Add ability to filter out services from being bound to server factories

[onobc]

The main feature request from #144 was solved in a087eac.
However, one improvement would be the ability to filter out services from being bound to the InProcess server / factory.

Similarly to how we are filtering out client side interceptors from channel factories, we should allow users to configure a filter(s) that does the same for the server-side factory.

[therepanic]

Hi, @onobc! Since this feature is similar to what I implemented, can I try it too?

[onobc]

Hi @therepanic ! I was hoping you were keeping your eye on the issue board (as you usually are 😺 - which is much appreciated). I reached out the team to get agreement on the need to do this filtering but I am 99% sure it is something we will all agree on. Feel free to submit a code proposal.

Note

While digging around to add some details to this issue, I also noticed that we will likely want to add filtering of the server-side global interceptors. I created #208 to cover this separately though.

Details

I think we will want these service filtering components to live in the core module, like we did for the client filter components (namely ClientInterceptorsConfigurer). The DefaultGrpcServerFactory#addService method could do something like:

  @Override
  public void addService(ServerServiceDefinition service) {
    if (this.serviceFilter == null || this.serviceFilter.filter(service, this)) {
      this.serviceList.add(service);
    }
  }

Wdyt?

[therepanic]

Thanks.

Yes, I think that's okay, I will do that.

[therepanic]

Hello @onobc again. I assume the team has approved everything? If so, I will send the PR tomorrow.

[onobc]

Yes @therepanic - please go forward w/ this. Thank you.

[therepanic]

To be honest, I don't quite understand how we can test this. I think we want to check that the filter has been applied and that we haven't added a ServerServiceDefinition instance to DefaultGrpcServerFactory#serviceList field. However, this field itself is private and there are no getters. On the other hand, I think it would be good to have a constructor for serviceList. I don't think it's a good idea to use reflection. Or is there another way?

[onobc]

To be honest, I don't quite understand how we can test this. I think we want to check that the filter has been applied and that we haven't added a ServerServiceDefinition instance to DefaultGrpcServerFactory#serviceList field. However, this field itself is private and there are no getters. On the other hand, I think it would be good to have a constructor for serviceList. I don't think it's a good idea to use reflection. Or is there another way?

Hi @therepanic , so AssertJ makes "digging down into the details" very easy w/ its extracting method. As to whether this is the best practice for testing - it comes through in cases like this and I am not against using it. You can see GrpcServerAutoConfigurationTests for an example.