Do not rotate MatrixRTC media encryption key when a new member joins a session (#4472)

* Do not rotate MatrixRTC media encryption key when a new member joins a call

This change reverts #4422.

Instead, the rotation when a new member joins will be reintroduced as part of supporting to-device based MatrixRTC encryption key distribution.

* Improve function name

Author: hughns

spec/unit/matrixrtc/MatrixRTCSession.spec.ts

@@ -773,7 +773,7 @@ describe("MatrixRTCSession", () => {
                 expect(client.cancelPendingEvent).toHaveBeenCalledWith(eventSentinel);
             });
 
-            it("rotates key if a new member joins", async () => {
+            it("Re-sends key if a new member joins", async () => {
                 jest.useFakeTimers();
                 try {
                     const mockRoom = makeMockRoom([membershipTemplate]);
@@ -784,9 +784,7 @@ describe("MatrixRTCSession", () => {
                     });
 
                     sess.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
-                    const firstKeysPayload = await keysSentPromise1;
-                    expect(firstKeysPayload.keys).toHaveLength(1);
-                    expect(firstKeysPayload.keys[0].index).toEqual(0);
+                    await keysSentPromise1;
                     expect(sess!.statistics.counters.roomEventEncryptionKeysSent).toEqual(1);
 
                     sendEventMock.mockClear();
@@ -808,14 +806,9 @@ describe("MatrixRTCSession", () => {
                         .mockReturnValue(makeMockRoomState([membershipTemplate, member2], mockRoom.roomId));
                     sess.onMembershipUpdate();
 
-                    jest.advanceTimersByTime(10000);
-
-                    const secondKeysPayload = await keysSentPromise2;
+                    await keysSentPromise2;
 
                     expect(sendEventMock).toHaveBeenCalled();
-                    expect(secondKeysPayload.keys).toHaveLength(1);
-                    expect(secondKeysPayload.keys[0].index).toEqual(1);
-                    expect(secondKeysPayload.keys[0].key).not.toEqual(firstKeysPayload.keys[0].key);
                     expect(sess!.statistics.counters.roomEventEncryptionKeysSent).toEqual(2);
                 } finally {
                     jest.useRealTimers();
@@ -1103,8 +1096,8 @@ describe("MatrixRTCSession", () => {
                 }
                 jest.useFakeTimers();
                 try {
-                    // start with a single member
-                    const mockRoom = makeMockRoom(members.slice(0, 1));
+                    // start with all members
+                    const mockRoom = makeMockRoom(members);
 
                     for (let i = 0; i < membersToTest; i++) {
                         const keysSentPromise = new Promise<EncryptionKeysEventContent>((resolve) => {
@@ -1116,10 +1109,12 @@ describe("MatrixRTCSession", () => {
                             sess = MatrixRTCSession.roomSessionForRoom(client, mockRoom);
                             sess.joinRoomSession([mockFocus], mockFocus, { manageMediaKeys: true });
                         } else {
-                            // otherwise update the state
+                            // otherwise update the state reducing the membership each time in order to trigger key rotation
                             mockRoom.getLiveTimeline().getState = jest
                                 .fn()
-                                .mockReturnValue(makeMockRoomState(members.slice(0, i + 1), mockRoom.roomId));
+                                .mockReturnValue(
+                                    makeMockRoomState(members.slice(0, membersToTest - i), mockRoom.roomId),
+                                );
                         }
 
                         sess!.onMembershipUpdate();

src/matrixrtc/MatrixRTCSession.ts

@@ -328,7 +328,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
         logger.info(`Joining call session in room ${this.room.roomId} with manageMediaKeys=${this.manageMediaKeys}`);
         if (joinConfig?.manageMediaKeys) {
             this.makeNewSenderKey();
-            this.requestKeyEventSend();
+            this.requestSendCurrentKey();
         }
         // We don't wait for this, mostly because it may fail and schedule a retry, so this
         // function returning doesn't really mean anything at all.
@@ -546,10 +546,10 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
     }
 
     /**
-     * Requests that we resend our keys to the room. May send a keys event immediately
+     * Requests that we resend our current keys to the room. May send a keys event immediately
      * or queue for alter if one has already been sent recently.
      */
-    private requestKeyEventSend(): void {
+    private requestSendCurrentKey(): void {
         if (!this.manageMediaKeys) return;
 
         if (
@@ -795,8 +795,8 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
                 logger.debug(`Member(s) have left: queueing sender key rotation`);
                 this.makeNewKeyTimeout = setTimeout(this.onRotateKeyTimeout, MAKE_KEY_DELAY);
             } else if (anyJoined) {
-                logger.debug(`New member(s) have joined: queueing sender key rotation`);
-                this.makeNewKeyTimeout = setTimeout(this.onRotateKeyTimeout, MAKE_KEY_DELAY);
+                logger.debug(`New member(s) have joined: re-sending keys`);
+                this.requestSendCurrentKey();
             } else if (oldFingerprints) {
                 // does it look like any of the members have updated their memberships?
                 const newFingerprints = this.lastMembershipFingerprints!;
@@ -808,7 +808,7 @@ export class MatrixRTCSession extends TypedEventEmitter<MatrixRTCSessionEvent, M
                     Array.from(newFingerprints).some((x) => !oldFingerprints.has(x));
                 if (candidateUpdates) {
                     logger.debug(`Member(s) have updated/reconnected: re-sending keys to everyone`);
-                    this.requestKeyEventSend();
+                    this.requestSendCurrentKey();
                 }
             }
         }