Implement V1 compat API for PubSub #1782

shettyvarun268 · 2025-12-04T19:28:49Z

This PR adds the v1-compatible argument getters (context and message) directly to the v2 Pub/Sub CloudEvent class.
This allows developers to access v1-style arguments via property access, e.g., const { message, context } = event;, for a smoother migration of existing business logic to the v2 function signature.Implementation Details

The v1-compatible context getter is implemented as a lazily-computed property on the CloudEvent object. To correctly construct the v1 EventContext from the v2 event's properties, the following two internal helper functions are introduced:

attachPubSubContext<T>(event: CloudEvent<MessagePublishedData<T>>, topic: string):
Adds the v1-style context property to the v2 event object using Object.defineProperty.
The getter computes the EventContext by mapping v2 properties (event.id, event.time) and by calling getResourceName.
This ensures the context is only computed once upon first access.
getResourceName(event: CloudEvent<MessagePublishedData<any>>, topic: string):
Extracts the full resource name for the v1 EventContext resource object.
It attempts to parse the project ID and topic name from event.source or falls back to environment variables and the function's topic name parameter if necessary.

This is the first of a series of PRs aimed at simplifying the migration from v1 to v2. By introducing this new
onMessagePublished function, we are providing a more robust and flexible way to handle Pub/Sub events in Cloud Functions for Firebase v2.

gemini-code-assist · 2025-12-04T19:29:08Z

Summary of Changes

Hello @shettyvarun268, 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 introduces a significant enhancement to the v2 Pub/Sub CloudEvent handling by integrating v1-compatible argument accessors. The primary goal is to facilitate a seamless migration for developers transitioning their existing v1 Cloud Functions to the v2 signature. By providing direct property access to message and context in a v1-like manner, it reduces the friction associated with adapting business logic to the new event structure, making the upgrade path more straightforward.

Highlights

V1 Compatibility: Adds v1-compatible context and message getters directly to the v2 Pub/Sub CloudEvent<MessagePublishedData> class.
Migration Simplification: Enables direct property access (e.g., const { message, context } = event;) for smoother migration of existing v1 business logic to v2 function signatures.
Lazy Context Computation: Implements the v1-compatible context getter as a lazily-computed property on the CloudEvent object, ensuring it's only computed upon first access.
New Helper Functions: Introduces two internal helper functions: attachPubSubContext to add the v1-style context and getResourceName to extract the full resource name for the v1 EventContext, including robust fallback logic for project and topic names.
Strategic Initiative: This pull request is the first in a series aimed at simplifying the overall migration process from v1 to v2 Cloud Functions for Firebase.

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shettyvarun268 · 2025-12-04T19:29:57Z

/gemini review

gemini-code-assist

Code Review

This pull request introduces a v1-compatibility layer for v2 Pub/Sub functions by adding a lazily-computed context property to the CloudEvent object. The implementation is well-structured, using Object.defineProperty for lazy evaluation and providing fallbacks for constructing the resource name. I've identified a bug in the resource name construction for a fallback case and a couple of areas for improvement in the tests to make them more robust and accurate. My feedback includes a high-severity fix for the resource name format and medium-severity suggestions to improve test coverage and correctness.

src/v2/providers/pubsub.ts

spec/v2/providers/pubsub.spec.ts

gemini-code-assist

Code Review

The pull request successfully implements V1-compatible API for PubSub events in V2 Cloud Functions, which will greatly assist in migrating existing business logic. The changes introduce "context" and "message" getters to the CloudEvent<MessagePublishedData> class, along with robust helper functions attachPubSubContext and getResourceName to construct the V1 EventContext. The new test cases thoroughly cover the functionality, including handling existing contexts and fallback mechanisms for resource name extraction.

src/v2/providers/pubsub.ts

taeold · 2025-12-05T18:45:20Z

src/v2/providers/pubsub.ts

+ * @param event - The event to add the context to.
+ * @param topic - The topic the event is for.
+ */
+function attachPubSubContext<T>(event: CloudEvent<MessagePublishedData<T>>, topic: string) {


i don't think we strictly need topic. all information should be derivable from event obj.

