Poc/strip client headers on 304 (#5574)

To reduce traffic returned on 304.

src/lib/__snapshots__/create-config.test.ts.snap

@@ -102,6 +102,7 @@ exports[`should create default config 1`] = `
       "responseTimeWithAppNameKillSwitch": false,
       "scheduledConfigurationChanges": false,
       "strictSchemaValidation": false,
+      "stripClientHeadersOn304": false,
     },
     "externalResolver": {
       "getVariant": [Function],

src/lib/features/client-feature-toggles/client-feature-toggle.controller.ts

@@ -248,6 +248,11 @@ export default class FeatureController extends Controller {
 
         if (etag === userVersion) {
             res.status(304);
+            if (this.flagResolver.isEnabled('stripClientHeadersOn304')) {
+                res.getHeaderNames().forEach((header) =>
+                    res.removeHeader(header),
+                );
+            }
             res.end();
             return;
         } else {

src/lib/routes/client-api/metrics.ts

@@ -1,6 +1,6 @@
 import { Response } from 'express';
 import Controller from '../controller';
-import { IUnleashConfig, IUnleashServices } from '../../types';
+import { IFlagResolver, IUnleashConfig, IUnleashServices } from '../../types';
 import ClientInstanceService from '../../services/client-metrics/instance-service';
 import { Logger } from '../../logger';
 import { IAuthRequest } from '../unleash-types';
@@ -24,6 +24,8 @@ export default class ClientMetricsController extends Controller {
 
     metricsV2: ClientMetricsServiceV2;
 
+    flagResolver: IFlagResolver;
+
     constructor(
         {
             clientInstanceService,
@@ -44,6 +46,7 @@ export default class ClientMetricsController extends Controller {
         this.clientInstanceService = clientInstanceService;
         this.openApiService = openApiService;
         this.metricsV2 = clientMetricsServiceV2;
+        this.flagResolver = config.flagResolver;
 
         this.route({
             method: 'post',
@@ -90,6 +93,11 @@ export default class ClientMetricsController extends Controller {
                 );
 
                 await this.metricsV2.registerClientMetrics(data, clientIp);
+                if (this.flagResolver.isEnabled('stripClientHeadersOn304')) {
+                    res.getHeaderNames().forEach((header) =>
+                        res.removeHeader(header),
+                    );
+                }
                 res.status(202).end();
             } catch (e) {
                 res.status(400).end();

src/lib/types/experimental.ts

@@ -29,7 +29,8 @@ export type IFlagKey =
     | 'featureSearchAPI'
     | 'featureSearchFrontend'
     | 'scheduledConfigurationChanges'
-    | 'detectSegmentUsageInChangeRequests';
+    | 'detectSegmentUsageInChangeRequests'
+    | 'stripClientHeadersOn304';
 
 export type IFlags = Partial<{ [key in IFlagKey]: boolean | Variant }>;
 
@@ -130,6 +131,11 @@ const flags: IFlags = {
             .UNLEASH_EXPERIMENTAL_DETECT_SEGMENT_USAGE_IN_CHANGE_REQUESTS,
         false,
     ),
+    stripClientHeadersOn304: parseEnvVarBoolean(
+        process.env
+            .UNLEASH_EXPERIMENTAL_DETECT_SEGMENT_USAGE_IN_CHANGE_REQUESTS,
+        false,
+    ),
 };
 
 export const defaultExperimentalOptions: IExperimentalOptions = {

src/server-dev.ts

@@ -26,7 +26,7 @@ process.nextTick(async () => {
                     enableHeapSnapshotEnpoint: true,
                 },
                 logLevel: LogLevel.debug,
-                // secureHeaders: true,
+                secureHeaders: true,
                 versionCheck: {
                     enable: false,
                 },
@@ -40,6 +40,7 @@ process.nextTick(async () => {
                         privateProjects: true,
                         featureSearchAPI: true,
                         featureSearchFrontend: true,
+                        stripClientHeadersOn304: true,
                     },
                 },
                 authentication: {