Re-insert room IDs when decrypting bundled redaction events returned by /sync (#2531)

spec/integ/megolm-integ.spec.ts

@@ -114,7 +114,7 @@ function encryptMegolmEvent(opts: {
     }
 
     return {
-        event_id: 'test_megolm_event',
+        event_id: 'test_megolm_event_' + Math.random(),
         content: {
             algorithm: "m.megolm.v1.aes-sha2",
             ciphertext: opts.groupSession.encrypt(JSON.stringify(plaintext)),
@@ -980,4 +980,69 @@ describe("megolm", () => {
         expect(decryptedEvent.getContent()).toEqual({});
         expect(decryptedEvent.getClearContent()).toBeUndefined();
     });
+
+    it(
+        "should successfully decrypt bundled redaction events that don't include a room_id in their /sync data",
+        async () => {
+            await aliceTestClient.start();
+            const p2pSession = await createOlmSession(testOlmAccount, aliceTestClient);
+            const groupSession = new Olm.OutboundGroupSession();
+            groupSession.create();
+
+            // make the room_key event
+            const roomKeyEncrypted = encryptGroupSessionKey({
+                senderKey: testSenderKey,
+                recipient: aliceTestClient,
+                p2pSession: p2pSession,
+                groupSession: groupSession,
+                room_id: ROOM_ID,
+            });
+
+            // encrypt a message with the group session
+            const messageEncrypted = encryptMegolmEvent({
+                senderKey: testSenderKey,
+                groupSession: groupSession,
+                room_id: ROOM_ID,
+            });
+
+            const redactionEncrypted = encryptMegolmEvent({
+                senderKey: testSenderKey,
+                groupSession: groupSession,
+                plaintext: {
+                    room_id: ROOM_ID,
+                    type: "m.room.redaction",
+                    redacts: messageEncrypted.event_id,
+                    content: { reason: "redaction test" },
+                },
+            });
+
+            const messageEncryptedWithRedaction = {
+                ...messageEncrypted,
+                unsigned: { redacted_because: redactionEncrypted },
+            };
+
+            const syncResponse = {
+                next_batch: 1,
+                to_device: {
+                    events: [roomKeyEncrypted],
+                },
+                rooms: {
+                    join: {
+                        [ROOM_ID]: { timeline: { events: [messageEncryptedWithRedaction] } },
+                    },
+                },
+            };
+
+            aliceTestClient.httpBackend.when("GET", "/sync").respond(200, syncResponse);
+            await aliceTestClient.flushSync();
+
+            const room = aliceTestClient.client.getRoom(ROOM_ID);
+            const event = room.getLiveTimeline().getEvents()[0];
+            expect(event.isEncrypted()).toBe(true);
+            await event.attemptDecryption(aliceTestClient.client.crypto);
+            expect(event.getContent()).toEqual({});
+            const redactionEvent: any = event.getRedactionEvent();
+            expect(redactionEvent.content.reason).toEqual("redaction test");
+        },
+    );
 });

src/crypto/index.ts

@@ -2859,7 +2859,10 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      */
     public async decryptEvent(event: MatrixEvent): Promise<IEventDecryptionResult> {
         if (event.isRedacted()) {
-            const redactionEvent = new MatrixEvent(event.getUnsigned().redacted_because);
+            const redactionEvent = new MatrixEvent({
+                room_id: event.getRoomId(),
+                ...event.getUnsigned().redacted_because,
+            });
             const decryptedEvent = await this.decryptEvent(redactionEvent);
 
             return {