hashMessageHash

src/utils/hashMessageHash.test.ts

@@ -0,0 +1,11 @@
+import { hashMessageHash } from './hashMessageHash'
+import { test, expect } from 'vitest'
+
+test('returns correct source hash', async () => {
+  const hash =
+    '0xB1C3824DEF40047847145E069BF467AA67E906611B9F5EF31515338DB0AABFA2'
+  // checked result of same method in OP SDK
+  expect(hashMessageHash(hash)).toEqual(
+    '0x4a932049252365b3eedbc5190e18949f2ec11f39d3bef2d259764799a1b27d99',
+  )
+})

src/utils/hashMessageHash.ts

@@ -0,0 +1,20 @@
+import { Hex, encodeAbiParameters, keccak256, parseAbiParameters } from 'viem'
+
+// from https://github.com/ethereum-optimism/optimism/blob/develop/packages/sdk/src/utils/message-utils.ts#L42
+// adapted to viem
+
+/**
+ * Utility for hashing a message hash. This computes the storage slot
+ * where the message hash will be stored in state. HashZero is used
+ * because the first mapping in the contract is used.
+ *
+ * @param messageHash Message hash to hash.
+ * @returns Hash of the given message hash.
+ */
+export const hashMessageHash = (messageHash: Hex): string => {
+  const data = encodeAbiParameters(parseAbiParameters(['bytes32, uint256']), [
+    messageHash,
+    0n,
+  ])
+  return keccak256(data)
+}