feat: Add Fastly Edge SDK (#723)

**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)
- [x] I have validated my changes against all supported platform
versions

**Describe the solution you've provided**

This PR adds a new Fastly Compute SDK. This SDK must be used in
conjunction with our upcoming Fastly KV integration. The SDK is
essentially the same as the other edge integrations (Akamai, Cloudflare,
Vercel), with the following changes:
- `node:events` is not compatible with Fastly's runtime. As a result, we
cannot use `@launchdarkly/sdk-server-edge`. Instead, I copied the
contents of `@launchdarkly/sdk-server-edge` into the fastly package and
replaced `createCallbacks.ts` with an empty implementation.
- Enabled `sendEvents` by default.
- Added the `eventsUri` option to allow for sending events to a custom
endpoint.
- Added a new optional `eventsBackendName` option. A [Fastly
Backend](https://developer.fastly.com/reference/api/services/backend/)
configured to `https://events.launchdarkly.com` is required for sending
events. The default value is `launchdarkly`. This option is passed to
[Fastly's customized
fetch()](https://js-compute-reference-docs.edgecompute.app/docs/globals/fetch#explicit-backends).


I added an example app that demonstrates using the SDK to evaluate a
feature flag edge to control the static image served.

I published an beta version to npm
[here](https://www.npmjs.com/package/@launchdarkly/fastly-server-sdk?activeTab=readme).

Author: ldhenry

.github/workflows/fastly.yml

@@ -0,0 +1,24 @@
+name: sdk/fastly
+
+on:
+  push:
+    branches: [main, 'feat/**']
+    paths-ignore:
+      - '**.md' #Do not need to run CI for markdown changes.
+  pull_request:
+    branches: [main, 'feat/**']
+    paths-ignore:
+      - '**.md'
+
+jobs:
+  build-test-fastly:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+      - id: shared
+        name: Shared CI Steps
+        uses: ./actions/ci
+        with:
+          workspace_name: '@launchdarkly/fastly-server-sdk'
+          workspace_path: packages/sdk/fastly

.github/workflows/manual-publish-docs.yml

@@ -12,6 +12,7 @@ on:
           - packages/shared/sdk-server-edge
           - packages/shared/akamai-edgeworker-sdk
           - packages/sdk/cloudflare
+          - packages/sdk/fastly
           - packages/sdk/server-node
           - packages/sdk/vercel
           - packages/sdk/akamai-base

.github/workflows/manual-publish.yml

@@ -22,6 +22,7 @@ on:
           - packages/shared/sdk-server-edge
           - packages/shared/akamai-edgeworker-sdk
           - packages/sdk/cloudflare
+          - packages/sdk/fastly
           - packages/sdk/react-native
           - packages/sdk/server-node
           - packages/sdk/react-universal

.github/workflows/release-please.yml

@@ -14,6 +14,7 @@ jobs:
       package-sdk-server-edge-released: ${{ steps.release.outputs['packages/shared/sdk-server-edge--release_created'] }}
       package-akamai-edgeworker-sdk-released: ${{ steps.release.outputs['packages/shared/akamai-edgeworker-sdk--release_created'] }}
       package-cloudflare-released: ${{ steps.release.outputs['packages/sdk/cloudflare--release_created'] }}
+      package-fastly-released: ${{ steps.release.outputs['packages/sdk/fastly--release_created'] }}
       package-react-native-released: ${{ steps.release.outputs['packages/sdk/react-native--release_created'] }}
       package-server-node-released: ${{ steps.release.outputs['packages/sdk/server-node--release_created'] }}
       package-vercel-released: ${{ steps.release.outputs['packages/sdk/vercel--release_created'] }}
@@ -153,6 +154,26 @@ jobs:
           workspace_path: packages/sdk/cloudflare
           aws_assume_role: ${{ vars.AWS_ROLE_ARN }}
 
