How do I add type safety to my Pub/Sub Cloud Run (gen2) function?

I have a Google Cloud Run Function (formerly Cloud Functions 2nd Gen) running TypeScript/Node.js. The documentation in the Pub/Sub tutorial shows that you get a cloudEvent, but how can I add type safety to it?

Specifically if I want to define the the type of the attributes or the message body.

This is their example:

const functions = require('@google-cloud/functions-framework');

// Register a CloudEvent callback with the Functions Framework that will
// be executed when the Pub/Sub trigger topic receives a message.
functions.cloudEvent('helloPubSub', cloudEvent => {
  // The Pub/Sub message is passed as the CloudEvent's data payload.
  const base64name = cloudEvent.data.message.data;

  const name = base64name
    ? Buffer.from(base64name, 'base64').toString()
    : 'World';

  console.log(`Hello, ${name}!`);
});

There are some types defined in @google-cloud/functions-framework.

npm install @google-cloud/functions-framework@^3.3.0

Then you can define your own types with the following code:

import functions, { CloudEvent } from '@google-cloud/functions-framework'
import { RawPubSubBody } from '@google-cloud/functions-framework/build/src/pubsub_middleware'

/**
 * We get them as `attributes?: { [key: string]: string }`
 * But since we know the structure, we can define it as an interface
 */
interface PubSubAttributes {
  myTestAttribute: string
}

/** Extend the RawPubSubBody to use PubSubAttributes */
interface FunctionPubSubBody extends RawPubSubBody {
  message: {
    attributes: PubSubAttributes
  } & RawPubSubBody['message']
}

/** An interface that defines the shape of the body of the message */
interface PubSubBodyData {
  testBodyParam: string
}

// https://cloudevents.github.io/sdk-javascript/classes/CloudEvent.html
functions.cloudEvent<FunctionPubSubBody>(
  'syncAllMoviesNode',
  // You don't technically need to declare this type (it's inferred from above)
  async (cloudEvent: CloudEvent<FunctionPubSubBody>) => {
    console.log(cloudEvent)

    // The Pub/Sub message is passed as the CloudEvent's data payload.
    // It's base64 encoded, so we need to decode it and parse it as JSON.
    const base64Data = cloudEvent.data.message.data
    const base64String = Buffer.from(base64Data, 'base64').toString()
    const pubSubBody: PubSubBodyData = JSON.parse(base64String)

    const pubSubAttributes: PubSubAttributes = cloudEvent.data.message.attributes

    // The "Message Body" with type PubSubBodyData
    console.log(pubSubBody)

    // The "Attributes" as PubSubAttributes
    console.log(pubSubAttributes)
  }
)

Configuring in Cloud Scheduler

Attributes vs Body

This Reddit thread has some thoughts, but my takeaway is:

• Use attributes for structured metadata that will apply across invocations
• Use body for things that may change depending on the invocation / event (you may have a few different "types" you support, keying off the attribute for example)
  • One attribute bodyType which is an enum of SYNC | CLEAR
  • Two different message body "types" SyncMessageBody and ClearMessageBody

But honestly you can use them however you want.