add emitInvalidate option

Author: sastcsgh

packages/client/lib/client/index.ts

@@ -144,6 +144,11 @@ 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;
 }
 
 export type WithCommands<
@@ -465,15 +470,20 @@ export default class RedisClient<
         this.#clientSideCache = new BasicClientSideCache(cscConfig);
       }
       this.#queue.setInvalidateCallback(this.#clientSideCache.invalidate.bind(this.#clientSideCache));
+    } else if (options?.emitInvalidate) {
+      this.#queue.setInvalidateCallback((key) => this.emit('invalidate', key));
     }
   }
 
   #validateOptions(options?: RedisClientOptions<M, F, S, RESP, TYPE_MAPPING>) {
     if (options?.clientSideCache && options?.RESP !== 3) {
       throw new Error('Client Side Caching is only supported with RESP3');
     }
-
+    if (options?.clientSideCache && options?.emitInvalidate) {
+      throw new Error('emitInvalidate is not supported (or necessary) when clientSideCache is enabled');
+    }
   }
+
   #initiateOptions(options?: RedisClientOptions<M, F, S, RESP, TYPE_MAPPING>): RedisClientOptions<M, F, S, RESP, TYPE_MAPPING> | undefined {
 
     // Convert username/password to credentialsProvider if no credentialsProvider is already in place
@@ -674,11 +684,14 @@ export default class RedisClient<
         }
       });
     }
-
+    
     if (this.#clientSideCache) {
       commands.push({cmd: this.#clientSideCache.trackingOn()});
     }
 
+    if (this.#options?.emitInvalidate) {
+      commands.push({cmd: ['CLIENT', 'TRACKING', 'ON']});
+    }
     return commands;
   }