+  release-fastly:
+    runs-on: ubuntu-latest
+    needs: ['release-please', 'release-sdk-server']
+    permissions:
+      id-token: write
+      contents: write
+    if: ${{ always() && !failure() && !cancelled() && needs.release-please.outputs.package-fastly-released == 'true'}}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20.x
+          registry-url: 'https://registry.npmjs.org'
+      - id: release-fastly
+        name: Full release of packages/sdk/fastly
+        uses: ./actions/full-release
+        with:
+          workspace_path: packages/sdk/fastly
+          aws_assume_role: ${{ vars.AWS_ROLE_ARN }}
+
   release-react-native:
     runs-on: ubuntu-latest
     needs: ['release-please', 'release-sdk-client']

.release-please-manifest.json

@@ -3,6 +3,7 @@
   "packages/shared/sdk-server": "2.11.1",
   "packages/sdk/server-node": "9.7.4",
   "packages/sdk/cloudflare": "2.6.5",
+  "packages/sdk/fastly": "0.0.1",
   "packages/shared/sdk-server-edge": "2.5.4",
   "packages/sdk/vercel": "1.3.23",
   "packages/sdk/akamai-base": "3.0.0",

.sdk_metadata.json

@@ -28,6 +28,15 @@
         "tag-prefix": "cloudflare-server-sdk-"
       }
     },
+    "fastly": {
+      "name": "Fastly SDK",
+      "type": "edge",
+      "path": "packages/sdk/fastly",
+      "languages": ["JavaScript", "TypeScript"],
+      "releases": {
+        "tag-prefix": "fastly-server-sdk-"
+      }
+    },
     "react-native": {
       "name": "React Native SDK",
       "type": "client-side",

package.json

@@ -9,6 +9,8 @@
     "packages/sdk/server-node",
     "packages/sdk/cloudflare",
     "packages/sdk/cloudflare/example",
+    "packages/sdk/fastly",
+    "packages/sdk/fastly/example",
     "packages/sdk/react-native",
     "packages/sdk/react-native/example",
     "packages/sdk/react-universal",

