feat: frontend API POST endpoint (#9291)

https://linear.app/unleash/issue/2-3260/implement-post-request-support-in-unleashs-frontend-api

Implements the POST endpoint in Unleash's frontend API.

src/lib/features/frontend-api/create-context.ts

@@ -2,7 +2,7 @@
 import crypto from 'crypto';
 import type { Context } from 'unleash-client';
 
-export function createContext(value: any): Context {
+export function createContext(contextData: any): Context {
     const {
         appName,
         environment,
@@ -11,7 +11,7 @@ export function createContext(value: any): Context {
         remoteAddress,
         properties,
         ...rest
-    } = value;
+    } = contextData;
 
     // move non root context fields to properties
     const context: Context = {
@@ -31,8 +31,9 @@ export function createContext(value: any): Context {
     return cleanContext;
 }
 
-export const enrichContextWithIp = (query: any, ip: string): Context => {
+export const enrichContextWithIp = (contextData: any, ip: string): Context => {
-    query.remoteAddress = query.remoteAddress || ip;
+    contextData.remoteAddress = contextData.remoteAddress || ip;
-    query.sessionId = query.sessionId || crypto.randomBytes(18).toString('hex');
+    contextData.sessionId =
-    return createContext(query);
+        contextData.sessionId || crypto.randomBytes(18).toString('hex');
+    return createContext(contextData);
 };

src/lib/features/frontend-api/frontend-api-controller.ts

@@ -83,8 +83,25 @@ export default class FrontendAPIController extends Controller {
         this.route({
             method: 'post',
             path: '',
-            handler: FrontendAPIController.endpointNotImplemented,
+            handler: this.getFrontendApiFeatures,
             permission: NONE,
+            middleware: [
+                this.services.openApiService.validPath({
+                    tags: ['Frontend API'],
+                    operationId: 'getFrontendApiFeaturesWithPost',
+                    requestBody: createRequestSchema(
+                        'frontendApiFeaturesPostSchema',
+                    ),
+                    responses: {
+                        200: createResponseSchema('frontendApiFeaturesSchema'),
+                        ...getStandardResponses(401, 404),
+                    },
+                    summary:
+                        'Retrieve enabled feature flags for the provided context, using POST.',
+                    description:
+                        'This endpoint returns the list of feature flags that the frontend API evaluates to enabled for the given context, using POST. Context values are provided as a `context` property in the request body. If the Frontend API is disabled 404 is returned.',
+                }),
+            ],
         });
 
         this.route({
@@ -233,7 +250,11 @@ export default class FrontendAPIController extends Controller {
     }
 
     private static createContext(req: ApiUserRequest): Context {
-        const { query } = req;
+        const { query, body } = req;
-        return enrichContextWithIp(query, req.ip);
+
+        const bodyContext = body.context ?? {};
+        const contextData = req.method === 'POST' ? bodyContext : query;
+
+        return enrichContextWithIp(contextData, req.ip);
     }
 }

src/lib/features/frontend-api/frontend-api.e2e.test.ts

@@ -278,12 +278,6 @@ test('should allow requests with a frontend token', async () => {
 
