Implements the unary unary interceptor for the client-side. Interceptors
can be now installed by passing them as a new parameter of the `Channel`
constructor or by giving them as part of the `insecure_channel`
function.
Interceptors are executed within an Asyncio task for making some work before
the RPC invocation, and after for accessing to the intercepted call that has
been invoked.
* Remove the weird cancellation_future;
* Convert all CancelledError into RpcError with CANCELLED;
* Move part of call logic from Cython to Python layer;
* Make unary-stream call based on reader API instead of async generator.
* Refactors how Task wrapper work on the client-side
* Refactors final status propagation and unify similar classes
* Adds unary-stream API for both-sides
* Refactors each abstraction layer multicallable / call / channel
* Revisits the design of cancellation on client-side
* Makes server methods interuptable
* Fixes a zombie coroutine issue in shutdown path
* Make graceful shutdown support calls from multi-coroutine
* Added comments
* Make graceful shutdown success test case more strict
* Add 2 more concurrent graceful shutdown tests
Call interface, implemented by the new `grpc.experimental.aio.Call`
object is the unique entry point for handling RPC calls and is the
one returned by, for now, the `unary_unary` method. It supports all
in one the three interfaces `with_call`, `__call__` and `future` implemented
by the synchronous API.
Pau Freixes
Yihua Zhang
Lidi Zheng
Esun Kim
Richard Belleville
Jan Tattermusch
Yash Tibrewal