From ac11af8c05fab4f6d11d01cead39cebd01c69931 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gast=C3=B3n=20Fournier?= <gaston@getunleash.io>
Date: Mon, 25 Aug 2025 07:26:36 -0700
Subject: [PATCH] chore: add some debug statements controlled by a flag
 (#10532)

## About the changes
Add some **info** logs prefixed with `[etag]` so que can control them
and with this investigate the increase in traffic after the new etag
implementation.
---
 .../client-feature-toggle.controller.ts       | 28 +++++++++++++------
 .../configuration-revision-service.ts         | 18 ++++++++++--
 src/lib/types/experimental.ts                 |  3 +-
 3 files changed, 37 insertions(+), 12 deletions(-)

diff --git a/src/lib/features/client-feature-toggles/client-feature-toggle.controller.ts b/src/lib/features/client-feature-toggles/client-feature-toggle.controller.ts
index bbf8343587..7e532603cb 100644
--- a/src/lib/features/client-feature-toggles/client-feature-toggle.controller.ts
+++ b/src/lib/features/client-feature-toggles/client-feature-toggle.controller.ts
@@ -147,15 +147,13 @@ export default class FeatureController extends Controller {
 
         if (clientFeatureCaching.enabled) {
             this.featuresAndSegments = memoizee(
-                // eslint-disable-next-line @typescript-eslint/no-unused-vars
-                (query: IFeatureToggleQuery, etag: string) =>
+                (query: IFeatureToggleQuery, _etag: string) =>
                     this.resolveFeaturesAndSegments(query),
                 {
                     promise: true,
                     maxAge: clientFeatureCaching.maxAge,
-                    normalizer(args) {
-                        // args is arguments object as accessible in memoized function
-                        return args[1];
+                    normalizer([_query, etag]) {
+                        return etag;
                     },
                 },
             );
@@ -167,6 +165,11 @@ export default class FeatureController extends Controller {
     private async resolveFeaturesAndSegments(
         query?: IFeatureToggleQuery,
     ): Promise<[FeatureConfigurationClient[], IClientSegment[]]> {
+        if (this.flagResolver.isEnabled('debugEtag')) {
+            this.logger.info(
+                `[etag] Flags and segments cache miss for ${JSON.stringify(query)}`,
+            );
+        }
         if (this.flagResolver.isEnabled('deltaApi')) {
             const features =
                 await this.clientFeatureToggleService.getClientFeatures(query);
@@ -324,9 +327,11 @@ export default class FeatureController extends Controller {
             res.end();
             return;
         } else {
-            this.logger.debug(
-                `Provided revision: ${userVersion}, calculated revision: ${etag}`,
-            );
+            if (this.flagResolver.isEnabled('debugEtag')) {
+                this.logger.info(
+                    `[etag] Provided revision: ${userVersion}, calculated revision: ${etag}`,
+                );
+            }
         }
 
         const [features, segments] = await this.featuresAndSegments(
@@ -364,6 +369,13 @@ export default class FeatureController extends Controller {
             );
 
         const queryHash = hashSum(query);
+        if (this.flagResolver.isEnabled('debugEtag')) {
+            this.logger.info(
+                `[etag] for query ${JSON.stringify(
+                    query,
+                )} is "${queryHash}:${revisionId}" (revision id query with env ${etagByEnvEnabled ? query.environment : undefined})`,
+            );
+        }
         const etagVariant = this.flagResolver.getVariant('etagVariant');
         if (etagVariant.feature_enabled && etagVariant.enabled) {
             const etag = `"${queryHash}:${revisionId}:${etagVariant.name}"`;
diff --git a/src/lib/features/feature-toggle/configuration-revision-service.ts b/src/lib/features/feature-toggle/configuration-revision-service.ts
index d46e7544e7..8ffd85a576 100644
--- a/src/lib/features/feature-toggle/configuration-revision-service.ts
+++ b/src/lib/features/feature-toggle/configuration-revision-service.ts
@@ -80,6 +80,12 @@ export default class ConfigurationRevisionService extends EventEmitter {
             this.maxRevisionId[environment] = envRevisionId;
         }
 
+        if (this.flagResolver.isEnabled('debugEtag')) {
+            this.logger.info(
+                `[etag] Computed ETag for environment ${environment}: ${envRevisionId} stored as "${this.maxRevisionId[environment]}"`,
+            );
+        }
+
         return this.maxRevisionId[environment];
     }
 
@@ -92,9 +98,15 @@ export default class ConfigurationRevisionService extends EventEmitter {
             this.revisionId,
         );
         if (this.revisionId !== revisionId) {
-            this.logger.debug(
-                `Updating feature configuration with new revision Id ${revisionId} and all envs: ${Object.keys(this.maxRevisionId).join(', ')}`,
-            );
+            if (this.flagResolver.isEnabled('debugEtag')) {
+                this.logger.info(
+                    `[etag] Updating feature configuration with new revision Id ${revisionId} and all envs: ${Object.keys(this.maxRevisionId).join(', ')}`,
+                );
+            } else {
+                this.logger.debug(
+                    `Updating feature configuration with new revision Id ${revisionId} and all envs: ${Object.keys(this.maxRevisionId).join(', ')}`,
+                );
+            }
             await Promise.allSettled(
                 Object.keys(this.maxRevisionId).map((environment) =>
                     this.updateMaxEnvironmentRevisionId(environment),
diff --git a/src/lib/types/experimental.ts b/src/lib/types/experimental.ts
index 7257b00f85..c106de9df8 100644
--- a/src/lib/types/experimental.ts
+++ b/src/lib/types/experimental.ts
@@ -61,7 +61,8 @@ export type IFlagKey =
     | 'addConfiguration'
     | 'filterFlagsToArchive'
     | 'fetchMode'
-    | 'etagByEnv';
+    | 'etagByEnv'
+    | 'debugEtag';
 
 export type IFlags = Partial<{ [key in IFlagKey]: boolean | Variant }>;