feat: add a reusable retry state controller for RETRY-conformant backoff

.github/workflows/common.yml

@@ -35,4 +35,4 @@ jobs:
           target_file: 'packages/shared/common/dist/esm/index.mjs'
           package_name: '@launchdarkly/js-sdk-common'
           pr_number: ${{ github.event.number }}
-          size_limit: 29000
+          size_limit: 29500

packages/shared/common/__tests__/datasource/retry/ResetPolicy.test.ts

@@ -0,0 +1,91 @@
+import {
+  createAfterConsecutiveSuccesses,
+  createAfterHealthyFor,
+} from '../../../src/datasource/retry/ResetPolicy';
+
+const MINUTE = 60 * 1000;
+
+let now = 0;
+const clock = (): number => now;
+
+beforeEach(() => {
+  now = 0;
+});
+
+it('is not satisfied before any healthy report', () => {
+  const policy = createAfterHealthyFor(MINUTE, clock);
+  now = 10 * MINUTE;
+  expect(policy.isSatisfied()).toEqual(false);
+});
+
+it('is satisfied once the healthy stretch reaches the threshold, and not a moment sooner', () => {
+  const policy = createAfterHealthyFor(MINUTE, clock);
+  policy.noteHealthy();
+  now = MINUTE - 1;
+  expect(policy.isSatisfied()).toEqual(false);
+  now = MINUTE;
+  expect(policy.isSatisfied()).toEqual(true);
+});
+
+it('does not move the start of the stretch on repeated healthy reports', () => {
+  const policy = createAfterHealthyFor(MINUTE, clock);
+  policy.noteHealthy();
+  for (let i = 1; i < 60; i += 1) {
+    now = i * 1000;
+    policy.noteHealthy();
+    expect(policy.isSatisfied()).toEqual(false);
+  }
+  now = MINUTE;
+  expect(policy.isSatisfied()).toEqual(true);
+});
+
+it('clears the healthy stretch on a failure', () => {
+  const policy = createAfterHealthyFor(MINUTE, clock);
+  policy.noteHealthy();
+  now = 30 * 1000;
+  policy.noteFailure();
+  now = 15 * MINUTE;
+  expect(policy.isSatisfied()).toEqual(false);
+});
+
+it('is satisfied by consecutive successes and not by fewer', () => {
+  const policy = createAfterConsecutiveSuccesses(2);
+  expect(policy.isSatisfied()).toEqual(false);
+  policy.noteHealthy();
+  expect(policy.isSatisfied()).toEqual(false);
+  policy.noteHealthy();
+  expect(policy.isSatisfied()).toEqual(true);
+});
+
+it('starts the success count over on a failure', () => {
+  const policy = createAfterConsecutiveSuccesses(2);
+  policy.noteHealthy();
+  policy.noteFailure();
+  policy.noteHealthy();
+  expect(policy.isSatisfied()).toEqual(false);
+  policy.noteHealthy();
+  expect(policy.isSatisfied()).toEqual(true);
+});
+
+it('measures the healthy stretch with the default clock', () => {
+  const policy = createAfterHealthyFor(60 * MINUTE);
+  expect(policy.isSatisfied()).toEqual(false);
+  policy.noteHealthy();
+  expect(policy.isSatisfied()).toEqual(false);
+});
+
+it('falls back to the wall clock when no monotonic source exists', () => {
+  const savedPerformance = (globalThis as any).performance;
+  const nowSpy = jest.spyOn(Date, 'now').mockReturnValue(0);
+  delete (globalThis as any).performance;
+  try {
+    const policy = createAfterHealthyFor(MINUTE);
+    policy.noteHealthy();
+    expect(policy.isSatisfied()).toEqual(false);
+    nowSpy.mockReturnValue(MINUTE);
+    expect(policy.isSatisfied()).toEqual(true);
+  } finally {
+    nowSpy.mockRestore();
+    (globalThis as any).performance = savedPerformance;
+  }
+});