chore: websocket rate limiting

NestJS/Throttling/websockets.md

@@ -0,0 +1,35 @@
+### Rate Limiting a WebSocket connection
+Create a guard like so:
+```
+@Injectable()
+export class WsThrottlerGuard extends ThrottlerGuard {
+  async handleRequest({
+    context,
+    limit,
+    ttl,
+    throttler,
+  }: {
+    context: ExecutionContext;
+    limit: number; // limit of requests before connection should be rate limited
+    ttl: number; // how long requests are considered to be of the same session
+    throttler: ThrottlerOptions; 
+  }): Promise<boolean> {
+    const client = context.switchToWs().getClient();
+    const ip = client.conn.remoteAddress;
+    const key = this.generateKey(context, ip, throttler.name); 
+    // Increment number of requests made by this key (which is unique for each user and session)
+    const out = await this.storageService.increment(
+      key,
+      ttl,
+      limit,
+      60000, // blocked for a minute
+      'default', // name of the throttler
+    );
+    if (out.totalHits > limit) {
+      throw new ThrottlerException();
+    }
+    return true;
+  }
+}
+```
+This guard can then be applied to a websocket controller or event using UseGuards or to the whole module. Docs: https://docs.nestjs.com/security/rate-limiting