fix: ensure the order of the commands

Before this change, the broadcast() method would send the BROADCAST
command and then apply it locally (which is required to retrieve the
offset of the message, when connection state recovery is enabled),
while the other commands like disconnectSockets() would first apply it
locally and then send the command to the other nodes.

So, for example:

```js
io.emit("bye");
io.disconnectSockets();
```

In that case, the clients connected to the io instance would not receive
the "bye" event, while the clients connected to the other server
instances would receive it before being disconnected.

Related:

- socketio/socket.io-redis-streams-adapter#13
- socketio/socket.io-postgres-adapter#12

lib/cluster-adapter.ts

@@ -503,55 +503,64 @@ export abstract class ClusterAdapter extends Adapter {
     super.broadcastWithAck(packet, opts, clientCountCallback, ack);
   }
 
-  override addSockets(opts: BroadcastOptions, rooms: Room[]) {
-    super.addSockets(opts, rooms);
-
+  override async addSockets(opts: BroadcastOptions, rooms: Room[]) {
     const onlyLocal = opts.flags?.local;
-    if (onlyLocal) {
-      return;
+
+    if (!onlyLocal) {
+      try {
+        await this.publishAndReturnOffset({
+          type: MessageType.SOCKETS_JOIN,
+          data: {
+            opts: encodeOptions(opts),
+            rooms,
+          },
+        });
+      } catch (e) {
+        debug("[%s] error while publishing message: %s", this.uid, e.message);
+      }
     }
 
-    this.publish({
-      type: MessageType.SOCKETS_JOIN,
-      data: {
-        opts: encodeOptions(opts),
-        rooms,
-      },
-    });
+    super.addSockets(opts, rooms);
   }
 
-  override delSockets(opts: BroadcastOptions, rooms: Room[]) {
-    super.delSockets(opts, rooms);
-
+  override async delSockets(opts: BroadcastOptions, rooms: Room[]) {
     const onlyLocal = opts.flags?.local;
-    if (onlyLocal) {
-      return;
+
+    if (!onlyLocal) {
+      try {
+        await this.publishAndReturnOffset({
+          type: MessageType.SOCKETS_LEAVE,
+          data: {
+            opts: encodeOptions(opts),
+            rooms,
+          },
+        });
+      } catch (e) {
+        debug("[%s] error while publishing message: %s", this.uid, e.message);
+      }
     }
 
-    this.publish({
-      type: MessageType.SOCKETS_LEAVE,
-      data: {
-        opts: encodeOptions(opts),
-        rooms,
-      },
-    });
+    super.delSockets(opts, rooms);
   }
 
-  override disconnectSockets(opts: BroadcastOptions, close: boolean) {
-    super.disconnectSockets(opts, close);
-
+  override async disconnectSockets(opts: BroadcastOptions, close: boolean) {
     const onlyLocal = opts.flags?.local;
-    if (onlyLocal) {
-      return;
+
+    if (!onlyLocal) {
+      try {
+        await this.publishAndReturnOffset({
+          type: MessageType.DISCONNECT_SOCKETS,
+          data: {
+            opts: encodeOptions(opts),
+            close,
+          },
+        });
+      } catch (e) {
+        debug("[%s] error while publishing message: %s", this.uid, e.message);
+      }
     }
 
-    this.publish({
-      type: MessageType.DISCONNECT_SOCKETS,
-      data: {
-        opts: encodeOptions(opts),
-        close,
-      },
-    });
+    super.disconnectSockets(opts, close);
   }
 
   async fetchSockets(opts: BroadcastOptions): Promise<any[]> {

test/cluster-adapter.ts

@@ -3,7 +3,7 @@ import { Server, Socket as ServerSocket } from "socket.io";
 import { io as ioc, Socket as ClientSocket } from "socket.io-client";
 import expect = require("expect.js");
 import type { AddressInfo } from "net";
-import { times, shouldNotHappen } from "./util";
+import { times, shouldNotHappen, sleep } from "./util";
 import {
   ClusterAdapterWithHeartbeat,
   type ClusterMessage,
@@ -243,6 +243,8 @@ describe("cluster adapter", () => {
     it("makes all socket instances join the specified room", async () => {
       servers[0].socketsJoin("room1");
 
+      await sleep();
+
       expect(serverSockets[0].rooms.has("room1")).to.be(true);
       expect(serverSockets[1].rooms.has("room1")).to.be(true);
       expect(serverSockets[2].rooms.has("room1")).to.be(true);
@@ -254,6 +256,8 @@ describe("cluster adapter", () => {
 
       servers[0].in("room1").socketsJoin("room2");
 
+      await sleep();
+
       expect(serverSockets[0].rooms.has("room2")).to.be(true);
       expect(serverSockets[1].rooms.has("room2")).to.be(false);
       expect(serverSockets[2].rooms.has("room2")).to.be(true);
@@ -275,6 +279,8 @@ describe("cluster adapter", () => {
 
       servers[0].socketsLeave("room1");
 
+      await sleep();
+
       expect(serverSockets[0].rooms.has("room1")).to.be(false);
       expect(serverSockets[1].rooms.has("room1")).to.be(false);
       expect(serverSockets[2].rooms.has("room1")).to.be(false);
@@ -287,6 +293,8 @@ describe("cluster adapter", () => {
 
       servers[0].in("room1").socketsLeave("room2");
 
+      await sleep();
+
       expect(serverSockets[0].rooms.has("room2")).to.be(false);
       expect(serverSockets[1].rooms.has("room2")).to.be(false);
       expect(serverSockets[2].rooms.has("room2")).to.be(true);
@@ -318,6 +326,22 @@ describe("cluster adapter", () => {
 
       servers[0].disconnectSockets(true);
     });
+
+    it("sends a packet before all socket instances disconnect", (done) => {
+      const partialDone = times(3, done);
+
+      clientSockets.forEach((clientSocket) => {
+        clientSocket.on("disconnect", shouldNotHappen(done));
+
+        clientSocket.on("bye", () => {
+          clientSocket.off("disconnect");
+          clientSocket.on("disconnect", partialDone);
+        });
+      });
+
+      servers[0].emit("bye");
+      servers[0].disconnectSockets(true);
+    });
   });
 
   describe("fetchSockets", () => {

test/util.ts

@@ -13,3 +13,7 @@ export function times(count: number, fn: () => void) {
 export function shouldNotHappen(done) {
   return () => done(new Error("should not happen"));
 }
+
+export function sleep() {
+  return new Promise<void>((resolve) => process.nextTick(resolve));
+}