decode obfuscated bandit

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@eppo/js-client-sdk-common",
-  "version": "4.8.2",
+  "version": "4.8.3",
   "description": "Common library for Eppo JavaScript SDKs (web, react native, and node)",
   "main": "dist/index.js",
   "files": [
@@ -78,4 +78,4 @@
     "uuid": "^11.0.5"
   },
   "packageManager": "[email protected]+sha512.a6b2f7906b721bba3d67d4aff083df04dad64c399707841b7acf00f6b133b7ac24255f2652fa22ae3534329dc6180534e98d17432037ff6fd140556e2bb3137e"
-}
+}

src/client/eppo-precomputed-client.ts

@@ -18,7 +18,7 @@ import {
   MAX_EVENT_QUEUE_SIZE,
   PRECOMPUTED_BASE_URL,
 } from '../constants';
-import { decodePrecomputedFlag } from '../decoding';
+import { decodePrecomputedBandit, decodePrecomputedFlag } from '../decoding';
 import { FlagEvaluationWithoutDetails } from '../evaluator';
 import FetchHttpClient from '../http-client';
 import {
@@ -307,7 +307,7 @@ export default class EppoPrecomputedClient {
     );
   }
 
-  getBanditAction(
+  public getBanditAction(
     flagKey: string,
     defaultValue: string,
   ): Omit<IAssignmentDetails<string>, 'evaluationDetails'> {
@@ -318,6 +318,8 @@ export default class EppoPrecomputedClient {
       return { variation: defaultValue, action: null };
     }
 
+    const assignedVariation = this.getStringAssignment(flagKey, defaultValue);
+
     const banditEvent: IBanditEvent = {
       timestamp: new Date().toISOString(),
       featureFlag: flagKey,
@@ -341,7 +343,7 @@ export default class EppoPrecomputedClient {
       logger.error(`${loggerPrefix} Error logging bandit action: ${error}`);
     }
 
-    return { variation: defaultValue, action: banditEvent.action };
+    return { variation: assignedVariation, action: banditEvent.action };
   }
 
   private getPrecomputedFlag(flagKey: string): DecodedPrecomputedFlag | null {
@@ -358,13 +360,17 @@ export default class EppoPrecomputedClient {
   }
 
   private getPrecomputedBandit(banditKey: string): IPrecomputedBandit | null {
-    return this.getObfuscatedPrecomputedBandit(banditKey);
+    const obfuscatedBandit = this.getObfuscatedPrecomputedBandit(banditKey);
+    return obfuscatedBandit ? decodePrecomputedBandit(obfuscatedBandit) : null;
   }
 
   private getObfuscatedPrecomputedBandit(banditKey: string): IObfuscatedPrecomputedBandit | null {
     const salt = this.precomputedBanditStore?.salt;
     const saltedAndHashedBanditKey = getMD5Hash(banditKey, salt);
-    return this.precomputedBanditStore?.get(saltedAndHashedBanditKey) ?? null;
+    const precomputedBandit: IObfuscatedPrecomputedBandit | null = this.precomputedBanditStore?.get(
+      saltedAndHashedBanditKey,
+    ) as IObfuscatedPrecomputedBandit;
+    return precomputedBandit ?? null;
   }
 
   public isInitialized() {

src/decoding.spec.ts

@@ -1,5 +1,16 @@
-import { decodeAllocation, decodeSplit, decodeValue, decodeVariations } from './decoding';
-import { VariationType, ObfuscatedVariation, Variation } from './interfaces';
+import {
+  decodeAllocation,
+  decodePrecomputedBandit,
+  decodeSplit,
+  decodeValue,
+  decodeVariations,
+} from './decoding';
+import {
+  VariationType,
+  ObfuscatedVariation,
+  Variation,
+  IObfuscatedPrecomputedBandit,
+} from './interfaces';
 
 describe('decoding', () => {
   describe('decodeVariations', () => {
@@ -175,4 +186,38 @@ describe('decoding', () => {
       expect(decodeAllocation(obfuscatedAllocation)).toEqual(expectedAllocation);
     });
   });
+
+  describe('decode bandit', () => {
+    it('should correctly decode bandit', () => {
+      const encodedBandit = {
+        action: 'Z3JlZW5CYWNrZ3JvdW5k',
+        actionCategoricalAttributes: {
+          'Y29sb3I=': 'Z3JlZW4=',
+          'dHlwZQ==': 'YmFja2dyb3VuZA==',
+        },
+        actionNumericAttributes: { Zm9udEhlaWdodEVt: 'MTA=' },
+        actionProbability: 0.95,
+        banditKey: 'bGF1bmNoLWJ1dHRvbi10cmVhdG1lbnQ=',
+        modelVersion: 'MzI0OQ==',
+        optimalityGap: 0,
+      } as IObfuscatedPrecomputedBandit;
+
+      const decodedBandit = decodePrecomputedBandit(encodedBandit);
+
+      expect(decodedBandit).toEqual({
+        action: 'greenBackground',
+        actionCategoricalAttributes: {
+          color: 'green',
+          type: 'background',
+        },
+        actionNumericAttributes: {
+          fontHeightEm: 10,
+        },
+        actionProbability: 0.95,
+        banditKey: 'launch-button-treatment',
+        modelVersion: '3249',
+        optimalityGap: 0,
+      });
+    });
+  });
 });

src/decoding.ts

@@ -11,6 +11,8 @@ import {
   ObfuscatedSplit,
   PrecomputedFlag,
   DecodedPrecomputedFlag,
+  IPrecomputedBandit,
+  IObfuscatedPrecomputedBandit,
 } from './interfaces';
 import { decodeBase64 } from './obfuscation';
 
