array -> prop|null in discoverLocalTransport

sdk/src/RTCParticipation.ts

@@ -135,7 +135,7 @@ export function createRTCParticipation(
   // If the backend is LiveKit, we check it for transports as well, as a
   // fallback: another member's SFU may let us publish (MSC4195). LiveKit only,
   // so it stays out of the backend interface
-  const transportsFromBackends = async (): Promise<Transport[]> =>
+  const transportFromBackends = async (): Promise<Transport | null> =>
     backend.transportType === "livekit"
       ? findRemotePublishLivekitTransport({
           client,
@@ -146,20 +146,22 @@ export function createRTCParticipation(
           roomId: room.roomId,
           slotId: jsSdkSession.slotId,
           logger,
-        }).then((transport) => (transport === null ? [] : [transport]))
+        })
-      : [];
+      : null;
 
   const preparedTransport$ = from(
     discoverLocalTransport(
       client,
       backend.transportType,
       options,
-      transportsFromBackends,
+      transportFromBackends,
       logger,
-    ).then(async (transport): Promise<PreparedTransport> => ({
+    ).then(
-      transport,
+      async (transport): Promise<PreparedTransport> => ({
-      ...(await backend.prepareLocalTransport(transport)),
+        transport,
-    })),
+        ...(await backend.prepareLocalTransport(transport)),
+      }),
+    ),
   );
 
   const localMembership = createLocalMembership$({

sdk/src/matrixrtc/LocalTransport.test.ts

@@ -25,11 +25,6 @@ const bobsTransport: Transport = {
   url: "wss://sfu.bob.com",
   server_name: "bob.com",
 };
-const carolsTransport: Transport = {
-  type: "livekit",
-  url: "wss://sfu.carol.com",
-  server_name: "carol.com",
-};
 
 function client(
   advertised: Transport[],
@@ -41,9 +36,9 @@ function client(
 }
 
 function fromBackends(
-  transports: Transport[] = [],
+  transport: Transport|null = null,
-): ReturnType<typeof vi.fn<() => Promise<Transport[]>>> {
+): ReturnType<typeof vi.fn<() => Promise<Transport|null>>> {
-  return vi.fn(async () => Promise.resolve(transports));
+  return vi.fn(async () => Promise.resolve(transport));
 }
 
 describe("discoverLocalTransport", () => {
@@ -87,7 +82,7 @@ describe("discoverLocalTransport", () => {
   });
 
   it("prefers a local transport over the backends' without asking them", async () => {
-    const backends = fromBackends([bobsTransport]);
+    const backends = fromBackends(bobsTransport);
 
     await expect(
       discoverLocalTransport(
@@ -101,18 +96,6 @@ describe("discoverLocalTransport", () => {
     expect(backends).not.toHaveBeenCalled();
   });
 
-  it("takes the first transport the backends provide where there is no local one", async () => {
-    await expect(
-      discoverLocalTransport(
-        client([]),
-        "livekit",
-        {},
-        fromBackends([bobsTransport, carolsTransport]),
-        logger,
-      ),
-    ).resolves.toEqual(bobsTransport);
-  });
-
   it("fails naming the homeserver where there is no transport at all", async () => {
     const promise = discoverLocalTransport(
       client([]),

sdk/src/matrixrtc/LocalTransport.ts

@@ -27,7 +27,7 @@ export async function discoverLocalTransport(
     transport: override,
     fallbackTransport,
   }: Pick<RTCParticipationOptions, "transport" | "fallbackTransport">,
-  transportsFromBackends: () => Promise<Transport[]>,
+  transportFromBackends: () => Promise<Transport | null>,
   logger: Logger,
 ): Promise<Transport> {
   const transport =
@@ -38,7 +38,7 @@ export async function discoverLocalTransport(
       fallbackTransport,
       logger,
     }).discoverPreferredTransport()) ??
-    (await transportsFromBackends()).at(0) ??
+    (await transportFromBackends()) ??
     null;
   if (transport === null)
     throw new MatrixRTCTransportMissingError(client.getDomain() ?? "");