Logically separate the advertised transport from the active transport

To correctly implement the legacy "oldest membership" mode, we need the code to be more nuanced about the local transport. Specifically, it needs to allow for the transport we advertise in our membership to be different from the transport that we connect to and publish media on. Otherwise, if these two are yoked together, members will resend their memberships whenever an SFU hop occurs, which an attacker could use to cause an amplified wave of state changes.

src/state/CallViewModel/remoteMembers/ConnectionManager.ts

@@ -90,7 +90,7 @@ export interface IConnectionManager {
  * @param props - Configuration object
  * @param props.scope - The observable scope used by this object
  * @param props.connectionFactory - Used to create new connections
- * @param props.localTransport$ - The local transport to use. (deduplicated with remoteTransports$)
+ * @param props.localTransport$ - The transport to publish local media on. (deduplicated with remoteTransports$)
  * @param props.remoteTransports$ - All other transports. The connection manager will create connections for each transport. (deduplicated with localTransport$)
  * @param props.ownMembershipIdentity - The own membership identity to use.
  * @param props.logger - The logger to use.
@@ -164,21 +164,21 @@ export function createConnectionManager$({
       generateItemsWithEpoch(
         "ConnectionManager connections$",
         function* (transports) {
-          for (const transportWithOrWithoutSfuConfig of transports) {
-            if (
-              isLocalTransportWithSFUConfig(transportWithOrWithoutSfuConfig)
-            ) {
-              // This is the local transport only the `LocalTransportWithSFUConfig` has a `sfuConfig` field
-              const { transport, sfuConfig } = transportWithOrWithoutSfuConfig;
+          for (const transport of transports) {
+            if (isLocalTransportWithSFUConfig(transport)) {
+              // This is the local transport; only the `LocalTransportWithSFUConfig` has a `sfuConfig` field.
               yield {
-                keys: [transport.livekit_service_url, sfuConfig],
+                keys: [
+                  transport.transport.livekit_service_url,
+                  transport.sfuConfig,
+                ],
                 data: undefined,
               };
             } else {
               yield {
                 keys: [
-                  transportWithOrWithoutSfuConfig.livekit_service_url,
-                  undefined as undefined | SFUConfig,
+                  transport.livekit_service_url,
+                  undefined as SFUConfig | undefined,
                 ],
                 data: undefined,
               };
@@ -194,6 +194,8 @@ export function createConnectionManager$({
             },
             ownMembershipIdentity,
             logger,
+            // TODO: This whole optional SFUConfig parameter is not particularly elegant.
+            // I would like it if connections always fetched the SFUConfig by themselves.
             sfuConfig,
           );
           // Start the connection immediately