feat: Implement Google PubSub receiver

TODO:

- [ ] Rename custom attributes to match original CE names.
- [ ] Implement

src/lib/googlePubSub.ts

@@ -1,4 +1,4 @@
-import type { CloudEvent, EmitterFunction } from 'cloudevents';
+import type { CloudEvent, EmitterFunction, type CloudEventV1, type Headers } from 'cloudevents';
 import { PubSub } from '@google-cloud/pubsub';
 import { google } from '@google-cloud/pubsub/build/protos/protos.js';
 import { getUnixTime } from 'date-fns';
@@ -73,3 +73,7 @@ export function makeGooglePubSubEmitter(): EmitterFunction {
     await topic.publishMessage(message);
   };
 }
+
+export function convertGooglePubSubMessage(headers: Headers, body: Buffer): CloudEventV1<Buffer> {
+  throw new Error(`Not implemented${headers}${body}`);
+}

src/lib/receivers.spec.ts

@@ -7,6 +7,15 @@ jest.unstable_mockModule('./ceBinary.js', () => {
   return { convertCeBinaryMessage: mockCeBinaryConverter };
 });
 
+const mockGooglePubSubConverter = Symbol('mockGooglePubSubConverter');
+let wasGooglePubSubImported = false;
+jest.unstable_mockModule('./googlePubSub.ts', () => {
+  wasGooglePubSubImported = true;
+  return {
+    convertGooglePubSubMessage: mockGooglePubSubConverter,
+  };
+});
+
 const { makeReceiver } = await import('./receivers.js');
 
 describe('makeReceiver', () => {
@@ -15,12 +24,20 @@ describe('makeReceiver', () => {
 
     await makeReceiver('ce-http-binary');
     expect(wasCeImported).toBeTrue();
+    expect(wasGooglePubSubImported).toBeFalse();
+
+    await makeReceiver('google-pubsub');
+    expect(wasGooglePubSubImported).toBeTrue();
   });
 
   test('CloudEvents binary receiver should be returned if requested', async () => {
     await expect(makeReceiver('ce-http-binary')).resolves.toBe(mockCeBinaryConverter);
   });
 
+  test('Google PubSub receiver should be returned if requested', async () => {
+    await expect(makeReceiver('google-pubsub')).resolves.toBe(mockGooglePubSubConverter);
+  });
+
   test('Unsupported transport should be refused', async () => {
     await expect(makeReceiver('unsupported')).rejects.toThrowWithMessage(
       Error,

src/lib/receivers.ts

@@ -6,6 +6,9 @@ export async function makeReceiver(transport: string): Promise<Receiver> {
   if (transport === 'ce-http-binary') {
     const { convertCeBinaryMessage } = await import('./ceBinary.js');
     receiver = convertCeBinaryMessage;
+  } else if (transport === 'google-pubsub') {
+    const { convertGooglePubSubMessage } = await import('./googlePubSub.js');
+    receiver = convertGooglePubSubMessage;
   } else {
     throw new Error(`Unsupported receiver type (${transport})`);
   }