Update makeTransport to fetch backend transports and validate all transports before response.

src/state/CallViewModel/localMember/LocalTransport.test.ts

@@ -32,6 +32,7 @@ describe("LocalTransport", () => {
       memberships$: constant(new Epoch<CallMembership[]>([])),
       client: {
         getDomain: () => "",
+        _unstable_getRTCTransports: async () => [],
         // These won't be called in this error path but satisfy the type
         getOpenIdToken: vi.fn(),
         getDeviceId: vi.fn(),
@@ -67,6 +68,7 @@ describe("LocalTransport", () => {
       client: {
         // Use empty domain to skip .well-known and use config directly
         getDomain: () => "",
+        _unstable_getRTCTransports: async () => [],
         getOpenIdToken: vi.fn(),
         getDeviceId: vi.fn(),
       },
@@ -103,6 +105,7 @@ describe("LocalTransport", () => {
       memberships$: constant(new Epoch<CallMembership[]>([])),
       client: {
         getDomain: () => "",
+        _unstable_getRTCTransports: async () => [],
         getOpenIdToken: vi.fn(),
         getDeviceId: vi.fn(),
       },
@@ -138,6 +141,7 @@ describe("LocalTransport", () => {
       memberships$,
       client: {
         getDomain: () => "",
+        _unstable_getRTCTransports: async () => [],
         getOpenIdToken: vi.fn(),
         getDeviceId: vi.fn(),
       },

src/state/CallViewModel/localMember/LocalTransport.ts

@@ -8,11 +8,11 @@ Please see LICENSE in the repository root for full details.
 import {
   type CallMembership,
   isLivekitTransport,
-  type LivekitTransportConfig,
   type LivekitTransport,
   isLivekitTransportConfig,
+  type Transport,
 } from "matrix-js-sdk/lib/matrixrtc";
-import { type MatrixClient } from "matrix-js-sdk";
+import { MatrixError, type MatrixClient } from "matrix-js-sdk";
 import {
   combineLatest,
   distinctUntilChanged,
@@ -45,7 +45,8 @@ const logger = rootLogger.getChild("[LocalTransport]");
 interface Props {
   scope: ObservableScope;
   memberships$: Behavior<Epoch<CallMembership[]>>;
-  client: Pick<MatrixClient, "getDomain"> & OpenIDClientParts;
+  client: Pick<MatrixClient, "getDomain" | "_unstable_getRTCTransports"> &
+    OpenIDClientParts;
   roomId: string;
   useOldestMember$: Behavior<boolean>;
 }
@@ -116,73 +117,125 @@ export const createLocalTransport$ = ({
 const FOCI_WK_KEY = "org.matrix.msc4143.rtc_foci";
 
 /**
+ * Determine the correct Transport for the current session, including
+ * validating auth against the service to ensure it's correct.
+ * Prefers in order:
  *
- * @param client
- * @param roomId
- * @returns
+ * 1. The transports returned via the homeserver.
+ * 2. The transports returned via .well-known.
+ * 3. The transport configured in Element Call's config.
+ *
+ * @param client The authenticated Matrix client for the current user
+ * @param roomId The ID of the room to be connected to.
+ * @param urlFromDevSettings Override URL provided by the user's local config.
+ * @returns A fully validated transport config.
  * @throws MatrixRTCTransportMissingError | FailToGetOpenIdToken
  */
 async function makeTransport(
-  client: Pick<MatrixClient, "getDomain"> & OpenIDClientParts,
+  client: Pick<MatrixClient, "getDomain" | "_unstable_getRTCTransports"> &
+    OpenIDClientParts,
   roomId: string,
   urlFromDevSettings: string | null,
 ): Promise<LivekitTransport> {
-  let transport: LivekitTransport | undefined;
   logger.trace("Searching for a preferred transport");
-  //TODO refactor this to use the jwt service returned alias.
   const livekitAlias = roomId;
 
   // DEVTOOL: Highest priority: Load from devtool setting
   if (urlFromDevSettings !== null) {
-    const transportFromStorage: LivekitTransport = {
+    logger.info("Using LiveKit transport from dev tools: ", urlFromDevSettings);
+    // Validate that the SFU is up. Otherwise, we want to fail on this
+    // as we don't permit other SFUs.
+    await getSFUConfigWithOpenID(client, urlFromDevSettings, livekitAlias);
+    return {
       type: "livekit",
       livekit_service_url: urlFromDevSettings,
       livekit_alias: livekitAlias,
     };
-    logger.info(
-      "Using LiveKit transport from dev tools: ",
-      transportFromStorage,
-    );
-    transport = transportFromStorage;
   }
 
