impl(o11y): introduce body.size

[diegomarquezp]

Description

This PR extends the OpenTelemetry integration in GAX HTTP/JSON transport to capture and record the http.response.body.size attribute.

Key Changes:

• GAX Core Tracing (gax):

  • Added HTTP_RESPONSE_BODY_SIZE constant to ObservabilityAttributes.
  • Updated ApiTracer interface and SpanTracer implementation to support responseHeadersReceived.
  • Implemented Content-Length extraction in SpanTracer, handling both single values and lists (due to google-http-java-client returning lists of values for some headers).

• HTTP/JSON Transport (gax-httpjson):

  • Threaded ApiTracer through HttpJsonCallContext and HttpJsonCallOptions to ensure it's available during request execution.
  • Forwarded response headers to the tracer in HttpJsonClientCallImpl upon receipt.

• Testing and Verification:

  • Added unit tests in SpanTracerTest to verify attribute extraction for various header formats.
  • Added integration tests in ITOtelTracing (using gapic-showcase) to validate the recorded size against expected message sizes (accounting for serialization overhead).

[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 significantly improves the OpenTelemetry integration for HTTP JSON transports by introducing the http.response.body.size attribute. This enhancement provides more granular observability into the size of HTTP response bodies, which is crucial for performance monitoring and debugging. The changes involve updating core tracing components to capture and propagate this new attribute, along with robust parsing logic for content length headers and comprehensive test coverage to ensure accuracy.

Highlights

• OpenTelemetry Integration: Introduced the http.response.body.size attribute for OpenTelemetry spans in HTTP JSON transports to provide granular observability into response body sizes.
• Content-Length Extraction Robustness: Enhanced the extractContentLength logic in SpanTracer and TestApiTracer to safely parse Content-Length from various header formats, including List-type strings, and to handle cases where chunked encoding omits the header.
• ApiTracer Propagation: Integrated ApiTracer into HttpJsonCallOptions and updated HttpJsonCallContext to correctly propagate the tracer throughout the call context.
• Response Header Callback: Added a responseHeadersReceived callback to the ApiTracer interface and its implementations (SpanTracer, TestApiTracer) to capture response header information, enabling the recording of body size.
• Comprehensive Testing: Implemented new test cases in HttpJsonClientCallImplTest to validate the accurate recording of response body sizes for both unary and server-streaming calls, and updated ITOtelTracing to include assertions for the new attribute.
• Mock Service Enhancement: Modified MockHttpService to explicitly add Content-Length headers to mock HTTP responses for non-streaming calls, ensuring accurate testing of the new observability feature.

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[gemini-code-assist]

Code Review

This pull request implements tracing for HTTP JSON calls, specifically to record the response body size. This involves adding ApiTracer support to HttpJsonCallOptions and HttpJsonCallContext, updating HttpJsonClientCallImpl to report response headers to the tracer, and enhancing ApiTracer and SpanTracer to process Content-Length from response headers. New tests were added to verify this functionality. Feedback includes addressing code duplication in the extractContentLength method, correcting a flawed test case in SpanTracerTest for bad Content-Length formats, and improving the robustness of a test in ITOtelTracing by asserting the presence of the http.response.body.size attribute.