chore(release): 4.7.1

Diff: https://github.com/socketio/socket.io/compare/4.7.0...4.7.1

.github/workflows/ci.yml

@@ -16,7 +16,9 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12, 14, 16]
+        node-version:
+          - 16
+          - 20
 
     steps:
       - name: Checkout repository

CHANGELOG.md

@@ -1,5 +1,13 @@
 # History
 
+## 2023
+
+- [4.7.1](#471-2023-06-28) (Jun 2023)
+- [4.7.0](#470-2023-06-22) (Jun 2023)
+- [4.6.2](#462-2023-05-31) (May 2023)
+- [4.6.1](#461-2023-02-20) (Feb 2023)
+- [4.6.0](#460-2023-02-07) (Feb 2023)
+
 ## 2022
 
 - [4.5.4](#454-2022-11-22) (Nov 2022)
@@ -52,6 +60,315 @@
 
 # Release notes
 
+## [4.7.1](https://github.com/socketio/socket.io/compare/4.7.0...4.7.1) (2023-06-28)
+
+The client bundle contains a few fixes regarding the WebTransport support.
+
+### Dependencies
+
+- [`engine.io@~6.5.0`](https://github.com/socketio/engine.io/releases/tag/6.5.0) (no change)
+- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)
+
+
+
+## [4.7.0](https://github.com/socketio/socket.io/compare/4.6.2...4.7.0) (2023-06-22)
+
+
+### Bug Fixes
+
+* remove the Partial modifier from the socket.data type ([#4740](https://github.com/socketio/socket.io/issues/4740)) ([e5c62ca](https://github.com/socketio/socket.io/commit/e5c62cad60fc7d16fbb024fd9be1d1880f4e6f5f))
+
+
+### Features
+
+#### Support for WebTransport
+
+The Socket.IO server can now use WebTransport as the underlying transport.
+
+WebTransport is a web API that uses the HTTP/3 protocol as a bidirectional transport. It's intended for two-way communications between a web client and an HTTP/3 server.
+
+References:
+
+- https://w3c.github.io/webtransport/
+- https://developer.mozilla.org/en-US/docs/Web/API/WebTransport
+- https://developer.chrome.com/articles/webtransport/
+
+Until WebTransport support lands [in Node.js](https://github.com/nodejs/node/issues/38478), you can use the `@fails-components/webtransport` package:
+
+```js
+import { readFileSync } from "fs";
+import { createServer } from "https";
+import { Server } from "socket.io";
+import { Http3Server } from "@fails-components/webtransport";
+
+// WARNING: the total length of the validity period MUST NOT exceed two weeks (https://w3c.github.io/webtransport/#custom-certificate-requirements)
+const cert = readFileSync("/path/to/my/cert.pem");
+const key = readFileSync("/path/to/my/key.pem");
+
+const httpsServer = createServer({
+  key,
+  cert
+});
+
+httpsServer.listen(3000);
+
+const io = new Server(httpsServer, {
+  transports: ["polling", "websocket", "webtransport"] // WebTransport is not enabled by default
+});
+
+const h3Server = new Http3Server({
+  port: 3000,
+  host: "0.0.0.0",
+  secret: "changeit",
+  cert,
+  privKey: key,
+});
+
+(async () => {
+  const stream = await h3Server.sessionStream("/socket.io/");
+  const sessionReader = stream.getReader();
+
+  while (true) {
+    const { done, value } = await sessionReader.read();
+    if (done) {
+      break;
+    }
+    io.engine.onWebTransportSession(value);
+  }
+})();
+
+h3Server.startServer();
+```
+
+Added in [123b68c](https://github.com/socketio/engine.io/commit/123b68c04f9e971f59b526e0f967a488ee6b0116).
+
+
+#### Client bundles with CORS headers
+
+The bundles will now have the right `Access-Control-Allow-xxx` headers.
+
+Added in [63f181c](https://github.com/socketio/socket.io/commit/63f181cc12cbbbf94ed40eef52d60f36a1214fbe).
+
+
+### Dependencies
+
+- [`engine.io@~6.5.0`](https://github.com/socketio/engine.io/releases/tag/6.5.0) ([diff](https://github.com/socketio/engine.io/compare/6.4.2...6.5.0))
+- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)
+
+
+
+## [4.6.2](https://github.com/socketio/socket.io/compare/4.6.1...4.6.2) (2023-05-31)
+
+
+### Bug Fixes
+
+* **exports:** move `types` condition to the top ([#4698](https://github.com/socketio/socket.io/issues/4698)) ([3d44aae](https://github.com/socketio/socket.io/commit/3d44aae381af38349fdb808d510d9f47a0c2507e))
+
+
+### Dependencies
+
+- [`engine.io@~6.4.2`](https://github.com/socketio/engine.io/releases/tag/6.4.0) ([diff](https://github.com/socketio/engine.io/compare/6.4.1...6.4.2))
+- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)
+
+
+
+## [4.6.1](https://github.com/socketio/socket.io/compare/4.6.0...4.6.1) (2023-02-20)
+
+
+### Bug Fixes
+
+* properly handle manually created dynamic namespaces ([0d0a7a2](https://github.com/socketio/socket.io/commit/0d0a7a22b5ff95f864216c529114b7dd41738d1e))
+* **types:** fix nodenext module resolution compatibility ([#4625](https://github.com/socketio/socket.io/issues/4625)) ([d0b22c6](https://github.com/socketio/socket.io/commit/d0b22c630208669aceb7ae013180c99ef90279b0))
+
+
+### Dependencies
+
+- [`engine.io@~6.4.1`](https://github.com/socketio/engine.io/releases/tag/6.4.1) ([diff](https://github.com/socketio/engine.io/compare/6.4.0...6.4.1))
+- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)
+
+
+
+## [4.6.0](https://github.com/socketio/socket.io/compare/4.5.4...4.6.0) (2023-02-07)
+
+
+### Bug Fixes
+
+* add timeout method to remote socket ([#4558](https://github.com/socketio/socket.io/issues/4558)) ([0c0eb00](https://github.com/socketio/socket.io/commit/0c0eb0016317218c2be3641e706cfaa9bea39a2d))
+* **typings:** properly type emits with timeout ([f3ada7d](https://github.com/socketio/socket.io/commit/f3ada7d8ccc02eeced2b9b9ac8e4bc921eb630d2))
+
+
+### Features
+
+#### Promise-based acknowledgements
+
+This commit adds some syntactic sugar around acknowledgements:
+
+- `emitWithAck()`
+
+```js
+try {
+  const responses = await io.timeout(1000).emitWithAck("some-event");
+  console.log(responses); // one response per client
+} catch (e) {
+  // some clients did not acknowledge the event in the given delay
+}
+
+io.on("connection", async (socket) => {
+    // without timeout
+  const response = await socket.emitWithAck("hello", "world");
+
+  // with a specific timeout
+  try {
+    const response = await socket.timeout(1000).emitWithAck("hello", "world");
+  } catch (err) {
+    // the client did not acknowledge the event in the given delay
+  }
+});
+```
+
+- `serverSideEmitWithAck()`
+
+```js
+try {
+  const responses = await io.timeout(1000).serverSideEmitWithAck("some-event");
+  console.log(responses); // one response per server (except itself)
+} catch (e) {
+  // some servers did not acknowledge the event in the given delay
+}
+```
+
+Added in [184f3cf](https://github.com/socketio/socket.io/commit/184f3cf7af57acc4b0948eee307f25f8536eb6c8).
+
+#### Connection state recovery
+
+This feature allows a client to reconnect after a temporary disconnection and restore its state:
+
+- id
+- rooms
+- data
+- missed packets
+
+Usage:
+
+```js
+import { Server } from "socket.io";
+
+const io = new Server({
+  connectionStateRecovery: {
+    // default values
+    maxDisconnectionDuration: 2 * 60 * 1000,
+    skipMiddlewares: true,
+  },
+});
+
+io.on("connection", (socket) => {
+  console.log(socket.recovered); // whether the state was recovered or not
+});
+```
+
+Here's how it works:
+
+- the server sends a session ID during the handshake (which is different from the current `id` attribute, which is public and can be freely shared)
+- the server also includes an offset in each packet (added at the end of the data array, for backward compatibility)
+- upon temporary disconnection, the server stores the client state for a given delay (implemented at the adapter level)
+- upon reconnection, the client sends both the session ID and the last offset it has processed, and the server tries to restore the state
+
+The in-memory adapter already supports this feature, and we will soon update the Postgres and MongoDB adapters. We will also create a new adapter based on [Redis Streams](https://redis.io/docs/data-types/streams/), which will support this feature.
+
+Added in [54d5ee0](https://github.com/socketio/socket.io/commit/54d5ee05a684371191e207b8089f09fc24eb5107).
+
+#### Compatibility (for real) with Express middlewares
+
+This feature implements middlewares at the Engine.IO level, because Socket.IO middlewares are meant for namespace authorization and are not executed during a classic HTTP request/response cycle.
+
+Syntax:
+
+```js
+io.engine.use((req, res, next) => {
+  // do something
+
+  next();
+});
+
+// with express-session
+import session from "express-session";
+
+io.engine.use(session({
+  secret: "keyboard cat",
+  resave: false,
+  saveUninitialized: true,
+  cookie: { secure: true }
+}));
+
+// with helmet
+import helmet from "helmet";
+
+io.engine.use(helmet());
+```
+
+A workaround was possible by using the allowRequest option and the "headers" event, but this feels way cleaner and works with upgrade requests too.
+
+Added in [24786e7](https://github.com/socketio/engine.io/commit/24786e77c5403b1c4b5a2bc84e2af06f9187f74a).
+
+#### Error details in the disconnecting and disconnect events
+
+The `disconnect` event will now contain additional details about the disconnection reason.
+
+```js
+io.on("connection", (socket) => {
+  socket.on("disconnect", (reason, description) => {
+    console.log(description);
+  });
+});
+```
+
+Added in [8aa9499](https://github.com/socketio/socket.io/commit/8aa94991cee5518567d6254eec04b23f81510257).
+
+#### Automatic removal of empty child namespaces
+
+This commit adds a new option, "cleanupEmptyChildNamespaces". With this option enabled (disabled by default), when a socket disconnects from a dynamic namespace and if there are no other sockets connected to it then the namespace will be cleaned up and its adapter will be closed. 
+
+```js
+import { createServer } from "node:http";
+import { Server } from "socket.io";
+
+const httpServer = createServer();
+const io = new Server(httpServer, {
+  cleanupEmptyChildNamespaces: true
+});
+```
+
+Added in [5d9220b](https://github.com/socketio/socket.io/commit/5d9220b69adf73e086c27bbb63a4976b348f7c4c).
+
+#### A new "addTrailingSlash" option
+
+The trailing slash which was added by default can now be disabled:
+
+```js
+import { createServer } from "node:http";
+import { Server } from "socket.io";
+
+const httpServer = createServer();
+const io = new Server(httpServer, {
+  addTrailingSlash: false
+});
+```
+
+In the example above, the clients can omit the trailing slash and use `/socket.io` instead of `/socket.io/`.
+
+Added in [d0fd474](https://github.com/socketio/engine.io/commit/d0fd4746afa396297f07bb62e539b0c1c4018d7c).
+
+### Performance Improvements
+
+* precompute the WebSocket frames when broadcasting ([da2b542](https://github.com/socketio/socket.io/commit/da2b54279749adc5279c9ac4742b01b36c01cff0))
+
+
+### Dependencies
+
+- [`engine.io@~6.4.0`](https://github.com/socketio/engine.io/releases/tag/6.4.0) (https://github.com/socketio/engine.io/compare/6.2.1...6.4.0)
+- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (https://github.com/websockets/ws/compare/8.2.3...8.11.0)
+
+
 ## [4.5.4](https://github.com/socketio/socket.io/compare/4.5.3...4.5.4) (2022-11-22)
 
 This release contains a bump of:
@@ -61,8 +378,8 @@ This release contains a bump of:
 
 ### Dependencies
 
-- [`engine.io@~6.2.1`](https://github.com/socketio/engine.io-client/tree/6.2.1) ([diff](https://github.com/socketio/engine.io/compare/6.2.0...6.2.1))
-- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3)
+- [`engine.io@~6.2.1`](https://github.com/socketio/engine.io/releases/tag/6.2.1) ([diff](https://github.com/socketio/engine.io/compare/6.2.0...6.2.1))
+- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)
 
 
 
@@ -74,6 +391,11 @@ This release contains a bump of:
 * **typings:** accept an HTTP2 server in the constructor ([d3d0a2d](https://github.com/socketio/socket.io/commit/d3d0a2d5beaff51fd145f810bcaf6914213f8a06))
 * **typings:** apply types to "io.timeout(...).emit()" calls ([e357daf](https://github.com/socketio/socket.io/commit/e357daf5858560bc84e7e50cd36f0278d6721ea1))
 
+### Dependencies
+
+- [`engine.io@~6.2.0`](https://github.com/socketio/engine.io/releases/tag/6.2.1) (no change)
+- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)
+
 
 
 ## [4.5.2](https://github.com/socketio/socket.io/compare/4.5.1...4.5.2) (2022-09-02)
@@ -84,10 +406,21 @@ This release contains a bump of:
 * prevent the socket from joining a room after disconnection ([18f3fda](https://github.com/socketio/socket.io/commit/18f3fdab12947a9fee3e9c37cfc1da97027d1473))
 * **uws:** prevent the server from crashing after upgrade ([ba497ee](https://github.com/socketio/socket.io/commit/ba497ee3eb52c4abf1464380d015d8c788714364))
 
+### Dependencies
+
+- [`engine.io@~6.2.0`](https://github.com/socketio/engine.io/releases/tag/6.2.0) (no change)
+- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)
+
 
 
 # [2.5.0](https://github.com/socketio/socket.io/compare/2.4.1...2.5.0) (2022-06-26)
 
+⚠️ WARNING ⚠️
+
+The default value of the `maxHttpBufferSize` option has been decreased from 100 MB to 1 MB, in order to prevent attacks by denial of service.
+
+Security advisory: [GHSA-j4f2-536g-r55m](https://github.com/advisories/GHSA-j4f2-536g-r55m)
+
 
 ### Bug Fixes
 
@@ -96,6 +429,11 @@ This release contains a bump of:
 * only set 'connected' to true after middleware execution ([226cc16](https://github.com/socketio/socket.io/commit/226cc16165f9fe60f16ff4d295fb91c8971cde35))
 * prevent the socket from joining a room after disconnection ([f223178](https://github.com/socketio/socket.io/commit/f223178eb655a7713303b21a78f9ef9e161d6458))
 
+### Dependencies
+
+- [`engine.io@~3.6.0`](https://github.com/socketio/engine.io/releases/tag/3.6.0) (https://github.com/socketio/engine.io/compare/3.5.0...3.6.0)
+- [`ws@~7.4.2`](https://github.com/websockets/ws/releases/tag/7.4.2) (no change)
+
 
 
 ## [4.5.1](https://github.com/socketio/socket.io/compare/4.5.0...4.5.1) (2022-05-17)
@@ -106,6 +444,11 @@ This release contains a bump of:
 * forward the local flag to the adapter when using fetchSockets() ([30430f0](https://github.com/socketio/socket.io/commit/30430f0985f8e7c49394543d4c84913b6a15df60))
 * **typings:** add HTTPS server to accepted types ([#4351](https://github.com/socketio/socket.io/issues/4351)) ([9b43c91](https://github.com/socketio/socket.io/commit/9b43c9167cff817c60fa29dbda2ef7cd938aff51))
 
+### Dependencies
+
+- [`engine.io@~6.2.0`](https://github.com/socketio/engine.io/releases/tag/6.2.0) (no change)
+- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)
+
 
 
 # [4.5.0](https://github.com/socketio/socket.io/compare/4.4.1...4.5.0) (2022-04-23)
@@ -118,7 +461,7 @@ This release contains a bump of:
 
 ### Features
 
-* add support for catch-all listeners for outgoing packets ([531104d](https://github.com/socketio/socket.io/commit/531104d332690138b7aab84d5583d6204132c8b4))
+#### Catch-all listeners for outgoing packets
 
 This is similar to `onAny()`, but for outgoing packets.
 
@@ -130,7 +473,9 @@ socket.onAnyOutgoing((event, ...args) => {
 });
 ```
 
-* broadcast and expect multiple acks ([8b20457](https://github.com/socketio/socket.io/commit/8b204570a94979bbec307f23ca078f30f5cf07b0))
+Added in [531104d](https://github.com/socketio/socket.io/commit/531104d332690138b7aab84d5583d6204132c8b4).
+
+#### Broadcast and expect multiple acknowledgements
 
 Syntax:
 
@@ -140,18 +485,25 @@ io.timeout(1000).emit("some-event", (err, responses) => {
 });
 ```
 
-* add the "maxPayload" field in the handshake details ([088dcb4](https://github.com/socketio/engine.io/commit/088dcb4dff60df39785df13d0a33d3ceaa1dff38))
+Added in [8b20457](https://github.com/socketio/socket.io/commit/8b204570a94979bbec307f23ca078f30f5cf07b0).
 
