From bf2a769b42874d41dbcf5a7798f6d47b3299d697 Mon Sep 17 00:00:00 2001
From: Kenny Yi <kenny@statsig.com>
Date: Mon, 5 Aug 2024 13:48:44 -0700
Subject: [PATCH] custom hash function plugin

---
 src/StatsigOnPrem.ts     |  6 +++++-
 src/utils/HashUtils.ts   | 30 +++++++++++++++++++-----------
 tests/HashPlugin.test.ts | 26 ++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 12 deletions(-)
 create mode 100644 tests/HashPlugin.test.ts

diff --git a/src/StatsigOnPrem.ts b/src/StatsigOnPrem.ts
index 1ebbdb6..22bf0f4 100644
--- a/src/StatsigOnPrem.ts
+++ b/src/StatsigOnPrem.ts
@@ -17,7 +17,7 @@ import EntityFeatureGate from "./entities/EntityFeatureGate";
 import { IDUtils } from "./utils/IDUtils";
 import { SpecsCacheInterface } from "./interfaces/SpecsCacheInterface";
 import StorageHandler from "./utils/StorageHandler";
-import HashUtils from "./utils/HashUtils";
+import HashUtils, { HashFn } from "./utils/HashUtils";
 import { TargetAppNames } from "./types/TargetAppNames";
 import CacheHandler from "./utils/CacheHandler";
 import { SDKKeysCacheInterface } from "./interfaces/SDKKeyCacheInterface";
@@ -25,6 +25,7 @@ import { SDKKeysCacheInterface } from "./interfaces/SDKKeyCacheInterface";
 type Plugins = Partial<{
   specsCache: SpecsCacheInterface;
   sdkKeysCache: SDKKeysCacheInterface;
+  hash: HashFn;
 }>;
 
 export default class StatsigOnPrem implements StatsigInterface {
@@ -36,6 +37,9 @@ export default class StatsigOnPrem implements StatsigInterface {
       specs: plugins?.specsCache,
       keys: plugins?.sdkKeysCache,
     });
+    if (plugins?.hash !== undefined) {
+      HashUtils.setHashFn(plugins.hash);
+    }
   }
 
   public async initialize(): Promise<void> {
diff --git a/src/utils/HashUtils.ts b/src/utils/HashUtils.ts
index 5292b56..750ac6e 100644
--- a/src/utils/HashUtils.ts
+++ b/src/utils/HashUtils.ts
@@ -1,19 +1,27 @@
+export type HashFn = (input: string) => string;
+
+let hash_fn: HashFn = djb2Hash;
+
 export default class HashUtils {
   public static hashString(str: string): string {
-    return this.djb2Hash(str);
+    return hash_fn(str);
   }
 
-  private static fasthash(value: string): number {
-    let hash = 0;
-    for (let i = 0; i < value.length; i++) {
-      const character = value.charCodeAt(i);
-      hash = (hash << 5) - hash + character;
-      hash = hash & hash; // Convert to 32bit integer
-    }
-    return hash;
+  public static setHashFn(fn: HashFn): void {
+    hash_fn = fn;
   }
+}
 
-  private static djb2Hash(value: string): string {
-    return String(this.fasthash(value) >>> 0);
+function fasthash(value: string): number {
+  let hash = 0;
+  for (let i = 0; i < value.length; i++) {
+    const character = value.charCodeAt(i);
+    hash = (hash << 5) - hash + character;
+    hash = hash & hash; // Convert to 32bit integer
   }
+  return hash;
+}
+
+function djb2Hash(value: string): string {
+  return String(fasthash(value) >>> 0);
 }
diff --git a/tests/HashPlugin.test.ts b/tests/HashPlugin.test.ts
new file mode 100644
index 0000000..8cbae94
--- /dev/null
+++ b/tests/HashPlugin.test.ts
@@ -0,0 +1,26 @@
+import StatsigStorageExample from "../examples/StatsigStorageExample";
+import SDKKeysCache from "../src/SDKKeysCache";
+import StatsigOnPrem from "../src/StatsigOnPrem";
+
+describe("Hash plugin", () => {
+  const storage = new StatsigStorageExample();
+  const sdkKeysCache = new SDKKeysCache();
+  const hashFn = (input: string) => `hashed:${input}`;
+  const statsig = new StatsigOnPrem(storage, { sdkKeysCache, hash: hashFn });
+
+  beforeAll(async () => {
+    await statsig.initialize();
+  });
+
+  afterAll(async () => {
+    storage.clearAll();
+    await statsig.clearCache();
+  });
+
+  it("Uses custom hash function", async () => {
+    await statsig.registerSDKKey("secret-123");
+    expect(storage.get("statsig:sdkKey:hashed:secret-123")).resolves.toEqual(
+      "registered"
+    );
+  });
+});