fix(gax): update error messages to be set to span.status.message

[shivanee-p]

No description provided.

[gemini-code-assist]

Code Review

This pull request enhances telemetry tracing and adds robust deadline/timeout enforcement for the REST fallback transport in google-gax. It integrates OpenTelemetry tracing into API calls, maps transport-specific timeout failures to DEADLINE_EXCEEDED errors, and tracks HTTP status codes on fallback errors. The review feedback highlights critical compatibility and robustness improvements: avoiding AbortSignal.any to maintain Node.js 18 compatibility, handling invalid Date objects for deadlines to prevent runtime crashes, and filtering out null or undefined metadata values to avoid sending literal string headers.

[gemini-code-assist]

AbortSignal.any is only supported in Node.js v20+ and modern browsers. Since this library supports Node.js 18, using AbortSignal.any will cause runtime crashes in Node.js 18 environments. We can avoid this by manually listening to the timeoutSignal and calling cancelController.abort() when it fires. This eliminates the need for AbortSignal.any entirely and is fully backward-compatible.

      // Arm the deadline here rather than handing `timeout` to gaxios, which
      // would build the identical `AbortSignal.timeout` internally. The
      // difference is bookkeeping: both a deadline expiry and a `cancel()`
      // abort the same request and surface the same error, so unless we record
      // which one fired, the handlers below cannot tell them apart.
      let timedOut = false;
      if (timeoutMs !== undefined) {
        const timeoutSignal = AbortSignal.timeout(timeoutMs);
        timeoutSignal.addEventListener('abort', () => {
          timedOut = true;
          cancelController.abort();
        }, {
          once: true,
        });
      }

[gemini-code-assist]

Since we are avoiding AbortSignal.any and instead aborting cancelController directly on timeout, we should pass cancelSignal as the request signal instead of requestSignal.

        signal: cancelSignal,

[gemini-code-assist]

If callOptions.deadline is an invalid Date object, getTime() will return NaN. This will result in timeoutMs being NaN, which can cause unexpected behavior or crashes when passed to AbortSignal.timeout(). We should check if the parsed time is a valid number before calculating timeoutMs.

      let timeoutMs: number | undefined;
      if (callOptions?.deadline && !rpc.responseStream) {
        const time = callOptions.deadline.getTime();
        if (!isNaN(time)) {
          // `AbortSignal.timeout` rejects a negative delay with a RangeError, so
          // an already-expired deadline is clamped. Zero is a fine value here: it
          // aborts on the next tick, which is the right answer for a deadline
          // that has already passed.
          timeoutMs = Math.max(0, time - Date.now());
        }
      }

[gemini-code-assist]

If any metadata key has an undefined or null value, converting it directly using String(value) will set the header value to the literal string "undefined" or "null". We should defensively filter out undefined or null values to prevent sending invalid headers.

      for (const key of Object.keys(metadata)) {
        const value = metadata[key];
        if (value === undefined || value === null) {
          continue;
        }
        if (Array.isArray(value)) {
          headers.delete(key);
          for (const item of value) {
            if (item !== undefined && item !== null) {
              headers.append(key, String(item));
            }
          }
        } else {
          headers.set(key, String(value));
        }
      }