Implement tower::Service for OtelGrpcService

[timvermeulen]

Implementing Service gives you the GrpcService implementation for free, and it also comes with the benefits of the Service trait, such as being able to use interceptors:

struct MyInterceptor;

impl tonic::service::Interceptor for MyInterceptor {
    fn call(&mut self, request: tonic::Request<()>) -> Result<tonic::Request<()>, tonic::Status> {
        Ok(request)
    }
}

# examples/grpc/src/client.rs

  let channel = ServiceBuilder::new().layer(OtelGrpcLayer).service(channel);

- let mut client = GreeterClient::new(channel);
+ let mut client = GreeterClient::with_interceptor(channel, MyInterceptor);

The above change currently fails to compile because MyInterceptor doesn't implement Service (which InterceptedService requires), only GrpcService.

[davidB]

Thank you