packages/sdk/fastly/README.md

@@ -0,0 +1,61 @@
+# LaunchDarkly SDK for Fastly
+
+The LaunchDarkly SDK for Fastly is designed for use in [Fastly Compute Platform](https://www.fastly.com/documentation/guides/compute/). It follows the server-side LaunchDarkly model for multi-user contexts. It is not intended for use in desktop and embedded systems applications.
+
+## Install
+
+```shell
+# npm
+npm i @launchdarkly/fastly-server-sdk
+
+# yarn
+yarn add @launchdarkly/fastly-server-sdk
+```
+
+## Usage notes
+
+- The SDK must be initialized and used when processing requests, not during build-time initialization.
+- The SDK caches all KV data during initialization to reduce the number of backend requests needed to fetch KV data. This means changes to feature flags or segments will not be picked up during the lifecycle of a single request instance.
+- Events should flushed using the [`waitUntil()` method](https://js-compute-reference-docs.edgecompute.app/docs/globals/FetchEvent/prototype/waitUntil).
+
+## Quickstart
+
+See the full [example app](https://github.com/launchdarkly/js-core/tree/main/packages/sdk/fastly/example).
+
+## Developing this SDK
+
+```shell
+# at js-core repo root
+yarn && yarn build && cd packages/sdk/fastly
+
+# run tests
+yarn test
+```
+
+## Verifying SDK build provenance with the SLSA framework
+
+LaunchDarkly uses the [SLSA framework](https://slsa.dev/spec/v1.0/about) (Supply-chain Levels for Software Artifacts) to help developers make their supply chain more secure by ensuring the authenticity and build integrity of our published SDK packages. To learn more, see the [provenance guide](PROVENANCE.md).
+
+## About LaunchDarkly
+
+- LaunchDarkly is a continuous delivery platform that provides feature flags as a service and allows developers to iterate quickly and safely. We allow you to easily flag your features and manage them from the LaunchDarkly dashboard. With LaunchDarkly, you can:
+  - Roll out a new feature to a subset of your users (like a group of users who opt-in to a beta tester group), gathering feedback and bug reports from real-world use cases.
+  - Gradually roll out a feature to an increasing percentage of users, and track the effect that the feature has on key metrics (for instance, how likely is a user to complete a purchase if they have feature A versus feature B?).
+  - Turn off a feature that you realize is causing performance problems in production, without needing to re-deploy, or even restart the application with a changed configuration file.
+  - Grant access to certain features based on user attributes, like payment plan (eg: users on the 'gold' plan get access to more features than users in the 'silver' plan).
+  - Disable parts of your application to facilitate maintenance, without taking everything offline.
+- LaunchDarkly provides feature flag SDKs for a wide variety of languages and technologies. Read [our documentation](https://docs.launchdarkly.com/sdk) for a complete list.
+- Explore LaunchDarkly
+  - [launchdarkly.com](https://www.launchdarkly.com/ 'LaunchDarkly Main Website') for more information
+  - [docs.launchdarkly.com](https://docs.launchdarkly.com/ 'LaunchDarkly Documentation') for our documentation and SDK reference guides
+  - [apidocs.launchdarkly.com](https://apidocs.launchdarkly.com/ 'LaunchDarkly API Documentation') for our API documentation
+  - [blog.launchdarkly.com](https://blog.launchdarkly.com/ 'LaunchDarkly Blog Documentation') for the latest product updates
+
+[sdk-fastly-ci-badge]: https://github.com/launchdarkly/js-core/actions/workflows/fastly.yml/badge.svg
+[sdk-fastly-ci]: https://github.com/launchdarkly/js-core/actions/workflows/fastly.yml
+[sdk-fastly-npm-badge]: https://img.shields.io/npm/v/@launchdarkly/fastly-server-sdk.svg?style=flat-square
+[sdk-fastly-npm-link]: https://www.npmjs.com/package/@launchdarkly/fastly-server-sdk
+[sdk-fastly-ghp-badge]: https://img.shields.io/static/v1?label=GitHub+Pages&message=API+reference&color=00add8
+[sdk-fastly-ghp-link]: https://launchdarkly.github.io/js-core/packages/sdk/fastly/docs/
+[sdk-fastly-dm-badge]: https://img.shields.io/npm/dm/@launchdarkly/fastly-server-sdk.svg?style=flat-square
+[sdk-fastly-dt-badge]: https://img.shields.io/npm/dt/@launchdarkly/fastly-server-sdk.svg?style=flat-square

packages/sdk/fastly/__mocks__/fastly:kv-store.ts

@@ -0,0 +1,8 @@
+export const KVStore = jest.fn().mockImplementation(() => ({
+  get: jest.fn(),
+  put: jest.fn(),
+  delete: jest.fn(),
+  getMulti: jest.fn(),
+  putMulti: jest.fn(),
+  deleteMulti: jest.fn(),
+}));

