chore: adds CompositeDataSource for FDv2 support (#787)

**Requirements**

- [x] I have added test coverage for new or changed functionality

- [x] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [ ] I have validated my changes against all supported platform
versions
Will be done on target temp branch eventually.

**Related issues**

SDK-857

Author: tanderson-ld

package.json

@@ -43,7 +43,7 @@
     "test": "echo Please run tests for individual packages.",
     "coverage": "npm run test -- --coverage",
     "contract-test-service": "npm --prefix contract-tests install && npm --prefix contract-tests start",
-    "contract-test-harness": "curl -s https://raw.githubusercontent.com/launchdarkly/sdk-test-harness/master/downloader/run.sh \\ | VERSION=v2 PARAMS=\"-url http://localhost:8000 -debug -stop-service-at-end $TEST_HARNESS_PARAMS\" sh",
+    "contract-test-harness": "curl -s https://raw.githubusercontent.com/launchdarkly/sdk-test-harness/master/downloader/run.sh \\ | VERSION=v2 PARAMS=\"-url http://localhost:8000 -debug --skip-from=./contract-tests/testharness-suppressions.txt -stop-service-at-end $TEST_HARNESS_PARAMS\" sh",
     "contract-tests": "npm run contract-test-service & npm run contract-test-harness",
     "prettier": "npx prettier --write \"**/*.{js,ts,tsx,json,yaml,yml,md}\" --log-level warn",
     "check": "yarn && yarn prettier && yarn lint && tsc && yarn build"

packages/sdk/browser/src/platform/DefaultBrowserEventSource.ts

@@ -1,13 +1,12 @@
 import {
+  DefaultBackoff,
   EventListener,
   EventName,
   EventSourceInitDict,
   HttpErrorResponse,
   EventSource as LDEventSource,
 } from '@launchdarkly/js-client-sdk-common';
 
-import Backoff from './Backoff';
-
 /**
  * Implementation Notes:
  *
@@ -22,7 +21,7 @@ import Backoff from './Backoff';
  */
 export default class DefaultBrowserEventSource implements LDEventSource {
   private _es?: EventSource;
-  private _backoff: Backoff;
+  private _backoff: DefaultBackoff;
   private _errorFilter: (err: HttpErrorResponse) => boolean;
 
   // The type of the handle can be platform specific and we treat is opaquely.
@@ -34,7 +33,10 @@ export default class DefaultBrowserEventSource implements LDEventSource {
     private readonly _url: string,
     options: EventSourceInitDict,
   ) {
-    this._backoff = new Backoff(options.initialRetryDelayMillis, options.retryResetIntervalMillis);
+    this._backoff = new DefaultBackoff(
+      options.initialRetryDelayMillis,
+      options.retryResetIntervalMillis,
+    );
     this._errorFilter = options.errorFilter;
     this._openConnection();
   }

packages/sdk/browser/__tests__/platform/Backoff.test.ts renamed to packages/shared/common/__tests__/datasource/Backoff.test.ts

@@ -1,29 +1,29 @@
-import Backoff from '../../src/platform/Backoff';
+import { DefaultBackoff } from '../../src/datasource/Backoff';
 
 const noJitter = (): number => 0;
 const maxJitter = (): number => 1;
 const defaultResetInterval = 60 * 1000;
 
 it.each([1, 1000, 5000])('has the correct starting delay', (initialDelay) => {
-  const backoff = new Backoff(initialDelay, defaultResetInterval, noJitter);
+  const backoff = new DefaultBackoff(initialDelay, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(initialDelay);
 });
 
 it.each([1, 1000, 5000])('doubles delay on consecutive failures', (initialDelay) => {
-  const backoff = new Backoff(initialDelay, defaultResetInterval, noJitter);
+  const backoff = new DefaultBackoff(initialDelay, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(initialDelay);
   expect(backoff.fail()).toEqual(initialDelay * 2);
   expect(backoff.fail()).toEqual(initialDelay * 4);
 });
 
 it('stops increasing delay when the max backoff is encountered', () => {
-  const backoff = new Backoff(5000, defaultResetInterval, noJitter);
+  const backoff = new DefaultBackoff(5000, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(5000);
   expect(backoff.fail()).toEqual(10000);
   expect(backoff.fail()).toEqual(20000);
   expect(backoff.fail()).toEqual(30000);
 
-  const backoff2 = new Backoff(1000, defaultResetInterval, noJitter);
+  const backoff2 = new DefaultBackoff(1000, defaultResetInterval, noJitter);
   expect(backoff2.fail()).toEqual(1000);
   expect(backoff2.fail()).toEqual(2000);
   expect(backoff2.fail()).toEqual(4000);
@@ -33,12 +33,12 @@ it('stops increasing delay when the max backoff is encountered', () => {
 });
 
 it('handles an initial retry delay longer than the maximum retry delay', () => {
-  const backoff = new Backoff(40000, defaultResetInterval, noJitter);
+  const backoff = new DefaultBackoff(40000, defaultResetInterval, noJitter);
   expect(backoff.fail()).toEqual(30000);
 });
 
 it('jitters the backoff value', () => {
-  const backoff = new Backoff(1000, defaultResetInterval, maxJitter);
+  const backoff = new DefaultBackoff(1000, defaultResetInterval, maxJitter);
   expect(backoff.fail()).toEqual(500);
   expect(backoff.fail()).toEqual(1000);
   expect(backoff.fail()).toEqual(2000);
@@ -51,7 +51,7 @@ it.each([10 * 1000, 60 * 1000])(
   'resets the delay when the last successful connection was connected greater than the retry reset interval',
   (retryResetInterval) => {
     let time = 1000;
-    const backoff = new Backoff(1000, retryResetInterval, noJitter);
+    const backoff = new DefaultBackoff(1000, retryResetInterval, noJitter);
     expect(backoff.fail(time)).toEqual(1000);
     time += 1;
     backoff.success(time);
@@ -69,7 +69,7 @@ it.each([10 * 1000, 60 * 1000])(
 it.each([10 * 1000, 60 * 1000])(
   'does not reset the delay when the connection did not persist longer than the retry reset interval',
   (retryResetInterval) => {
-    const backoff = new Backoff(1000, retryResetInterval, noJitter);
+    const backoff = new DefaultBackoff(1000, retryResetInterval, noJitter);
 
     let time = 1000;
     expect(backoff.fail(time)).toEqual(1000);