Grpc channel API breaks when using grpc client instrumentor

[ianmcnally]

Describe your environment
I'm using GrpcInstrumentorClient (https://opentelemetry-python-contrib.readthedocs.io/en/latest/instrumentation/grpc/grpc.html#usage-client) version 0.30b1 in a python (3.7) flask application. When closing the channel, using a custom wrapper around channel, calls to the grpc.Channel._channel API fail.

Steps to reproduce

1. Instrument with GrpcInstrumentorClient().instrument()
2. In a grpc middleware, or anywhere with access to the grpc channel object, call a method on channel._channel, like channel._channel.check_connectivity_state()

What is the expected behavior?
the grpc channel._channel is an instance of grpc._cython.cygrpc.Channel

What is the actual behavior?
the grpc channel._channel is an instance of grpc._channel.Channel

Additional context
GRPCInstrumentorClient works fine with no middleware or other interceptors present.

[ianmcnally]

One potential fix:

Setting _channel here to channel._channel and renaming the current instance variable (_channel)

That would keep the same channel._channel API for other middleware or interceptors.

[ianmcnally]

I think the ideal solution though would not be to wrap grpc.Channel with InterceptorChannel

[ianmcnally]

semi-related, but trying to use client_interceptor also fails validation in grpc/_interceptor.py (grpc version 3.13)

[ocelotl]

2. In a grpc middleware, or anywhere with access to the grpc channel object, call a method on channel._channel, like channel._channel.check_connectivity_state()

Why are you calling an attribute of the private _channel?