feat: throw upon reserved event names

These events cannot be used by the end users, because they are part of
the Socket.IO public API, so using them will now throw an error
explicitly.

dist/namespace.js

@@ -10,14 +10,6 @@ const socket_io_parser_1 = require("socket.io-parser");
 const has_binary2_1 = __importDefault(require("has-binary2"));
 const debug_1 = __importDefault(require("debug"));
 const debug = debug_1.default("socket.io:namespace");
-/**
- * Blacklisted events.
- */
-const events = [
-    "connect",
-    "connection",
-    "newListener"
-];
 class Namespace extends events_1.EventEmitter {
     /**
      * Namespace constructor.
@@ -158,9 +150,8 @@ class Namespace extends events_1.EventEmitter {
      */
     // @ts-ignore
     emit(ev, ...args) {
-        if (~events.indexOf(ev)) {
-            super.emit.apply(this, arguments);
-            return this;
+        if (socket_1.RESERVED_EVENTS.has(ev)) {
+            throw new Error(`"${ev}" is a reserved event name`);
         }
         // set up packet object
         args.unshift(ev);

dist/socket.d.ts

@@ -4,6 +4,7 @@ import { Client } from "./client";
 import { Namespace } from "./namespace";
 import { IncomingMessage } from "http";
 import { Room, SocketId } from "socket.io-adapter";
+export declare const RESERVED_EVENTS: Set<string>;
 /**
  * The handshake details
  */
@@ -76,7 +77,7 @@ export declare class Socket extends EventEmitter {
      *
      * @return {Socket} self
      */
-    emit(ev: any): this;
+    emit(ev: string, ...args: any[]): this;
     /**
      * Targets a room when broadcasting.
      *

dist/socket.js

@@ -3,25 +3,23 @@ var __importDefault = (this && this.__importDefault) || function (mod) {
     return (mod && mod.__esModule) ? mod : { "default": mod };
 };
 Object.defineProperty(exports, "__esModule", { value: true });
-exports.Socket = void 0;
+exports.Socket = exports.RESERVED_EVENTS = void 0;
 const events_1 = require("events");
 const socket_io_parser_1 = require("socket.io-parser");
 const has_binary2_1 = __importDefault(require("has-binary2"));
 const url_1 = __importDefault(require("url"));
 const debug_1 = __importDefault(require("debug"));
 const base64id_1 = __importDefault(require("base64id"));
 const debug = debug_1.default("socket.io:socket");
-/**
- * Blacklisted events.
- */
-const events = [
+exports.RESERVED_EVENTS = new Set([
     "error",
     "connect",
     "disconnect",
     "disconnecting",
+    // EventEmitter reserved events: https://nodejs.org/api/events.html#events_event_newlistener
     "newListener",
     "removeListener"
-];
+]);
 class Socket extends events_1.EventEmitter {
     /**
      * Interface to a `Client` for a given `Namespace`.
@@ -69,12 +67,11 @@ class Socket extends events_1.EventEmitter {
      * @return {Socket} self
      */
     // @ts-ignore
-    emit(ev) {
-        if (~events.indexOf(ev)) {
-            super.emit.apply(this, arguments);
-            return this;
+    emit(ev, ...args) {
+        if (exports.RESERVED_EVENTS.has(ev)) {
+            throw new Error(`"${ev}" is a reserved event name`);
         }
-        const args = Array.prototype.slice.call(arguments);
+        args.unshift(ev);
         const packet = {
             type: (this.flags.binary !== undefined
                 ? this.flags.binary

lib/namespace.ts

@@ -1,4 +1,4 @@
-import { Socket } from "./socket";
+import { Socket, RESERVED_EVENTS } from "./socket";
 import { Server } from "./index";
 import { Client } from "./client";
 import { EventEmitter } from "events";
@@ -9,16 +9,6 @@ import { Adapter, Room, SocketId } from "socket.io-adapter";
 
 const debug = debugModule("socket.io:namespace");
 
-/**
- * Blacklisted events.
- */
-
-const events = [
-  "connect", // for symmetry with client
-  "connection",
-  "newListener"
-];
-
 export class Namespace extends EventEmitter {
   public readonly name: string;
   public readonly connected: Map<SocketId, Socket> = new Map();
@@ -176,9 +166,8 @@ export class Namespace extends EventEmitter {
    */
   // @ts-ignore
   public emit(ev: string, ...args: any[]): Namespace {
-    if (~events.indexOf(ev)) {
-      super.emit.apply(this, arguments);
-      return this;
+    if (RESERVED_EVENTS.has(ev)) {
+      throw new Error(`"${ev}" is a reserved event name`);
     }
     // set up packet object
     args.unshift(ev);

lib/socket.ts

@@ -12,18 +12,15 @@ import base64id from "base64id";
 
 const debug = debugModule("socket.io:socket");
 
-/**
- * Blacklisted events.
- */
-
-const events = [
+export const RESERVED_EVENTS = new Set([
   "error",
   "connect",
   "disconnect",
   "disconnecting",
+  // EventEmitter reserved events: https://nodejs.org/api/events.html#events_event_newlistener
   "newListener",
   "removeListener"
-];
+]);
 
 /**
  * The handshake details
@@ -133,13 +130,11 @@ export class Socket extends EventEmitter {
    * @return {Socket} self
    */
   // @ts-ignore
-  public emit(ev) {
-    if (~events.indexOf(ev)) {
-      super.emit.apply(this, arguments);
-      return this;
+  public emit(ev: string, ...args: any[]) {
+    if (RESERVED_EVENTS.has(ev)) {
+      throw new Error(`"${ev}" is a reserved event name`);
     }
-
-    const args = Array.prototype.slice.call(arguments);
+    args.unshift(ev);
     const packet: any = {
       type: (this.flags.binary !== undefined
       ? this.flags.binary

test/socket.io.ts

@@ -693,6 +693,14 @@ describe("socket.io", () => {
       });
     });
 
+    it("should throw on reserved event", () => {
+      const sio = new Server();
+
+      expect(() => sio.emit("connect")).to.throwException(
+        /"connect" is a reserved event name/
+      );
+    });
+
     describe("dynamic namespaces", () => {
       it("should allow connections to dynamic namespaces with a regex", done => {
         const srv = createServer();
@@ -1657,6 +1665,22 @@ describe("socket.io", () => {
         });
       });
     });
+
+    it("should throw on reserved event", done => {
+      const srv = createServer();
+      const sio = new Server(srv);
+
+      srv.listen(() => {
+        const socket = client(srv);
+        sio.on("connection", s => {
+          expect(() => s.emit("error")).to.throwException(
+            /"error" is a reserved event name/
+          );
+          socket.close();
+          done();
+        });
+      });
+    });
   });
 
   describe("messaging many", () => {