identifying the
+      ticket's place in the stream of tickets sent in one direction for the
+      particular operation.
+    group: The group to which the method of the operation belongs. Must be
+      present in the first ticket from invocation side to service side. Ignored
+      for all other tickets exchanged during the operation.
+    method: The name of an operation. Must be present in the first ticket from
+      invocation side to service side. Ignored for all other tickets exchanged
+      during the operation.
+    subscription: A Subscription value describing the interest one side has in
+      receiving information from the other side. Must be present in the first
+      ticket from either side. Ignored for all other tickets exchanged during
+      the operation.
+    timeout: A nonzero length of time (measured from the beginning of the
+      operation) to allow for the entire operation. Must be present in the first
+      ticket from invocation side to service side. Optional for all other
+      tickets exchanged during the operation. Receipt of a value from the other
+      side of the operation indicates the value in use by that side. Setting a
+      value on a later ticket allows either side to request time extensions (or
+      even time reductions!) on in-progress operations.
+    allowance: A positive integer granting permission for a number of payloads
+      to be transmitted to the communicating side of the operation, or None if
+      no additional allowance is being granted with this ticket.
+    initial_metadata: An optional metadata value communicated from one side to
+      the other at the beginning of the operation. May be non-None in at most
+      one ticket from each side. Any non-None value must appear no later than
+      the first payload value.
+    payload: A customer payload object. May be None.
+    terminal_metadata: A metadata value comminicated from one side to the other
+      at the end of the operation. May be non-None in the same ticket as
+      the code and message, but must be None for all earlier tickets.
+    code: A value communicated at operation completion. May be None.
+    message: A value communicated at operation completion. May be None.
+    termination: A Termination value describing the end of the operation, or
+      None if the operation has not yet terminated. If set, no further tickets
+      may be sent in the same direction.
+  """
+
+  @enum.unique
+  class Subscription(enum.Enum):
+    """Identifies the level of subscription of a side of an operation."""
+
+    NONE = 'none'
+    TERMINATION = 'termination'
+    FULL = 'full'
+
+  @enum.unique
+  class Termination(enum.Enum):
+    """Identifies the termination of an operation."""
+
+    COMPLETION = 'completion'
+    CANCELLATION = 'cancellation'
+    EXPIRATION = 'expiration'
+    LOCAL_SHUTDOWN = 'local shutdown'
+    RECEPTION_FAILURE = 'reception failure'
+    TRANSMISSION_FAILURE = 'transmission failure'
+    LOCAL_FAILURE = 'local failure'
+    REMOTE_FAILURE = 'remote failure'
+
+
+class Link(object):
+  """Accepts and emits tickets."""
+  __metaclass__ = abc.ABCMeta
+
+  @abc.abstractmethod
+  def accept_ticket(self, ticket):
+    """Accept a Ticket.
+
+    Args:
+      ticket: Any Ticket.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def join_link(self, link):
+    """Mates this object with a peer with which it will exchange tickets."""
+    raise NotImplementedError()
diff --git a/src/python/src/grpc/framework/interfaces/links/test_cases.py b/src/python/src/grpc/framework/interfaces/links/test_cases.py
new file mode 100644
index 0000000000..3ac212ebdf
--- /dev/null
+++ b/src/python/src/grpc/framework/interfaces/links/test_cases.py
@@ -0,0 +1,332 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Tests of the links interface of RPC Framework."""
+
+# unittest is referenced from specification in this module.
+import abc
+import unittest  # pylint: disable=unused-import
+
+from grpc.framework.common import test_constants
+from grpc.framework.interfaces.links import links
+from grpc.framework.interfaces.links import test_utilities
+
+
+def at_least_n_payloads_received_predicate(n):
+  def predicate(ticket_sequence):
+    payload_count = 0
+    for ticket in ticket_sequence:
+      if ticket.payload is not None:
+        payload_count += 1
+        if n <= payload_count:
+          return True
+    else:
+      return False
+  return predicate
+
+
+def terminated(ticket_sequence):
+  return ticket_sequence and ticket_sequence[-1].termination is not None
+
+_TRANSMISSION_GROUP = 'test.Group'
+_TRANSMISSION_METHOD = 'TestMethod'
+
+
+class TransmissionTest(object):
+  """Tests ticket transmission between two connected links.
