feat: default session id in frontend api (#5083)

src/lib/services/proxy-service.ts

@@ -74,12 +74,19 @@ export class ProxyService {
         const client = await this.clientForProxyToken(token);
         const definitions = client.getFeatureToggleDefinitions() || [];
 
+        const sessionId = context.sessionId || String(Math.random());
+
         return definitions
-            .filter((feature) => client.isEnabled(feature.name, context))
+            .filter((feature) =>
+                client.isEnabled(feature.name, { ...context, sessionId }),
+            )
             .map((feature) => ({
                 name: feature.name,
                 enabled: Boolean(feature.enabled),
-                variant: client.forceGetVariant(feature.name, context),
+                variant: client.getVariant(feature.name, {
+                    ...context,
+                    sessionId,
+                }),
                 impressionData: Boolean(feature.impressionData),
             }));
     }

src/test/e2e/api/proxy/proxy.e2e.test.ts

@@ -1236,3 +1236,43 @@ test('should return 204 if metrics are disabled', async () => {
         })
         .expect(204);
 });
+
+test('should resolve variable rollout percentage consistently', async () => {
+    const frontendToken = await createApiToken(ApiTokenType.FRONTEND);
+    await createFeatureToggle({
+        name: 'randomFeature',
+        enabled: true,
+        strategies: [
+            {
+                name: 'flexibleRollout',
+                constraints: [],
+                parameters: {
+                    rollout: '50',
+                    stickiness: 'default',
+                    groupId: 'some-new',
+                },
+                variants: [
+                    {
+                        name: 'a',
+                        stickiness: 'default',
+                        weightType: 'variable',
+                        weight: 1000,
+                    },
+                ],
+            },
+        ],
+    });
+
+    for (let i = 0; i < 10; ++i) {
+        const { body } = await app.request
+            .get('/api/frontend')
+            .set('Authorization', frontendToken.secret)
+            .expect('Content-Type', /json/)
+            .expect(200);
+
+        if (body.toggles.length > 0) {
+            // disabled variant should not be possible for enabled toggles
+            expect(body.toggles[0].variant.name).toBe('a');
+        }
+    }
+});