-So that clients in HTTP long-polling can decide how many packets they have to send to stay under the maxHttpBufferSize
-value.
+#### `maxHttpBufferSize` value negotiation
 
-This is a backward compatible change which should not mandate a new major revision of the protocol (we stay in v4), as
-we only add a field in the JSON-encoded handshake data:
+A "maxPayload" field is now included in the Engine.IO handshake, so that clients in HTTP long-polling can decide how many packets they have to send to stay under the `maxHttpBufferSize` value.
+
+This is a backward compatible change which should not mandate a new major revision of the protocol (we stay in v4), as we only add a field in the JSON-encoded handshake data:
 
 ```
 0{"sid":"lv_VI97HAXpY6yYWAAAC","upgrades":["websocket"],"pingInterval":25000,"pingTimeout":5000,"maxPayload":1000000}
 ```
 
+Added in [088dcb4](https://github.com/socketio/engine.io/commit/088dcb4dff60df39785df13d0a33d3ceaa1dff38).
+
+### Dependencies
+
+- [`engine.io@~6.2.0`](https://github.com/socketio/engine.io/releases/tag/6.2.0) (https://github.com/socketio/engine.io/compare/6.1.0...6.2.0)
+- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)
+
 
 
 ## [4.4.1](https://github.com/socketio/socket.io/compare/4.4.0...4.4.1) (2022-01-06)

Readme.md

@@ -21,6 +21,7 @@ Some implementations in other languages are also available:
 - [Dart](https://github.com/rikulo/socket.io-client-dart)
 - [Python](https://github.com/miguelgrinberg/python-socketio)
 - [.NET](https://github.com/doghappy/socket.io-client-csharp)
+- [Rust](https://github.com/1c3t3a/rust-socketio)
 
 Its main features are:
 
@@ -125,7 +126,7 @@ io.listen(3000);
 
