code: @Override
    public void getSubchannel(
        GetSubchannelRequest request, StreamObserver<GetSubchannelResponse> responseObserver) {
      InternalInstrumented<ChannelStats> s = channelz.getSubchannel(request.getSubchannelId());
      if (s == null) {
        responseObserver.onError(
            Status.NOT_FOUND.withDescription("Can't find subchannel " + request.getSubchannelId())
                .asRuntimeException());
        return;
      }
  
      GetSubchannelResponse resp;
      try {
        resp = GetSubchannelResponse
            .newBuilder()
            .setSubchannel(ChannelzProtoUtil.toSubchannel(s))
            .build();
      } catch (StatusRuntimeException e) {
        responseObserver.onError(e);
        return;
      }
  
      responseObserver.onNext(resp);
      responseObserver.onCompleted();
    }
docs: Returns a subchannel.