feat: add details to the disconnect event

The "disconnect" event will now include additional details to help
debugging if anything has gone wrong.

Example when a payload is over the maxHttpBufferSize value in HTTP
long-polling mode:

```js
socket.on("disconnect", (reason, details) => {
  console.log(reason); // "transport error"

  // in that case, details is an error object
  console.log(details.message); "xhr post error"
  console.log(details.description); // 413 (the HTTP status of the response)

  // details.context refers to the XMLHttpRequest object
  console.log(details.context.status); // 413
  console.log(details.context.responseText); // ""
});
```

Related: socketio/engine.io-client@b9252e2

Author: darrachequesne

lib/manager.ts

@@ -3,7 +3,7 @@ import {
   SocketOptions as EngineOptions,
   installTimerFunctions,
 } from "engine.io-client";
-import { Socket, SocketOptions } from "./socket.js";
+import { Socket, SocketOptions, DisconnectDescription } from "./socket.js";
 import * as parser from "socket.io-parser";
 import { Decoder, Encoder, Packet } from "socket.io-parser";
 import { on } from "./on.js";
@@ -90,7 +90,7 @@ interface ManagerReservedEvents {
   error: (err: Error) => void;
   ping: () => void;
   packet: (packet: Packet) => void;
-  close: (reason: string) => void;
+  close: (reason: string, description?: DisconnectDescription) => void;
   reconnect_failed: () => void;
   reconnect_attempt: (attempt: number) => void;
   reconnect_error: (err: Error) => void;
@@ -538,13 +538,13 @@ export class Manager<
    *
    * @private
    */
-  private onclose(reason: string): void {
+  private onclose(reason: string, description?: DisconnectDescription): void {
     debug("closed due to %s", reason);
 
     this.cleanup();
     this.backoff.reset();
     this._readyState = "closed";
-    this.emitReserved("close", reason);
+    this.emitReserved("close", reason, description);
 
     if (this._reconnection && !this.skipReconnect) {
       this.reconnect();

lib/socket.ts

@@ -39,10 +39,20 @@ interface Flags {
   timeout?: number;
 }
 
+export type DisconnectDescription =
+  | Error
+  | {
+      description: string;
+      context?: CloseEvent | XMLHttpRequest;
+    };
+
 interface SocketReservedEvents {
   connect: () => void;
   connect_error: (err: Error) => void;
-  disconnect: (reason: Socket.DisconnectReason) => void;
+  disconnect: (
+    reason: Socket.DisconnectReason,
+    description?: DisconnectDescription
+  ) => void;
 }
 
 export class Socket<
@@ -266,14 +276,18 @@ export class Socket<
    * Called upon engine `close`.
    *
    * @param reason
+   * @param description
    * @private
    */
-  private onclose(reason: Socket.DisconnectReason): void {
+  private onclose(
+    reason: Socket.DisconnectReason,
+    description?: DisconnectDescription
+  ): void {
     debug("close (%s)", reason);
     this.connected = false;
     this.disconnected = true;
     delete this.id;
-    this.emitReserved("disconnect", reason);
+    this.emitReserved("disconnect", reason, description);
   }
 
   /**

lib/url.ts

@@ -1,4 +1,4 @@
-import parseuri from "parseuri";
+import { parse } from "engine.io-client";
 import debugModule from "debug"; // debug()
 
 const debug = debugModule("socket.io-client:url"); // debug()
@@ -68,7 +68,7 @@ export function url(
 
     // parse
     debug("parse %s", uri);
-    obj = parseuri(uri) as ParsedUrl;
+    obj = parse(uri) as ParsedUrl;
   }
 
   // make sure we treat `localhost:80` and `localhost` equally

package-lock.json

@@ -32,12 +32,11 @@
   },
   "types": "./build/esm/index.d.ts",
   "dependencies": {
-    "@socket.io/component-emitter": "~3.0.0",
+    "@socket.io/component-emitter": "~3.1.0",
     "backo2": "~1.0.2",
     "debug": "~4.3.2",
-    "engine.io-client": "~6.1.1",
-    "parseuri": "0.0.6",
-    "socket.io-parser": "~4.1.1"
+    "engine.io-client": "~6.2.1",
+    "socket.io-parser": "~4.2.0"
   },
   "devDependencies": {
     "@babel/core": "^7.15.0",