+
+  This class must be mixed into a unittest.TestCase that implements the abstract
+  methods it provides.
+  """
+  __metaclass__ = abc.ABCMeta
+
+  # This is a unittest.TestCase mix-in.
+  # pylint: disable=invalid-name
+
+  @abc.abstractmethod
+  def create_transmitting_links(self):
+    """Creates two connected links for use in this test.
+
+    Returns:
+      Two links.Links, the first of which will be used on the invocation side
+        of RPCs and the second of which will be used on the service side of
+        RPCs.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def destroy_transmitting_links(self, invocation_side_link, service_side_link):
+    """Destroys the two connected links created for this test.
+
+
+    Args:
+      invocation_side_link: The link used on the invocation side of RPCs in
+        this test.
+      service_side_link: The link used on the service side of RPCs in this
+        test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def create_invocation_initial_metadata(self):
+    """Creates a value for use as invocation-side initial metadata.
+
+    Returns:
+      A metadata value appropriate for use as invocation-side initial metadata
+        or None if invocation-side initial metadata transmission is not
+        supported by the links under test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def create_invocation_terminal_metadata(self):
+    """Creates a value for use as invocation-side terminal metadata.
+
+    Returns:
+      A metadata value appropriate for use as invocation-side terminal
+        metadata or None if invocation-side terminal metadata transmission is
+        not supported by the links under test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def create_service_initial_metadata(self):
+    """Creates a value for use as service-side initial metadata.
+
+    Returns:
+      A metadata value appropriate for use as service-side initial metadata or
+        None if service-side initial metadata transmission is not supported by
+        the links under test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def create_service_terminal_metadata(self):
+    """Creates a value for use as service-side terminal metadata.
+
+    Returns:
+      A metadata value appropriate for use as service-side terminal metadata or
+        None if service-side terminal metadata transmission is not supported by
+        the links under test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def create_invocation_completion(self):
+    """Creates values for use as invocation-side code and message.
+
+    Returns:
+      An invocation-side code value and an invocation-side message value.
+        Either or both may be None if invocation-side code and/or
+        invocation-side message transmission is not supported by the links
+        under test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def create_service_completion(self):
+    """Creates values for use as service-side code and message.
+
+    Returns:
+      A service-side code value and a service-side message value. Either or
+        both may be None if service-side code and/or service-side message
+        transmission is not supported by the links under test.
+    """
+    raise NotImplementedError()
+
+  @abc.abstractmethod
+  def assertMetadataEqual(self, original_metadata, transmitted_metadata):
+    """Asserts that two metadata objects are equal.
+
+    Args:
+      original_metadata: A metadata object used in this test.
+      transmitted_metadata: A metadata object obtained after transmission
+        through the system under test.
+
+    Raises:
+      AssertionError: if the two metadata objects are not equal.
+    """
+    raise NotImplementedError()
+
+  def group_and_method(self):
+    """Returns the group and method used in this test case.
+
+    Returns:
+      A pair of the group and method used in this test case.
+    """
+    return _TRANSMISSION_GROUP, _TRANSMISSION_METHOD
+
+  def serialize_request(self, request):
+    """Serializes a request value used in this test case.
+
+    Args:
+      request: A request value created by this test case.
+
+    Returns:
+      A bytestring that is the serialization of the given request.
+    """
+    return request
+
+  def deserialize_request(self, serialized_request):
+    """Deserializes a request value used in this test case.
+
+    Args:
+      serialized_request: A bytestring that is the serialization of some request
+        used in this test case.
+
+    Returns:
+      The request value encoded by the given bytestring.
+    """
+    return serialized_request
+
+  def serialize_response(self, response):
+    """Serializes a response value used in this test case.
+
+    Args:
+      response: A response value created by this test case.
+
+    Returns:
+      A bytestring that is the serialization of the given response.
+    """
+    return response
+
+  def deserialize_response(self, serialized_response):
+    """Deserializes a response value used in this test case.
+
+    Args:
+      serialized_response: A bytestring that is the serialization of some
+        response used in this test case.
+
+    Returns:
+      The response value encoded by the given bytestring.
