Remove MatrixRTC legacy mode

This is the mode in which we sent membership events with the 'oldest membership' transport selection algorithm, which stopped being the default back in version 0.21.0. Users will no longer be able to select this mode in developer settings, and admins will no longer be able to select legacy mode through the config either. The app will still continue to support *receiving* membership events with the 'oldest membership' transport selection algorithm from others, however.

src/state/CallViewModel/localMember/LocalTransport.ts

@@ -7,23 +7,16 @@ Please see LICENSE in the repository root for full details.
 
 import {
   type CallMembership,
-  isLivekitTransportConfig,
   type LivekitTransportConfig,
 } from "matrix-js-sdk/lib/matrixrtc";
 import { type MatrixClient } from "matrix-js-sdk";
 import {
-  catchError,
   combineLatest,
   distinctUntilChanged,
-  first,
   from,
   map,
-  merge,
-  type Observable,
   of,
-  startWith,
   switchMap,
-  tap,
 } from "rxjs";
 import { logger as rootLogger, type Logger } from "matrix-js-sdk/lib/logger";
 import { type CallMembershipIdentityParts } from "matrix-js-sdk/lib/matrixrtc/EncryptionManager";
@@ -47,8 +40,7 @@ import { RtcTransportAutoDiscovery } from "./RtcTransportAutoDiscovery.ts";
 
 /*
  * It figures out “which LiveKit focus URL/alias the local user should use,”
- * optionally aligning with the oldest member, and ensures the SFU path is primed
- * before advertising that choice.
+ * and ensures the SFU path is primed before advertising that choice.
  */
 interface Props {
   scope: ObservableScope;
@@ -61,7 +53,6 @@ interface Props {
     OpenIDClientParts;
   // Used by the jwt service to create the livekit room and compute the livekit alias.
   roomId: string;
-  useOldestMember: boolean;
   forceJwtEndpoint: JwtEndpointVersion;
   delayId$: Behavior<string | null>;
 }
@@ -119,8 +110,6 @@ export interface LocalTransport {
 /**
  * Connects to the JWT service and determines the transports that the local member should use.
  *
- * @prop useOldestMember Whether to use the same transport as the oldest member.
- * This will only update once the first oldest member appears. Will not recompute if the oldest member leaves.
  * @prop useOldJwtEndpoint Whether to set forceOldJwtEndpoint on the returned transport and to use the old JWT endpoint.
  * This is used when the connection manager needs to know if it has to use the legacy endpoint which implies a string concatenated rtcBackendIdentity.
  * (which is expected for non sticky event based rtc member events)
@@ -133,18 +122,10 @@ export const createLocalTransport$ = ({
   ownMembershipIdentity,
   client,
   roomId,
-  useOldestMember,
   forceJwtEndpoint,
   delayId$,
 }: Props): LocalTransport => {
   const logger = rootLogger.getChild("[LocalTransport]");
-  // The LiveKit transport in use by the oldest RTC membership. `null` when the
-  // oldest member has no such transport.
-  const oldestMemberTransport$ = observerOldestMembership$(
-    scope,
-    memberships$,
-    logger,
-  );
 
   const transportDiscovery = new RtcTransportAutoDiscovery({
     client: client,
@@ -203,19 +184,6 @@ export const createLocalTransport$ = ({
     }),
   );
 
-  if (useOldestMember) {
-    return observeLocalTransportForOldestMembership(
-      scope,
-      oldestMemberTransport$,
-      preferredTransport$,
-      client,
-      ownMembershipIdentity,
-      roomId,
-      logger,
-    );
-  }
-
-  // --- Multi-SFU mode ---
   // Always publish on and advertise the preferred transport.
   return {
     advertised$: scope.behavior(
@@ -243,47 +211,6 @@ export const createLocalTransport$ = ({
   };
 };
 
