Close webchannel instances on terminate (#9041)

Explicitly close any unclosed WebChannel instances on Firestore#terminate()

Author: MarkDuckworth

.changeset/spotty-ghosts-kneel.md

@@ -0,0 +1,5 @@
+---
+"@firebase/firestore": patch
+---
+
+Clean up leaked WebChannel instances when the Firestore instance is terminated.

packages/firestore/src/platform/browser/webchannel_connection.ts

@@ -59,6 +59,9 @@ export class WebChannelConnection extends RestConnection {
   private readonly useFetchStreams: boolean;
   private readonly longPollingOptions: ExperimentalLongPollingOptions;
 
+  /** A collection of open WebChannel instances */
+  private openWebChannels: WebChannel[] = [];
+
   constructor(info: DatabaseInfo) {
     super(info);
     this.forceLongPolling = info.forceLongPolling;
@@ -239,6 +242,7 @@ export class WebChannelConnection extends RestConnection {
       request
     );
     const channel = webchannelTransport.createWebChannel(url, request);
+    this.addOpenWebChannel(channel);
 
     // WebChannel supports sending the first message with the handshake - saving
     // a network round trip. However, it will have to call send in the same
@@ -321,6 +325,7 @@ export class WebChannelConnection extends RestConnection {
           `RPC '${rpcName}' stream ${streamId} transport closed`
         );
         streamBridge.callOnClose();
+        this.removeOpenWebChannel(channel);
       }
     });
 
@@ -427,4 +432,32 @@ export class WebChannelConnection extends RestConnection {
     }, 0);
     return streamBridge;
   }
+
+  /**
+   * Closes and cleans up any resources associated with the connection.
+   */
+  terminate(): void {
+    // If the Firestore instance is terminated, we will explicitly
+    // close any remaining open WebChannel instances.
+    this.openWebChannels.forEach(webChannel => webChannel.close());
+    this.openWebChannels = [];
+  }
+
+  /**
+   * Add a WebChannel instance to the collection of open instances.
+   * @param webChannel
+   */
+  addOpenWebChannel(webChannel: WebChannel): void {
+    this.openWebChannels.push(webChannel);
+  }
+
+  /**
+   * Remove a WebChannel instance from the collection of open instances.
+   * @param webChannel
+   */
+  removeOpenWebChannel(webChannel: WebChannel): void {
+    this.openWebChannels = this.openWebChannels.filter(
+      instance => instance === webChannel
+    );
+  }
 }