fix: zeroPad util (#87)

* fix: idCommitmnet little endianess

* stop double conversion

* fix problem with zeroPad

* fix test

example/package-lock.json

@@ -19,6 +19,7 @@
       }
     },
     "..": {
+      "name": "@waku/rln",
       "version": "0.1.1",
       "license": "MIT OR Apache-2.0",
       "dependencies": {

src/byte_utils.ts

@@ -47,3 +47,17 @@ export function buildBigIntFromUint8Array(array: Uint8Array): bigint {
   const dataView = new DataView(array.buffer);
   return dataView.getBigUint64(0, true);
 }
+
+/**
+ * Fills with zeros to set length
+ * @param array little endian Uint8Array
+ * @param length amount to pad
+ * @returns little endian Uint8Array padded with zeros to set length
+ */
+export function zeroPadLE(array: Uint8Array, length: number): Uint8Array {
+  const result = new Uint8Array(length);
+  for (let i = 0; i < length; i++) {
+    result[i] = array[i] || 0;
+  }
+  return result;
+}

src/rln_contract.spec.ts

@@ -66,7 +66,7 @@ describe("RLN Contract abstraction", () => {
 function mockEvent(): ethers.Event {
   return {
     args: {
-      idCommitment: "0x9e7d3f8f8c7a1d2bef96a2e8dbb8e7c1ea9a9ab78d6b3c6c3c",
+      idCommitment: { _hex: "0xb3df1c4e5600ef2b" },
       index: ethers.BigNumber.from(1),
     },
   } as unknown as ethers.Event;

src/rln_contract.ts

@@ -1,6 +1,7 @@
 import { hexToBytes } from "@waku/utils/bytes";
 import { ethers } from "ethers";
 
+import { zeroPadLE } from "./byte_utils.js";
 import { RLN_REGISTRY_ABI, RLN_STORAGE_ABI } from "./constants.js";
 import { IdentityCredential, RLNInstance } from "./rln.js";
 import { MerkleRootTracker } from "./root_tracker.js";
@@ -170,7 +171,7 @@ export class RLNContract {
           return;
         }
 
-        const idCommitment = hexToBytes(_idCommitment?._hex);
+        const idCommitment = zeroPadLE(hexToBytes(_idCommitment?._hex), 32);
         rlnInstance.insertMember(idCommitment);
         this._members.set(index.toNumber(), {
           index,