+    """
+    return serialized_response
+
+  def _assert_is_valid_metadata_payload_sequence(
+      self, ticket_sequence, payloads, initial_metadata, terminal_metadata):
+    initial_metadata_seen = False
+    seen_payloads = []
+    terminal_metadata_seen = False
+
+    for ticket in ticket_sequence:
+      if ticket.initial_metadata is not None:
+        self.assertFalse(initial_metadata_seen)
+        self.assertFalse(seen_payloads)
+        self.assertFalse(terminal_metadata_seen)
+        self.assertMetadataEqual(initial_metadata, ticket.initial_metadata)
+        initial_metadata_seen = True
+
+      if ticket.payload is not None:
+        self.assertFalse(terminal_metadata_seen)
+        seen_payloads.append(ticket.payload)
+
+      if ticket.terminal_metadata is not None:
+        self.assertFalse(terminal_metadata_seen)
+        self.assertMetadataEqual(terminal_metadata, ticket.terminal_metadata)
+        terminal_metadata_seen = True
+    self.assertSequenceEqual(payloads, seen_payloads)
+
+  def _assert_is_valid_invocation_sequence(
+      self, ticket_sequence, group, method, payloads, initial_metadata,
+      terminal_metadata, termination):
+    self.assertLess(0, len(ticket_sequence))
+    self.assertEqual(group, ticket_sequence[0].group)
+    self.assertEqual(method, ticket_sequence[0].method)
+    self._assert_is_valid_metadata_payload_sequence(
+        ticket_sequence, payloads, initial_metadata, terminal_metadata)
+    self.assertIs(termination, ticket_sequence[-1].termination)
+
+  def _assert_is_valid_service_sequence(
+      self, ticket_sequence, payloads, initial_metadata, terminal_metadata,
+      code, message, termination):
+    self.assertLess(0, len(ticket_sequence))
+    self._assert_is_valid_metadata_payload_sequence(
+        ticket_sequence, payloads, initial_metadata, terminal_metadata)
+    self.assertEqual(code, ticket_sequence[-1].code)
+    self.assertEqual(message, ticket_sequence[-1].message)
+    self.assertIs(termination, ticket_sequence[-1].termination)
+
+  def setUp(self):
+    self._invocation_link, self._service_link = self.create_transmitting_links()
+    self._invocation_mate = test_utilities.RecordingLink()
+    self._service_mate = test_utilities.RecordingLink()
+    self._invocation_link.join_link(self._invocation_mate)
+    self._service_link.join_link(self._service_mate)
+
+  def tearDown(self):
+    self.destroy_transmitting_links(self._invocation_link, self._service_link)
+
+  def testSimplestRoundTrip(self):
+    """Tests transmission of one ticket in each direction."""
+    invocation_operation_id = object()
+    invocation_payload = b'\x07' * 1023
+    timeout = test_constants.LONG_TIMEOUT
+    invocation_initial_metadata = self.create_invocation_initial_metadata()
+    invocation_terminal_metadata = self.create_invocation_terminal_metadata()
+    invocation_code, invocation_message = self.create_invocation_completion()
+    service_payload = b'\x08' * 1025
+    service_initial_metadata = self.create_service_initial_metadata()
+    service_terminal_metadata = self.create_service_terminal_metadata()
+    service_code, service_message = self.create_service_completion()
+
+    original_invocation_ticket = links.Ticket(
+        invocation_operation_id, 0, _TRANSMISSION_GROUP, _TRANSMISSION_METHOD,
+        links.Ticket.Subscription.FULL, timeout, 0, invocation_initial_metadata,
+        invocation_payload, invocation_terminal_metadata, invocation_code,
+        invocation_message, links.Ticket.Termination.COMPLETION)
+    self._invocation_link.accept_ticket(original_invocation_ticket)
+
+    # TODO(nathaniel): This shouldn't be necessary. Detecting the end of the
+    # invocation-side ticket sequence shouldn't require granting allowance for
+    # another payload.
