fix: add timeout method to remote socket (#4558)

The RemoteSocket interface, which is returned when the client is
connected on another Socket.IO server of the cluster, was lacking the
`timeout()` method.

Syntax:

```js
const sockets = await io.fetchSockets();

for (const socket of sockets) {
  if (someCondition) {
    socket.timeout(1000).emit("some-event", (err) => {
      if (err) {
        // the client did not acknowledge the event in the given delay
      }
    });
  }
}
```

Related: #4595

lib/broadcast-operator.ts

@@ -7,6 +7,7 @@ import type {
   EventNames,
   EventsMap,
   TypedEventBroadcaster,
+  DecorateAcknowledgements,
   DecorateAcknowledgementsWithTimeoutAndMultipleResponses,
   AllButLast,
   Last,
@@ -20,7 +21,9 @@ export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
     private readonly adapter: Adapter,
     private readonly rooms: Set<Room> = new Set<Room>(),
     private readonly exceptRooms: Set<Room> = new Set<Room>(),
-    private readonly flags: BroadcastFlags = {}
+    private readonly flags: BroadcastFlags & {
+      expectSingleResponse?: boolean;
+    } = {}
   ) {}
 
   /**
@@ -232,7 +235,10 @@ export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
 
     const timer = setTimeout(() => {
       timedOut = true;
-      ack.apply(this, [new Error("operation has timed out"), responses]);
+      ack.apply(this, [
+        new Error("operation has timed out"),
+        this.flags.expectSingleResponse ? null : responses,
+      ]);
     }, this.flags.timeout);
 
     let expectedServerCount = -1;
@@ -246,7 +252,10 @@ export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
         responses.length === expectedClientCount
       ) {
         clearTimeout(timer);
-        ack.apply(this, [null, responses]);
+        ack.apply(this, [
+          null,
+          this.flags.expectSingleResponse ? null : responses,
+        ]);
       }
     };
 
@@ -476,10 +485,44 @@ export class RemoteSocket<EmitEvents extends EventsMap, SocketData>
     this.data = details.data;
     this.operator = new BroadcastOperator<EmitEvents, SocketData>(
       adapter,
-      new Set([this.id])
+      new Set([this.id]),
+      new Set(),
+      {
+        expectSingleResponse: true, // so that remoteSocket.emit() with acknowledgement behaves like socket.emit()
+      }
     );
   }
 
+  /**
+   * Adds a timeout in milliseconds for the next operation.
+   *
+   * @example
+   * const sockets = await io.fetchSockets();
+   *
+   * for (const socket of sockets) {
+   *   if (someCondition) {
+   *     socket.timeout(1000).emit("some-event", (err) => {
+   *       if (err) {
+   *         // the client did not acknowledge the event in the given delay
+   *       }
+   *     });
+   *   }
+   * }
+   *
+   * // note: if possible, using a room instead of looping over all sockets is preferable
+   * io.timeout(1000).to(someConditionRoom).emit("some-event", (err, responses) => {
+   *   // ...
+   * });
+   *
+   * @param timeout
+   */
+  public timeout(timeout: number) {
+    return this.operator.timeout(timeout) as BroadcastOperator<
+      DecorateAcknowledgements<EmitEvents>,
+      SocketData
+    >;
+  }
+
   public emit<Ev extends EventNames<EmitEvents>>(
     ev: Ev,
     ...args: EventParams<EmitEvents, Ev>