Fix UnaryStreamMultiCallable and StreamStreamMultiCallable Future/Call

[shabbyrobe]

See #41

[bkeryan]

That's not quite it. The UnaryStreamMultiCallable is not itself the stream. Calling the UnaryStreamMultiCallable (i.e. the __call__ method) returns the stream.

CallIterator[TResponse] currently inherits from Call. I think it should inherit from CallFuture[TResponse].

[bkeryan]

Correction: CallFuture[TResponse] implies that stream.result() returns a TResponse, but that doesn't seem to be the case.

The behavior of stream.result() doesn't seem to be documented, but as far as I can tell from testing: for server-streaming RPCs, result() waits for the RPC to complete (stream closed, canceled, or error). When the stream is closed, it returns None.

Tested with a modified version of https://github.com/grpc/grpc/blob/master/examples/python/hellostreamingworld/async_greeter_client.py:

import logging

import grpc
import hellostreamingworld_pb2
import hellostreamingworld_pb2_grpc


def run() -> None:
    with grpc.insecure_channel("localhost:50051") as channel:
        stub = hellostreamingworld_pb2_grpc.MultiGreeterStub(channel)

        hello_stream = stub.sayHello(
            hellostreamingworld_pb2.HelloRequest(name="you"))
        while True:
            try:
                response = hello_stream.result(timeout=0.1)
                print(f"result() returned {type(response)}: {repr(response)}")
                if response is None:
                    break
            except grpc.FutureTimeoutError:
                response = next(hello_stream, None)
                print(f"next() returned {type(response)}: {repr(response)}")
                if response is None: 
                    break

if __name__ == "__main__":
    logging.basicConfig()
    run()

python greeter_client.py
next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 0, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 1, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 2, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 3, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 4, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 5, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 6, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 7, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 8, you!"

next() returned <class 'hellostreamingworld_pb2.HelloReply'>: message: "Hello number 9, you!"

result() returned <class 'NoneType'>: None

[bkeryan]

This function returns the multi-callable object, not the stream. Call the multi-callable to get the stream.