refactor: import single-file 3rd party modules

This commit allows to:

- provide an ESM version of those modules ([1])
- reduce the attack surface in case of supply chain attacks
- reduce the size of the bundle with tree-shaking

As a downside, we won't receive security updates for those modules
anymore.

[1]: #1536

Related: socketio/engine.io-client@df32277

.prettierignore

@@ -0,0 +1 @@
+lib/contrib/*

lib/contrib/backo2.ts

@@ -0,0 +1,78 @@
+/**
+ * Initialize backoff timer with `opts`.
+ *
+ * - `min` initial timeout in milliseconds [100]
+ * - `max` max timeout [10000]
+ * - `jitter` [0]
+ * - `factor` [2]
+ *
+ * @param {Object} opts
+ * @api public
+ */
+
+export function Backoff(opts) {
+  opts = opts || {};
+  this.ms = opts.min || 100;
+  this.max = opts.max || 10000;
+  this.factor = opts.factor || 2;
+  this.jitter = opts.jitter > 0 && opts.jitter <= 1 ? opts.jitter : 0;
+  this.attempts = 0;
+}
+
+/**
+ * Return the backoff duration.
+ *
+ * @return {Number}
+ * @api public
+ */
+
+Backoff.prototype.duration = function(){
+  var ms = this.ms * Math.pow(this.factor, this.attempts++);
+  if (this.jitter) {
+    var rand =  Math.random();
+    var deviation = Math.floor(rand * this.jitter * ms);
+    ms = (Math.floor(rand * 10) & 1) == 0  ? ms - deviation : ms + deviation;
+  }
+  return Math.min(ms, this.max) | 0;
+};
+
+/**
+ * Reset the number of attempts.
+ *
+ * @api public
+ */
+
+Backoff.prototype.reset = function(){
+  this.attempts = 0;
+};
+
+/**
+ * Set the minimum duration
+ *
+ * @api public
+ */
+
+Backoff.prototype.setMin = function(min){
+  this.ms = min;
+};
+
+/**
+ * Set the maximum duration
+ *
+ * @api public
+ */
+
+Backoff.prototype.setMax = function(max){
+  this.max = max;
+};
+
+/**
+ * Set the jitter
+ *
+ * @api public
+ */
+
+Backoff.prototype.setJitter = function(jitter){
+  this.jitter = jitter;
+};
+

lib/manager.ts

@@ -7,7 +7,7 @@ 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";
-import Backoff from "backo2";
+import { Backoff } from "./contrib/backo2.js";
 import {
   DefaultEventsMap,
   EventsMap,
@@ -125,6 +125,7 @@ export class Manager<
 
   private nsps: Record<string, Socket> = {};
   private subs: Array<ReturnType<typeof on>> = [];
+  // @ts-ignore
   private backoff: Backoff;
   private setTimeoutFn: typeof setTimeout;
   private _reconnection: boolean;

package.json

@@ -33,7 +33,6 @@
   "types": "./build/esm/index.d.ts",
   "dependencies": {
     "@socket.io/component-emitter": "~3.1.0",
-    "backo2": "~1.0.2",
     "debug": "~4.3.2",
     "engine.io-client": "~6.2.1",
     "socket.io-parser": "~4.2.0"