feat(client): Emit invalidate events from client (#3076)

* add emitInvalidate option

* Add documentation for event

* Re-write emitInvalidate logic

* Fix issues after merge

---------

Co-authored-by: Nikolay Karadzhov <[email protected]>

Author: sastcsgh

README.md

@@ -293,6 +293,7 @@ The Node Redis client class is an Nodejs EventEmitter and it emits an event each
 | `error`                 | An error has occurred—usually a network issue such as "Socket closed unexpectedly" | `(error: Error)`                                          |
 | `reconnecting`          | Client is trying to reconnect to the server                                        | _No arguments_                                            |
 | `sharded-channel-moved` | See [here](https://github.com/redis/node-redis/blob/master/docs/pub-sub.md#sharded-channel-moved-event)                          | See [here](https://github.com/redis/node-redis/blob/master/docs/pub-sub.md#sharded-channel-moved-event) |
+| `invalidate`            | Client Tracking is on with `emitInvalidate` and a key is invalidated               | `(key: RedisItem \| null)`                                 |
 
 > :warning: You **MUST** listen to `error` events. If a client doesn't have at least one `error` listener registered and
 > an `error` occurs, that error will be thrown and the Node.js process will exit. See the [ > `EventEmitter` docs](https://nodejs.org/api/events.html#events_error_events) for more details.

packages/client/lib/client/index.ts

@@ -145,6 +145,11 @@ export interface RedisClientOptions<
    * Tag to append to library name that is sent to the Redis server
    */
   clientInfoTag?: string;
+  /**
+   * When set to true, client tracking is turned on and the client emits `invalidate` events when it receives invalidation messages from the redis server.
+   * Mutually exclusive with `clientSideCache` option.
+   */
+  emitInvalidate?: boolean;
   /**
    * Controls how the client handles Redis Enterprise maintenance push notifications.
    *
@@ -525,6 +530,19 @@ export default class RedisClient<
           this.#clientSideCache?.invalidate(null)
         }
 
+        return true
+      });
+    } else if (options?.emitInvalidate) {
+      this.#queue.addPushHandler((push: Array<any>): boolean => {
+        if (push[0].toString() !== 'invalidate') return false;
+
+        if (push[1] !== null) {
+          for (const key of push[1]) {
+            this.emit('invalidate', key);
+          }
+        } else {
+          this.emit('invalidate', null);
+        }
         return true
       });
     }
@@ -534,11 +552,15 @@ export default class RedisClient<
     if (options?.clientSideCache && options?.RESP !== 3) {
       throw new Error('Client Side Caching is only supported with RESP3');
     }
-
+    if (options?.emitInvalidate && options?.RESP !== 3) {
+      throw new Error('emitInvalidate is only supported with RESP3');
+    }
+    if (options?.clientSideCache && options?.emitInvalidate) {
+      throw new Error('emitInvalidate is not supported (or necessary) when clientSideCache is enabled');
+    }
     if (options?.maintNotifications && options?.maintNotifications !== 'disabled' && options?.RESP !== 3) {
       throw new Error('Graceful Maintenance is only supported with RESP3');
     }
-
   }
 
   #initiateOptions(options: RedisClientOptions<M, F, S, RESP, TYPE_MAPPING> = {}): RedisClientOptions<M, F, S, RESP, TYPE_MAPPING> {
@@ -743,12 +765,17 @@ export default class RedisClient<
         }
       });
     }
-
+    
     if (this.#clientSideCache) {
       commands.push({cmd: this.#clientSideCache.trackingOn()});
     }
 
+    if (this.#options?.emitInvalidate) {
+      commands.push({cmd: ['CLIENT', 'TRACKING', 'ON']});
+    }
+    
     const maintenanceHandshakeCmd = await EnterpriseMaintenanceManager.getHandshakeCommand(this.#options);
+    
     if(maintenanceHandshakeCmd) {
       commands.push(maintenanceHandshakeCmd);
     };