Made the change and got rid of the topic.

taeold · 2025-12-05T18:46:53Z

src/v2/providers/pubsub.ts

+ */
+function getResourceName(event: CloudEvent<MessagePublishedData<any>>, topic: string) {
+  const match = event.source?.match(/projects\/([^/]+)\/topics\/([^/]+)/);
+  const project =


i think this code is overly defensive.

cloudevent is a standard format, and it's unlikely you won't be able to retrieve project/topic information from the event payload. defaulitng to "unknown" or "" is probably fine in the unlikely case we can't derive the info.

Good point. Removed the condition. Also removed the corresponding test case because it won't be needed.

taeold · 2025-12-05T18:50:34Z

src/v2/providers/pubsub.ts

    messagePublishedData.message = new Message(messagePublishedData.message);
-    return wrapTraceContext(withInit(handler))(raw as CloudEvent<MessagePublishedData<T>>);
+    const event = raw as CloudEvent<MessagePublishedData<T>>;
+    attachPubSubContext(event, topic);


ptal look at v1 pubsub signature:

(message: Message, context: EventContext) => PromiseLike<any>

We also need a getter for message as well as context

Got it. Made the needed changes. Added the message getter. This would allow us to access event.messag directly now.

taeold · 2025-12-05T18:50:58Z

spec/v2/providers/pubsub.spec.ts

    );
  });
+
+  //Test case to ensure Idempotency. makes things dont break if there is already context present


this comment seems redudant

Noted. Addressed this by removing the test case below.

taeold · 2025-12-05T18:52:07Z

spec/v2/providers/pubsub.spec.ts

+
+    let receivedEvent: CloudEvent<pubsub.MessagePublishedData<any>>;
+    const func = pubsub.onMessagePublished("topic", (e) => {
+      receivedEvent = e;


i'd prefer we try to use the context here directly:

Suggested change

receivedEvent = e;

{ message, context } = e;

Made the changes. Used deconstructedMessage and context instead

taeold · 2025-12-05T18:53:45Z

spec/v2/providers/pubsub.spec.ts

  });
+
+  //Test case to ensure Idempotency. makes things dont break if there is already context present
+  it("should not modify a CloudEvent that already has a context", async () => {


not sure why this exist? why would there be existing context?

Understood. The real cases won't have an existing case. Removed this test case.

jhuleatt · 2025-12-05T18:57:10Z

src/v2/core.ts

+  /** V1- compatible context of this event.
+   * 
+   * This getter is added at runtime for V1 compatibility.
+   * May be undefined it not set by a provider
+   */


@egilmorez heads up, copy here will go into the reference docs on this page: https://firebase.google.com/docs/reference/functions/2nd-gen/node/firebase-functions.cloudevent

Would you like me to make the comments more informative and developer friendly. Considering it might be put into the reference docs directly from here?

jhuleatt · 2025-12-05T19:01:46Z

src/v2/providers/pubsub.ts

+
+  };
+
+  Object.defineProperty(event, "context", {


for my own learning, is defineProperty used here so that event.context isn't settable?

That's correct. This is to ensure event.context a read-only property so as to not accidentally end up changing it inside the function.

jhuleatt · 2025-12-05T19:03:41Z

src/v2/core.ts

 * @packageDocumentation
 */

+import type { EventContext } from "../v1/cloud-functions";


Would it be worth redefining this as 1stGenEventContext or LegacyEventContext so that it's clear it is not really meant for people using 2nd gen?

Does v1EventContext sound more clear and concise?

jhuleatt · 2025-12-05T19:05:48Z

src/v2/providers/pubsub.ts

+ * @param topic - The topic the event is for.
+ */
+function attachPubSubContext<T>(event: CloudEvent<MessagePublishedData<T>>, topic: string) {
+  if ("context" in event && event.context) {


when would context already be in the event? should this throw if that happens?

Good point. Changed the code to throw an error in this case. The context existing would be unlikely. Would you prefer I get rid of the check altogether?

Implement V1 compat API for PubSub

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shettyvarun268 requested review from brittanycho, jhuleatt and taeold December 4, 2025 19:28

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jhuleatt requested a review from egilmorez December 5, 2025 18:57

jhuleatt reviewed Dec 5, 2025

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Addressing the PR comments

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Implement V1 compat API for PubSub #1782

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