 Starting with **3.0**, express applications have become request handler
 functions that you pass to `http` or `http` `Server` instances. You need
-to pass the `Server` to `socket.io`, and not the express application
+to pass the `Server` to `socket.io`, not the express application
 function. Also make sure to call `.listen` on the `server`, not the `app`.
 
 ```js

SECURITY.md

@@ -0,0 +1,22 @@
+# Security Policy
+
+## Supported Versions
+
+| Version | Supported          |
+|---------|--------------------|
+| 4.x     | :white_check_mark: |
+| 3.x     | :white_check_mark: |
+| 2.4.x   | :white_check_mark: |
+| < 2.4.0 | :x:                |
+
+## Reporting a Vulnerability
+
+To report a security vulnerability in this package, please send an email to [@darrachequesne](https://github.com/darrachequesne) (see address in profile) describing the vulnerability and how to reproduce it.
+
+We will get back to you as soon as possible and publish a fix if necessary.
+
+:warning: IMPORTANT :warning: please do not create an issue in this repository, as attackers might take advantage of it. Thank you in advance for your responsible disclosure.
+
+## History
+
+No security vulnerability were reported yet.

examples/basic-websocket-client/README.md

@@ -0,0 +1,18 @@
+# Basic Socket.IO client
+
+Please check the associated guide: https://socket.io/how-to/build-a-basic-client
+
+Content:
+
+```
+├── bundle
+│   └── socket.io.min.js
+├── src
+│   └── index.js
+├── test
+│   └── index.js
+├── check-bundle-size.js
+├── package.json
+├── README.md
+└── rollup.config.js
+```

examples/basic-websocket-client/bundle/socket.io.min.js

@@ -0,0 +1 @@
+class e{#e=new Map;on(e,t){let s=this.#e.get(e);s||this.#e.set(e,s=[]),s.push(t)}emit(e,...t){const s=this.#e.get(e);if(s)for(const e of s)e.apply(null,t)}}const t="0",s="1",n="2",i="3",o="4",r={CONNECT:0,DISCONNECT:1,EVENT:2};function c(){}class a extends e{id;connected=!1;#t;#s;#n;#i;#o;#r=[];#c;#a=!0;constructor(e,t){super(),this.#t=e,this.#s=Object.assign({path:"/socket.io/",reconnectionDelay:2e3},t),this.#h()}#h(){this.#n=new WebSocket(this.#u()),this.#n.onmessage=({data:e})=>this.#p(e),this.#n.onerror=c,this.#n.onclose=()=>this.#l("transport close")}#u(){return`${this.#t.replace(/^http/,"ws")}${this.#s.path}?EIO=4&transport=websocket`}#p(e){if("string"==typeof e)switch(e[0]){case t:this.#d(e);break;case s:this.#l("transport close");break;case n:this.#T(),this.#m(i);break;case o:let c;try{c=function(e){let t=1;const s={type:parseInt(e.charAt(t++),10)};e.charAt(t)&&(s.data=JSON.parse(e.substring(t)));if(!function(e){switch(e.type){case r.CONNECT:return"object"==typeof e.data;case r.DISCONNECT:return void 0===e.data;case r.EVENT:{const t=e.data;return Array.isArray(t)&&t.length>0&&"string"==typeof t[0]}default:return!1}}(s))throw new Error("invalid format");return s}(e)}catch(e){return this.#l("parse error")}this.#f(c);break;default:this.#l("parse error")}}#d(e){let t;try{t=JSON.parse(e.substring(1))}catch(e){return this.#l("parse error")}this.#o=t.pingInterval+t.pingTimeout,this.#T(),this.#C()}#f(e){switch(e.type){case r.CONNECT:this.#g(e);break;case r.DISCONNECT:this.#a=!1,this.#l("io server disconnect");break;case r.EVENT:super.emit.apply(this,e.data);break;default:this.#l("parse error")}}#g(e){this.id=e.data.sid,this.connected=!0,this.#r.forEach((e=>this.#y(e))),this.#r.slice(0),super.emit("connect")}#l(e){this.#n&&(this.#n.onclose=c,this.#n.close()),clearTimeout(this.#i),clearTimeout(this.#c),this.connected?(this.connected=!1,this.id=void 0,super.emit("disconnect",e)):super.emit("connect_error",e),this.#a&&(this.#c=setTimeout((()=>this.#h()),this.#s.reconnectionDelay))}#T(){clearTimeout(this.#i),this.#i=setTimeout((()=>{this.#l("ping timeout")}),this.#o)}#m(e){this.#n.readyState===WebSocket.OPEN&&this.#n.send(e)}#y(e){this.#m(o+function(e){let t=""+e.type;e.data&&(t+=JSON.stringify(e.data));return t}(e))}#C(){this.#y({type:r.CONNECT})}emit(...e){const t={type:r.EVENT,data:e};this.connected?this.#y(t):this.#r.push(t)}disconnect(){this.#a=!1,this.#l("io client disconnect")}}function h(e,t){return"string"!=typeof e&&(t=e,e=location.origin),new a(e,t)}export{h as io};

examples/basic-websocket-client/check-bundle-size.js

@@ -0,0 +1,17 @@
+import { rollup } from "rollup";
+import terser from "@rollup/plugin-terser";
+import { brotliCompressSync } from "node:zlib";
+
+const rollupBuild = await rollup({
+  input: "./src/index.js"
+});
+
+const rollupOutput = await rollupBuild.generate({
+  format: "esm",
+  plugins: [terser()],
+});
+
+const bundleAsString = rollupOutput.output[0].code;
+const brotliedBundle = brotliCompressSync(Buffer.from(bundleAsString));
+
+console.log(`Bundle size: ${brotliedBundle.length} B`);

examples/basic-websocket-client/package.json

@@ -0,0 +1,18 @@
+{
+  "type": "module",
+  "devDependencies": {
+    "@rollup/plugin-terser": "^0.4.0",
+    "chai": "^4.3.7",
+    "mocha": "^10.2.0",
+    "prettier": "^2.8.4",
+    "rollup": "^3.20.2",
+    "socket.io": "^4.6.1",
+    "ws": "^8.13.0"
+  },
+  "scripts": {
+    "bundle": "rollup -c",
+    "check-bundle-size": "node check-bundle-size.js",
+    "format": "prettier -w src/ test/",
+    "test": "mocha"
+  }
+}

examples/basic-websocket-client/rollup.config.js

@@ -0,0 +1,10 @@
+import terser from "@rollup/plugin-terser";
+
+export default {
+  input: "./src/index.js",
+  output: {
+    file: "./bundle/socket.io.min.js",
+    format: "esm",
+    plugins: [terser()],
+  }
+};

examples/basic-websocket-client/src/index.js

@@ -0,0 +1,273 @@
+class EventEmitter {
+  #listeners = new Map();
+
+  on(event, listener) {
+    let listeners = this.#listeners.get(event);
+    if (!listeners) {
+      this.#listeners.set(event, (listeners = []));
+    }
+    listeners.push(listener);
+  }
+
+  emit(event, ...args) {
+    const listeners = this.#listeners.get(event);
+    if (listeners) {
+      for (const listener of listeners) {
+        listener.apply(null, args);
+      }
+    }
+  }
+}
+
+const EIOPacketType = {
+  OPEN: "0",
+  CLOSE: "1",
+  PING: "2",
+  PONG: "3",
+  MESSAGE: "4",
+};
+
+const SIOPacketType = {
+  CONNECT: 0,
+  DISCONNECT: 1,
+  EVENT: 2,
+};
+
+function noop() {}
+
+class Socket extends EventEmitter {
+  id;
+  connected = false;
+
+  #uri;
+  #opts;
+  #ws;
+  #pingTimeoutTimer;
+  #pingTimeoutDelay;
+  #sendBuffer = [];
+  #reconnectTimer;
+  #shouldReconnect = true;
+
+  constructor(uri, opts) {
+    super();
+    this.#uri = uri;
+    this.#opts = Object.assign(
+      {
+        path: "/socket.io/",
+        reconnectionDelay: 2000,
+      },
+      opts
+    );
+    this.#open();
+  }
+
+  #open() {
+    this.#ws = new WebSocket(this.#createUrl());
+    this.#ws.onmessage = ({ data }) => this.#onMessage(data);
+    // dummy handler for Node.js
+    this.#ws.onerror = noop;
+    this.#ws.onclose = () => this.#onClose("transport close");
+  }
+
+  #createUrl() {
+    const uri = this.#uri.replace(/^http/, "ws");
+    const queryParams = "?EIO=4&transport=websocket";
+    return `${uri}${this.#opts.path}${queryParams}`;
+  }
+
+  #onMessage(data) {
+    if (typeof data !== "string") {
+      // TODO handle binary payloads
+      return;
+    }
+
+    switch (data[0]) {
+      case EIOPacketType.OPEN:
+        this.#onOpen(data);
+        break;
+
+      case EIOPacketType.CLOSE:
+        this.#onClose("transport close");
+        break;
+
+      case EIOPacketType.PING:
+        this.#resetPingTimeout();
+        this.#send(EIOPacketType.PONG);
+        break;
+
+      case EIOPacketType.MESSAGE:
+        let packet;
+        try {
+          packet = decode(data);
+        } catch (e) {
+          return this.#onClose("parse error");
+        }
+        this.#onPacket(packet);
+        break;
+
+      default:
+        this.#onClose("parse error");
+        break;
+    }
+  }
+
+  #onOpen(data) {
+    let handshake;
+    try {
+      handshake = JSON.parse(data.substring(1));
+    } catch (e) {
+      return this.#onClose("parse error");
+    }
+    this.#pingTimeoutDelay = handshake.pingInterval + handshake.pingTimeout;
+    this.#resetPingTimeout();
+    this.#doConnect();
+  }
+
+  #onPacket(packet) {
+    switch (packet.type) {
+      case SIOPacketType.CONNECT:
+        this.#onConnect(packet);
+        break;
+
+      case SIOPacketType.DISCONNECT:
+        this.#shouldReconnect = false;
+        this.#onClose("io server disconnect");
+        break;
+
+      case SIOPacketType.EVENT:
+        super.emit.apply(this, packet.data);
+        break;
+
+      default:
+        this.#onClose("parse error");
+        break;
+    }
+  }
+
+  #onConnect(packet) {
+    this.id = packet.data.sid;
+    this.connected = true;
+
+    this.#sendBuffer.forEach((packet) => this.#sendPacket(packet));
+    this.#sendBuffer.slice(0);
+
+    super.emit("connect");
+  }
+
+  #onClose(reason) {
+    if (this.#ws) {
+      this.#ws.onclose = noop;
+      this.#ws.close();
+    }
+
+    clearTimeout(this.#pingTimeoutTimer);
+    clearTimeout(this.#reconnectTimer);
+
+    if (this.connected) {
+      this.connected = false;
+      this.id = undefined;
+      super.emit("disconnect", reason);
+    } else {
+      super.emit("connect_error", reason);
+    }
+
+    if (this.#shouldReconnect) {
+      this.#reconnectTimer = setTimeout(
+        () => this.#open(),
+        this.#opts.reconnectionDelay
+      );
+    }
+  }
+
+  #resetPingTimeout() {
+    clearTimeout(this.#pingTimeoutTimer);
+    this.#pingTimeoutTimer = setTimeout(() => {
+      this.#onClose("ping timeout");
+    }, this.#pingTimeoutDelay);
+  }
+
+  #send(data) {
+    if (this.#ws.readyState === WebSocket.OPEN) {
+      this.#ws.send(data);
+    }
+  }
+
+  #sendPacket(packet) {
+    this.#send(EIOPacketType.MESSAGE + encode(packet));
+  }
+
+  #doConnect() {
+    this.#sendPacket({ type: SIOPacketType.CONNECT });
+  }
+
+  emit(...args) {
+    const packet = {
+      type: SIOPacketType.EVENT,
+      data: args,
+    };
+
+    if (this.connected) {
+      this.#sendPacket(packet);
+    } else {
+      this.#sendBuffer.push(packet);
+    }
+  }
+
+  disconnect() {
+    this.#shouldReconnect = false;
+    this.#onClose("io client disconnect");
+  }
+}
+
+function encode(packet) {
+  let output = "" + packet.type;
+
+  if (packet.data) {
+    output += JSON.stringify(packet.data);
+  }
+
+  return output;
+}
+
+function decode(data) {
+  let i = 1; // skip "4" prefix
+
+  const packet = {
+    type: parseInt(data.charAt(i++), 10),
+  };
+
+  if (data.charAt(i)) {
+    packet.data = JSON.parse(data.substring(i));
+  }
+
+  if (!isPacketValid(packet)) {
+    throw new Error("invalid format");
+  }
+
+  return packet;
+}
+
+function isPacketValid(packet) {
+  switch (packet.type) {
+    case SIOPacketType.CONNECT:
+      return typeof packet.data === "object";
+    case SIOPacketType.DISCONNECT:
+      return packet.data === undefined;
+    case SIOPacketType.EVENT: {
+      const args = packet.data;
+      return (
+        Array.isArray(args) && args.length > 0 && typeof args[0] === "string"
+      );
+    }
+    default:
+      return false;
+  }
+}
+
+export function io(uri, opts) {
+  if (typeof uri !== "string") {
+    opts = uri;
+    uri = location.origin;
+  }
+  return new Socket(uri, opts);
+}

examples/basic-websocket-client/test/index.js

@@ -0,0 +1,162 @@
+import { createServer } from "node:http";
+import { io as ioc } from "../src/index.js";
+import { WebSocket } from "ws";
+import { Server } from "socket.io";
+import { expect } from "chai";
+
+// @ts-ignore for Node.js
+globalThis.WebSocket = WebSocket;
+
+function waitFor(emitter, eventName) {
+  return new Promise((resolve) => {
+    emitter.on(eventName, resolve);
+  });
+}
+
+function sleep(delay) {
+  return new Promise((resolve) => {
+    setTimeout(resolve, delay);
+  });
+}
+
+describe("basic client", () => {
+  let io, port, socket;
+
+  beforeEach(() => {
+    const httpServer = createServer();
+    io = new Server(httpServer);
+
+    httpServer.listen(0);
+    port = httpServer.address().port;
+  });
+
+  afterEach(() => {
+    io.close();
+    socket.disconnect();
+  });
+
+  it("should connect", async () => {
+    socket = ioc(`ws://localhost:${port}`);
+
+    await waitFor(socket, "connect");
+
+    expect(socket.connected).to.eql(true);
+    expect(socket.id).to.be.a("string");
+  });
+
+  it("should connect with 'http://' scheme", async () => {
+    socket = ioc(`http://localhost:${port}`);
+
+    await waitFor(socket, "connect");
+  });
+
+  it("should connect with URL inferred from 'window.location'", async () => {
+    globalThis.location = {
+      origin: `http://localhost:${port}`,
+    };
+    socket = ioc();
+
+    await waitFor(socket, "connect");
+  });
+
+  it("should fail to connect to an invalid URL", async () => {
+    socket = ioc(`http://localhost:4321`);
+
+    await waitFor(socket, "connect_error");
+  });
+
+  it("should receive an event", async () => {
+    io.on("connection", (socket) => {
+      socket.emit("foo", 123);
+    });
+
+    socket = ioc(`ws://localhost:${port}`);
+
+    const value = await waitFor(socket, "foo");
+
+    expect(value).to.eql(123);
+  });
+
+  it("should send an event (not buffered)", async () => {
+    socket = ioc(`ws://localhost:${port}`);
+
+    const [serverSocket] = await Promise.all([
+      waitFor(io, "connection"),
+      waitFor(socket, "connect"),
+    ]);
+
+    socket.emit("foo", 456);
+
+    const value = await waitFor(serverSocket, "foo");
+
+    expect(value).to.eql(456);
+  });
+
+  it("should send an event (buffered)", async () => {
+    socket = ioc(`ws://localhost:${port}`);
+
+    socket.emit("foo", 789);
+
+    const [serverSocket] = await Promise.all([
+      waitFor(io, "connection"),
+      waitFor(socket, "connect"),
+    ]);
+
+    const value = await waitFor(serverSocket, "foo");
+
+    expect(value).to.eql(789);
+  });
+
+  it("should reconnect", async () => {
+    socket = ioc(`ws://localhost:${port}`, {
+      reconnectionDelay: 50,
+    });
+
+    await waitFor(socket, "connect");
+
+    io.close();
+
+    await waitFor(socket, "disconnect");
+
+    io.listen(port);
+
+    await waitFor(socket, "connect");
+  });
+
+  it("should respond to PING packets", async () => {
+    io.engine.opts.pingInterval = 50;
+    io.engine.opts.pingTimeout = 20;
+
+    socket = ioc(`ws://localhost:${port}`);
+
+    await waitFor(socket, "connect");
+
+    await sleep(500);
+
+    expect(socket.connected).to.eql(true);
+  });
+
+  it("should disconnect (client side)", async () => {
+    socket = ioc(`ws://localhost:${port}`);
+
+    await waitFor(socket, "connect");
+
+    socket.disconnect();
+
+    expect(socket.connected).to.eql(false);
+    expect(socket.id).to.eql(undefined);
+  });
+
+  it("should disconnect (server side)", async () => {
+    socket = ioc(`ws://localhost:${port}`);
+
+    const [serverSocket] = await Promise.all([
+      waitFor(io, "connection"),
+      waitFor(socket, "connect"),
+    ]);
+
+    serverSocket.disconnect();
+
+    await waitFor(socket, "disconnect");
+  });
+});

examples/cluster-haproxy/docker-compose.yml

@@ -1,51 +1,53 @@
+services:
+  haproxy:
+    image: haproxy:1.7-alpine
+    volumes:
+      - ./haproxy.cfg:/usr/local/etc/haproxy/haproxy.cfg:ro
+    links:
+      - server-john
+      - server-paul
+      - server-george
+      - server-ringo
+    ports:
+     - "3000:80"
 
-haproxy:
-  build: ./haproxy
-  links:
-    - server-john
-    - server-paul
-    - server-george
-    - server-ringo
-  ports:
-   - "3000:80"
+  server-john:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=John
 
-server-john:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=John
+  server-paul:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=Paul
 
-server-paul:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=Paul
+  server-george:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=George
 
-server-george:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=George
+  server-ringo:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=Ringo
 
-server-ringo:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=Ringo
-
-redis:
-  image: redis:alpine
-  expose:
-    - "6379"
+  redis:
+    image: redis:alpine
+    expose:
+      - "6379"

examples/cluster-haproxy/haproxy/Dockerfile

@@ -1,2 +0,0 @@
-FROM haproxy:1.7-alpine
-COPY haproxy.cfg /usr/local/etc/haproxy/haproxy.cfg

examples/cluster-httpd/docker-compose.yml

@@ -1,51 +1,53 @@
+services:
+  httpd:
+    image: httpd:2.4-alpine
+    volumes:
+      - ./httpd.conf:/usr/local/apache2/conf/httpd.conf:ro
+    links:
+      - server-john
+      - server-paul
+      - server-george
+      - server-ringo
+    ports:
+     - "3000:80"
 
-httpd:
-  build: ./httpd
-  links:
-    - server-john
-    - server-paul
-    - server-george
-    - server-ringo
-  ports:
-   - "3000:80"
+  server-john:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=John
 
-server-john:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=John
+  server-paul:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=Paul
 
-server-paul:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=Paul
+  server-george:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=George
 
-server-george:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=George
+  server-ringo:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=Ringo
 
-server-ringo:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=Ringo
-
-redis:
-  image: redis:alpine
-  expose:
-    - "6379"
+  redis:
+    image: redis:6
+    expose:
+      - "6379"

examples/cluster-httpd/httpd.conf

@@ -51,4 +51,5 @@ RewriteRule /(.*) balancer://nodes_ws/$1 [P,L]
 RewriteCond %{HTTP:Upgrade} !=websocket [NC]
 RewriteRule /(.*) balancer://nodes_polling/$1 [P,L]
 
-ProxyTimeout 3
+# must be bigger than pingInterval (25s by default) + pingTimeout (20s by default)
