impl(o11y): introduce resend_count logic

[diegomarquezp]

Introduces gcp.grpc.resend_count and http.request.resend_count by relying on the parameter passed to ApiTracer.

---

Reliability of attemptNumber in ApiTracer

The attemptNumber is passed from the retrying logic in gax-java/gax.

For unary calls, here is an example of how the overall attempt count behaves:

How it is updated:
The attempt count is managed by the retry algorithms. For example, ExponentialRetryAlgorithm is thread-safe and creates immutable TimedAttemptSettings. It initializes overallAttemptCount to 0 and increments it for each subsequent attempt.

// gax-java/gax/src/main/java/com/google/api/gax/retrying/ExponentialRetryAlgorithm.java

  @Override
  public TimedAttemptSettings createFirstAttempt() {
    return TimedAttemptSettings.newBuilder()
        // ...
        .setOverallAttemptCount(0)
        // ...
        .build();
  }

  @Override
  public TimedAttemptSettings createNextAttempt(TimedAttemptSettings previousSettings) {
    // ...
    return TimedAttemptSettings.newBuilder()
        // ...
        .setOverallAttemptCount(previousSettings.getOverallAttemptCount() + 1)
        // ...
        .build();
  }

How it is consumed:
AttemptCallable executes unary calls. externalFuture is marked as volatile to handle potential visibility between the thread that schedules the retry and the thread executing call(). Before starting the RPC call, AttemptCallable invokes attemptStarted using the overallAttemptCount from externalFuture.

// gax-java/gax/src/main/java/com/google/api/gax/rpc/AttemptCallable.java

class AttemptCallable<RequestT, ResponseT> implements Callable<ResponseT> {
  // ...
  private volatile RetryingFuture<ResponseT> externalFuture;
  // ...
  @Override
  public ResponseT call() {
    // ...
    callContext
        .getTracer()
        .attemptStarted(request, externalFuture.getAttemptSettings().getOverallAttemptCount());
    // ...
  }
}

Thread Safety:
Attempts for a single RPC are strictly sequential; a new attempt is only constructed and scheduled after the previous attempt fails and the retry delay elapses. ExponentialRetryAlgorithm is thread-safe, TimedAttemptSettings is immutable, and the externalFuture reference inside AttemptCallable is volatile. This combination ensures thread-safe observation of the linearly increasing overallAttemptCount.

Conclusion

Since the retrying infrastructure sequentially updates and consumes getOverallAttemptCount() in a thread-safe manner, we can confidently and safely use attemptNumber in SpanTracer to populate the rpc.grpc.resend_count or rpc.http.resend_count attributes. This approach directly leverages the existing reliable retry logic rather than implementing a redundant internal counter.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the observability of client-side operations by introducing a resend_count attribute to tracing spans. This attribute, applied to both gRPC and HTTP requests, provides crucial context for understanding and analyzing retry behavior, which is vital for debugging transient errors and optimizing performance in distributed systems.

Highlights

• New Observability Attributes: Introduced new constants, "HTTP_RESEND_COUNT_ATTRIBUTE" and "GRPC_RESEND_COUNT_ATTRIBUTE", to ObservabilityAttributes for tracking the number of times a request has been resent due to retries.
• SpanTracer Enhancement: Modified SpanTracer to track and include a resendCount attribute in attempt spans for retried requests, differentiating between HTTP and gRPC transports.
• Attribute Type Handling: Updated ObservabilityUtils to correctly handle Long type attributes when converting them to OpenTelemetry attributes.
• Comprehensive Testing: Added new unit tests in SpanTracerTest and integration tests in ITOtelTracing to validate the correct propagation and value of the resend_count attribute for both gRPC and HTTP retries.

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[gemini-code-assist]

Code Review

This pull request introduces logic to add a resend_count attribute to observability spans for retried requests. The implementation in SpanTracer is solid, correctly incrementing the count for each retry and adding the appropriate transport-specific attribute. The unit tests for this logic are also well-written.

However, I've found issues in the new integration tests in ITOtelTracing.java. The verification logic for the resend_count attribute is flawed in both the gRPC and HTTP JSON test cases. I've provided suggestions to correct the test logic to ensure it properly validates the new feature.

[sonarqubecloud]

Quality Gate failed for 'gapic-generator-java-root'

Failed conditions
71.4% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
82.1% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud