Return UNKNOWN on GenericRpcHandler failure

A GenericRpcHandler registered on a gRPC Server is not supposed to raise
an exception and if it does so it is considered a programming defect.
However, gRPC is supposed to respond to the client with an UNKNOWN
status code.  Previously, this situation was left unhandled and the
client ended up receiving a response with CANCELLED status code.

This commit fixes the issue https://github.com/grpc/grpc/issues/13629.

2 files changed, 29 insertions, 1 deletions

diff --git a/src/python/grpcio/grpc/_server.py b/src/python/grpcio/grpc/_server.py
index cd59b07c04..04f943c079 100644
--- a/src/python/grpcio/grpc/_server.py
+++ b/src/python/grpcio/grpc/_server.py
@@ -591,7 +591,13 @@ def _handle_call(rpc_event, generic_handlers, thread_pool,
     if not rpc_event.success:
         return None, None
     if rpc_event.request_call_details.method is not None:
-        method_handler = _find_method_handler(rpc_event, generic_handlers)
+        try:
+            method_handler = _find_method_handler(rpc_event, generic_handlers)
+        except Exception as e:  # pylint: disable=broad-except
+            details = 'Exception servicing handler: {}'.format(e)
+            logging.exception(details)
+            return _reject_rpc(rpc_event, cygrpc.StatusCode.unknown,
+                               b'Error in service handler!'), None
         if method_handler is None:
             return _reject_rpc(rpc_event, cygrpc.StatusCode.unimplemented,
                                b'Method not found!'), None
diff --git a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
index 0a1e50c94c..2a1a49ce74 100644
--- a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
+++ b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
@@ -32,6 +32,7 @@ _UNARY_UNARY = '/test/UnaryUnary'
 _UNARY_STREAM = '/test/UnaryStream'
 _STREAM_UNARY = '/test/StreamUnary'
 _STREAM_STREAM = '/test/StreamStream'
+_DEFECTIVE_GENERIC_RPC_HANDLER = '/test/DefectiveGenericRpcHandler'
 
 
 class _Callback(object):
@@ -95,6 +96,9 @@ class _Handler(object):
             yield request
         self._control.control()
 
+    def defective_generic_rpc_handler(self):
+        raise test_control.Defect()
+
 
 class _MethodHandler(grpc.RpcMethodHandler):
 
@@ -132,6 +136,8 @@ class _GenericHandler(grpc.GenericRpcHandler):
         elif handler_call_details.method == _STREAM_STREAM:
             return _MethodHandler(True, True, None, None, None, None, None,
                                   self._handler.handle_stream_stream)
+        elif handler_call_details.method == _DEFECTIVE_GENERIC_RPC_HANDLER:
+            return self._handler.defective_generic_rpc_handler()
         else:
             return None
 
@@ -176,6 +182,10 @@ def _stream_stream_multi_callable(channel):
     return channel.stream_stream(_STREAM_STREAM)
 
 
+def _defective_handler_multi_callable(channel):
+    return channel.unary_unary(_DEFECTIVE_GENERIC_RPC_HANDLER)
+
+
 class InvocationDefectsTest(unittest.TestCase):
 
     def setUp(self):
@@ -235,6 +245,18 @@ class InvocationDefectsTest(unittest.TestCase):
             for _ in range(test_constants.STREAM_LENGTH // 2 + 1):
                 next(response_iterator)
 
+    def testDefectiveGenericRpcHandlerUnaryResponse(self):
+        request = b'\x07\x08'
+        multi_callable = _defective_handler_multi_callable(self._channel)
+
+        with self.assertRaises(grpc.RpcError) as exception_context:
+            response = multi_callable(
+                request,
+                metadata=(('test', 'DefectiveGenericRpcHandlerUnary'),))
+
+        self.assertIs(grpc.StatusCode.UNKNOWN,
+                      exception_context.exception.code())
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)