+ProxyTimeout 60

examples/cluster-httpd/httpd/Dockerfile

@@ -1,2 +0,0 @@
-FROM httpd:2.4-alpine
-COPY ./httpd.conf /usr/local/apache2/conf/httpd.conf

examples/cluster-httpd/server/Dockerfile

@@ -1,4 +1,4 @@
-FROM mhart/alpine-node:6
+FROM node:14-alpine
 
 # Create app directory
 RUN mkdir -p /usr/src/app

examples/cluster-nginx/docker-compose.yml

@@ -1,58 +1,58 @@
+services:
+  nginx:
+    image: nginx:alpine
+    volumes:
+      - ./nginx.conf:/etc/nginx/nginx.conf:ro
+    links:
+      - server-john
+      - server-paul
+      - server-george
+      - server-ringo
+    ports:
+     - "3000:80"
 
-nginx:
-  image: nginx:alpine
-  volumes:
-    - ./nginx.conf:/etc/nginx/nginx.conf:ro
-  links:
-    - server-john
-    - server-paul
-    - server-george
-    - server-ringo
-  ports:
-   - "3000:80"
+  server-john:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=John
 
-server-john:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=John
+  server-paul:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=Paul
 
-server-paul:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=Paul
+  server-george:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=George
 
-server-george:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=George
+  server-ringo:
+    build: ./server
+    links:
+      - redis
+    expose:
+      - "3000"
+    environment:
+      - NAME=Ringo
 
-server-ringo:
-  build: ./server
-  links:
-    - redis
-  expose:
-    - "3000"
-  environment:
-    - NAME=Ringo
+  client:
+    build: ./client
+    links:
+      - nginx
 
-client:
-  build: ./client
-  links:
-    - nginx
-
-redis:
-  image: redis:alpine
-  expose:
-    - "6379"
+  redis:
+    image: redis:6
+    expose:
+      - "6379"

examples/create-react-app-example/package.json

@@ -3,14 +3,14 @@
   "version": "0.1.0",
   "private": true,
   "dependencies": {
-    "@testing-library/jest-dom": "^4.2.4",
-    "@testing-library/react": "^9.3.2",
-    "@testing-library/user-event": "^7.1.2",
-    "react": "^16.13.1",
-    "react-dom": "^16.13.1",
-    "react-scripts": "3.4.1",
-    "socket.io": "4",
-    "socket.io-client": "4"
+    "@testing-library/jest-dom": "^5.16.5",
+    "@testing-library/react": "^14.0.0",
+    "@testing-library/user-event": "^14.4.3",
+    "react": "^18.2.0",
+    "react-dom": "^18.2.0",
+    "react-scripts": "^5.0.1",
+    "socket.io": "^4.6.1",
+    "socket.io-client": "^4.6.1"
   },
   "scripts": {
     "start": "react-scripts start",

examples/create-react-app-example/src/index.js

@@ -1,14 +1,15 @@
 import React from 'react';
-import ReactDOM from 'react-dom';
+import { createRoot } from 'react-dom/client';
 import './index.css';
 import App from './App';
 import * as serviceWorker from './serviceWorker';
 
-ReactDOM.render(
+const container = document.getElementById('root');
+const root = createRoot(container)
+root.render(
   <React.StrictMode>
     <App />
-  </React.StrictMode>,
-  document.getElementById('root')
+  </React.StrictMode>
 );
 
 // If you want your app to work offline and load faster, you can change

examples/private-messaging/package.json

@@ -8,18 +8,19 @@
     "lint": "vue-cli-service lint"
   },
   "dependencies": {
-    "core-js": "^3.6.5",
+    "core-js": "^3.8.3",
     "socket.io-client": "^4.0.0",
-    "vue": "^2.6.11"
+    "vue": "^2.6.14"
   },
   "devDependencies": {
-    "@vue/cli-plugin-babel": "~4.5.0",
-    "@vue/cli-plugin-eslint": "~4.5.0",
-    "@vue/cli-service": "~4.5.0",
-    "babel-eslint": "^10.1.0",
-    "eslint": "^6.7.2",
-    "eslint-plugin-vue": "^6.2.2",
-    "vue-template-compiler": "^2.6.11"
+    "@babel/core": "^7.12.16",
+    "@babel/eslint-parser": "^7.12.16",
+    "@vue/cli-plugin-babel": "~5.0.0",
+    "@vue/cli-plugin-eslint": "~5.0.0",
+    "@vue/cli-service": "~5.0.0",
+    "eslint": "^7.32.0",
+    "eslint-plugin-vue": "^8.0.3",
+    "vue-template-compiler": "^2.6.14"
   },
   "eslintConfig": {
     "root": true,
@@ -31,9 +32,11 @@
       "eslint:recommended"
     ],
     "parserOptions": {
-      "parser": "babel-eslint"
+      "parser": "@babel/eslint-parser"
     },
-    "rules": {}
+    "rules": {
+      "vue/multi-word-component-names": "off"
+    }
   },
   "browserslist": [
     "> 1%",

examples/private-messaging/src/App.vue

@@ -68,7 +68,7 @@ body {
 
 @font-face {
   font-family: Lato;
-  src: url("/fonts/Lato-Regular.ttf");
+  src: "~/public/fonts/Lato-Regular.ttf";
 }
 
 #app {

lib/broadcast-operator.ts

@@ -7,6 +7,11 @@ import type {
   EventNames,
   EventsMap,
   TypedEventBroadcaster,
+  DecorateAcknowledgements,
+  DecorateAcknowledgementsWithTimeoutAndMultipleResponses,
+  AllButLast,
+  Last,
+  SecondArg,
 } from "./typed-events";
 
 export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
@@ -16,7 +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;
+    } = {}
   ) {}
 
   /**
@@ -169,12 +176,10 @@ export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
    */
   public timeout(timeout: number) {
     const flags = Object.assign({}, this.flags, { timeout });
-    return new BroadcastOperator<EmitEvents, SocketData>(
-      this.adapter,
-      this.rooms,
-      this.exceptRooms,
-      flags
-    );
+    return new BroadcastOperator<
+      DecorateAcknowledgementsWithTimeoutAndMultipleResponses<EmitEvents>,
+      SocketData
+    >(this.adapter, this.rooms, this.exceptRooms, flags);
   }
 
   /**
@@ -230,7 +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;
@@ -244,7 +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,
+        ]);
       }
     };
 
@@ -276,6 +287,36 @@ export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
     return true;
   }
 
+  /**
+   * Emits an event and waits for an acknowledgement from all clients.
+   *
+   * @example
+   * try {
+   *   const responses = await io.timeout(1000).emitWithAck("some-event");
+   *   console.log(responses); // one response per client
+   * } catch (e) {
+   *   // some clients did not acknowledge the event in the given delay
+   * }
+   *
+   * @return a Promise that will be fulfilled when all clients have acknowledged the event
+   */
+  public emitWithAck<Ev extends EventNames<EmitEvents>>(
+    ev: Ev,
+    ...args: AllButLast<EventParams<EmitEvents, Ev>>
+  ): Promise<SecondArg<Last<EventParams<EmitEvents, Ev>>>> {
+    return new Promise((resolve, reject) => {
+      args.push((err, responses) => {
+        if (err) {
+          err.responses = responses;
+          return reject(err);
+        } else {
+          return resolve(responses);
+        }
+      });
+      this.emit(ev, ...(args as any[] as EventParams<EmitEvents, Ev>));
+    });
+  }
+
   /**
    * Gets a list of clients.
    *
@@ -444,10 +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>

lib/client.ts

@@ -114,7 +114,7 @@ export class Client<
    * @param {Object} auth - the auth parameters
    * @private
    */
-  private connect(name: string, auth: object = {}): void {
+  private connect(name: string, auth: Record<string, unknown> = {}): void {
     if (this.server._nsps.has(name)) {
       debug("connecting to namespace %s", name);
       return this.doConnect(name, auth);
@@ -152,10 +152,10 @@ export class Client<
    *
    * @private
    */
-  private doConnect(name: string, auth: object): void {
+  private doConnect(name: string, auth: Record<string, unknown>): void {
     const nsp = this.server.of(name);
 
-    const socket = nsp._add(this, auth, () => {
+    nsp._add(this, auth, (socket) => {
       this.sockets.set(socket.id, socket);
       this.nsps.set(nsp.name, socket);
 
@@ -228,7 +228,7 @@ export class Client<
   }
 
   private writeToEngine(
-    encodedPackets: Array<String | Buffer>,
+    encodedPackets: Array<string | Buffer>,
     opts: WriteOptions
   ): void {
     if (opts.volatile && !this.conn.transport.writable) {
@@ -267,7 +267,7 @@ export class Client<
    */
   private ondecoded(packet: Packet): void {
     let namespace: string;
-    let authPayload;
+    let authPayload: Record<string, unknown>;
     if (this.conn.protocol === 3) {
       const parsed = url.parse(packet.nsp, true);
       namespace = parsed.pathname!;
@@ -311,9 +311,13 @@ export class Client<
    * Called upon transport close.
    *
    * @param reason
+   * @param description
    * @private
    */
-  private onclose(reason: CloseReason | "forced server close"): void {
+  private onclose(
+    reason: CloseReason | "forced server close",
+    description?: any
+  ): void {
     debug("client close with reason %s", reason);
 
     // ignore a potential subsequent `close` event
@@ -321,7 +325,7 @@ export class Client<
 
     // `nsps` and `sockets` are cleaned up seamlessly
     for (const socket of this.sockets.values()) {
-      socket._onclose(reason);
+      socket._onclose(reason, description);
     }
     this.sockets.clear();
 

lib/index.ts

@@ -6,22 +6,26 @@ import { createDeflate, createGzip, createBrotliCompress } from "zlib";
 import accepts = require("accepts");
 import { pipeline } from "stream";
 import path = require("path");
-import {
-  attach,
-  Server as Engine,
+import { attach, Server as Engine, uServer } from "engine.io";
+import type {
   ServerOptions as EngineOptions,
   AttachOptions,
-  uServer,
+  BaseServer,
 } from "engine.io";
 import { Client } from "./client";
 import { EventEmitter } from "events";
 import { ExtendedError, Namespace, ServerReservedEventsMap } from "./namespace";
 import { ParentNamespace } from "./parent-namespace";
-import { Adapter, Room, SocketId } from "socket.io-adapter";
+import {
+  Adapter,
+  SessionAwareAdapter,
+  Room,
+  SocketId,
+} from "socket.io-adapter";
 import * as parser from "socket.io-parser";
 import type { Encoder } from "socket.io-parser";
 import debugModule from "debug";
-import { Socket } from "./socket";
+import { Socket, DisconnectReason } from "./socket";
 import type { BroadcastOperator, RemoteSocket } from "./broadcast-operator";
 import {
   EventsMap,
@@ -29,8 +33,14 @@ import {
   EventParams,
   StrictEventEmitter,
   EventNames,
+  DecorateAcknowledgementsWithTimeoutAndMultipleResponses,
+  AllButLast,
+  Last,
+  FirstArg,
+  SecondArg,
 } from "./typed-events";
 import { patchAdapter, restoreAdapter, serveFile } from "./uws";
+import corsMiddleware from "cors";
 
 const debug = debugModule("socket.io:server");
 
@@ -71,6 +81,30 @@ interface ServerOptions extends EngineOptions, AttachOptions {
    * @default 45000
    */
   connectTimeout: number;
+  /**
+   * Whether to enable the recovery of connection state when a client temporarily disconnects.
+   *
+   * The connection state includes the missed packets, the rooms the socket was in and the `data` attribute.
+   */
+  connectionStateRecovery: {
+    /**
+     * The backup duration of the sessions and the packets.
+     *
+     * @default 120000 (2 minutes)
+     */
+    maxDisconnectionDuration?: number;
+    /**
+     * Whether to skip middlewares upon successful connection state recovery.
+     *
+     * @default true
+     */
+    skipMiddlewares?: boolean;
+  };
+  /**
+   * Whether to remove child namespaces that have no sockets connected to them
+   * @default false
+   */
+  cleanupEmptyChildNamespaces: boolean;
 }
 
 /**
@@ -127,7 +161,7 @@ export class Server<
    * const clientsCount = io.engine.clientsCount;
    *
    */
-  public engine: any;
+  public engine: BaseServer;
 
   /** @private */
   readonly _parser: typeof parser;
@@ -145,9 +179,21 @@ export class Server<
     ParentNspNameMatchFn,
     ParentNamespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>
   > = new Map();
+
+  /**
+   * A subset of the {@link parentNsps} map, only containing {@link ParentNamespace} which are based on a regular
+   * expression.
+   *
+   * @private
+   */
+  private parentNamespacesFromRegExp: Map<
+    RegExp,
+    ParentNamespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData>
+  > = new Map();
+
   private _adapter?: AdapterConstructor;
   private _serveClient: boolean;
-  private opts: Partial<EngineOptions>;
+  private readonly opts: Partial<ServerOptions>;
   private eio: Engine;
   private _path: string;
   private clientPathRegex: RegExp;
@@ -157,6 +203,11 @@ export class Server<
    */
   _connectTimeout: number;
   private httpServer: http.Server | HTTPSServer | Http2SecureServer;
+  private _corsMiddleware: (
+    req: http.IncomingMessage,
+    res: http.ServerResponse,
+    next: () => void
+  ) => void;
 
   /**
    * Server constructor.
@@ -203,13 +254,33 @@ export class Server<
     this.serveClient(false !== opts.serveClient);
     this._parser = opts.parser || parser;
     this.encoder = new this._parser.Encoder();
-    this.adapter(opts.adapter || Adapter);
-    this.sockets = this.of("/");
     this.opts = opts;
+    if (opts.connectionStateRecovery) {
+      opts.connectionStateRecovery = Object.assign(
+        {
+          maxDisconnectionDuration: 2 * 60 * 1000,
+          skipMiddlewares: true,
+        },
+        opts.connectionStateRecovery
+      );
+      this.adapter(opts.adapter || SessionAwareAdapter);
+    } else {
+      this.adapter(opts.adapter || Adapter);
+    }
+    opts.cleanupEmptyChildNamespaces = !!opts.cleanupEmptyChildNamespaces;
+    this.sockets = this.of("/");
     if (srv || typeof srv == "number")
       this.attach(
         srv as http.Server | HTTPSServer | Http2SecureServer | number
       );
+
+    if (this.opts.cors) {
+      this._corsMiddleware = corsMiddleware(this.opts.cors);
+    }
+  }
+
+  get _opts() {
+    return this.opts;
   }
 
   /**
@@ -265,8 +336,6 @@ export class Server<
         }
         const namespace = this.parentNsps.get(nextFn.value)!.createChild(name);
         debug("dynamic namespace %s was created", name);
-        // @ts-ignore
-        this.sockets.emitReserved("new_namespace", namespace);
         fn(namespace);
       });
     };
@@ -437,7 +506,7 @@ export class Server<
         res.writeHeader("cache-control", "public, max-age=0");
         res.writeHeader(
           "content-type",
-          "application/" + (isMap ? "json" : "javascript")
+          "application/" + (isMap ? "json" : "javascript") + "; charset=utf-8"
         );
         res.writeHeader("etag", expectedEtag);
 
@@ -489,7 +558,13 @@ export class Server<
     srv.removeAllListeners("request");
     srv.on("request", (req, res) => {
       if (this.clientPathRegex.test(req.url!)) {
-        this.serve(req, res);
+        if (this._corsMiddleware) {
+          this._corsMiddleware(req, res, () => {
+            this.serve(req, res);
+          });
+        } else {
+          this.serve(req, res);
+        }
       } else {
         for (let i = 0; i < evs.length; i++) {
           evs[i].call(srv, req, res);
@@ -530,7 +605,7 @@ export class Server<
     res.setHeader("Cache-Control", "public, max-age=0");
     res.setHeader(
       "Content-Type",
-      "application/" + (isMap ? "json" : "javascript")
+      "application/" + (isMap ? "json" : "javascript") + "; charset=utf-8"
     );
     res.setHeader("ETag", expectedEtag);
 
@@ -582,10 +657,10 @@ export class Server<
   /**
    * Binds socket.io to an engine.io instance.
    *
-   * @param {engine.Server} engine engine.io (or compatible) server
+   * @param engine engine.io (or compatible) server
    * @return self
    */
-  public bind(engine): this {
+  public bind(engine: BaseServer): this {
     this.engine = engine;
     this.engine.on("connection", this.onconnection.bind(this));
     return this;
@@ -642,6 +717,7 @@ export class Server<
           (nsp, conn, next) => next(null, (name as RegExp).test(nsp)),
           parentNsp
         );
+        this.parentNamespacesFromRegExp.set(name, parentNsp);
       }
       if (fn) {
         // @ts-ignore
@@ -654,6 +730,13 @@ export class Server<
 
     let nsp = this._nsps.get(name);
     if (!nsp) {
+      for (const [regex, parentNamespace] of this.parentNamespacesFromRegExp) {
+        if (regex.test(name as string)) {
+          debug("attaching namespace %s to parent namespace %s", name, regex);
+          return parentNamespace.createChild(name as string);
+        }
+      }
+
       debug("initializing namespace %s", name);
       nsp = new Namespace(this, name);
       this._nsps.set(name, nsp);
@@ -763,6 +846,26 @@ export class Server<
     return this.sockets.except(room);
   }
 
+  /**
+   * Emits an event and waits for an acknowledgement from all clients.
+   *
+   * @example
+   * try {
+   *   const responses = await io.timeout(1000).emitWithAck("some-event");
+   *   console.log(responses); // one response per client
+   * } catch (e) {
+   *   // some clients did not acknowledge the event in the given delay
+   * }
+   *
+   * @return a Promise that will be fulfilled when all clients have acknowledged the event
+   */
+  public emitWithAck<Ev extends EventNames<EmitEvents>>(
+    ev: Ev,
+    ...args: AllButLast<EventParams<EmitEvents, Ev>>
+  ): Promise<SecondArg<Last<EventParams<EmitEvents, Ev>>>> {
+    return this.sockets.emitWithAck(ev, ...args);
+  }
+
   /**
    * Sends a `message` event to all clients.
    *
@@ -806,9 +909,9 @@ export class Server<
    * // acknowledgements (without binary content) are supported too:
    * io.serverSideEmit("ping", (err, responses) => {
    *  if (err) {
-   *     // some clients did not acknowledge the event in the given delay
+   *     // some servers did not acknowledge the event in the given delay
    *   } else {
-   *     console.log(responses); // one response per client
+   *     console.log(responses); // one response per server (except the current one)
    *   }
    * });
    *
@@ -821,11 +924,37 @@ export class Server<
    */
   public serverSideEmit<Ev extends EventNames<ServerSideEvents>>(
     ev: Ev,
-    ...args: EventParams<ServerSideEvents, Ev>
+    ...args: EventParams<
+      DecorateAcknowledgementsWithTimeoutAndMultipleResponses<ServerSideEvents>,
+      Ev
+    >
   ): boolean {
     return this.sockets.serverSideEmit(ev, ...args);
   }
 
+  /**
+   * Sends a message and expect an acknowledgement from the other Socket.IO servers of the cluster.
+   *
+   * @example
+   * try {
+   *   const responses = await io.serverSideEmitWithAck("ping");
+   *   console.log(responses); // one response per server (except the current one)
+   * } catch (e) {
+   *   // some servers did not acknowledge the event in the given delay
+   * }
+   *
+   * @param ev - the event name
+   * @param args - an array of arguments
+   *
+   * @return a Promise that will be fulfilled when all servers have acknowledged the event
+   */
+  public serverSideEmitWithAck<Ev extends EventNames<ServerSideEvents>>(
+    ev: Ev,
+    ...args: AllButLast<EventParams<ServerSideEvents, Ev>>
+  ): Promise<FirstArg<Last<EventParams<ServerSideEvents, Ev>>>[]> {
+    return this.sockets.serverSideEmitWithAck(ev, ...args);
+  }
+
   /**
    * Gets a list of socket ids.
    *
@@ -999,5 +1128,12 @@ module.exports.Server = Server;
 module.exports.Namespace = Namespace;
 module.exports.Socket = Socket;
 
-export { Socket, ServerOptions, Namespace, BroadcastOperator, RemoteSocket };
+export {
+  Socket,
+  DisconnectReason,
+  ServerOptions,
+  Namespace,
+  BroadcastOperator,
+  RemoteSocket,
+};
 export { Event } from "./socket";

lib/namespace.ts

@@ -6,11 +6,16 @@ import {
   EventsMap,
   StrictEventEmitter,
   DefaultEventsMap,
+  DecorateAcknowledgementsWithTimeoutAndMultipleResponses,
+  AllButLast,
+  Last,
+  FirstArg,
+  SecondArg,
 } from "./typed-events";
 import type { Client } from "./client";
 import debugModule from "debug";
 import type { Adapter, Room, SocketId } from "socket.io-adapter";
-import { BroadcastOperator, RemoteSocket } from "./broadcast-operator";
+import { BroadcastOperator } from "./broadcast-operator";
 
 const debug = debugModule("socket.io:namespace");
 
@@ -296,13 +301,25 @@ export class Namespace<
    * @return {Socket}
    * @private
    */
-  _add(
+  async _add(
     client: Client<ListenEvents, EmitEvents, ServerSideEvents>,
-    query,
-    fn?: () => void
-  ): Socket<ListenEvents, EmitEvents, ServerSideEvents, SocketData> {
+    auth: Record<string, unknown>,
+    fn: (
+      socket: Socket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>
+    ) => void
+  ) {
     debug("adding socket to nsp %s", this.name);
-    const socket = new Socket(this, client, query);
+    const socket = await this._createSocket(client, auth);
+
+    if (
+      // @ts-ignore
+      this.server.opts.connectionStateRecovery?.skipMiddlewares &&
+      socket.recovered &&
+      client.conn.readyState === "open"
+    ) {
+      return this._doConnect(socket, fn);
+    }
+
     this.run(socket, (err) => {
       process.nextTick(() => {
         if ("open" !== client.conn.readyState) {
@@ -324,22 +341,56 @@ export class Namespace<
           }
         }
 
-        // track socket
-        this.sockets.set(socket.id, socket);
-
-        // it's paramount that the internal `onconnect` logic
-        // fires before user-set events to prevent state order
-        // violations (such as a disconnection before the connection
-        // logic is complete)
-        socket._onconnect();
-        if (fn) fn();
-
-        // fire user-set events
-        this.emitReserved("connect", socket);
-        this.emitReserved("connection", socket);
+        this._doConnect(socket, fn);
       });
     });
-    return socket;
+  }
+
+  private async _createSocket(
+    client: Client<ListenEvents, EmitEvents, ServerSideEvents>,
+    auth: Record<string, unknown>
+  ) {
+    const sessionId = auth.pid;
+    const offset = auth.offset;
+    if (
+      // @ts-ignore
+      this.server.opts.connectionStateRecovery &&
+      typeof sessionId === "string" &&
+      typeof offset === "string"
+    ) {
+      let session;
+      try {
+        session = await this.adapter.restoreSession(sessionId, offset);
+      } catch (e) {
+        debug("error while restoring session: %s", e);
+      }
+      if (session) {
+        debug("connection state recovered for sid %s", session.sid);
+        return new Socket(this, client, auth, session);
+      }
+    }
+    return new Socket(this, client, auth);
+  }
+
+  private _doConnect(
+    socket: Socket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>,
+    fn: (
+      socket: Socket<ListenEvents, EmitEvents, ServerSideEvents, SocketData>
+    ) => void
+  ) {
+    // track socket
+    this.sockets.set(socket.id, socket);
+
+    // it's paramount that the internal `onconnect` logic
+    // fires before user-set events to prevent state order
+    // violations (such as a disconnection before the connection
+    // logic is complete)
+    socket._onconnect();
+    if (fn) fn(socket);
+
+    // fire user-set events
+    this.emitReserved("connect", socket);
+    this.emitReserved("connection", socket);
   }
 
   /**
@@ -389,6 +440,30 @@ export class Namespace<
     );
   }
 
+  /**
+   * Emits an event and waits for an acknowledgement from all clients.
+   *
+   * @example
+   * const myNamespace = io.of("/my-namespace");
+   *
+   * try {
+   *   const responses = await myNamespace.timeout(1000).emitWithAck("some-event");
+   *   console.log(responses); // one response per client
+   * } catch (e) {
+   *   // some clients did not acknowledge the event in the given delay
+   * }
+   *
+   * @return a Promise that will be fulfilled when all clients have acknowledged the event
+   */
+  public emitWithAck<Ev extends EventNames<EmitEvents>>(
+    ev: Ev,
+    ...args: AllButLast<EventParams<EmitEvents, Ev>>
+  ): Promise<SecondArg<Last<EventParams<EmitEvents, Ev>>>> {
+    return new BroadcastOperator<EmitEvents, SocketData>(
+      this.adapter
+    ).emitWithAck(ev, ...args);
+  }
+
   /**
    * Sends a `message` event to all clients.
    *
@@ -436,9 +511,9 @@ export class Namespace<
    * // acknowledgements (without binary content) are supported too:
    * myNamespace.serverSideEmit("ping", (err, responses) => {
    *  if (err) {
-   *     // some clients did not acknowledge the event in the given delay
+   *     // some servers did not acknowledge the event in the given delay
    *   } else {
-   *     console.log(responses); // one response per client
+   *     console.log(responses); // one response per server (except the current one)
    *   }
    * });
    *
@@ -451,7 +526,10 @@ export class Namespace<
    */
   public serverSideEmit<Ev extends EventNames<ServerSideEvents>>(
     ev: Ev,
-    ...args: EventParams<ServerSideEvents, Ev>
+    ...args: EventParams<
+      DecorateAcknowledgementsWithTimeoutAndMultipleResponses<ServerSideEvents>,
+      Ev
+    >
   ): boolean {
     if (RESERVED_EVENTS.has(ev)) {
       throw new Error(`"${String(ev)}" is a reserved event name`);
@@ -461,6 +539,44 @@ export class Namespace<
     return true;
   }
 
+  /**
+   * Sends a message and expect an acknowledgement from the other Socket.IO servers of the cluster.
+   *
+   * @example
+   * const myNamespace = io.of("/my-namespace");
+   *
+   * try {
+   *   const responses = await myNamespace.serverSideEmitWithAck("ping");
+   *   console.log(responses); // one response per server (except the current one)
+   * } catch (e) {
+   *   // some servers did not acknowledge the event in the given delay
+   * }
+   *
+   * @param ev - the event name
+   * @param args - an array of arguments
+   *
+   * @return a Promise that will be fulfilled when all servers have acknowledged the event
+   */
+  public serverSideEmitWithAck<Ev extends EventNames<ServerSideEvents>>(
+    ev: Ev,
+    ...args: AllButLast<EventParams<ServerSideEvents, Ev>>
+  ): Promise<FirstArg<Last<EventParams<ServerSideEvents, Ev>>>[]> {
+    return new Promise((resolve, reject) => {
+      args.push((err, responses) => {
+        if (err) {
+          err.responses = responses;
+          return reject(err);
+        } else {
+          return resolve(responses);
+        }
+      });
+      this.serverSideEmit(
+        ev,
+        ...(args as any[] as EventParams<ServerSideEvents, Ev>)
+      );
+    });
+  }
+
   /**
    * Called when a packet is received from another Socket.IO server
    *

lib/parent-namespace.ts

@@ -7,7 +7,25 @@ import type {
   DefaultEventsMap,
 } from "./typed-events";
 import type { BroadcastOptions } from "socket.io-adapter";
+import debugModule from "debug";
 
+const debug = debugModule("socket.io:parent-namespace");
+
+/**
+ * A parent namespace is a special {@link Namespace} that holds a list of child namespaces which were created either
+ * with a regular expression or with a function.
+ *
+ * @example
+ * const parentNamespace = io.of(/\/dynamic-\d+/);
+ *
+ * parentNamespace.on("connection", (socket) => {
+ *   const childNamespace = socket.nsp;
+ * }
+ *
+ * // will reach all the clients that are in one of the child namespaces, like "/dynamic-101"
+ * parentNamespace.emit("hello", "world");
+ *
+ */
 export class ParentNamespace<
   ListenEvents extends EventsMap = DefaultEventsMap,
   EmitEvents extends EventsMap = ListenEvents,
@@ -52,6 +70,7 @@ export class ParentNamespace<
   createChild(
     name: string
   ): Namespace<ListenEvents, EmitEvents, ServerSideEvents, SocketData> {
+    debug("creating child namespace %s", name);
     const namespace = new Namespace(this.server, name);
     namespace._fns = this._fns.slice(0);
     this.listeners("connect").forEach((listener) =>
@@ -61,7 +80,26 @@ export class ParentNamespace<
       namespace.on("connection", listener)
     );
     this.children.add(namespace);
+
+    if (this.server._opts.cleanupEmptyChildNamespaces) {
+      const remove = namespace._remove;
+
+      namespace._remove = (socket) => {
+        remove.call(namespace, socket);
+        if (namespace.sockets.size === 0) {
+          debug("closing child namespace %s", name);
+          namespace.adapter.close();
+          this.server._nsps.delete(namespace.name);
+          this.children.delete(namespace);
+        }
+      };
+    }
+
     this.server._nsps.set(name, namespace);
+
+    // @ts-ignore
+    this.server.sockets.emitReserved("new_namespace", namespace);
+
     return namespace;
   }
 

lib/socket.ts

@@ -2,19 +2,26 @@ import { Packet, PacketType } from "socket.io-parser";
 import debugModule from "debug";
 import type { Server } from "./index";
 import {
-  EventParams,
-  EventNames,
-  EventsMap,
-  StrictEventEmitter,
+  AllButLast,
+  DecorateAcknowledgements,
+  DecorateAcknowledgementsWithMultipleResponses,
   DefaultEventsMap,
+  EventNames,
+  EventParams,
+  EventsMap,
+  FirstArg,
+  Last,
+  StrictEventEmitter,
 } from "./typed-events";
 import type { Client } from "./client";
 import type { Namespace, NamespaceReservedEventsMap } from "./namespace";
-import type { IncomingMessage, IncomingHttpHeaders } from "http";
+import type { IncomingHttpHeaders, IncomingMessage } from "http";
 import type {
   Adapter,
   BroadcastFlags,
+  PrivateSessionId,
   Room,
+  Session,
   SocketId,
 } from "socket.io-adapter";
 import base64id from "base64id";
@@ -39,9 +46,18 @@ export type DisconnectReason =
   | "client namespace disconnect"
   | "server namespace disconnect";
 
+const RECOVERABLE_DISCONNECT_REASONS: ReadonlySet<DisconnectReason> = new Set([
+  "transport error",
+  "transport close",
+  "forced close",
+  "ping timeout",
+  "server shutting down",
+  "forced server close",
+]);
+
 export interface SocketReservedEventsMap {
-  disconnect: (reason: DisconnectReason) => void;
-  disconnecting: (reason: DisconnectReason) => void;
+  disconnect: (reason: DisconnectReason, description?: any) => void;
+  disconnecting: (reason: DisconnectReason, description?: any) => void;
   error: (err: Error) => void;
 }
 
@@ -173,6 +189,11 @@ export class Socket<
    * An unique identifier for the session.
    */
   public readonly id: SocketId;
+  /**
+   * Whether the connection state was recovered after a temporary disconnection. In that case, any missed packets will
+   * be transmitted to the client, the data attribute and the rooms will be restored.
+   */
+  public readonly recovered: boolean = false;
   /**
    * The handshake details.
    */
@@ -181,7 +202,7 @@ export class Socket<
    * Additional information that can be attached to the Socket instance and which will be used in the
    * {@link Server.fetchSockets()} method.
    */
-  public data: Partial<SocketData> = {};
+  public data: SocketData = {} as SocketData;
   /**
    * Whether the socket is currently connected or not.
    *
@@ -197,6 +218,14 @@ export class Socket<
    */
   public connected: boolean = false;
 
+  /**
+   * The session ID, which must not be shared (unlike {@link id}).
+   *
+   * @private
+   */
+  private readonly pid: PrivateSessionId;
+
+  // TODO: remove this unused reference
   private readonly server: Server<
     ListenEvents,
     EmitEvents,
@@ -221,18 +250,39 @@ export class Socket<
   constructor(
     readonly nsp: Namespace<ListenEvents, EmitEvents, ServerSideEvents>,
     readonly client: Client<ListenEvents, EmitEvents, ServerSideEvents>,
-    auth: object
+    auth: Record<string, unknown>,
+    previousSession?: Session
   ) {
     super();
     this.server = nsp.server;
     this.adapter = this.nsp.adapter;
-    if (client.conn.protocol === 3) {
-      // @ts-ignore
-      this.id = nsp.name !== "/" ? nsp.name + "#" + client.id : client.id;
+    if (previousSession) {
+      this.id = previousSession.sid;
+      this.pid = previousSession.pid;
+      previousSession.rooms.forEach((room) => this.join(room));
+      this.data = previousSession.data as SocketData;
+      previousSession.missedPackets.forEach((packet) => {
+        this.packet({
+          type: PacketType.EVENT,
+          data: packet,
+        });
+      });
+      this.recovered = true;
     } else {
-      this.id = base64id.generateId(); // don't reuse the Engine.IO id because it's sensitive information
+      if (client.conn.protocol === 3) {
+        // @ts-ignore
+        this.id = nsp.name !== "/" ? nsp.name + "#" + client.id : client.id;
+      } else {
+        this.id = base64id.generateId(); // don't reuse the Engine.IO id because it's sensitive information
+      }
+      if (this.server._opts.connectionStateRecovery) {
+        this.pid = base64id.generateId();
+      }
     }
     this.handshake = this.buildHandshake(auth);
+
+    // prevents crash when the socket receives an "error" event without listener
+    this.on("error", noop);
   }
 
   /**
@@ -299,12 +349,58 @@ export class Socket<
     const flags = Object.assign({}, this.flags);
     this.flags = {};
 
-    this.notifyOutgoingListeners(packet);
-    this.packet(packet, flags);
+    // @ts-ignore
+    if (this.nsp.server.opts.connectionStateRecovery) {
+      // this ensures the packet is stored and can be transmitted upon reconnection
+      this.adapter.broadcast(packet, {
+        rooms: new Set([this.id]),
+        except: new Set(),
+        flags,
+      });
+    } else {
+      this.notifyOutgoingListeners(packet);
+      this.packet(packet, flags);
+    }
 
     return true;
   }
 
+  /**
+   * Emits an event and waits for an acknowledgement
+   *
+   * @example
+   * io.on("connection", async (socket) => {
+   *   // without timeout
+   *   const response = await socket.emitWithAck("hello", "world");
+   *
+   *   // with a specific timeout
+   *   try {
+   *     const response = await socket.timeout(1000).emitWithAck("hello", "world");
+   *   } catch (err) {
+   *     // the client did not acknowledge the event in the given delay
+   *   }
+   * });
+   *
+   * @return a Promise that will be fulfilled when the client acknowledges the event
+   */
+  public emitWithAck<Ev extends EventNames<EmitEvents>>(
+    ev: Ev,
+    ...args: AllButLast<EventParams<EmitEvents, Ev>>
+  ): Promise<FirstArg<Last<EventParams<EmitEvents, Ev>>>> {
+    // the timeout flag is optional
+    const withErr = this.flags.timeout !== undefined;
+    return new Promise((resolve, reject) => {
+      args.push((arg1, arg2) => {
+        if (withErr) {
+          return arg1 ? reject(arg1) : resolve(arg2);
+        } else {
+          return resolve(arg1);
+        }
+      });
+      this.emit(ev, ...(args as any[] as EventParams<EmitEvents, Ev>));
+    });
+  }
+
   /**
    * @private
    */
@@ -508,7 +604,10 @@ export class Socket<
     if (this.conn.protocol === 3) {
       this.packet({ type: PacketType.CONNECT });
     } else {
-      this.packet({ type: PacketType.CONNECT, data: { sid: this.id } });
+      this.packet({
+        type: PacketType.CONNECT,
+        data: { sid: this.id, pid: this.pid },
+      });
     }
   }
 
@@ -624,31 +723,45 @@ export class Socket<
    * @private
    */
   _onerror(err: Error): void {
-    if (this.listeners("error").length) {
-      this.emitReserved("error", err);
-    } else {
-      console.error("Missing error handler on `socket`.");
-      console.error(err.stack);
-    }
+    // FIXME the meaning of the "error" event is overloaded:
+    //  - it can be sent by the client (`socket.emit("error")`)
+    //  - it can be emitted when the connection encounters an error (an invalid packet for example)
+    //  - it can be emitted when a packet is rejected in a middleware (`socket.use()`)
+    this.emitReserved("error", err);
   }
 
   /**
    * Called upon closing. Called by `Client`.
    *
    * @param {String} reason
+   * @param description
    * @throw {Error} optional error object
    *
    * @private
    */
-  _onclose(reason: DisconnectReason): this | undefined {
+  _onclose(reason: DisconnectReason, description?: any): this | undefined {
     if (!this.connected) return this;
     debug("closing socket - reason %s", reason);
-    this.emitReserved("disconnecting", reason);
+    this.emitReserved("disconnecting", reason, description);
+
+    if (
+      this.server._opts.connectionStateRecovery &&
+      RECOVERABLE_DISCONNECT_REASONS.has(reason)
+    ) {
+      debug("connection state recovery is enabled for sid %s", this.id);
+      this.adapter.persistSession({
+        sid: this.id,
+        pid: this.pid,
+        rooms: [...this.rooms],
+        data: this.data,
+      });
+    }
+
     this._cleanup();
     this.nsp._remove(this);
     this.client._remove(this);
     this.connected = false;
-    this.emitReserved("disconnect", reason);
+    this.emitReserved("disconnect", reason, description);
     return;
   }
 
@@ -778,7 +891,14 @@ export class Socket<
    *
    * @returns self
    */
-  public timeout(timeout: number): this {
+  public timeout(
+    timeout: number
+  ): Socket<
+    ListenEvents,
+    DecorateAcknowledgements<EmitEvents>,
+    ServerSideEvents,
+    SocketData
+  > {
     this.flags.timeout = timeout;
     return this;
   }
@@ -1088,11 +1208,9 @@ export class Socket<
   private newBroadcastOperator() {
     const flags = Object.assign({}, this.flags);
     this.flags = {};
-    return new BroadcastOperator<EmitEvents, SocketData>(
-      this.adapter,
-      new Set<Room>(),
-      new Set<Room>([this.id]),
-      flags
-    );
+    return new BroadcastOperator<
+      DecorateAcknowledgementsWithMultipleResponses<EmitEvents>,
+      SocketData
+    >(this.adapter, new Set<Room>(), new Set<Room>([this.id]), flags);
   }
 }

lib/typed-events.ts

@@ -178,3 +178,66 @@ export abstract class StrictEventEmitter<
     >[];
   }
 }
+
+export type Last<T extends any[]> = T extends [...infer H, infer L] ? L : any;
+export type AllButLast<T extends any[]> = T extends [...infer H, infer L]
+  ? H
+  : any[];
+export type FirstArg<T> = T extends (arg: infer Param) => infer Result
+  ? Param
+  : any;
+export type SecondArg<T> = T extends (
+  err: Error,
+  arg: infer Param
+) => infer Result
+  ? Param
+  : any;
+
+type PrependTimeoutError<T extends any[]> = {
+  [K in keyof T]: T[K] extends (...args: infer Params) => infer Result
+    ? (err: Error, ...args: Params) => Result
+    : T[K];
+};
+
+type ExpectMultipleResponses<T extends any[]> = {
+  [K in keyof T]: T[K] extends (err: Error, arg: infer Param) => infer Result
+    ? (err: Error, arg: Param[]) => Result
+    : T[K];
+};
+
+/**
+ * Utility type to decorate the acknowledgement callbacks with a timeout error.
+ *
+ * This is needed because the timeout() flag breaks the symmetry between the sender and the receiver:
+ *
+ * @example
+ * interface Events {
+ *   "my-event": (val: string) => void;
+ * }
+ *
+ * socket.on("my-event", (cb) => {
+ *   cb("123"); // one single argument here
+ * });
+ *
+ * socket.timeout(1000).emit("my-event", (err, val) => {
+ *   // two arguments there (the "err" argument is not properly typed)
+ * });
+ *
+ */
+export type DecorateAcknowledgements<E> = {
+  [K in keyof E]: E[K] extends (...args: infer Params) => infer Result
+    ? (...args: PrependTimeoutError<Params>) => Result
+    : E[K];
+};
+
+export type DecorateAcknowledgementsWithTimeoutAndMultipleResponses<E> = {
+  [K in keyof E]: E[K] extends (...args: infer Params) => infer Result
+    ? (...args: ExpectMultipleResponses<PrependTimeoutError<Params>>) => Result
+    : E[K];
+};
+
+export type DecorateAcknowledgementsWithMultipleResponses<E> = {
+  [K in keyof E]: E[K] extends (...args: infer Params) => infer Result
+    ? (...args: ExpectMultipleResponses<Params>) => Result
+    : E[K];
+};

package-lock.json

@@ -1,20 +1,21 @@
 {
   "name": "socket.io",
-  "version": "4.5.3",
+  "version": "4.7.0",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "socket.io",
-      "version": "4.5.3",
+      "version": "4.7.0",
       "license": "MIT",
       "dependencies": {
         "accepts": "~1.3.4",
         "base64id": "~2.0.0",
+        "cors": "~2.8.5",
         "debug": "~4.3.2",
-        "engine.io": "~6.2.1",
-        "socket.io-adapter": "~2.4.0",
-        "socket.io-parser": "~4.2.1"
+        "engine.io": "~6.5.0",
+        "socket.io-adapter": "~2.5.2",
+        "socket.io-parser": "~4.2.4"
       },
       "devDependencies": {
         "@types/mocha": "^9.0.0",
@@ -23,14 +24,14 @@
         "nyc": "^15.1.0",
         "prettier": "^2.3.2",
         "rimraf": "^3.0.2",
-        "socket.io-client": "4.5.4",
+        "socket.io-client": "4.7.1",
         "socket.io-client-v2": "npm:socket.io-client@^2.4.0",
         "superagent": "^8.0.0",
         "supertest": "^6.1.6",
         "ts-node": "^10.2.1",
         "tsd": "^0.21.0",
         "typescript": "^4.4.2",
-        "uWebSockets.js": "github:uNetworking/uWebSockets.js#v20.0.0"
+        "uWebSockets.js": "github:uNetworking/uWebSockets.js#v20.30.0"
       },
       "engines": {
         "node": ">=10.0.0"
@@ -1228,9 +1229,9 @@
       }
     },
     "node_modules/cookiejar": {
-      "version": "2.1.3",
-      "resolved": "https://registry.npmjs.org/cookiejar/-/cookiejar-2.1.3.tgz",
-      "integrity": "sha512-JxbCBUdrfr6AQjOXrxoTvAMJO4HBTUIlBzslcJPAz+/KT8yk53fXun51u+RenNYvad/+Vc2DIz5o9UxlCDymFQ==",
+      "version": "2.1.4",
+      "resolved": "https://registry.npmjs.org/cookiejar/-/cookiejar-2.1.4.tgz",
+      "integrity": "sha512-LDx6oHrK+PhzLKJU9j5S7/Y3jM/mUHvD/DeI1WQmJn652iPC5Y4TBzC9l+5OMOXlyTTA+SmVUPm0HQUwpD5Jqw==",
       "dev": true
     },
     "node_modules/cors": {
@@ -1334,9 +1335,9 @@
       }
     },
     "node_modules/dezalgo": {
-      "version": "1.0.3",
-      "resolved": "https://registry.npmjs.org/dezalgo/-/dezalgo-1.0.3.tgz",
-      "integrity": "sha512-K7i4zNfT2kgQz3GylDw40ot9GAE47sFZ9EXHFSPP6zONLgH6kWXE0KWJchkbQJLBkRazq4APwZ4OwiFFlT95OQ==",
+      "version": "1.0.4",
+      "resolved": "https://registry.npmjs.org/dezalgo/-/dezalgo-1.0.4.tgz",
+      "integrity": "sha512-rXSP0bf+5n0Qonsb+SVVfNfIsimO4HEtmnIpPHY8Q1UCzKlQrDMfdobr8nJOOsRgWCyMRqeSBQzmWUMq7zvVig==",
       "dev": true,
       "dependencies": {
         "asap": "^2.0.0",
@@ -1377,9 +1378,9 @@
       "dev": true
     },
     "node_modules/engine.io": {
-      "version": "6.2.1",
-      "resolved": "https://registry.npmjs.org/engine.io/-/engine.io-6.2.1.tgz",
-      "integrity": "sha512-ECceEFcAaNRybd3lsGQKas3ZlMVjN3cyWwMP25D2i0zWfyiytVbTpRPa34qrr+FHddtpBVOmq4H/DCv1O0lZRA==",
+      "version": "6.5.0",
+      "resolved": "https://registry.npmjs.org/engine.io/-/engine.io-6.5.0.tgz",
+      "integrity": "sha512-UlfoK1iD62Hkedw2TmuHdhDsZCGaAyp+LZ/AvnImjYBeWagA3qIEETum90d6shMeFZiDuGT66zVCdx1wKYKGGg==",
       "dependencies": {
         "@types/cookie": "^0.4.1",
         "@types/cors": "^2.8.12",
@@ -1389,30 +1390,30 @@
         "cookie": "~0.4.1",
         "cors": "~2.8.5",
         "debug": "~4.3.1",
-        "engine.io-parser": "~5.0.3",
-        "ws": "~8.2.3"
+        "engine.io-parser": "~5.1.0",
+        "ws": "~8.11.0"
       },
       "engines": {
         "node": ">=10.0.0"
       }
     },
     "node_modules/engine.io-client": {
-      "version": "6.2.3",
-      "resolved": "https://registry.npmjs.org/engine.io-client/-/engine.io-client-6.2.3.tgz",
-      "integrity": "sha512-aXPtgF1JS3RuuKcpSrBtimSjYvrbhKW9froICH4s0F3XQWLxsKNxqzG39nnvQZQnva4CMvUK63T7shevxRyYHw==",
+      "version": "6.5.1",
+      "resolved": "https://registry.npmjs.org/engine.io-client/-/engine.io-client-6.5.1.tgz",
+      "integrity": "sha512-hE5wKXH8Ru4L19MbM1GgYV/2Qo54JSMh1rlJbfpa40bEWkCKNo3ol2eOtGmowcr+ysgbI7+SGL+by42Q3pt/Ng==",
       "dev": true,
       "dependencies": {
         "@socket.io/component-emitter": "~3.1.0",
         "debug": "~4.3.1",
-        "engine.io-parser": "~5.0.3",
-        "ws": "~8.2.3",
+        "engine.io-parser": "~5.1.0",
+        "ws": "~8.11.0",
         "xmlhttprequest-ssl": "~2.0.0"
       }
     },
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-      "resolved": "https://registry.npmjs.org/engine.io-parser/-/engine.io-parser-5.0.4.tgz",
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+      "version": "5.1.0",
+      "resolved": "https://registry.npmjs.org/engine.io-parser/-/engine.io-parser-5.1.0.tgz",
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@@ -1613,32 +1614,20 @@
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-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/formidable/-/formidable-2.0.1.tgz",
-      "integrity": "sha512-rjTMNbp2BpfQShhFbR3Ruk3qk2y9jKpvMW78nJgx8QKtxjDVrwbZG+wvDOmVbifHyOUOQJXxqEy6r0faRrPzTQ==",
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/formidable/-/formidable-2.1.1.tgz",
+      "integrity": "sha512-0EcS9wCFEzLvfiks7omJ+SiYJAiD+TzK4Pcw1UlUoGnhUxDcMKjt0P7x8wEb0u6OHu8Nb98WG3nxtlF5C7bvUQ==",
       "dev": true,
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-        "dezalgo": "1.0.3",
-        "hexoid": "1.0.0",
-        "once": "1.4.0",
-        "qs": "6.9.3"
+        "dezalgo": "^1.0.4",
+        "hexoid": "^1.0.0",
+        "once": "^1.4.0",
+        "qs": "^6.11.0"
       },
       "funding": {
         "url": "https://ko-fi.com/tunnckoCore/commissions"
       }
     },
-    "node_modules/formidable/node_modules/qs": {
-      "version": "6.9.3",
-      "resolved": "https://registry.npmjs.org/qs/-/qs-6.9.3.tgz",
-      "integrity": "sha512-EbZYNarm6138UKKq46tdx08Yo/q9ZhFoAXAI1meAFd2GtbRDhbZY2WQSICskT0c5q99aFzLG1D4nvTk9tqfXIw==",
-      "dev": true,
-      "engines": {
-        "node": ">=0.6"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/ljharb"
-      }
-    },
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       "resolved": "https://registry.npmjs.org/fromentries/-/fromentries-1.3.2.tgz",
@@ -2254,9 +2243,9 @@
       "dev": true
     },
     "node_modules/json5": {
-      "version": "2.2.1",
-      "resolved": "https://registry.npmjs.org/json5/-/json5-2.2.1.tgz",
-      "integrity": "sha512-1hqLFMSrGHRHxav9q9gNjJ5EXznIxGVO09xQRrwplcS8qs28pZ8s8hupZAmqDwZUmVZ2Qb2jnyPOWcDH8m8dlA==",
+      "version": "2.2.3",
+      "resolved": "https://registry.npmjs.org/json5/-/json5-2.2.3.tgz",
+      "integrity": "sha512-XmOWe7eyHYH14cLdVPoyg+GOH3rYX++KpzrylJwSW98t3Nk+U8XOl8FWKOgwtzdb8lXGf6zYwDUzeHMWfxasyg==",
       "dev": true,
       "bin": {
         "json5": "lib/cli.js"
@@ -3467,20 +3456,23 @@
       }
     },
     "node_modules/socket.io-adapter": {
-      "version": "2.4.0",
-      "resolved": "https://registry.npmjs.org/socket.io-adapter/-/socket.io-adapter-2.4.0.tgz",
-      "integrity": "sha512-W4N+o69rkMEGVuk2D/cvca3uYsvGlMwsySWV447y99gUPghxq42BxqLNMndb+a1mm/5/7NeXVQS7RLa2XyXvYg=="
+      "version": "2.5.2",
+      "resolved": "https://registry.npmjs.org/socket.io-adapter/-/socket.io-adapter-2.5.2.tgz",
+      "integrity": "sha512-87C3LO/NOMc+eMcpcxUBebGjkpMDkNBS9tf7KJqcDsmL936EChtVva71Dw2q4tQcuVC+hAUy4an2NO/sYXmwRA==",
+      "dependencies": {
+        "ws": "~8.11.0"
+      }
     },
     "node_modules/socket.io-client": {
-      "version": "4.5.4",
-      "resolved": "https://registry.npmjs.org/socket.io-client/-/socket.io-client-4.5.4.tgz",
-      "integrity": "sha512-ZpKteoA06RzkD32IbqILZ+Cnst4xewU7ZYK12aS1mzHftFFjpoMz69IuhP/nL25pJfao/amoPI527KnuhFm01g==",
+      "version": "4.7.1",
+      "resolved": "https://registry.npmjs.org/socket.io-client/-/socket.io-client-4.7.1.tgz",
+      "integrity": "sha512-Qk3Xj8ekbnzKu3faejo4wk2MzXA029XppiXtTF/PkbTg+fcwaTw1PlDrTrrrU4mKoYC4dvlApOnSeyLCKwek2w==",
       "dev": true,
       "dependencies": {
         "@socket.io/component-emitter": "~3.1.0",
         "debug": "~4.3.2",
-        "engine.io-client": "~6.2.3",
-        "socket.io-parser": "~4.2.1"
+        "engine.io-client": "~6.5.1",
+        "socket.io-parser": "~4.2.4"
       },
       "engines": {
         "node": ">=10.0.0"
@@ -3595,9 +3587,9 @@
       }
     },
     "node_modules/socket.io-parser": {
-      "version": "4.2.1",
-      "resolved": "https://registry.npmjs.org/socket.io-parser/-/socket.io-parser-4.2.1.tgz",
-      "integrity": "sha512-V4GrkLy+HeF1F/en3SpUaM+7XxYXpuMUWLGde1kSSh5nQMN4hLrbPIkD+otwh6q9R6NOQBN4AMaOZ2zVjui82g==",
+      "version": "4.2.4",
+      "resolved": "https://registry.npmjs.org/socket.io-parser/-/socket.io-parser-4.2.4.tgz",
+      "integrity": "sha512-/GbIKmo8ioc+NIWIhwdecY0ge+qVBSMdgxGygevmdHj24bsfgtCmcUUcQ5ZzcylGFHsN3k4HB4Cgkl96KVnuew==",
       "dependencies": {
         "@socket.io/component-emitter": "~3.1.0",
         "debug": "~4.3.1"
@@ -4114,8 +4106,8 @@
       }
     },
     "node_modules/uWebSockets.js": {
-      "version": "20.0.0",
-      "resolved": "git+https://git@github.com/uNetworking/uWebSockets.js.git#4558ee00f9f1f686fffe1accbfc2e85b1af9c50f",
+      "version": "20.30.0",
+      "resolved": "git+https://git@github.com/uNetworking/uWebSockets.js.git#d39d4181daf5b670d44cbc1b18f8c28c85fd4142",
       "dev": true
     },
     "node_modules/v8-compile-cache-lib": {
@@ -4205,9 +4197,9 @@
       }
     },
     "node_modules/ws": {
-      "version": "8.2.3",
-      "resolved": "https://registry.npmjs.org/ws/-/ws-8.2.3.tgz",
-      "integrity": "sha512-wBuoj1BDpC6ZQ1B7DWQBYVLphPWkm8i9Y0/3YdHjHKHiohOJ1ws+3OccDWtH+PoC9DZD5WOTrJvNbWvjS6JWaA==",
+      "version": "8.11.0",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.11.0.tgz",
+      "integrity": "sha512-HPG3wQd9sNQoT9xHyNCXoDUa+Xw/VevmY9FoHyQ+g+rrMn4j6FB4np7Z0OhdTgjx6MgQLK7jwSy1YecU1+4Asg==",
       "engines": {
         "node": ">=10.0.0"
       },
@@ -5280,9 +5272,9 @@
       "integrity": "sha512-aSWTXFzaKWkvHO1Ny/s+ePFpvKsPnjc551iI41v3ny/ow6tBG5Vd+FuqGNhh1LxOmVzOlGUriIlOaokOvhaStA=="
     },
     "cookiejar": {
-      "version": "2.1.3",
-      "resolved": "https://registry.npmjs.org/cookiejar/-/cookiejar-2.1.3.tgz",
-      "integrity": "sha512-JxbCBUdrfr6AQjOXrxoTvAMJO4HBTUIlBzslcJPAz+/KT8yk53fXun51u+RenNYvad/+Vc2DIz5o9UxlCDymFQ==",
+      "version": "2.1.4",
+      "resolved": "https://registry.npmjs.org/cookiejar/-/cookiejar-2.1.4.tgz",
+      "integrity": "sha512-LDx6oHrK+PhzLKJU9j5S7/Y3jM/mUHvD/DeI1WQmJn652iPC5Y4TBzC9l+5OMOXlyTTA+SmVUPm0HQUwpD5Jqw==",
       "dev": true
     },
     "cors": {
@@ -5359,9 +5351,9 @@
       "dev": true
     },
     "dezalgo": {
-      "version": "1.0.3",
-      "resolved": "https://registry.npmjs.org/dezalgo/-/dezalgo-1.0.3.tgz",
-      "integrity": "sha512-K7i4zNfT2kgQz3GylDw40ot9GAE47sFZ9EXHFSPP6zONLgH6kWXE0KWJchkbQJLBkRazq4APwZ4OwiFFlT95OQ==",
+      "version": "1.0.4",
+      "resolved": "https://registry.npmjs.org/dezalgo/-/dezalgo-1.0.4.tgz",
+      "integrity": "sha512-rXSP0bf+5n0Qonsb+SVVfNfIsimO4HEtmnIpPHY8Q1UCzKlQrDMfdobr8nJOOsRgWCyMRqeSBQzmWUMq7zvVig==",
       "dev": true,
       "requires": {
         "asap": "^2.0.0",
@@ -5396,9 +5388,9 @@
       "dev": true
     },
     "engine.io": {
-      "version": "6.2.1",
-      "resolved": "https://registry.npmjs.org/engine.io/-/engine.io-6.2.1.tgz",
-      "integrity": "sha512-ECceEFcAaNRybd3lsGQKas3ZlMVjN3cyWwMP25D2i0zWfyiytVbTpRPa34qrr+FHddtpBVOmq4H/DCv1O0lZRA==",
+      "version": "6.5.0",
+      "resolved": "https://registry.npmjs.org/engine.io/-/engine.io-6.5.0.tgz",
+      "integrity": "sha512-UlfoK1iD62Hkedw2TmuHdhDsZCGaAyp+LZ/AvnImjYBeWagA3qIEETum90d6shMeFZiDuGT66zVCdx1wKYKGGg==",
       "requires": {
         "@types/cookie": "^0.4.1",
         "@types/cors": "^2.8.12",
@@ -5408,27 +5400,27 @@
         "cookie": "~0.4.1",
         "cors": "~2.8.5",
         "debug": "~4.3.1",
-        "engine.io-parser": "~5.0.3",
-        "ws": "~8.2.3"
+        "engine.io-parser": "~5.1.0",
+        "ws": "~8.11.0"
       }
     },
     "engine.io-client": {
-      "version": "6.2.3",
-      "resolved": "https://registry.npmjs.org/engine.io-client/-/engine.io-client-6.2.3.tgz",
-      "integrity": "sha512-aXPtgF1JS3RuuKcpSrBtimSjYvrbhKW9froICH4s0F3XQWLxsKNxqzG39nnvQZQnva4CMvUK63T7shevxRyYHw==",
+      "version": "6.5.1",
+      "resolved": "https://registry.npmjs.org/engine.io-client/-/engine.io-client-6.5.1.tgz",
+      "integrity": "sha512-hE5wKXH8Ru4L19MbM1GgYV/2Qo54JSMh1rlJbfpa40bEWkCKNo3ol2eOtGmowcr+ysgbI7+SGL+by42Q3pt/Ng==",
       "dev": true,
       "requires": {
         "@socket.io/component-emitter": "~3.1.0",
         "debug": "~4.3.1",
-        "engine.io-parser": "~5.0.3",
-        "ws": "~8.2.3",
+        "engine.io-parser": "~5.1.0",
+        "ws": "~8.11.0",
         "xmlhttprequest-ssl": "~2.0.0"
       }
     },
     "engine.io-parser": {
-      "version": "5.0.4",
-      "resolved": "https://registry.npmjs.org/engine.io-parser/-/engine.io-parser-5.0.4.tgz",
-      "integrity": "sha512-+nVFp+5z1E3HcToEnO7ZIj3g+3k9389DvWtvJZz0T6/eOCPIyyxehFcedoYrZQrp0LgQbD9pPXhpMBKMd5QURg=="
+      "version": "5.1.0",
+      "resolved": "https://registry.npmjs.org/engine.io-parser/-/engine.io-parser-5.1.0.tgz",
+      "integrity": "sha512-enySgNiK5tyZFynt3z7iqBR+Bto9EVVVvDFuTT0ioHCGbzirZVGDGiQjZzEp8hWl6hd5FSVytJGuScX1C1C35w=="
     },
     "error-ex": {
       "version": "1.3.2",
@@ -5577,23 +5569,15 @@
       }
     },
     "formidable": {
-      "version": "2.0.1",
-      "resolved": "https://registry.npmjs.org/formidable/-/formidable-2.0.1.tgz",
-      "integrity": "sha512-rjTMNbp2BpfQShhFbR3Ruk3qk2y9jKpvMW78nJgx8QKtxjDVrwbZG+wvDOmVbifHyOUOQJXxqEy6r0faRrPzTQ==",
+      "version": "2.1.1",
+      "resolved": "https://registry.npmjs.org/formidable/-/formidable-2.1.1.tgz",
+      "integrity": "sha512-0EcS9wCFEzLvfiks7omJ+SiYJAiD+TzK4Pcw1UlUoGnhUxDcMKjt0P7x8wEb0u6OHu8Nb98WG3nxtlF5C7bvUQ==",
       "dev": true,
       "requires": {
-        "dezalgo": "1.0.3",
-        "hexoid": "1.0.0",
-        "once": "1.4.0",
-        "qs": "6.9.3"
-      },
-      "dependencies": {
-        "qs": {
-          "version": "6.9.3",
-          "resolved": "https://registry.npmjs.org/qs/-/qs-6.9.3.tgz",
-          "integrity": "sha512-EbZYNarm6138UKKq46tdx08Yo/q9ZhFoAXAI1meAFd2GtbRDhbZY2WQSICskT0c5q99aFzLG1D4nvTk9tqfXIw==",
-          "dev": true
-        }
+        "dezalgo": "^1.0.4",
+        "hexoid": "^1.0.0",
