feat: implement the serverSideEmit functionality

Syntax:

```js
emitter.serverSideEmit("hello", "world");

// Socket.IO server
io.on("hello", (arg) => {
  console.log(arg); // prints "world"
});
```

Author: darrachequesne

Readme.md

@@ -17,7 +17,7 @@ The emitter is also available in other programming languages:
 - Perl: https://metacpan.org/pod/SocketIO::Emitter
 - Rust: https://github.com/epli2/socketio-rust-emitter
 
-It must be used in conjunction with [socket.io-redis](https://github.com/socketio/socket.io-redis/).
+It must be used in conjunction with [`@socket.io/redis-adapter`](https://github.com/socketio/socket.io-redis-adapter/).
 
 The current version is compatible with both:
 

lib/index.ts

@@ -24,6 +24,7 @@ enum RequestType {
   REMOTE_LEAVE = 3,
   REMOTE_DISCONNECT = 4,
   REMOTE_FETCH = 5,
+  SERVER_SIDE_EMIT = 6,
 }
 
 export interface EmitterOptions {
@@ -201,6 +202,27 @@ export class Emitter<EmitEvents extends EventsMap = DefaultEventsMap> {
       this.broadcastOptions
     ).disconnectSockets(close);
   }
+
+  /**
+   * Send a packet to the Socket.IO servers in the cluster
+   *
+   * @param args - any number of serializable arguments
+   */
+  public serverSideEmit(...args: any[]): void {
+    const withAck = typeof args[args.length - 1] === "function";
+
+    if (withAck) {
+      throw new Error("Acknowledgements are not supported");
+    }
+
+    const request = JSON.stringify({
+      uid: UID,
+      type: RequestType.SERVER_SIDE_EMIT,
+      data: args,
+    });
+
+    this.redisClient.publish(this.broadcastOptions.requestChannel, request);
+  }
 }
 
 export const RESERVED_EVENTS: ReadonlySet<string | Symbol> = new Set(<const>[

package-lock.json

@@ -24,6 +24,7 @@
     "socket.io-parser": "~4.0.4"
   },
   "devDependencies": {
+    "@socket.io/redis-adapter": "^7.0.0",
     "@types/mocha": "^8.2.1",
     "@types/node": "^14.14.35",
     "@types/redis": "^2.8.28",
@@ -32,9 +33,8 @@
     "nyc": "^15.1.0",
     "prettier": "^2.2.1",
     "redis": "^3.0.2",
-    "socket.io": "^4.0.0",
-    "socket.io-client": "^4.0.0",
-    "socket.io-redis": "^6.1.0",
+    "socket.io": "^4.1.1",
+    "socket.io-client": "^4.1.1",
     "ts-node": "^9.1.1",
     "typescript": "^4.2.3"
   }

package.json

@@ -2,7 +2,7 @@ import expect = require("expect.js");
 import { createClient, RedisClient } from "redis";
 import { Server, Socket } from "socket.io";
 import { io as ioc, Socket as ClientSocket } from "socket.io-client";
-import { createAdapter } from "socket.io-redis";
+import { createAdapter } from "@socket.io/redis-adapter";
 import { createServer } from "http";
 import { Emitter } from "..";
 import type { AddressInfo } from "net";
@@ -44,10 +44,7 @@ describe("emitter", () => {
     subClient = createClient();
 
     io = new Server(httpServer, {
-      adapter: createAdapter({
-        pubClient,
-        subClient,
-      }),
+      adapter: createAdapter(pubClient, subClient),
     });
 
     httpServer.listen(() => {
@@ -274,5 +271,18 @@ describe("emitter", () => {
         clientSockets[2].on("disconnect", partialDone);
       });
     });
+
+    describe("serverSideEmit", () => {
+      it("sends an event to other server instances", (done) => {
+        emitter.serverSideEmit("hello", "world", 1, "2");
+
+        io.on("hello", (arg1, arg2, arg3) => {
+          expect(arg1).to.eql("world");
+          expect(arg2).to.eql(1);
+          expect(arg3).to.eql("2");
+          done();
+        });
+      });
+    });
   });
 });