-  // WELL_KNOWN: Prioritize the .well-known/matrix/client, if available, over the configured SFU
+  async function getFirstUsableTransport(
+    transports: Transport[],
+  ): Promise<LivekitTransport | null> {
+    for (const potentialTransport of transports) {
+      if (isLivekitTransportConfig(potentialTransport)) {
+        try {
+          await getSFUConfigWithOpenID(
+            client,
+            potentialTransport.livekit_service_url,
+            livekitAlias,
+          );
+          return {
+            ...potentialTransport,
+            livekit_alias: livekitAlias,
+          };
+        } catch (ex) {
+          logger.debug(
+            `Could not use SFU service "${potentialTransport.livekit_service_url}" as SFU`,
+            ex,
+          );
+        }
+      }
+    }
+    return null;
+  }
+
+  // MSC4143: Attempt to fetch transports from backend.
+  if ("_unstable_getRTCTransports" in client) {
+    try {
+      const selectedTransport = await getFirstUsableTransport(
+        await client._unstable_getRTCTransports(),
+      );
+      if (selectedTransport) {
+        logger.info("Using backend-configured SFU", selectedTransport);
+        return selectedTransport;
+      }
+    } catch (ex) {
+      if (ex instanceof MatrixError && ex.httpStatus === 404) {
+        // Expected, this is an unstable endpoint and it's not required.
+        logger.debug("Backend does not provide any RTC transports", ex);
+      } else {
+        // We got an error that wasn't just missing support for the feature, so log it loudly.
+        logger.error(
+          "Unexpected error fetching RTC transports from backend",
+          ex,
+        );
+      }
+    }
+  }
+
+  // Legacy MSC4143 (to be removed) WELL_KNOWN: Prioritize the .well-known/matrix/client, if available.
   const domain = client.getDomain();
-  if (domain && transport === undefined) {
+  if (domain) {
     // we use AutoDiscovery instead of relying on the MatrixClient having already
     // been fully configured and started
     const wellKnownFoci = (await AutoDiscovery.getRawClientConfig(domain))?.[
       FOCI_WK_KEY
     ];
-    if (Array.isArray(wellKnownFoci)) {
-      const wellKnownTransport: LivekitTransportConfig | undefined =
-        wellKnownFoci.find((f) => f && isLivekitTransportConfig(f));
-      if (wellKnownTransport !== undefined) {
-        logger.info("Using LiveKit transport from .well-known: ", transport);
-        transport = { ...wellKnownTransport, livekit_alias: livekitAlias };
-      }
+    const selectedTransport = Array.isArray(wellKnownFoci)
+      ? await getFirstUsableTransport(wellKnownFoci)
+      : null;
+    if (selectedTransport) {
+      logger.info("Using .well-known SFU", selectedTransport);
+      return selectedTransport;
     }
   }
 
   // CONFIG: Least prioritized; Load from config file
   const urlFromConf = Config.get().livekit?.livekit_service_url;
-  if (urlFromConf && transport === undefined) {
-    const transportFromConf: LivekitTransport = {
-      type: "livekit",
-      livekit_service_url: urlFromConf,
-      livekit_alias: livekitAlias,
-    };
-    logger.info("Using LiveKit transport from config: ", transportFromConf);
-    transport = transportFromConf;
+  if (urlFromConf) {
+    try {
+      await getSFUConfigWithOpenID(client, urlFromConf, roomId);
+      const selectedTransport: LivekitTransport = {
+        type: "livekit",
+        livekit_service_url: urlFromConf,
+        livekit_alias: livekitAlias,
+      };
+      logger.info("Using config SFU", selectedTransport);
+      return selectedTransport;
+    } catch (ex) {
+      logger.error("Failed to validate config SFU", ex);
+    }
   }
 
-  if (!transport) throw new MatrixRTCTransportMissingError(domain ?? ""); // this will call the jwt/sfu/get endpoint to pre create the livekit room.
-
-  await getSFUConfigWithOpenID(
-    client,
-    transport.livekit_service_url,
-    transport.livekit_alias,
-  );
-
-  return transport;
+  throw new MatrixRTCTransportMissingError(domain ?? "");
 }