fix(sharded): fix SSUBSCRIBE memory leak with ioredis (#529)

This pull request introduces a change to the sharded adapter's `SSUBSCRIBE` logic: Previously, for each dynamic channel/room, a unique listener was added to the client's `smessageBuffer`. This approach led to a large number of listeners (resulting in `MaxListenersExceededWarning`), especially in scenarios with many dynamic channels. Further, listeners were not being removed when unsubscribing, leading to a memory leak.

The new implementation replaces the multiple listeners with a single `smessageBuffer` listener. This listener is registered once and handles all dynamic channels by maintaining specific channel handlers in a `Map`. Listeners are added to this `Map` in `SSUBSCRIBE` and removed from the `Map` in `SUNSUBSCRIBE`.

Related: #528

lib/util.ts

@@ -58,6 +58,8 @@ function isRedisV4Client(redisClient: any) {
   return typeof redisClient.sSubscribe === "function";
 }
 
+const kHandlers = Symbol("handlers");
+
 export function SSUBSCRIBE(
   redisClient: any,
   channel: string,
@@ -66,13 +68,17 @@ export function SSUBSCRIBE(
   if (isRedisV4Client(redisClient)) {
     redisClient.sSubscribe(channel, handler, RETURN_BUFFERS);
   } else {
+    if (!redisClient[kHandlers]) {
+      redisClient[kHandlers] = new Map();
+      redisClient.on("smessageBuffer", (rawChannel, message) => {
+        redisClient[kHandlers].get(rawChannel.toString())?.(
+          message,
+          rawChannel
+        );
+      });
+    }
+    redisClient[kHandlers].set(channel, handler);
     redisClient.ssubscribe(channel);
-
-    redisClient.on("smessageBuffer", (rawChannel, message) => {
-      if (rawChannel.toString() === channel) {
-        handler(message, rawChannel);
-      }
-    });
   }
 }
 
@@ -81,6 +87,11 @@ export function SUNSUBSCRIBE(redisClient: any, channel: string | string[]) {
     redisClient.sUnsubscribe(channel);
   } else {
     redisClient.sunsubscribe(channel);
+    if (Array.isArray(channel)) {
+      channel.forEach((c) => redisClient[kHandlers].delete(c));
+    } else {
+      redisClient[kHandlers].delete(channel);
+    }
   }
 }