packages/sdk/fastly/__tests__/api/EdgeFeatureStore.test.ts

@@ -0,0 +1,130 @@
+import { AsyncStoreFacade, LDFeatureStore } from '@launchdarkly/js-server-sdk-common';
+
+import { EdgeFeatureStore } from '../../src/api/EdgeFeatureStore';
+import mockEdgeProvider from '../utils/mockEdgeProvider';
+import * as testData from './testData.json';
+
+describe('EdgeFeatureStore', () => {
+  const clientSideId = 'client-side-id';
+  const kvKey = `LD-Env-${clientSideId}`;
+  const mockLogger = {
+    error: jest.fn(),
+    warn: jest.fn(),
+    info: jest.fn(),
+    debug: jest.fn(),
+  };
+  const mockGet = mockEdgeProvider.get as jest.Mock;
+  let featureStore: LDFeatureStore;
+  let asyncFeatureStore: AsyncStoreFacade;
+
+  beforeEach(() => {
+    mockGet.mockImplementation(() => Promise.resolve(JSON.stringify(testData)));
+    featureStore = new EdgeFeatureStore(
+      mockEdgeProvider,
+      clientSideId,
+      'MockEdgeProvider',
+      mockLogger,
+    );
+    asyncFeatureStore = new AsyncStoreFacade(featureStore);
+  });
+
+  afterEach(() => {
+    jest.resetAllMocks();
+  });
+
+  describe('get', () => {
+    it('can retrieve valid flag', async () => {
+      const flag = await asyncFeatureStore.get({ namespace: 'features' }, 'testFlag1');
+
+      expect(mockGet).toHaveBeenCalledWith(kvKey);
+      expect(flag).toMatchObject(testData.flags.testFlag1);
+    });
+
+    it('returns undefined for invalid flag key', async () => {
+      const flag = await asyncFeatureStore.get({ namespace: 'features' }, 'invalid');
+
+      expect(flag).toBeUndefined();
+    });
+
+    it('can retrieve valid segment', async () => {
+      const segment = await asyncFeatureStore.get({ namespace: 'segments' }, 'testSegment1');
+
+      expect(mockGet).toHaveBeenCalledWith(kvKey);
+      expect(segment).toMatchObject(testData.segments.testSegment1);
+    });
+
+    it('returns undefined for invalid segment key', async () => {
+      const segment = await asyncFeatureStore.get({ namespace: 'segments' }, 'invalid');
+
+      expect(segment).toBeUndefined();
+    });
+
+    it('returns null for invalid kv key', async () => {
+      mockGet.mockImplementation(() => Promise.resolve(null));
+      const flag = await asyncFeatureStore.get({ namespace: 'features' }, 'testFlag1');
+
+      expect(flag).toBeNull();
+    });
+  });
+
+  describe('all', () => {
+    it('can retrieve all flags', async () => {
+      const flags = await asyncFeatureStore.all({ namespace: 'features' });
+
+      expect(mockGet).toHaveBeenCalledWith(kvKey);
+      expect(flags).toMatchObject(testData.flags);
+    });
+
+    it('can retrieve all segments', async () => {
+      const segment = await asyncFeatureStore.all({ namespace: 'segments' });
+
+      expect(mockGet).toHaveBeenCalledWith(kvKey);
+      expect(segment).toMatchObject(testData.segments);
+    });
+
+    it('returns empty object for invalid DataKind', async () => {
+      const flag = await asyncFeatureStore.all({ namespace: 'InvalidDataKind' });
+
+      expect(flag).toEqual({});
+    });
+
+    it('returns empty object for invalid kv key', async () => {
+      mockGet.mockImplementation(() => Promise.resolve(null));
+      const segment = await asyncFeatureStore.all({ namespace: 'segments' });
+
+      expect(segment).toEqual({});
+    });
+  });
+
+  describe('initialized', () => {
+    it('returns true when initialized', async () => {
+      const isInitialized = await asyncFeatureStore.initialized();
+
+      expect(mockGet).toHaveBeenCalledWith(kvKey);
+      expect(isInitialized).toBeTruthy();
+    });
+
+    it('returns false when not initialized', async () => {
+      mockGet.mockImplementation(() => Promise.resolve(null));
+      const isInitialized = await asyncFeatureStore.initialized();
+
+      expect(mockGet).toHaveBeenCalledWith(kvKey);
+      expect(isInitialized).toBeFalsy();
+    });
+  });
+
+  describe('init & getDescription', () => {
+    it('can initialize', (done) => {
+      const cb = jest.fn(() => {
+        done();
+      });
+      featureStore.init(testData, cb);
+    });
+
+    it('can retrieve description', async () => {
+      const description = featureStore.getDescription?.();
+
+      expect(description).toEqual('MockEdgeProvider');
+    });
+  });
+});