otel_cloud_functions

OpenTelemetry instrumentation for package:cloud_functions (Firebase Cloud Functions callable functions), built on the Dartastic OpenTelemetry SDK.

Wrap an HttpsCallable.call(...) invocation to get a CLIENT span with rpc.* semconv attributes.

import 'package:cloud_functions/cloud_functions.dart';
import 'package:otel_cloud_functions/otel_cloud_functions.dart';

final callable = FirebaseFunctions.instance.httpsCallable('addNumbers');

final result = await tracedHttpsCall(
  callable,
  name: 'addNumbers',
  parameters: {'a': 1, 'b': 2},
);

final sum = result.data as int;

The function name has to be passed explicitly because HttpsCallable does not expose it after construction.

Span shape

• Span name: firebase_functions <function name>
• Span kind: CLIENT
• Attributes:
  • rpc.system.name = firebase_functions
  • rpc.method = firebase_functions/<function name> (the registry expects rpc.method to be fully qualified)
• Span status: Error on FirebaseFunctionsException or any other thrown error. For FirebaseFunctionsException, error.type is set to the code field (e.g. not-found, permission-denied, unauthenticated, internal) — these are the canonical Google Cloud RPC code names, much better for alerting than the runtime class name.
• Spans inherit the surrounding active span as parent, so callable invocations inside Tracer.startActiveSpan nest naturally.

Lower-level helper

If you can't construct a real HttpsCallable (testing, mock backends, custom transports), use tracedCloudFunctionCall directly:

final result = await tracedCloudFunctionCall<MyResult>(
  name: 'myFunction',
  invoke: () => fakeBackend.invokeMyFunction(params),
);

tracedHttpsCall is a thin wrapper over this.

Self-recursion guard

await runWithoutCloudFunctionsInstrumentationAsync(() async {
  await tracedHttpsCall(callable, name: 'fn');
});

Inside the helper's zone, the traced wrappers become transparent passthroughs.

Caveats

• HttpsCallable does not expose the function name, so you must pass it as a named parameter to tracedHttpsCall. This is awkward but is the cost of cloud_functions not surfacing the name from its private constructor.
• Streaming callables (HttpsCallable.stream) aren't wrapped here yet — the streaming response shape needs different span semantics (one span per chunk? one for the stream?). Open an issue if you need this.
• The wrapper calls OTel.tracerProvider().getTracer(...) on each invocation — OTel.initialize() must have run first.

License

Apache 2.0 — see LICENSE.