+    self._service_mate.block_until_tickets_satisfy(
+        at_least_n_payloads_received_predicate(1))
+    service_operation_id = self._service_mate.tickets()[0].operation_id
+    self._service_link.accept_ticket(
+        links.Ticket(
+            service_operation_id, 0, None, None, links.Ticket.Subscription.FULL,
+            None, 1, None, None, None, None, None, None))
+
+    self._service_mate.block_until_tickets_satisfy(terminated)
+    self._assert_is_valid_invocation_sequence(
+        self._service_mate.tickets(), _TRANSMISSION_GROUP, _TRANSMISSION_METHOD,
+        (invocation_payload,), invocation_initial_metadata,
+        invocation_terminal_metadata, links.Ticket.Termination.COMPLETION)
+
+    original_service_ticket = links.Ticket(
+        service_operation_id, 1, None, None, links.Ticket.Subscription.FULL,
+        timeout, 0, service_initial_metadata, service_payload,
+        service_terminal_metadata, service_code, service_message,
+        links.Ticket.Termination.COMPLETION)
+    self._service_link.accept_ticket(original_service_ticket)
+    self._invocation_mate.block_until_tickets_satisfy(terminated)
+    self._assert_is_valid_service_sequence(
+        self._invocation_mate.tickets(), (service_payload,),
+        service_initial_metadata, service_terminal_metadata, service_code,
+        service_message, links.Ticket.Termination.COMPLETION)
diff --git a/src/python/src/grpc/framework/interfaces/links/test_utilities.py b/src/python/src/grpc/framework/interfaces/links/test_utilities.py
new file mode 100644
index 0000000000..6c2e3346aa
--- /dev/null
+++ b/src/python/src/grpc/framework/interfaces/links/test_utilities.py
@@ -0,0 +1,66 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""State and behavior appropriate for use in tests."""
+
+import threading
+
+from grpc.framework.interfaces.links import links
+
+
+class RecordingLink(links.Link):
+  """A Link that records every ticket passed to it."""
+
+  def __init__(self):
+    self._condition = threading.Condition()
+    self._tickets = []
+
+  def accept_ticket(self, ticket):
+    with self._condition:
+      self._tickets.append(ticket)
+      self._condition.notify_all()
+
+  def join_link(self, link):
+    pass
+
+  def block_until_tickets_satisfy(self, predicate):
+    """Blocks until the received tickets satisfy the given predicate.
+
+    Args:
+      predicate: A callable that takes a sequence of tickets and returns a
+        boolean value.
+    """
+    with self._condition:
+      while not predicate(self._tickets):
+        self._condition.wait()
+
+  def tickets(self):
+    """Returns a copy of the list of all tickets received by this Link."""
+    with self._condition:
+      return tuple(self._tickets)
diff --git a/src/python/src/grpc/framework/interfaces/links/utilities.py b/src/python/src/grpc/framework/interfaces/links/utilities.py
new file mode 100644
index 0000000000..6e4fd76d93
--- /dev/null
+++ b/src/python/src/grpc/framework/interfaces/links/utilities.py
@@ -0,0 +1,44 @@
+# Copyright 2015, Google Inc.
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#     * Neither the name of Google Inc. nor the names of its
+# contributors may be used to endorse or promote products derived from
+# this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+"""Utilities provided as part of the links interface."""
+
+from grpc.framework.interfaces.links import links
+
+
+class _NullLink(links.Link):
+  """A do-nothing links.Link."""
+
+  def accept_ticket(self, ticket):
+    pass
+
+  def join_link(self, link):
+    pass
+
+NULL_LINK = _NullLink()
diff --git a/src/python/src/setup.py b/src/python/src/setup.py
index b9764bdc07..a857ae98cc 100644
--- a/src/python/src/setup.py
+++ b/src/python/src/setup.py
@@ -76,6 +76,7 @@ _PACKAGES = (
     'grpc',
     'grpc._adapter',
     'grpc._junkdrawer',
+    'grpc._links',
     'grpc.early_adopter',
     'grpc.framework',
     'grpc.framework.alpha',
@@ -84,12 +85,15 @@ _PACKAGES = (
     'grpc.framework.face',
     'grpc.framework.face.testing',
     'grpc.framework.foundation',
+    'grpc.framework.interfaces',
+    'grpc.framework.interfaces.links',
 )
 
 _PACKAGE_DIRECTORIES = {
     'grpc': 'grpc',
     'grpc._adapter': 'grpc/_adapter',
     'grpc._junkdrawer': 'grpc/_junkdrawer',
+    'grpc._links': 'grpc/_links',
     'grpc.early_adopter': 'grpc/early_adopter',
     'grpc.framework': 'grpc/framework',
 }