Handling errors from streams in python

[li...@vedra.io]

Hi,

I've been trying ascertain the correct way to handle error behaviour from streaming endpoints.

My code effectively does the following:

service MyService {
    rpc StreamEndpoint(Request) returns (stream Response)
}

message Request {
    repeated string query_ids = 1;
}

message Response {
    string object_id = 1;
}

class MyService(MyServiceServicer):

    def StreamEndpoint(self, request, context):
        if not request.query_ids:
            context.set_code(grpc.StatusCode.INVALID_ARGUMENT)
            context.set_details('Must set at least one id')
            yield Empty()
        for obj in self.db.query(id_list=request.query_ids):
            yield obj.to_protobuf()

I was expecting the client upon calling StreamEndpoint without query_ids to throw an RpcError (the client is also in Python) upon getting a code that isn't OK. However, it doesn't, even though the code in the response is correctly set to INVALID_ARGUMENT.

Is this the correct behaviour? If so, what is usually the recommended way of handling these errors in python, as I have relied on the exception on non-streaming endpoints.

Thanks

[Mehrdad Afshari]

Can you please share a minimal client code that exhibits the behavior?

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[li...@vedra.io]

So, this is the unit test code that fails (the stub and server are initialized in the setUp):

    def test_list_invalid(self):
        request = service_pb2.Request()
        with self.assertRaises(expected_exception=grpc.RpcError) as error:
            for _ in self.stub.StreamEndpoint(request):
                pass
        self.assertEqual(error.exception.code(), grpc.StatusCode.INVALID_ARGUMENT)

This test completes with AssertionError: RpcError not raised. Although, if I check the response, it does have the correct status code.