fix: memory leak caused by many unclosed redis subscriptions (#750)

* fix: memory leak caused by many unclosed redis subscriptions

* chore: address pull request feedback

packages/api/src/router/widgets/app.ts

@@ -27,19 +27,15 @@ export const appRouter = createTRPCRouter({
       const pingResult = await sendPingRequestAsync(input.url);
 
       return observable<{ url: string; statusCode: number } | { url: string; error: string }>((emit) => {
-        let isConnectionClosed = false;
-
         emit.next({ url: input.url, ...pingResult });
-        pingChannel.subscribe((message) => {
-          if (isConnectionClosed) return;
-
+        const unsubscribe = pingChannel.subscribe((message) => {
           // Only emit if same url
           if (message.url !== input.url) return;
           emit.next(message);
         });
 
         return () => {
-          isConnectionClosed = true;
+          unsubscribe();
           void pingUrlChannel.removeAsync(input.url);
         };
       });