+        "once": "^1.4.0",
+        "qs": "^6.11.0"
       }
     },
     "fromentries": {
@@ -6050,9 +6034,9 @@
       "dev": true
     },
     "json5": {
-      "version": "2.2.1",
-      "resolved": "https://registry.npmjs.org/json5/-/json5-2.2.1.tgz",
-      "integrity": "sha512-1hqLFMSrGHRHxav9q9gNjJ5EXznIxGVO09xQRrwplcS8qs28pZ8s8hupZAmqDwZUmVZ2Qb2jnyPOWcDH8m8dlA==",
+      "version": "2.2.3",
+      "resolved": "https://registry.npmjs.org/json5/-/json5-2.2.3.tgz",
+      "integrity": "sha512-XmOWe7eyHYH14cLdVPoyg+GOH3rYX++KpzrylJwSW98t3Nk+U8XOl8FWKOgwtzdb8lXGf6zYwDUzeHMWfxasyg==",
       "dev": true
     },
     "kind-of": {
@@ -6931,20 +6915,23 @@
       "dev": true
     },
     "socket.io-adapter": {
-      "version": "2.4.0",
-      "resolved": "https://registry.npmjs.org/socket.io-adapter/-/socket.io-adapter-2.4.0.tgz",
-      "integrity": "sha512-W4N+o69rkMEGVuk2D/cvca3uYsvGlMwsySWV447y99gUPghxq42BxqLNMndb+a1mm/5/7NeXVQS7RLa2XyXvYg=="
+      "version": "2.5.2",
+      "resolved": "https://registry.npmjs.org/socket.io-adapter/-/socket.io-adapter-2.5.2.tgz",
+      "integrity": "sha512-87C3LO/NOMc+eMcpcxUBebGjkpMDkNBS9tf7KJqcDsmL936EChtVva71Dw2q4tQcuVC+hAUy4an2NO/sYXmwRA==",
+      "requires": {
+        "ws": "~8.11.0"
+      }
     },
     "socket.io-client": {
-      "version": "4.5.4",
-      "resolved": "https://registry.npmjs.org/socket.io-client/-/socket.io-client-4.5.4.tgz",
-      "integrity": "sha512-ZpKteoA06RzkD32IbqILZ+Cnst4xewU7ZYK12aS1mzHftFFjpoMz69IuhP/nL25pJfao/amoPI527KnuhFm01g==",
+      "version": "4.7.1",
+      "resolved": "https://registry.npmjs.org/socket.io-client/-/socket.io-client-4.7.1.tgz",
+      "integrity": "sha512-Qk3Xj8ekbnzKu3faejo4wk2MzXA029XppiXtTF/PkbTg+fcwaTw1PlDrTrrrU4mKoYC4dvlApOnSeyLCKwek2w==",
       "dev": true,
       "requires": {
         "@socket.io/component-emitter": "~3.1.0",
         "debug": "~4.3.2",
-        "engine.io-client": "~6.2.3",
-        "socket.io-parser": "~4.2.1"
+        "engine.io-client": "~6.5.1",
+        "socket.io-parser": "~4.2.4"
       }
     },
     "socket.io-client-v2": {
@@ -7040,9 +7027,9 @@
       }
     },
     "socket.io-parser": {
-      "version": "4.2.1",
-      "resolved": "https://registry.npmjs.org/socket.io-parser/-/socket.io-parser-4.2.1.tgz",
-      "integrity": "sha512-V4GrkLy+HeF1F/en3SpUaM+7XxYXpuMUWLGde1kSSh5nQMN4hLrbPIkD+otwh6q9R6NOQBN4AMaOZ2zVjui82g==",
+      "version": "4.2.4",
+      "resolved": "https://registry.npmjs.org/socket.io-parser/-/socket.io-parser-4.2.4.tgz",
+      "integrity": "sha512-/GbIKmo8ioc+NIWIhwdecY0ge+qVBSMdgxGygevmdHj24bsfgtCmcUUcQ5ZzcylGFHsN3k4HB4Cgkl96KVnuew==",
       "requires": {
         "@socket.io/component-emitter": "~3.1.0",
         "debug": "~4.3.1"
@@ -7416,9 +7403,9 @@
       "dev": true
     },
     "uWebSockets.js": {
-      "version": "git+https://git@github.com/uNetworking/uWebSockets.js.git#4558ee00f9f1f686fffe1accbfc2e85b1af9c50f",
+      "version": "git+https://git@github.com/uNetworking/uWebSockets.js.git#d39d4181daf5b670d44cbc1b18f8c28c85fd4142",
       "dev": true,
-      "from": "uWebSockets.js@github:uNetworking/uWebSockets.js#v20.0.0"
+      "from": "uWebSockets.js@github:uNetworking/uWebSockets.js#v20.30.0"
     },
     "v8-compile-cache-lib": {
       "version": "3.0.1",
@@ -7492,9 +7479,9 @@
       }
     },
     "ws": {
-      "version": "8.2.3",
-      "resolved": "https://registry.npmjs.org/ws/-/ws-8.2.3.tgz",
-      "integrity": "sha512-wBuoj1BDpC6ZQ1B7DWQBYVLphPWkm8i9Y0/3YdHjHKHiohOJ1ws+3OccDWtH+PoC9DZD5WOTrJvNbWvjS6JWaA==",
+      "version": "8.11.0",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.11.0.tgz",
+      "integrity": "sha512-HPG3wQd9sNQoT9xHyNCXoDUa+Xw/VevmY9FoHyQ+g+rrMn4j6FB4np7Z0OhdTgjx6MgQLK7jwSy1YecU1+4Asg==",
       "requires": {}
     },
     "xmlhttprequest-ssl": {

package.json

@@ -1,6 +1,6 @@
 {
   "name": "socket.io",
-  "version": "4.5.4",
+  "version": "4.7.1",
   "description": "node.js realtime framework server",
   "keywords": [
     "realtime",
@@ -26,9 +26,9 @@
   "type": "commonjs",
   "main": "./dist/index.js",
   "exports": {
+    "types": "./dist/index.d.ts",
     "import": "./wrapper.mjs",
-    "require": "./dist/index.js",
-    "types": "./dist/index.d.ts"
+    "require": "./dist/index.js"
   },
   "types": "./dist/index.d.ts",
   "license": "MIT",
@@ -48,10 +48,11 @@
   "dependencies": {
     "accepts": "~1.3.4",
     "base64id": "~2.0.0",
+    "cors": "~2.8.5",
     "debug": "~4.3.2",
-    "engine.io": "~6.2.1",
-    "socket.io-adapter": "~2.4.0",
-    "socket.io-parser": "~4.2.1"
+    "engine.io": "~6.5.0",
+    "socket.io-adapter": "~2.5.2",
+    "socket.io-parser": "~4.2.4"
   },
   "devDependencies": {
     "@types/mocha": "^9.0.0",
@@ -60,14 +61,14 @@
     "nyc": "^15.1.0",
     "prettier": "^2.3.2",
     "rimraf": "^3.0.2",
-    "socket.io-client": "4.5.4",
+    "socket.io-client": "4.7.1",
     "socket.io-client-v2": "npm:socket.io-client@^2.4.0",
     "superagent": "^8.0.0",
     "supertest": "^6.1.6",
     "ts-node": "^10.2.1",
     "tsd": "^0.21.0",
     "typescript": "^4.4.2",
-    "uWebSockets.js": "github:uNetworking/uWebSockets.js#v20.0.0"
+    "uWebSockets.js": "github:uNetworking/uWebSockets.js#v20.30.0"
   },
   "contributors": [
     {

test/close.ts

@@ -4,46 +4,13 @@ import { join } from "path";
 import { exec } from "child_process";
 import { Server } from "..";
 import expect from "expect.js";
-import { createClient, getPort } from "./support/util";
-import request from "supertest";
-
-// TODO: update superagent as latest release now supports promises
-const eioHandshake = (httpServer): Promise<string> => {
-  return new Promise((resolve) => {
-    request(httpServer)
-      .get("/socket.io/")
-      .query({ transport: "polling", EIO: 4 })
-      .end((err, res) => {
-        const sid = JSON.parse(res.text.substring(1)).sid;
-        resolve(sid);
-      });
-  });
-};
-
-const eioPush = (httpServer, sid: string, body: string): Promise<void> => {
-  return new Promise((resolve) => {
-    request(httpServer)
-      .post("/socket.io/")
-      .send(body)
-      .query({ transport: "polling", EIO: 4, sid })
-      .expect(200)
-      .end(() => {
-        resolve();
-      });
-  });
-};
-
-const eioPoll = (httpServer, sid): Promise<string> => {
-  return new Promise((resolve) => {
-    request(httpServer)
-      .get("/socket.io/")
-      .query({ transport: "polling", EIO: 4, sid })
-      .expect(200)
-      .end((err, res) => {
-        resolve(res.text);
-      });
-  });
-};
+import {
+  createClient,
+  eioHandshake,
+  eioPoll,
+  eioPush,
+  getPort,
+} from "./support/util";
 
 describe("close", () => {
   it("should be able to close sio sending a srv", (done) => {

test/connection-state-recovery.ts

@@ -0,0 +1,247 @@
+import { Server, Socket } from "..";
+import expect from "expect.js";
+import { waitFor, eioHandshake, eioPush, eioPoll } from "./support/util";
+import { createServer, Server as HttpServer } from "http";
+import { Adapter } from "socket.io-adapter";
+
+async function init(httpServer: HttpServer, io: Server) {
+  // Engine.IO handshake
+  const sid = await eioHandshake(httpServer);
+
+  // Socket.IO handshake
+  await eioPush(httpServer, sid, "40");
+  const handshakeBody = await eioPoll(httpServer, sid);
+
+  expect(handshakeBody.startsWith("40")).to.be(true);
+
+  const handshake = JSON.parse(handshakeBody.substring(2));
+
+  expect(handshake.sid).to.not.be(undefined);
+  // in that case, the handshake also contains a private session ID
+  expect(handshake.pid).to.not.be(undefined);
+
+  io.emit("hello");
+
+  const message = await eioPoll(httpServer, sid);
+
+  expect(message.startsWith('42["hello"')).to.be(true);
+
+  const offset = JSON.parse(message.substring(2))[1];
+  // in that case, each packet also includes an offset in the data array
+  expect(offset).to.not.be(undefined);
+
+  await eioPush(httpServer, sid, "1");
+
+  return [handshake.sid, handshake.pid, offset];
+}
+
+describe("connection state recovery", () => {
+  it("should restore session and missed packets", async () => {
+    const httpServer = createServer().listen(0);
+    const io = new Server(httpServer, {
+      connectionStateRecovery: {},
+    });
+
+    let serverSocket;
+
+    io.once("connection", (socket) => {
+      socket.join("room1");
+      serverSocket = socket;
+    });
+
+    const [sid, pid, offset] = await init(httpServer, io);
+
+    io.emit("hello1"); // broadcast
+    io.to("room1").emit("hello2"); // broadcast to room
+    serverSocket.emit("hello3"); // direct message
+
+    const newSid = await eioHandshake(httpServer);
+    await eioPush(
+      httpServer,
+      newSid,
+      `40{"pid":"${pid}","offset":"${offset}"}`
+    );
+
+    const payload = await eioPoll(httpServer, newSid);
+    const packets = payload.split("\x1e");
+
+    expect(packets.length).to.eql(4);
+
+    // note: EVENT packets are received before the CONNECT packet, which is a bit weird
+    // see also: https://github.com/socketio/socket.io-deno/commit/518f534e1c205b746b1cb21fe76b187dabc96f34
+    expect(packets[0].startsWith('42["hello1"')).to.be(true);
+    expect(packets[1].startsWith('42["hello2"')).to.be(true);
+    expect(packets[2].startsWith('42["hello3"')).to.be(true);
+    expect(packets[3]).to.eql(`40{"sid":"${sid}","pid":"${pid}"}`);
+
+    io.close();
+  });
+
+  it("should restore rooms and data attributes", async () => {
+    const httpServer = createServer().listen(0);
+    const io = new Server(httpServer, {
+      connectionStateRecovery: {},
+    });
+
+    io.once("connection", (socket) => {
+      expect(socket.recovered).to.eql(false);
+
+      socket.join("room1");
+      socket.join("room2");
+      socket.data.foo = "bar";
+    });
+
+    const [sid, pid, offset] = await init(httpServer, io);
+
+    const newSid = await eioHandshake(httpServer);
+
+    const [socket] = await Promise.all([
+      waitFor<Socket>(io, "connection"),
+      eioPush(httpServer, newSid, `40{"pid":"${pid}","offset":"${offset}"}`),
+    ]);
+
+    expect(socket.id).to.eql(sid);
+    expect(socket.recovered).to.eql(true);
+
+    expect(socket.rooms.has(socket.id)).to.eql(true);
+    expect(socket.rooms.has("room1")).to.eql(true);
+    expect(socket.rooms.has("room2")).to.eql(true);
+
+    expect(socket.data.foo).to.eql("bar");
+
+    await eioPoll(httpServer, newSid); // drain buffer
+    io.close();
+  });
+
+  it("should not run middlewares upon recovery by default", async () => {
+    const httpServer = createServer().listen(0);
+    const io = new Server(httpServer, {
+      connectionStateRecovery: {},
+    });
+
+    const [_, pid, offset] = await init(httpServer, io);
+
+    io.use((socket, next) => {
+      socket.data.middlewareWasCalled = true;
+
+      next();
+    });
+
+    const newSid = await eioHandshake(httpServer);
+
+    const [socket] = await Promise.all([
+      waitFor<Socket>(io, "connection"),
+      eioPush(httpServer, newSid, `40{"pid":"${pid}","offset":"${offset}"}`),
+    ]);
+
+    expect(socket.recovered).to.be(true);
+    expect(socket.data.middlewareWasCalled).to.be(undefined);
+
+    await eioPoll(httpServer, newSid); // drain buffer
+    io.close();
+  });
+
+  it("should run middlewares even upon recovery", async () => {
+    const httpServer = createServer().listen(0);
+    const io = new Server(httpServer, {
+      connectionStateRecovery: {
+        skipMiddlewares: false,
+      },
+    });
+
+    const [_, pid, offset] = await init(httpServer, io);
+
+    io.use((socket, next) => {
+      socket.data.middlewareWasCalled = true;
+
+      next();
+    });
+
+    const newSid = await eioHandshake(httpServer);
+
+    const [socket] = await Promise.all([
+      waitFor<Socket>(io, "connection"),
+      eioPush(httpServer, newSid, `40{"pid":"${pid}","offset":"${offset}"}`),
+    ]);
+
+    expect(socket.recovered).to.be(true);
+    expect(socket.data.middlewareWasCalled).to.be(true);
+
+    await eioPoll(httpServer, newSid); // drain buffer
+    io.close();
+  });
+
+  it("should fail to restore an unknown session", async () => {
+    const httpServer = createServer().listen(0);
+    const io = new Server(httpServer, {
+      connectionStateRecovery: {},
+    });
+
+    // Engine.IO handshake
+    const sid = await eioHandshake(httpServer);
+
+    // Socket.IO handshake
+    await eioPush(httpServer, sid, '40{"pid":"foo","offset":"bar"}');
+
+    const handshakeBody = await eioPoll(httpServer, sid);
+
+    expect(handshakeBody.startsWith("40")).to.be(true);
+
+    const handshake = JSON.parse(handshakeBody.substring(2));
+
+    expect(handshake.sid).to.not.eql("foo");
+    expect(handshake.pid).to.not.eql("bar");
+
+    io.close();
+  });
+
+  it("should be disabled by default", async () => {
+    const httpServer = createServer().listen(0);
+    const io = new Server(httpServer);
+
+    // Engine.IO handshake
+    const sid = await eioHandshake(httpServer);
+
+    // Socket.IO handshake
+    await eioPush(httpServer, sid, "40");
+
+    const handshakeBody = await eioPoll(httpServer, sid);
+
+    expect(handshakeBody.startsWith("40")).to.be(true);
+
+    const handshake = JSON.parse(handshakeBody.substring(2));
+
+    expect(handshake.sid).to.not.be(undefined);
+    expect(handshake.pid).to.be(undefined);
+
+    io.close();
+  });
+
+  it("should not call adapter#persistSession or adapter#restoreSession if disabled", async () => {
+    const httpServer = createServer().listen(0);
+
+    class DummyAdapter extends Adapter {
+      override persistSession(session) {
+        expect.fail();
+      }
+
+      override restoreSession(pid, offset) {
+        expect.fail();
+        return Promise.reject("should not happen");
+      }
+    }
+
+    const io = new Server(httpServer, {
+      adapter: DummyAdapter,
+    });
+
+    // Engine.IO handshake
+    const sid = await eioHandshake(httpServer);
+
+    await eioPush(httpServer, sid, '40{"pid":"foo","offset":"bar"}');
+    await eioPoll(httpServer, sid);
+    await eioPush(httpServer, sid, "1");
+
+    io.close();
+  });
+});

test/index.ts

@@ -20,4 +20,5 @@ describe("socket.io", () => {
   require("./socket-timeout");
   require("./uws");
   require("./utility-methods");
+  require("./connection-state-recovery");
 });

test/messaging-many.ts

@@ -471,6 +471,74 @@ describe("messaging many", () => {
     });
   });
 
+  it("should broadcast and expect multiple acknowledgements (promise)", (done) => {
+    const io = new Server(0);
+    const socket1 = createClient(io, "/", { multiplex: false });
+    const socket2 = createClient(io, "/", { multiplex: false });
+    const socket3 = createClient(io, "/", { multiplex: false });
+
+    socket1.on("some event", (cb) => {
+      cb(1);
+    });
+
+    socket2.on("some event", (cb) => {
+      cb(2);
+    });
+
+    socket3.on("some event", (cb) => {
+      cb(3);
+    });
+
+    Promise.all([
+      waitFor(socket1, "connect"),
+      waitFor(socket2, "connect"),
+      waitFor(socket3, "connect"),
+    ]).then(async () => {
+      const responses = await io.timeout(2000).emitWithAck("some event");
+      expect(responses).to.contain(1, 2, 3);
+
+      success(done, io, socket1, socket2, socket3);
+    });
+  });
+
+  it("should fail when a client does not acknowledge the event in the given delay (promise)", (done) => {
+    const io = new Server(0);
+    const socket1 = createClient(io, "/", { multiplex: false });
+    const socket2 = createClient(io, "/", { multiplex: false });
+    const socket3 = createClient(io, "/", { multiplex: false });
+
+    socket1.on("some event", (cb) => {
+      cb(1);
+    });
+
+    socket2.on("some event", (cb) => {
+      cb(2);
+    });
+
+    socket3.on("some event", () => {
+      // timeout
+    });
+
+    Promise.all([
+      waitFor(socket1, "connect"),
+      waitFor(socket2, "connect"),
+      waitFor(socket3, "connect"),
+    ]).then(async () => {
+      try {
+        await io.timeout(200).emitWithAck("some event");
+        expect.fail();
+      } catch (err) {
+        expect(err).to.be.an(Error);
+        // @ts-ignore
+        expect(err.responses).to.have.length(2);
+        // @ts-ignore
+        expect(err.responses).to.contain(1, 2);
+
+        success(done, io, socket1, socket2, socket3);
+      }
+    });
+  });
+
   it("should broadcast and return if the packet is sent to 0 client", (done) => {
     const io = new Server(0);
     const socket1 = createClient(io, "/", { multiplex: false });
@@ -498,4 +566,22 @@ describe("messaging many", () => {
         success(done, io, socket1, socket2, socket3);
       });
   });
+
+  it("should precompute the WebSocket frame when broadcasting", (done) => {
+    const io = new Server(0);
+    const socket = createClient(io, "/chat", {
+      transports: ["websocket"],
+    });
+    const partialDone = createPartialDone(2, successFn(done, io, socket));
+
+    io.of("/chat").on("connection", (s) => {
+      s.conn.once("packetCreate", (packet) => {
+        expect(packet.options.wsPreEncodedFrame).to.be.an(Array);
+        partialDone();
+      });
+      io.of("/chat").compress(false).emit("woot", "hi");
+    });
+
+    socket.on("woot", partialDone);
+  });
 });

test/namespaces.ts

@@ -473,6 +473,24 @@ describe("namespaces", () => {
     io.of("/nsp");
   });
 
+  it("should not clean up a non-dynamic namespace", (done) => {
+    const io = new Server(0, { cleanupEmptyChildNamespaces: true });
+    const c1 = createClient(io, "/chat");
+
+    c1.on("connect", () => {
+      c1.disconnect();
+
+      // Give it some time to disconnect the client
+      setTimeout(() => {
+        expect(io._nsps.has("/chat")).to.be(true);
+        expect(io._nsps.get("/chat")!.sockets.size).to.be(0);
+        success(done, io);
+      }, 100);
+    });
+
+    io.of("/chat");
+  });
+
   describe("dynamic namespaces", () => {
