getAttributes() always empty if called from SimpleForwardingClientCall

[maseev]

What version of gRPC are you using?

1.10.0

What did you expect to see?

Let's say we have the following client interceptor which is attached to our channel:

class LoggingClientInterceptor implements ClientInterceptor {

  private static final Logger log = LoggerFactory.getLogger(LoggingClientInterceptor.class);

  @Override
  public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method,
      CallOptions callOptions, Channel next) {
    return new SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
      @Override
      public void start(Listener<RespT> responseListener, Metadata headers) {
        log.info("grpc request; method: {}, attributes: {}", method.getFullMethodName(),
            getAttributes());

        super.start(responseListener, headers);
      }
    };
  }
}

When calling the getAttributes() method I expected to see a set of attributes which contains at least the information about the server to which the client is going to make a request to. Unfortunately, getAttributes() method always empty.

[dapengzhang0]

You seems to call getAttributes() too early that the call is not completely started. The safest timing to call getAttributes() is after the ClientCall.Listener receives anything, say after ClientCall.Listener::onHeader() is called.

[maseev]

Yes, you're right. According to the javadoc, the getAttributes() method may only be called after ClientCall.Listener.onHeaders(io.grpc.Metadata) or ClientCall.Listener.onClose(io.grpc.Status, io.grpc.Metadata). Unfortunately, it doesn't work either. Here's the updated version of the client interceptor:

class LoggingClientInterceptor implements ClientInterceptor {

  private static final Logger log = LoggerFactory.getLogger(LoggingClientInterceptor.class);

  @Override
  public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(MethodDescriptor<ReqT, RespT> method,
      CallOptions callOptions, Channel next) {
    return new SimpleForwardingClientCall<ReqT, RespT>(next.newCall(method, callOptions)) {
      @Override
      public void start(Listener<RespT> responseListener, Metadata headers) {
        final SimpleForwardingClientCallListener<RespT> listener =
            new SimpleForwardingClientCallListener<RespT>(responseListener) {
              @Override
              public void onMessage(RespT response) {
                log.debug("grpc response; method: {}, attributes: {}, response: {}",
                    method.getFullMethodName(), getAttributes(), response);
                super.onMessage(response);
              }
            };

        super.start(listener, headers);
      }

      @Override
      public void sendMessage(ReqT request) {
        log.debug("grpc request; method: {}, request: {}", method.getFullMethodName(), request);
        super.sendMessage(request);
      }
    };
  }
}

And again, I get the empty set of attributes when I call getAttributes().
If I understand correctly (according to my logs), the default "lifecycle" of the client call with the attached listener looks like the following:

ClientCall::start
ClientCall::sendMessage
ClientCall.Listener::onReady
ClientCall.Listener::onHeaders
ClientCall.Listener::onMessage
ClientCall.Listener::onClose

So, it should be pretty safe to call the getAttributes() method from the ClientCall.Listener::onMessage, according to the documentation. Maybe I'm missing something.

[dapengzhang0]

@maseev , what attribute are you expecting? What transport are you using: Netty, OkHttp, or InProcess?

[maseev]

@dapengzhang0 I'm expecting an attribute which contains the information about the server to which the client is going to send a request. I'm using the Netty transport.

[zpencer]

Do you happen to be using plaintext?

[dapengzhang0]

+1

Do you happen to be using plaintext?

@maseev, your updated interceptor will work correctly. But if you are using plaintext, no attributes will be added by the grpc library. If you are using Netty transport with TLS, two attributes may be added:
Grpc.TRANSPORT_ATTR_SSL_SESSION and Grpc.TRANSPORT_ATTR_REMOTE_ADDR

[maseev]

Oh, I didn't know that. I do use plaintext actually. I guess that explains everything. Thank you for your help @zpencer @dapengzhang0.