gRPC integration

[c24t]

This is a port of grpcio-opentracing, and borrows from opencensus-ext-grpc. It adds client and server interceptors that wrap each request in a span and use the new context API to inject/extract the traceparent header to/from gRPC metadata.

The PR includes two examples copied from grpc-python itself:

• helloworld (source, docs) which shows how to instrument the client and server in a basic unary-unary call pattern
• route_guide (source, docs) which includes examples for unary-unary, client-streaming, server-streaming, and bidirectional streaming

Running the examples

% cd ext/opentelemetry-ext-grpc/examples
% ./hello_world_server.py
Span(name="/helloworld.Greeter/SayHello", context=SpanContext(trace_id=0xdc68d08b983225bf3b86eabfc9a9f02c, span_id=0x12aa95fc91338970, trace_state={}), kind=SpanKind.SERVER, parent=<opentelemetry.trace.DefaultSpan object at 0x10943d190>, start_time=2020-03-25T00:23:31.605991Z, end_time=2020-03-25T00:23:31.606155Z)

% ./hello_world_client.py
Span(name="/helloworld.Greeter/SayHello", context=SpanContext(trace_id=0xdc68d08b983225bf3b86eabfc9a9f02c, span_id=0xb4766ea78457996c, trace_state={}), kind=SpanKind.CLIENT, parent=None, start_time=2020-03-25T00:23:31.574011Z, end_time=2020-03-25T00:23:31.606996Z)
Greeter client received: Hello, YOU!

Note that the client's trace ID gets propagated to the server.

You should see something similar running ./route_guide_server.py and route_guide_client.py.

Comparing to grpcio-opentracing

88e9467 copied some files from grpcio-opentracing. To see what changed between OpenTracing and OpenTelemetry, check the diff against 88e94672. The important files are _client.py and _server.py.

The grpcext package is copied from grpcio-opentracing. It implemented interceptors before grpc-python had proper support for them. grpc-python has since added interceptors, but grpcio-opentracing still uses its own implementation.

This PR still uses grpcext, but we should replace this with the official interceptor API in a follow up PR.

See for background:

• Add support for Python. grpc-ecosystem/grpc-opentracing#32
• Create an "interceptor" mechanism for GRPC Python grpc/grpc#8767

How to review

Please ignore the generated _pb2.py and _pb2_grpc.py files. The meat of the PR is in _client.py and _server.py.

Try running the tests and examples.

Still TODO

• This PR only includes server-side unary-unary tests, add tests for both sides for all calling patterns.
• Add span attributes following the semantic conventions in the spec.
• Use the new gRPC interceptor API instead of grpcext.

[codeboten]

Just a couple of questions regarding some code that's commented out. I'm still trying to figure out if there's an underlying bug re. the context but that doesn't have to block this PR.

[johananl]

I've experimented with the code by running a Python gRPC server with a Go gRPC client (code is here and here). Seems to work nicely 👍 Hope this helps.

[c24t]

Thanks @johananl and @codeboten!

[toumorokoshi]

grpc.txt

trying to figure out how to send PRs over, but here's a patch for tox directives.

[toumorokoshi]

not super knowledgeable on GRPC, but verified behavior worked as expected. Thanks!