@@ -74,8 +76,14 @@ export function decodeShard(shard: Shard): Shard {
 }
 
 export function decodeObject(obj: Record<string, string>): Record<string, string> {
+  return decodeObjectTo(obj, (v: string) => v);
+}
+export function decodeObjectTo<T>(
+  obj: Record<string, string>,
+  transform: (v: string) => T,
+): Record<string, T> {
   return Object.fromEntries(
-    Object.entries(obj).map(([key, value]) => [decodeBase64(key), decodeBase64(value)]),
+    Object.entries(obj).map(([key, value]) => [decodeBase64(key), transform(decodeBase64(value))]),
   );
 }
 
@@ -88,3 +96,19 @@ export function decodePrecomputedFlag(precomputedFlag: PrecomputedFlag): Decoded
     extraLogging: decodeObject(precomputedFlag.extraLogging ?? {}),
   };
 }
+
+export function decodePrecomputedBandit(
+  precomputedBandit: IObfuscatedPrecomputedBandit,
+): IPrecomputedBandit {
+  return {
+    ...precomputedBandit,
+    banditKey: decodeBase64(precomputedBandit.banditKey),
+    action: decodeBase64(precomputedBandit.action),
+    modelVersion: decodeBase64(precomputedBandit.modelVersion),
+    actionNumericAttributes: decodeObjectTo<number>(
+      precomputedBandit.actionNumericAttributes ?? {},
+      (v) => +v, // Convert to a number
+    ),
+    actionCategoricalAttributes: decodeObject(precomputedBandit.actionCategoricalAttributes ?? {}),
+  };
+}

src/obfuscation.spec.ts

@@ -1,4 +1,5 @@
-import { decodeBase64, encodeBase64 } from './obfuscation';
+import { IPrecomputedBandit } from './interfaces';
+import { decodeBase64, encodeBase64, obfuscatePrecomputedBanditMap } from './obfuscation';
 
 describe('obfuscation', () => {
   it('encodes strings to base64', () => {
@@ -27,4 +28,42 @@ describe('obfuscation', () => {
 
     expect(decodeBase64('a8O8bW1lcnQ=')).toEqual('kümmert');
   });
+
+  describe('bandit obfuscation', () => {
+    it('obfuscates precomputed bandits', () => {
+      const bandit: IPrecomputedBandit = {
+        action: 'greenBackground',
+        actionCategoricalAttributes: {
+          color: 'green',
+          type: 'background',
+        },
+        actionNumericAttributes: {
+          fontHeightEm: 10,
+        },
+        actionProbability: 0.95,
+        banditKey: 'launch-button-treatment',
+        modelVersion: '3249',
+        optimalityGap: 0,
+      };
+
+      const encodedBandit = obfuscatePrecomputedBanditMap('', {
+        'launch-button-treatment': bandit,
+      });
+
+      expect(encodedBandit).toEqual({
+        '0ae2ece7bf09e40dd6b28a02574a4826': {
+          action: 'Z3JlZW5CYWNrZ3JvdW5k',
+          actionCategoricalAttributes: {
+            'Y29sb3I=': 'Z3JlZW4=',
+            'dHlwZQ==': 'YmFja2dyb3VuZA==',
+          },
+          actionNumericAttributes: { Zm9udEhlaWdodEVt: 'MTA=' },
+          actionProbability: 0.95,
+          banditKey: 'bGF1bmNoLWJ1dHRvbi10cmVhdG1lbnQ=',
+          modelVersion: 'MzI0OQ==',
+          optimalityGap: 0,
+        },
+      });
+    });
+  });
 });

src/obfuscation.ts

@@ -29,17 +29,16 @@ export function obfuscatePrecomputedBanditMap(
   return Object.fromEntries(
     Object.entries(bandits).map(([variationValue, bandit]) => {
       const hashedKey = getMD5Hash(variationValue, salt);
-      return [hashedKey, obfuscatePrecomputedBandit(salt, bandit)];
+      return [hashedKey, obfuscatePrecomputedBandit(bandit)];
     }),
   );
 }
 
 function obfuscatePrecomputedBandit(
-  salt: string,
   banditResult: IPrecomputedBandit,
 ): IObfuscatedPrecomputedBandit {
   return {
-    banditKey: getMD5Hash(banditResult.banditKey, salt),
+    banditKey: encodeBase64(banditResult.banditKey),
     action: encodeBase64(banditResult.action),
     actionProbability: banditResult.actionProbability,
     optimalityGap: banditResult.optimalityGap,