Detect split-brains caused by parallel calls

This is another KPI for PostHog.

src/room/checkForParallelCalls.ts

@@ -0,0 +1,65 @@
+/*
+Copyright 2023 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { EventType } from "matrix-js-sdk/src/@types/event";
+import { RoomState } from "matrix-js-sdk/src/models/room-state";
+
+import { PosthogAnalytics } from "../analytics/PosthogAnalytics";
+
+function isObject(x: unknown): x is Record<string, unknown> {
+  return typeof x === "object" && x !== null;
+}
+
+/**
+ * Checks the state of a room for multiple calls happening in parallel, sending
+ * the details to PostHog if that is indeed what's happening. (This is unwanted
+ * as it indicates a split-brain scenario.)
+ */
+export function checkForParallelCalls(state: RoomState): void {
+  const now = Date.now();
+  const participantsPerCall = new Map<string, number>();
+
+  // For each participant in each call, increment the participant count
+  for (const e of state.getStateEvents(EventType.GroupCallMemberPrefix)) {
+    const content = e.getContent<Record<string, unknown>>();
+    const calls: unknown[] = Array.isArray(content["m.calls"])
+      ? content["m.calls"]
+      : [];
+
+    for (const call of calls) {
+      if (isObject(call) && typeof call["m.call_id"] === "string") {
+        const devices: unknown[] = Array.isArray(call["m.devices"])
+          ? call["m.devices"]
+          : [];
+
+        for (const device of devices) {
+          if (isObject(device) && (device["expires_ts"] as number) > now) {
+            const participantCount =
+              participantsPerCall.get(call["m.call_id"]) ?? 0;
+            participantsPerCall.set(call["m.call_id"], participantCount + 1);
+          }
+        }
+      }
+    }
+  }
+
+  if (participantsPerCall.size > 1) {
+    PosthogAnalytics.instance.trackEvent({
+      eventName: "ParallelCalls",
+      participantsPerCall: Object.fromEntries(participantsPerCall),
+    });
+  }
+}

src/room/useGroupCall.ts

@@ -29,7 +29,7 @@ import { CallFeed, CallFeedEvent } from "matrix-js-sdk/src/webrtc/callFeed";
 import { RoomMember } from "matrix-js-sdk/src/models/room-member";
 import { useTranslation } from "react-i18next";
 import { IWidgetApiRequest } from "matrix-widget-api";
-import { MatrixClient } from "matrix-js-sdk";
+import { MatrixClient, RoomStateEvent } from "matrix-js-sdk";
 import {
   ByteSentStatsReport,
   ConnectionStatsReport,
@@ -42,6 +42,7 @@ import { TranslatedError, translatedError } from "../TranslatedError";
 import { ElementWidgetActions, ScreenshareStartData, widget } from "../widget";
 import { OTelGroupCallMembership } from "../otel/OTelGroupCallMembership";
 import { ElementCallOpenTelemetry } from "../otel/otel";
+import { checkForParallelCalls } from "./checkForParallelCalls";
 
 export enum ConnectionState {
   EstablishingCall = "establishing call", // call hasn't been established yet
@@ -377,18 +378,19 @@ export function useGroupCall(
     groupCall.on(GroupCallEvent.CallsChanged, onCallsChanged);
     groupCall.on(GroupCallEvent.ParticipantsChanged, onParticipantsChanged);
     groupCall.on(GroupCallEvent.Error, onError);
-
     groupCall.on(
       GroupCallStatsReportEvent.ConnectionStats,
       onConnectionStatsReport
     );
-
     groupCall.on(
       GroupCallStatsReportEvent.ByteSentStats,
       onByteSentStatsReport
     );
-
     groupCall.on(GroupCallStatsReportEvent.SummaryStats, onSummaryStatsReport);
+    groupCall.room.currentState.on(
+      RoomStateEvent.Update,
+      checkForParallelCalls
+    );
 
     updateState({
       error: null,
@@ -448,6 +450,10 @@ export function useGroupCall(
         GroupCallStatsReportEvent.SummaryStats,
         onSummaryStatsReport
       );
+      groupCall.room.currentState.off(
+        RoomStateEvent.Update,
+        checkForParallelCalls
+      );
       leaveCall();
     };
   }, [groupCall, updateState, leaveCall]);