 test('should return 405 from unimplemented endpoints', async () => {
     const frontendToken = await createApiToken(ApiTokenType.FRONTEND);
-    await app.request
-        .post('/api/frontend')
-        .send({})
-        .set('Authorization', frontendToken.secret)
-        .expect('Content-Type', /json/)
-        .expect(405);
     await app.request
         .get('/api/frontend/client/features')
         .set('Authorization', frontendToken.secret)
@@ -1234,3 +1228,103 @@ test('should resolve variable rollout percentage consistently', async () => {
         }
     }
 });
+
+test('should return enabled feature flags using POST', async () => {
+    const frontendToken = await createApiToken(ApiTokenType.FRONTEND);
+    await createFeatureToggle({
+        name: 'enabledFeature1',
+        enabled: true,
+        strategies: [{ name: 'default', constraints: [], parameters: {} }],
+    });
+    await createFeatureToggle({
+        name: 'enabledFeature2',
+        enabled: true,
+        strategies: [{ name: 'default', constraints: [], parameters: {} }],
+    });
+    await createFeatureToggle({
+        name: 'disabledFeature',
+        enabled: false,
+        strategies: [{ name: 'default', constraints: [], parameters: {} }],
+    });
+    await frontendApiService.refreshData();
+    await app.request
+        .post('/api/frontend')
+        .set('Authorization', frontendToken.secret)
+        .set('Content-Type', 'application/json')
+        .send()
+        .expect('Content-Type', /json/)
+        .expect(200)
+        .expect((res) => {
+            expect(res.body).toEqual({
+                toggles: [
+                    {
+                        name: 'enabledFeature1',
+                        enabled: true,
+                        impressionData: false,
+                        variant: {
+                            enabled: false,
+                            name: 'disabled',
+                            feature_enabled: true,
+                            featureEnabled: true,
+                        },
+                    },
+                    {
+                        name: 'enabledFeature2',
+                        enabled: true,
+                        impressionData: false,
+                        variant: {
+                            enabled: false,
+                            name: 'disabled',
+                            feature_enabled: true,
+                            featureEnabled: true,
+                        },
+                    },
+                ],
+            });
+        });
+});
+
+test('should return enabled feature flags based on context using POST', async () => {
+    const frontendToken = await createApiToken(ApiTokenType.FRONTEND);
+    const featureName = 'featureWithEnvironmentConstraint';
+    await createFeatureToggle({
+        name: featureName,
+        enabled: true,
+        strategies: [
+            {
+                name: 'default',
+                constraints: [
+                    {
+                        contextName: 'userId',
+                        operator: 'IN',
+                        values: ['1337'],
+                    },
+                ],
+                parameters: {},
+            },
+        ],
+    });
+
+    await frontendApiService.refreshData();
+    await app.request
+        .post('/api/frontend')
+        .set('Authorization', frontendToken.secret)
+        .set('Content-Type', 'application/json')
+        .send({ context: { userId: '1337' } })
+        .expect('Content-Type', /json/)
+        .expect(200)
+        .expect((res) => {
+            expect(res.body.toggles).toHaveLength(1);
+            expect(res.body.toggles[0].name).toBe(featureName);
+        });
+
+    await app.request
+        .post('/api/frontend')
+        .set('Authorization', frontendToken.secret)
+        .send({ context: { appName: 'test', userId: '42' } })
+        .expect('Content-Type', /json/)
+        .expect(200)
+        .expect((res) => {
+            expect(res.body.toggles).toHaveLength(0);
+        });
+});

src/lib/openapi/spec/frontend-api-features-post-schema.ts

@@ -0,0 +1,22 @@
+import type { FromSchema } from 'json-schema-to-ts';
+import { sdkContextSchema } from './sdk-context-schema';
+
+export const frontendApiFeaturesPostSchema = {
+    $id: '#/components/schemas/frontendApiFeaturesPostContextSchema',
+    description: 'The Unleash frontend API POST request body.',
+    type: 'object',
+    additionalProperties: true,
+    properties: {
+        context: {
+            description: 'The Unleash context.',
+            type: 'object',
+            additionalProperties: true,
+            properties: sdkContextSchema.properties,
+        },
+    },
+    components: {},
+} as const;
+
+export type FrontendApiFeaturesPostSchema = FromSchema<
+    typeof frontendApiFeaturesPostSchema
+>;

src/lib/openapi/spec/index.ts

@@ -101,6 +101,7 @@ export * from './feedback-response-schema';
 export * from './feedback-update-schema';
 export * from './frontend-api-client-schema';
 export * from './frontend-api-feature-schema';
+export * from './frontend-api-features-post-schema';
 export * from './frontend-api-features-schema';
 export * from './group-schema';
 export * from './group-user-model-schema';