-/**
- * Observes the oldest member in the room and returns the transport that it uses if it is a livekit transport.
- * @param scope - The observable scope.
- * @param memberships$ - The observable of the call's memberships.'
- */
-function observerOldestMembership$(
-  scope: ObservableScope,
-  memberships$: Behavior<Epoch<CallMembership[]>>,
-  logger: Logger,
-): Behavior<LivekitTransportConfig | null> {
-  return scope.behavior<LivekitTransportConfig | null>(
-    memberships$.pipe(
-      map((memberships) => {
-        const oldestMember = memberships.value[0];
-        if (oldestMember === undefined) {
-          logger.info("Oldest member: not found");
-          return null;
-        }
-        const transport = oldestMember.getTransport(oldestMember);
-        if (transport === undefined) {
-          logger.warn(
-            `Oldest member: ${oldestMember.userId}|${oldestMember.deviceId}|${oldestMember.memberId} has no transport`,
-          );
-          return null;
-        }
-        if (!isLivekitTransportConfig(transport)) {
-          logger.warn(
-            `Oldest member: ${oldestMember.userId}|${oldestMember.deviceId}|${oldestMember.memberId} has invalid transport`,
-          );
-          return null;
-        }
-        logger.info(
-          "Oldest member: ${oldestMember.userId}|${oldestMember.deviceId}|${oldestMember.memberId} has valid transport",
-        );
-        return transport;
-      }),
-      distinctUntilChanged(areLivekitTransportsEqual),
-    ),
-  );
-}
-
 /**
  *  Utility to ensure the user can authenticate with the SFU.
  *  We will call `getSFUConfigWithOpenID` once per transport here as it's our
@@ -331,85 +258,6 @@ async function doOpenIdAndJWTFromUrl(
   };
 }
 
-function observeLocalTransportForOldestMembership(
-  scope: ObservableScope,
-  oldestMemberTransport$: Behavior<LivekitTransportConfig | null>,
-  preferredTransport$: Observable<LocalTransportWithSFUConfig>,
-  client: Pick<
-    MatrixClient,
-    "getDomain" | "baseUrl" | "_unstable_getRTCTransports"
-  > &
-    OpenIDClientParts,
-  ownMembershipIdentity: CallMembershipIdentityParts,
-  roomId: string,
-  logger: Logger,
-): LocalTransport {
-  // Ensure we can authenticate with the SFU.
-  const authenticatedOldestMemberTransport$ = oldestMemberTransport$.pipe(
-    switchMap((transport) => {
-      // Oldest member not available -we are first- (or invalid SFU config).
-      if (transport === null) return of(null);
-
-      // Whenever there is transport change we want to revert
-      // to no transport while we do the authentication.
-      // So do a from(promise) here to be able to startWith(null)
-      return from(
-        doOpenIdAndJWTFromUrl(
-          transport,
-          JwtEndpointVersion.Legacy,
-          ownMembershipIdentity,
-          roomId,
-          client,
-          undefined,
-          logger,
-        ),
-      ).pipe(
-        catchError((e: unknown) => {
-          logger.error(
-            `Failed to authenticate to transport ${transport.livekit_service_url}`,
-            e,
-          );
-          throw mapAuthErrorToUserFriendlyError(e);
-        }),
-        startWith(null),
-      );
-    }),
-  );
-
-  // --- Oldest member mode ---
-  return {
-    // Never update the transport that we advertise in our membership. Just
-    // take the first valid oldest member or preferred transport that we learn
-    // about, and stick with that. This avoids unnecessary SFU hops and room
-    // state changes.
-    advertised$: scope.behavior(
-      merge(
-        authenticatedOldestMemberTransport$.pipe(
-          map((t) => t?.transport ?? null),
-        ),
-        preferredTransport$.pipe(map((t) => t.transport)),
-      ).pipe(
-        first((t) => t !== null),
-        tap((t) =>
-          logger.info(`Advertise transport: ${t.livekit_service_url}`),
-        ),
-      ),
-      null,
-    ),
-    // Publish on the transport used by the oldest member.
-    active$: scope.behavior(
-      authenticatedOldestMemberTransport$.pipe(
-        tap((t) =>
-          logger.info(
-            `Publish on transport: ${t?.transport.livekit_service_url}`,
-          ),
-        ),
-      ),
-      null,
-    ),
-  };
-}
-
 function mapAuthErrorToUserFriendlyError(e: unknown): Error {
   if (
     e instanceof FailToGetOpenIdToken ||