Rename files

ts/util/BackOff.std.ts

@@ -0,0 +1,83 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+const SECOND = 1000;
+
+export const FIBONACCI: ReadonlyArray<number> = [1, 2, 3, 5, 8, 13, 21, 34, 55];
+
+export const FIBONACCI_TIMEOUTS: ReadonlyArray<number> = [
+  1 * SECOND,
+  2 * SECOND,
+  3 * SECOND,
+  5 * SECOND,
+  8 * SECOND,
+  13 * SECOND,
+  21 * SECOND,
+  34 * SECOND,
+  55 * SECOND,
+];
+
+export const EXTENDED_FIBONACCI_TIMEOUTS: ReadonlyArray<number> = [
+  ...FIBONACCI_TIMEOUTS,
+  89 * SECOND,
+  144 * SECOND,
+  233 * SECOND,
+  377 * SECOND,
+  610 * SECOND,
+  987 * SECOND,
+  1597 * SECOND, // ~26 minutes
+];
+
+export type BackOffOptionsType = Readonly<{
+  jitter?: number;
+
+  // Testing
+  random?: () => number;
+}>;
+
+const DEFAULT_RANDOM = () => Math.random();
+
+export class BackOff {
+  #count = 0;
+
+  constructor(
+    private timeouts: ReadonlyArray<number>,
+    private readonly options: BackOffOptionsType = {}
+  ) {}
+
+  public get(): number {
+    let result = this.timeouts[this.#count];
+    const { jitter = 0, random = DEFAULT_RANDOM } = this.options;
+
+    // Do not apply jitter larger than the timeout value. It is supposed to be
+    // activated for longer timeouts.
+    if (jitter < result) {
+      result += random() * jitter;
+    }
+    return result;
+  }
+
+  public getAndIncrement(): number {
+    const result = this.get();
+    if (!this.isFull()) {
+      this.#count += 1;
+    }
+
+    return result;
+  }
+
+  public reset(newTimeouts?: ReadonlyArray<number>): void {
+    if (newTimeouts !== undefined) {
+      this.timeouts = newTimeouts;
+    }
+    this.#count = 0;
+  }
+
+  public isFull(): boolean {
+    return this.#count === this.timeouts.length - 1;
+  }
+
+  public getIndex(): number {
+    return this.#count;
+  }
+}