fix: marshal attribute-only Pub/Sub messages

Author: winklemad

src/pubsub_middleware.ts

@@ -46,7 +46,7 @@ export interface RawPubSubBody {
      * Base64 encoded message data. If this field is empty, the message must contain at least one
      * attribute.
      */
-    data: string;
+    data?: string;
     /**
      * ID of this message, assigned by the server when the message is published. Guaranteed to be
      * unique within the topic.
@@ -82,7 +82,7 @@ export interface MarshalledPubSubBody {
   };
   data: {
     '@type': typeof PUBSUB_MESSAGE_TYPE;
-    data: string;
+    data?: string;
     attributes: {[key: string]: string};
   };
 }
@@ -99,7 +99,9 @@ const isRawPubSubRequestBody = (body: any): body is RawPubSubBody => {
     !body.context &&
     body.subscription &&
     body.message &&
-    body.message.data &&
+    (body.message.data ||
+      (body.message.attributes &&
+        Object.keys(body.message.attributes).length > 0)) &&
     body.message.messageId
   );
 };
@@ -145,7 +147,7 @@ const marshalPubSubRequestBody = (
   },
   data: {
     '@type': PUBSUB_MESSAGE_TYPE,
-    data: body.message.data,
+    ...(body.message.data !== undefined && {data: body.message.data}),
     attributes: body.message.attributes || {},
   },
 });

test/integration/cloud_event.ts

@@ -291,6 +291,38 @@ describe('CloudEvent Function', () => {
     });
   });
 
+  it('marshals attribute-only Pub/Sub emulator requests', async () => {
+    const server = getTestServer('testCloudEventFunction');
+    await supertest(server)
+      .post('/projects/FOO/topics/BAR_TOPIC')
+      .send({
+        subscription: 'projects/FOO/subscriptions/BAR_SUB',
+        message: {
+          messageId: 'attribute-only-message',
+          publishTime: '2026-07-22T00:00:00.000Z',
+          attributes: {attribute1: 'value1'},
+        },
+      })
+      .expect(204);
+
+    assert.deepStrictEqual(receivedCloudEvent, {
+      specversion: '1.0',
+      type: 'google.cloud.pubsub.topic.v1.messagePublished',
+      source: '//pubsub.googleapis.com/projects/FOO/topics/BAR_TOPIC',
+      id: 'attribute-only-message',
+      time: '2026-07-22T00:00:00.000Z',
+      datacontenttype: 'application/json',
+      data: {
+        message: {
+          '@type': 'type.googleapis.com/google.pubsub.v1.PubsubMessage',
+          attributes: {attribute1: 'value1'},
+          messageId: 'attribute-only-message',
+          publishTime: '2026-07-22T00:00:00.000Z',
+        },
+      },
+    });
+  });
+
   it('allows customers to provide a type parameter for the data payload', async () => {
     const testPayload = 'a test string';
 

test/integration/legacy_event.ts

@@ -211,6 +211,43 @@ describe('Event Function', () => {
     });
   });
 
+  it('marshals attribute-only Pub/Sub emulator requests', async () => {
+    let receivedData: {} | null = null;
+    let receivedContext: functions.CloudFunctionsContext | null = null;
+    const server = getServer((data: {}, context: functions.Context) => {
+      receivedData = data;
+      receivedContext = context as functions.CloudFunctionsContext;
+    }, testOptions);
+
+    await supertest(server)
+      .post('/projects/FOO/topics/BAR_TOPIC')
+      .send({
+        subscription: 'projects/FOO/subscriptions/BAR_SUB',
+        message: {
+          messageId: 'attribute-only-message',
+          publishTime: '2026-07-22T00:00:00.000Z',
+          attributes: {attribute1: 'value1'},
+        },
+      })
+      .set({'Content-Type': 'application/json'})
+      .expect(204);
+
+    assert.deepStrictEqual(receivedData, {
+      '@type': 'type.googleapis.com/google.pubsub.v1.PubsubMessage',
+      attributes: {attribute1: 'value1'},
+    });
+    assert.deepStrictEqual(receivedContext, {
+      eventId: 'attribute-only-message',
+      timestamp: '2026-07-22T00:00:00.000Z',
+      eventType: 'google.pubsub.topic.publish',
+      resource: {
+        service: 'pubsub.googleapis.com',
+        type: 'type.googleapis.com/google.pubsub.v1.PubsubMessage',
+        name: 'projects/FOO/topics/BAR_TOPIC',
+      },
+    });
+  });
+
   it('returns a 500 if the function throws an exception', async () => {
     const server = getServer(() => {
       throw 'I crashed';