Check conformance to grpc.GenericRpcHandler type

src/python/grpcio/grpc/__init__.py

@@ -1656,9 +1656,11 @@ def server(thread_pool,
       A Server object.
     """
     from grpc import _server  # pylint: disable=cyclic-import
-    return _server.Server(thread_pool, () if handlers is None else handlers, ()
-                          if interceptors is None else interceptors, () if
-                          options is None else options, maximum_concurrent_rpcs)
+    return _server.create_server(thread_pool, ()
+                                 if handlers is None else handlers, ()
+                                 if interceptors is None else interceptors, ()
+                                 if options is None else options,
+                                 maximum_concurrent_rpcs)
 
 
 ###################################  __all__  #################################

src/python/grpcio/grpc/_server.py

@@ -787,7 +787,16 @@ def _start(state):
         thread.start()
 
 
-class Server(grpc.Server):
+def _validate_generic_rpc_handlers(generic_rpc_handlers):
+    for generic_rpc_handler in generic_rpc_handlers:
+        service_attribute = getattr(generic_rpc_handler, 'service', None)
+        if service_attribute is None:
+            raise AttributeError(
+                '"{}" must conform to grpc.GenericRpcHandler type but does '
+                'not have "service" method!'.format(generic_rpc_handler))
+
+
+class _Server(grpc.Server):
 
     # pylint: disable=too-many-arguments
     def __init__(self, thread_pool, generic_handlers, interceptors, options,
@@ -800,6 +809,7 @@ class Server(grpc.Server):
                                    thread_pool, maximum_concurrent_rpcs)
 
     def add_generic_rpc_handlers(self, generic_rpc_handlers):
+        _validate_generic_rpc_handlers(generic_rpc_handlers)
         _add_generic_handlers(self._state, generic_rpc_handlers)
 
     def add_insecure_port(self, address):
@@ -817,3 +827,10 @@ class Server(grpc.Server):
 
     def __del__(self):
         _stop(self._state, None)
+
+
+def create_server(thread_pool, generic_rpc_handlers, interceptors, options,
+                  maximum_concurrent_rpcs):
+    _validate_generic_rpc_handlers(generic_rpc_handlers)
+    return _Server(thread_pool, generic_rpc_handlers, interceptors, options,
+                   maximum_concurrent_rpcs)

src/python/grpcio_tests/tests/tests.json

@@ -53,6 +53,7 @@
   "unit._server_ssl_cert_config_test.ServerSSLCertReloadTestCertConfigReuse",
   "unit._server_ssl_cert_config_test.ServerSSLCertReloadTestWithClientAuth",
   "unit._server_ssl_cert_config_test.ServerSSLCertReloadTestWithoutClientAuth",
+  "unit._server_test.ServerTest",
   "unit._session_cache_test.SSLSessionCacheTest",
   "unit.beta._beta_features_test.BetaFeaturesTest",
   "unit.beta._beta_features_test.ContextManagementAndLifecycleTest",

src/python/grpcio_tests/tests/unit/_server_test.py

@@ -0,0 +1,52 @@
+# Copyright 2018 The gRPC Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from concurrent import futures
+import unittest
+
+import grpc
+
+
+class _ActualGenericRpcHandler(grpc.GenericRpcHandler):
+
+    def service(self, handler_call_details):
+        return None
+
+
+class ServerTest(unittest.TestCase):
+
+    def test_not_a_generic_rpc_handler_at_construction(self):
+        with self.assertRaises(AttributeError) as exception_context:
+            grpc.server(
+                futures.ThreadPoolExecutor(max_workers=5),
+                handlers=[
+                    _ActualGenericRpcHandler(),
+                    object(),
+                ])
+        self.assertIn('grpc.GenericRpcHandler',
+                      str(exception_context.exception))
+
+    def test_not_a_generic_rpc_handler_after_construction(self):
+        server = grpc.server(futures.ThreadPoolExecutor(max_workers=5))
+        with self.assertRaises(AttributeError) as exception_context:
+            server.add_generic_rpc_handlers([
+                _ActualGenericRpcHandler(),
+                object(),
+            ])
+        self.assertIn('grpc.GenericRpcHandler',
+                      str(exception_context.exception))
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)