MatrixRTC: comply with the manageMediaKeys EncryptionConfig option (#4942)

* MatrixRTC: comply with the `manageMediaKeys` JoinConfig option

* add additional test for reception

* add comments about temporary solution

spec/unit/matrixrtc/RTCEncryptionManager.spec.ts

@@ -448,6 +448,23 @@ describe("RTCEncryptionManager", () => {
 
             expect(statistics.counters.roomEventEncryptionKeysSent).toBe(2);
         });
+
+        it("Should not distribute keys if encryption is disabled", async () => {
+            jest.useFakeTimers();
+            const members = [
+                aCallMembership("@bob:example.org", "BOBDEVICE"),
+                aCallMembership("@bob:example.org", "BOBDEVICE2"),
+                aCallMembership("@carl:example.org", "CARLDEVICE"),
+            ];
+            getMembershipMock.mockReturnValue(members);
+
+            encryptionManager.join({ manageMediaKeys: false });
+            encryptionManager.onMembershipsUpdate();
+            await jest.runOnlyPendingTimersAsync();
+
+            expect(mockTransport.sendKey).not.toHaveBeenCalled();
+            expect(onEncryptionKeysChanged).not.toHaveBeenCalled();
+        });
     });
 
     describe("Receiving Keys", () => {
@@ -471,6 +488,29 @@ describe("RTCEncryptionManager", () => {
             );
         });
 
+        it("should not accept keys when manageMediaKeys is disabled", async () => {
+            jest.useFakeTimers();
+
+            const members = [aCallMembership("@bob:example.org", "BOBDEVICE")];
+            getMembershipMock.mockReturnValue(members);
+
+            encryptionManager.join({ manageMediaKeys: false });
+            encryptionManager.onMembershipsUpdate();
+            await jest.advanceTimersByTimeAsync(10);
+
+            mockTransport.emit(
+                KeyTransportEvents.ReceivedKeys,
+                "@bob:example.org",
+                "BOBDEVICE",
+                "AAAAAAAAAAA",
+                0 /* KeyId */,
+                0 /* Timestamp */,
+            );
+
+            expect(onEncryptionKeysChanged).not.toHaveBeenCalled();
+            expect(statistics.counters.roomEventEncryptionKeysReceived).toBe(0);
+        });
+
         it("should accept keys from transport", async () => {
             jest.useFakeTimers();
 

src/matrixrtc/RTCEncryptionManager.ts

@@ -46,6 +46,11 @@ import {
  * XXX In the future we want to distribute a ratcheted key not the current one for new joiners.
  */
 export class RTCEncryptionManager implements IEncryptionManager {
+    // This is a stop-gap solution for now. The preferred way to handle this case would be instead
+    // to create a NoOpEncryptionManager that does nothing and use it for the session.
+    // This will be done when removing the legacy EncryptionManager.
+    private manageMediaKeys = false;
+
     /**
      * Store the key rings for each participant.
      * The encryption manager stores the keys because the application layer might not be ready yet to handle the keys.
@@ -126,6 +131,8 @@ export class RTCEncryptionManager implements IEncryptionManager {
     }
 
     public join(joinConfig: EncryptionConfig | undefined): void {
+        this.manageMediaKeys = joinConfig?.manageMediaKeys ?? true; // default to true
+
         this.logger?.info(`Joining room`);
         this.useKeyDelay = joinConfig?.useKeyDelay ?? 1000;
         this.keyRotationGracePeriodMs = joinConfig?.keyRotationGracePeriodMs ?? 10_000;
@@ -174,6 +181,10 @@ export class RTCEncryptionManager implements IEncryptionManager {
      * the calls will be coalesced to a single new distribution (that will start just after the current one has completed).
      */
     private ensureKeyDistribution(): void {
+        // `manageMediaKeys` is a stop-gap solution for now. The preferred way to handle this case would be instead
+        // to create a NoOpEncryptionManager that does nothing and use it for the session.
+        // This will be done when removing the legacy EncryptionManager.
+        if (!this.manageMediaKeys) return;
         if (this.currentKeyDistributionPromise == null) {
             this.logger?.debug(`No active rollout, start a new one`);
             // start a rollout
@@ -196,6 +207,15 @@ export class RTCEncryptionManager implements IEncryptionManager {
     }
 
     public onNewKeyReceived: KeyTransportEventListener = (userId, deviceId, keyBase64Encoded, index, timestamp) => {
+        // `manageMediaKeys` is a stop-gap solution for now. The preferred way to handle this case would be instead
+        // to create a NoOpEncryptionManager that does nothing and use it for the session.
+        // This will be done when removing the legacy EncryptionManager.
+        if (!this.manageMediaKeys) {
+            this.logger?.warn(
+                `Received key over transport ${userId}:${deviceId} at index ${index} but media keys are disabled`,
+            );
+            return;
+        }
         this.logger?.debug(`Received key over transport ${userId}:${deviceId} at index ${index}`);
 
         // We received a new key, notify the video layer of this new key so that it can decrypt the frames properly.