test/room/checkForParallelCalls-test.ts

@@ -0,0 +1,171 @@
+/*
+Copyright 2023 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { Mocked, mocked } from "jest-mock";
+import { RoomState } from "matrix-js-sdk/src/models/room-state";
+import { PosthogAnalytics } from "../../src/analytics/PosthogAnalytics";
+import { checkForParallelCalls } from "../../src/room/checkForParallelCalls";
+
+const withFakeTimers = (continuation: () => void) => {
+  jest.useFakeTimers();
+  try {
+    continuation();
+  } finally {
+    jest.useRealTimers();
+  }
+};
+
+const withMockedPosthog = (
+  continuation: (posthog: Mocked<PosthogAnalytics>) => void
+) => {
+  const posthog = mocked({
+    trackEvent: jest.fn(),
+  } as unknown as PosthogAnalytics);
+  const instanceSpy = jest
+    .spyOn(PosthogAnalytics, "instance", "get")
+    .mockReturnValue(posthog);
+  try {
+    continuation(posthog);
+  } finally {
+    instanceSpy.mockRestore();
+  }
+};
+
+const mockRoomState = (
+  groupCallMemberContents: Record<string, unknown>[]
+): RoomState => {
+  const stateEvents = groupCallMemberContents.map((content) => ({
+    getContent: () => content,
+  }));
+  return { getStateEvents: () => stateEvents } as unknown as RoomState;
+};
+
+test("checkForParallelCalls does nothing if all participants are in the same call", () => {
+  withFakeTimers(() => {
+    withMockedPosthog((posthog) => {
+      const roomState = mockRoomState([
+        {
+          "m.calls": [
+            {
+              "m.call_id": "1",
+              "m.devices": [
+                {
+                  device_id: "Element Call",
+                  session_id: "a",
+                  expires_ts: Date.now() + 1000,
+                },
+              ],
+            },
+            {
+              "m.call_id": null, // invalid
+              "m.devices": [
+                {
+                  device_id: "Element Android",
+                  session_id: "a",
+                  expires_ts: Date.now() + 1000,
+                },
+              ],
+            },
+            null, // invalid
+          ],
+        },
+        {
+          "m.calls": [
+            {
+              "m.call_id": "1",
+              "m.devices": [
+                {
+                  device_id: "Element Desktop",
+                  session_id: "a",
+                  expires_ts: Date.now() + 1000,
+                },
+              ],
+            },
+          ],
+        },
+      ]);
+
+      checkForParallelCalls(roomState);
+      expect(posthog.trackEvent).not.toHaveBeenCalled();
+    });
+  });
+});
+
+test("checkForParallelCalls sends diagnostics to PostHog if there is a split-brain", () => {
+  withFakeTimers(() => {
+    withMockedPosthog((posthog) => {
+      const roomState = mockRoomState([
+        {
+          "m.calls": [
+            {
+              "m.call_id": "1",
+              "m.devices": [
+                {
+                  device_id: "Element Call",
+                  session_id: "a",
+                  expires_ts: Date.now() + 1000,
+                },
+              ],
+            },
+            {
+              "m.call_id": "2",
+              "m.devices": [
+                {
+                  device_id: "Element Android",
+                  session_id: "a",
+                  expires_ts: Date.now() + 1000,
+                },
+              ],
+            },
+          ],
+        },
+        {
+          "m.calls": [
+            {
+              "m.call_id": "1",
+              "m.devices": [
+                {
+                  device_id: "Element Desktop",
+                  session_id: "a",
+                  expires_ts: Date.now() + 1000,
+                },
+              ],
+            },
+            {
+              "m.call_id": "2",
+              "m.devices": [
+                {
+                  device_id: "Element Call",
+                  session_id: "a",
+                  expires_ts: Date.now() - 1000,
+                },
+              ],
+            },
+          ],
+        },
+      ]);
+
+      checkForParallelCalls(roomState);
+      expect(posthog.trackEvent).toHaveBeenCalledWith({
+        eventName: "ParallelCalls",
+        participantsPerCall: {
+          "1": 2,
+          "2": 1,
+        },
+      });
+    });
+  });
+});