     it("should allow connections to dynamic namespaces with a regex", (done) => {
       const io = new Server(0);
@@ -571,5 +589,79 @@ describe("namespaces", () => {
       one.on("message", handler);
       two.on("message", handler);
     });
+
+    it("should clean up namespace when cleanupEmptyChildNamespaces is on and there are no more sockets in a namespace", (done) => {
+      const io = new Server(0, { cleanupEmptyChildNamespaces: true });
+      const c1 = createClient(io, "/dynamic-101");
+
+      c1.on("connect", () => {
+        c1.disconnect();
+
+        // Give it some time to disconnect and clean up the namespace
+        setTimeout(() => {
+          expect(io._nsps.has("/dynamic-101")).to.be(false);
+          success(done, io);
+        }, 100);
+      });
+
+      io.of(/^\/dynamic-\d+$/);
+    });
+
+    it("should allow a client to connect to a cleaned up namespace", (done) => {
+      const io = new Server(0, { cleanupEmptyChildNamespaces: true });
+      const c1 = createClient(io, "/dynamic-101");
+
+      c1.on("connect", () => {
+        c1.disconnect();
+
+        // Give it some time to disconnect and clean up the namespace
+        setTimeout(() => {
+          expect(io._nsps.has("/dynamic-101")).to.be(false);
+
+          const c2 = createClient(io, "/dynamic-101");
+
+          c2.on("connect", () => {
+            success(done, io, c2);
+          });
+
+          c2.on("connect_error", () => {
+            done(
+              new Error("Client got error when connecting to dynamic namespace")
+            );
+          });
+        }, 100);
+      });
+
+      io.of(/^\/dynamic-\d+$/);
+    });
+
+    it("should not clean up namespace when cleanupEmptyChildNamespaces is off and there are no more sockets in a namespace", (done) => {
+      const io = new Server(0);
+      const c1 = createClient(io, "/dynamic-101");
+
+      c1.on("connect", () => {
+        c1.disconnect();
+
+        // Give it some time to disconnect and clean up the namespace
+        setTimeout(() => {
+          expect(io._nsps.has("/dynamic-101")).to.be(true);
+          expect(io._nsps.get("/dynamic-101")!.sockets.size).to.be(0);
+          success(done, io);
+        }, 100);
+      });
+
+      io.of(/^\/dynamic-\d+$/);
+    });
+
+    it("should attach a child namespace to its parent upon manual creation", () => {
+      const io = new Server(0);
+      const parentNamespace = io.of(/^\/dynamic-\d+$/);
+      const childNamespace = io.of("/dynamic-101");
+
+      // @ts-ignore
+      expect(parentNamespace.children.has(childNamespace)).to.be(true);
+
+      io.close();
+    });
   });
 });

test/server-attachment.ts

@@ -16,7 +16,9 @@ describe("server attachment", () => {
         .buffer(true)
         .end((err, res) => {
           if (err) return done(err);
-          expect(res.headers["content-type"]).to.be("application/javascript");
+          expect(res.headers["content-type"]).to.be(
+            "application/javascript; charset=utf-8"
+          );
           expect(res.headers.etag).to.be('"' + clientVersion + '"');
           expect(res.headers["x-sourcemap"]).to.be(undefined);
           expect(res.text).to.match(/engine\.io/);
@@ -33,7 +35,9 @@ describe("server attachment", () => {
         .buffer(true)
         .end((err, res) => {
           if (err) return done(err);
-          expect(res.headers["content-type"]).to.be("application/json");
+          expect(res.headers["content-type"]).to.be(
+            "application/json; charset=utf-8"
+          );
           expect(res.headers.etag).to.be('"' + clientVersion + '"');
           expect(res.text).to.match(/engine\.io/);
           expect(res.status).to.be(200);
@@ -66,6 +70,27 @@ describe("server attachment", () => {
         });
     });
 
+    it("should serve client with necessary CORS headers", (done) => {
+      const srv = createServer();
+      new Server(srv, {
+        cors: {
+          origin: "https://good-origin.com",
+        },
+      });
+      request(srv)
+        .get("/socket.io/socket.io.js")
+        .set("origin", "https://good-origin.com")
+        .buffer(true)
+        .end((err, res) => {
+          if (err) return done(err);
+          expect(res.headers["access-control-allow-origin"]).to.be(
+            "https://good-origin.com"
+          );
+          expect(res.status).to.be(200);
+          done();
+        });
+    });
+
     it(
       "should serve bundle with msgpack parser",
       testSource("socket.io.msgpack.min.js")

test/socket-timeout.ts

@@ -54,4 +54,34 @@ describe("timeout", () => {
       });
     });
   });
+
+  it("should timeout if the client does not acknowledge the event (promise)", (done) => {
+    const io = new Server(0);
+    const client = createClient(io, "/");
+
+    io.on("connection", async (socket) => {
+      try {
+        await socket.timeout(50).emitWithAck("unknown");
+        expect.fail();
+      } catch (err) {
+        expect(err).to.be.an(Error);
+        success(done, io, client);
+      }
+    });
+  });
+
+  it("should not timeout if the client does acknowledge the event (promise)", (done) => {
+    const io = new Server(0);
+    const client = createClient(io, "/");
+
+    client.on("echo", (arg, cb) => {
+      cb(arg);
+    });
+
+    io.on("connection", async (socket) => {
+      const value = await socket.timeout(50).emitWithAck("echo", 42);
+      expect(value).to.be(42);
+      success(done, io, client);
+    });
+  });
 });

test/socket.io.test-d.ts

@@ -92,6 +92,28 @@ describe("server", () => {
         });
       });
     });
+
+    describe("emitWithAck", () => {
+      it("accepts any parameters", () => {
+        const srv = createServer();
+        const sio = new Server(srv);
+        srv.listen(async () => {
+          const value = await sio
+            .timeout(1000)
+            .emitWithAck("ackFromServerSingleArg", true, "123");
+          expectType<any>(value);
+
+          sio.on("connection", async (s) => {
+            const value1 = await s.emitWithAck(
+              "ackFromServerSingleArg",
+              true,
+              "123"
+            );
+            expectType<any>(value1);
+          });
+        });
+      });
+    });
   });
 
   describe("single event map", () => {
@@ -167,10 +189,32 @@ describe("server", () => {
   describe("listen and emit event maps", () => {
     interface ClientToServerEvents {
       helloFromClient: (message: string) => void;
+      ackFromClient: (
+        a: string,
+        b: number,
+        ack: (c: string, d: number) => void
+      ) => void;
     }
 
     interface ServerToClientEvents {
       helloFromServer: (message: string, x: number) => void;
+      ackFromServer: (
+        a: boolean,
+        b: string,
+        ack: (c: boolean, d: string) => void
+      ) => void;
+
+      ackFromServerSingleArg: (
+        a: boolean,
+        b: string,
+        ack: (c: string) => void
+      ) => void;
+
+      multipleAckFromServer: (
+        a: boolean,
+        b: string,
+        ack: (c: string) => void
+      ) => void;
     }
 
     describe("on", () => {
@@ -185,6 +229,13 @@ describe("server", () => {
               expectType<string>(message);
               done();
             });
+
+            s.on("ackFromClient", (a, b, cb) => {
+              expectType<string>(a);
+              expectType<number>(b);
+              expectType<(c: string, d: number) => void>(cb);
+              cb("123", 456);
+            });
           });
         });
       });
@@ -213,8 +264,41 @@ describe("server", () => {
           sio.to("room").emit("helloFromServer", "hi", 1);
           sio.timeout(1000).emit("helloFromServer", "hi", 1);
 
+          sio
+            .timeout(1000)
+            .emit("multipleAckFromServer", true, "123", (err, c) => {
+              expectType<Error>(err);
+              expectType<string[]>(c);
+            });
+
           sio.on("connection", (s) => {
             s.emit("helloFromServer", "hi", 10);
+
+            s.emit("ackFromServer", true, "123", (c, d) => {
+              expectType<boolean>(c);
+              expectType<string>(d);
+            });
+
+            s.timeout(1000).emit("ackFromServer", true, "123", (err, c, d) => {
+              expectType<Error>(err);
+              expectType<boolean>(c);
+              expectType<string>(d);
+            });
+
+            s.timeout(1000)
+              .to("room")
+              .emit("multipleAckFromServer", true, "123", (err, c) => {
+                expectType<Error>(err);
+                expectType<string[]>(c);
+              });
+
+            s.to("room")
+              .timeout(1000)
+              .emit("multipleAckFromServer", true, "123", (err, c) => {
+                expectType<Error>(err);
+                expectType<string[]>(c);
+              });
+
             done();
           });
         });
@@ -240,6 +324,42 @@ describe("server", () => {
         });
       });
     });
+
+    describe("emitWithAck", () => {
+      it("accepts arguments of the correct types", (done) => {
+        const srv = createServer();
+        const sio = new Server<ClientToServerEvents, ServerToClientEvents>(srv);
+        srv.listen(async () => {
+          const value = await sio
+            .timeout(1000)
+            .emitWithAck("multipleAckFromServer", true, "123");
+          expectType<string[]>(value);
+
+          sio.on("connection", async (s) => {
+            const value1 = await s
+              .timeout(1000)
+              .to("room")
+              .emitWithAck("multipleAckFromServer", true, "123");
+            expectType<string[]>(value1);
+
+            const value2 = await s
+              .to("room")
+              .timeout(1000)
+              .emitWithAck("multipleAckFromServer", true, "123");
+            expectType<string[]>(value2);
+
+            const value3 = await s.emitWithAck(
+              "ackFromServerSingleArg",
+              true,
+              "123"
+            );
+            expectType<string>(value3);
+
+            done();
+          });
+        });
+      });
+    });
   });
 
   describe("listen and emit event maps for the serverSideEmit method", () => {
@@ -253,6 +373,7 @@ describe("server", () => {
 
     interface InterServerEvents {
       helloFromServerToServer: (message: string, x: number) => void;
+      ackFromServerToServer: (foo: string, cb: (bar: number) => void) => void;
     }
 
     describe("on", () => {
@@ -267,7 +388,7 @@ describe("server", () => {
         expectType<
           Server<ClientToServerEvents, ServerToClientEvents, InterServerEvents>
         >(sio);
-        srv.listen(() => {
+        srv.listen(async () => {
           sio.serverSideEmit("helloFromServerToServer", "hello", 10);
           sio
             .of("/test")
@@ -281,6 +402,22 @@ describe("server", () => {
             expectType<string>(message);
             expectType<number>(x);
           });
+
+          sio.serverSideEmit("ackFromServerToServer", "foo", (err, bar) => {
+            expectType<Error>(err);
+            expectType<number[]>(bar);
+          });
+
+          const value = await sio.serverSideEmitWithAck(
+            "ackFromServerToServer",
+            "foo"
+          );
+          expectType<number[]>(value);
+
+          sio.on("ackFromServerToServer", (foo, cb) => {
+            expectType<string>(foo);
+            expectType<(bar: number) => void>(cb);
+          });
         });
       });
     });

test/socket.ts

@@ -1,6 +1,12 @@
 import fs = require("fs");
 import { join } from "path";
-import { createClient, getPort, success, successFn } from "./support/util";
+import {
+  createClient,
+  createPartialDone,
+  getPort,
+  success,
+  successFn,
+} from "./support/util";
 import { Server } from "..";
 import expect from "expect.js";
 
@@ -599,6 +605,24 @@ describe("socket", () => {
     });
   });
 
+  it("should emit an event and wait for the acknowledgement", (done) => {
+    const io = new Server(0);
+    const socket = createClient(io);
+
+    io.on("connection", async (s) => {
+      socket.on("hi", (a, b, fn) => {
+        expect(a).to.be(1);
+        expect(b).to.be(2);
+        fn(3);
+      });
+
+      const val = await s.emitWithAck("hi", 1, 2);
+      expect(val).to.be(3);
+
+      success(done, io, socket);
+    });
+  });
+
   it("should have access to the client", (done) => {
     const io = new Server(0);
     const socket = createClient(io);
@@ -731,7 +755,7 @@ describe("socket", () => {
     });
   });
 
-  it("should enable compresion by default", (done) => {
+  it("should enable compression by default", (done) => {
     const io = new Server(0);
     const socket = createClient(io, "/chat");
 
@@ -740,11 +764,11 @@ describe("socket", () => {
         expect(packet.options.compress).to.be(true);
         success(done, io, socket);
       });
-      io.of("/chat").emit("woot", "hi");
+      s.emit("woot", "hi");
     });
   });
 
-  it("should disable compresion", (done) => {
+  it("should disable compression", (done) => {
     const io = new Server(0);
     const socket = createClient(io, "/chat");
 
@@ -753,7 +777,7 @@ describe("socket", () => {
         expect(packet.options.compress).to.be(false);
         success(done, io, socket);
       });
-      io.of("/chat").compress(false).emit("woot", "hi");
+      s.compress(false).emit("woot", "hi");
     });
   });
 
@@ -828,10 +852,6 @@ describe("socket", () => {
   it("should not crash when messing with Object prototype (and other globals)", (done) => {
     // @ts-ignore
     Object.prototype.foo = "bar";
-    // @ts-ignore
-    global.File = "";
-    // @ts-ignore
-    global.Blob = [];
     const io = new Server(0);
     const socket = createClient(io);
 
@@ -995,6 +1015,22 @@ describe("socket", () => {
       });
     });
 
+    it("should call listener when broadcasting binary data", (done) => {
+      const io = new Server(0);
+      const clientSocket = createClient(io, "/", { multiplex: false });
+
+      io.on("connection", (socket) => {
+        socket.onAnyOutgoing((event, arg1) => {
+          expect(event).to.be("my-event");
+          expect(arg1).to.be.an(Uint8Array);
+
+          success(done, io, clientSocket);
+        });
+
+        io.emit("my-event", Uint8Array.of(1, 2, 3));
+      });
+    });
+
     it("should prepend listener", (done) => {
       const io = new Server(0);
       const clientSocket = createClient(io, "/", { multiplex: false });
@@ -1039,5 +1075,30 @@ describe("socket", () => {
         socket.emit("my-event", "123");
       });
     });
+
+    it("should disconnect all namespaces when calling disconnect(true)", (done) => {
+      const io = new Server(0);
+      io.of("/foo");
+      io.of("/bar");
+
+      const socket1 = createClient(io, "/", {
+        transports: ["websocket"],
+      });
+      const socket2 = createClient(io, "/foo");
+      const socket3 = createClient(io, "/bar");
+
+      io.of("/bar").on("connection", (socket) => {
+        socket.disconnect(true);
+      });
+
+      const partialDone = createPartialDone(
+        3,
+        successFn(done, io, socket1, socket2, socket3)
+      );
+
+      socket1.on("disconnect", partialDone);
+      socket2.on("disconnect", partialDone);
+      socket3.on("disconnect", partialDone);
+    });
   });
 });

test/support/util.ts

@@ -5,6 +5,7 @@ import {
   Socket as ClientSocket,
   SocketOptions,
 } from "socket.io-client";
+import request from "supertest";
 
 const expect = require("expect.js");
 const i = expect.stringify;
@@ -73,8 +74,46 @@ export function createPartialDone(count: number, done: (err?: Error) => void) {
   };
 }
 
-export function waitFor(emitter, event) {
-  return new Promise((resolve) => {
+export function waitFor<T = unknown>(emitter, event) {
+  return new Promise<T>((resolve) => {
     emitter.once(event, resolve);
   });
 }
+
+// TODO: update superagent as latest release now supports promises
+export function eioHandshake(httpServer): Promise<string> {
+  return new Promise((resolve) => {
+    request(httpServer)
+      .get("/socket.io/")
+      .query({ transport: "polling", EIO: 4 })
+      .end((err, res) => {
+        const sid = JSON.parse(res.text.substring(1)).sid;
+        resolve(sid);
+      });
+  });
+}
+
+export function eioPush(httpServer, sid: string, body: string): Promise<void> {
+  return new Promise((resolve) => {
+    request(httpServer)
+      .post("/socket.io/")
+      .send(body)
+      .query({ transport: "polling", EIO: 4, sid })
+      .expect(200)
+      .end(() => {
+        resolve();
+      });
+  });
+}
+
+export function eioPoll(httpServer, sid): Promise<string> {
+  return new Promise((resolve) => {
+    request(httpServer)
+      .get("/socket.io/")
+      .query({ transport: "polling", EIO: 4, sid })
+      .expect(200)
+      .end((err, res) => {
+        resolve(res.text);
+      });
+  });
+}

test/uws.ts

@@ -53,7 +53,7 @@ describe("socket.io with uWebSocket.js-based engine", () => {
 
     const partialDone = createPartialDone(done, 4);
     client.on("connect", partialDone);
-    clientWSOnly.on("connect", partialDone);
+    clientWSOnly.once("connect", partialDone);
     clientPollingOnly.on("connect", partialDone);
     clientCustomNamespace.on("connect", partialDone);
   });
@@ -200,7 +200,9 @@ describe("socket.io with uWebSocket.js-based engine", () => {
       .buffer(true)
       .end((err, res) => {
         if (err) return done(err);
-        expect(res.headers["content-type"]).to.be("application/javascript");
+        expect(res.headers["content-type"]).to.be(
+          "application/javascript; charset=utf-8"
+        );
         expect(res.headers.etag).to.be('"' + clientVersion + '"');
         expect(res.headers["x-sourcemap"]).to.be(undefined);
         expect(res.text).to.match(/engine\.io/);