Ping interval (#2321)

* fix #1598 fix #2276 - add `pingInterval` to client config

* setPingTimer on ready (instead of on connect)

* use isReady (instead of isOpen) and fix test

* Update client-configuration.md

Author: leibale

docs/client-configuration.md

@@ -25,6 +25,7 @@
 | readonly                 | `false`                                  | Connect in [`READONLY`](https://redis.io/commands/readonly) mode                                                                                                                                                                                    |
 | legacyMode               | `false`                                  | Maintain some backwards compatibility (see the [Migration Guide](./v3-to-v4.md))                                                                                                                                                                    |
 | isolationPoolOptions     |                                          | See the [Isolated Execution Guide](./isolated-execution.md)                                                                                                                                                                                         |
+| pingInterval             |                                          | Send `PING` command at interval (in ms). Useful with "[Azure Cache for Redis](https://learn.microsoft.com/en-us/azure/azure-cache-for-redis/cache-best-practices-connection#idle-timeout)"                                                          |
 
 ## Reconnect Strategy
 

packages/client/lib/client/index.spec.ts

@@ -862,4 +862,16 @@ describe('Client', () => {
         client.unref();
         client.ref();
     }, GLOBAL.SERVERS.OPEN);
+
+    testUtils.testWithClient('pingInterval', async client => {
+        assert.deepEqual(
+            await once(client, 'ping-interval'),
+            ['PONG']
+        );
+    }, {
+        ...GLOBAL.SERVERS.OPEN,
+        clientOptions: {
+            pingInterval: 1
+        }
+    });
 });

packages/client/lib/client/index.ts

@@ -31,6 +31,7 @@ export interface RedisClientOptions<
     readonly?: boolean;
     legacyMode?: boolean;
     isolationPoolOptions?: PoolOptions;
+    pingInterval?: number;
 }
 
 type WithCommands = {
@@ -281,9 +282,12 @@ export default class RedisClient<
                     this.#queue.flushAll(err);
                 }
             })
-            .on('connect', () => this.emit('connect'))
+            .on('connect', () => {
+                this.emit('connect');
+            })
             .on('ready', () => {
                 this.emit('ready');
+                this.#setPingTimer();
                 this.#tick();
             })
             .on('reconnecting', () => this.emit('reconnecting'))
@@ -348,6 +352,22 @@ export default class RedisClient<
             (...args: Array<unknown>): void => (this as any).sendCommand(name, ...args);
     }
 
+    #pingTimer?: NodeJS.Timer;
+
+    #setPingTimer(): void {
+        if (!this.#options?.pingInterval || !this.#socket.isReady) return;
+        clearTimeout(this.#pingTimer);
+
+        this.#pingTimer = setTimeout(() => {
+            if (!this.#socket.isReady) return;
+
+            (this as unknown as RedisClientType<M, F, S>).ping()
+                .then(reply => this.emit('ping-interval', reply))
+                .catch(err => this.emit('error', err))
+                .finally(() => this.#setPingTimer());
+        }, this.#options.pingInterval);
+    }
+
     duplicate(overrides?: Partial<RedisClientOptions<M, F, S>>): RedisClientType<M, F, S> {
         return new (Object.getPrototypeOf(this).constructor)({
             ...this.#options,