grpclib_client: handle trailer-only responses (#127)

Resolves: #123

tests/grpc/test_grpclib_client.py

@@ -9,6 +9,7 @@ from tests.output_betterproto.service.service import (
 )
 import grpclib
 import grpclib.metadata
+import grpclib.server
 from grpclib.testing import ChannelFor
 import pytest
 from betterproto.grpc.util.async_channel import AsyncChannel
@@ -32,12 +33,59 @@ def _assert_request_meta_received(deadline, metadata):
     return server_side_test
 
 
+@pytest.fixture
+def handler_trailer_only_unauthenticated():
+    async def handler(stream: grpclib.server.Stream):
+        await stream.recv_message()
+        await stream.send_initial_metadata()
+        await stream.send_trailing_metadata(status=grpclib.Status.UNAUTHENTICATED)
+
+    return handler
+
+
 @pytest.mark.asyncio
 async def test_simple_service_call():
     async with ChannelFor([ThingService()]) as channel:
         await _test_client(ThingServiceClient(channel))
 
 
+@pytest.mark.asyncio
+async def test_trailer_only_error_unary_unary(
+    mocker, handler_trailer_only_unauthenticated
+):
+    service = ThingService()
+    mocker.patch.object(
+        service,
+        "do_thing",
+        side_effect=handler_trailer_only_unauthenticated,
+        autospec=True,
+    )
+    async with ChannelFor([service]) as channel:
+        with pytest.raises(grpclib.exceptions.GRPCError) as e:
+            await ThingServiceClient(channel).do_thing(name="something")
+        assert e.value.status == grpclib.Status.UNAUTHENTICATED
+
+
+@pytest.mark.asyncio
+async def test_trailer_only_error_stream_unary(
+    mocker, handler_trailer_only_unauthenticated
+):
+    service = ThingService()
+    mocker.patch.object(
+        service,
+        "do_many_things",
+        side_effect=handler_trailer_only_unauthenticated,
+        autospec=True,
+    )
+    async with ChannelFor([service]) as channel:
+        with pytest.raises(grpclib.exceptions.GRPCError) as e:
+            await ThingServiceClient(channel).do_many_things(
+                request_iterator=[DoThingRequest(name="something")]
+            )
+            await _test_client(ThingServiceClient(channel))
+        assert e.value.status == grpclib.Status.UNAUTHENTICATED
+
+
 @pytest.mark.asyncio
 @pytest.mark.skipif(
     sys.version_info < (3, 8), reason="async mock spy does works for python3.8+"