Retry outbound read syncs for up to 24 hours

ts/test-both/util/exponentialBackoff_test.ts

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+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { assert } from 'chai';
+import * as moment from 'moment';
+
+import {
+  exponentialBackoffSleepTime,
+  exponentialBackoffMaxAttempts,
+} from '../../util/exponentialBackoff';
+
+describe('exponential backoff utilities', () => {
+  describe('exponentialBackoffSleepTime', () => {
+    it('returns slowly growing values', () => {
+      assert.strictEqual(exponentialBackoffSleepTime(1), 0);
+      assert.strictEqual(exponentialBackoffSleepTime(2), 190);
+      assert.strictEqual(exponentialBackoffSleepTime(3), 361);
+      assert.approximately(exponentialBackoffSleepTime(4), 686, 1);
+      assert.approximately(exponentialBackoffSleepTime(5), 1303, 1);
+    });
+
+    it('plateaus at a maximum after 15 attempts', () => {
+      const maximum = moment.duration(15, 'minutes').asMilliseconds();
+      for (let attempt = 16; attempt < 100; attempt += 1) {
+        assert.strictEqual(exponentialBackoffSleepTime(attempt), maximum);
+      }
+    });
+  });
+
+  describe('exponentialBackoffMaxAttempts', () => {
+    it('returns 2 attempts for a short period of time', () => {
+      assert.strictEqual(exponentialBackoffMaxAttempts(1), 2);
+      assert.strictEqual(exponentialBackoffMaxAttempts(99), 2);
+    });
+
+    it('returns 6 attempts for a 5 seconds', () => {
+      assert.strictEqual(exponentialBackoffMaxAttempts(5000), 6);
+    });
+
+    it('returns 110 attempts for 1 day', () => {
+      // This is a test case that is lifted from iOS's codebase.
+      const oneDay = moment.duration(24, 'hours').asMilliseconds();
+      assert.strictEqual(exponentialBackoffMaxAttempts(oneDay), 110);
+    });
+  });
+});