Kafka one-way with Brave

kakfa-oneway.java

/**
 * This is an example of a one-way or "messaging span", which is possible by use of the {@link
 * Span#flush()} operator.
 *
 * <p>Note that this uses a span as a kafka key, not because it is recommended, rather as it is
 * convenient for demonstration, since kafka doesn't have message properties.
 *
 * <p>See https://github.com/openzipkin/zipkin/issues/1243
 */
public class KafkaExampleIT {
  @Rule public KafkaJunitRule kafka = new KafkaJunitRule(EphemeralKafkaBroker.create());

  InMemoryStorage storage = new InMemoryStorage();

  Tracing tracing = Tracing.newBuilder()
      .localEndpoint(Endpoint.builder().serviceName("producer").build())
      .reporter(s -> storage.spanConsumer().accept(Collections.singletonList(s)))
      .build();

  KafkaProducer<Span, String> producer;
  KafkaConsumer<Span, String> consumer;
  Endpoint kafkaEndpoint;

  @Before public void setup() {
    producer = kafka.helper()
        .createProducer(new SpanSerializer(tracing), new StringSerializer(), null);
    consumer = kafka.helper()
        .createConsumer(new SpanDeserializer(storage), new StringDeserializer(), null);
    kafkaEndpoint =
        Endpoint.builder().serviceName("kafka").port(kafka.helper().kafkaPort()).build();
  }

  @Test
  public void startWithOneTracerAndStopWithAnother() throws Exception {
    String topic = "startWithOneTracerAndStopWithAnother";
    consumer.subscribe(Collections.singletonList(topic));

    Span span = tracing.tracer().newTrace().kind(Span.Kind.CLIENT).remoteEndpoint(kafkaEndpoint);
    producer.send(new ProducerRecord<>(topic, span, "foo")).get();
    span.flush();
    producer.close();

    consumer.poll(500L).forEach(record -> {
      record.key()
            .name(record.value())
            .kind(Span.Kind.SERVER)
            .remoteEndpoint(kafkaEndpoint)
            .flush();
    });
    consumer.close();
  }
}

/** This class simulates a consumer being on a different process, by not sharing a tracer */
final class SpanDeserializer implements Deserializer<Span> {
  final Tracing tracing;
  final TraceContext.Extractor<Properties> extractor;

  SpanDeserializer(InMemoryStorage storage) {
    tracing = Tracing.newBuilder()
        .localEndpoint(Endpoint.builder().serviceName("consumer").build())
        .reporter(s -> storage.spanConsumer().accept(Collections.singletonList(s)))
        .build();
    extractor = tracing.propagation().extractor(Properties::getProperty);
  }

  @Override public void configure(Map<String, ?> map, boolean b) {
  }

  /** Extract the span from the key or start a new trace if any problem. */
  @Override public Span deserialize(String s, byte[] bytes) {
    try {
      Properties properties = new Properties();
      properties.load(new ByteArrayInputStream(bytes));
      // in Brave 4.3 this will be simplified to tracing.tracer().nextSpan(extractor, properties)
      TraceContextOrSamplingFlags result = extractor.extract(properties);
      return result.context() != null
          ? tracer.joinSpan(result.context())
          : tracer.newTrace(result.samplingFlags());
    } catch (RuntimeException | IOException e) {
      return tracer.newTrace(); // return a new trace upon failure of any kind
    }
  }

  @Override public void close() {
  }
}

final class SpanSerializer implements Serializer<Span> {
  final TraceContext.Injector<Properties> injector;

  SpanSerializer(Tracing tracing) {
    injector = tracing.propagation().injector(Properties::setProperty);
  }

  @Override public void configure(Map<String, ?> map, boolean b) {
  }

  @Override public byte[] serialize(String s, Span span) {
    Properties properties = new Properties();
    injector.inject(span.context(), properties);
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    try {
      properties.store(out, "zipkin");
    } catch (IOException e) {
      throw new AssertionError(e);
    }
    return out.toByteArray();
  }

  @Override public void close() {
  }
}

Thanks a lot!