sdk: add tests for min gas util

packages/sdk/src/cross-chain-messenger.ts

@@ -26,7 +26,6 @@ import {
   BedrockCrossChainMessageProof,
   decodeVersionedNonce,
   encodeVersionedNonce,
-  calldataCost,
 } from '@eth-optimism/core-utils'
 import { getContractInterface, predeploys } from '@eth-optimism/contracts'
 import * as rlp from 'rlp'
@@ -66,6 +65,7 @@ import {
   makeMerkleTreeProof,
   makeStateTrieProof,
   hashLowLevelMessage,
+  migratedWithdrawalGasLimit,
   DEPOSIT_CONFIRMATION_BLOCKS,
   CHAIN_BLOCK_TIMES,
 } from './utils'
@@ -351,12 +351,7 @@ export class CrossChainMessenger {
       }
     }
 
-    // Compute the gas limit and cap at 25 million
-    const dataCost = calldataCost(resolved.message)
-    let minGasLimit = dataCost.add(200_000)
-    if (minGasLimit.gt(25_000_000)) {
-      minGasLimit = BigNumber.from(25_000_000)
-    }
+    const minGasLimit = migratedWithdrawalGasLimit(resolved.message)
 
     return {
       ...resolved,

packages/sdk/src/utils/message-utils.ts

-import { hashWithdrawal } from '@eth-optimism/core-utils'
+import { hashWithdrawal, calldataCost } from '@eth-optimism/core-utils'
+import { BigNumber } from 'ethers'
 
 import { LowLevelMessage } from '../interfaces'
 
@@ -18,3 +19,16 @@ export const hashLowLevelMessage = (message: LowLevelMessage): string => {
     message.message
   )
 }
+
+/**
+ * Compute the min gas limit for a migrated withdrawal.
+ */
+export const migratedWithdrawalGasLimit = (data: string): BigNumber => {
+  // Compute the gas limit and cap at 25 million
+  const dataCost = calldataCost(data)
+  let minGasLimit = dataCost.add(200_000)
+  if (minGasLimit.gt(25_000_000)) {
+    minGasLimit = BigNumber.from(25_000_000)
+  }
+  return minGasLimit
+}

packages/sdk/test/utils/message-utils.spec.ts

+import { BigNumber } from 'ethers'
+
+import { expect } from '../setup'
+import { migratedWithdrawalGasLimit } from '../../src/utils/message-utils'
+
+describe('Message Utils', () => {
+  describe('migratedWithdrawalGasLimit', () => {
+    it('should have a max of 25 million', () => {
+      const data = '0x' + 'ff'.repeat(15_000_000)
+      const result = migratedWithdrawalGasLimit(data)
+      expect(result).to.eq(BigNumber.from(25_000_000))
+    })
+
+    it('should work for mixes of zeros and ones', () => {
+      const tests = [
+        { input: '0x', result: BigNumber.from(200_000) },
+        { input: '0xff', result: BigNumber.from(200_000 + 16) },
+        { input: '0xff00', result: BigNumber.from(200_000 + 16 + 4) },
+        { input: '0x00', result: BigNumber.from(200_000 + 4) },
+        { input: '0x000000', result: BigNumber.from(200_000 + 4 + 4 + 4) },
+      ]
+
+      for (const test of tests) {
+        const result = migratedWithdrawalGasLimit(test.input)
+        expect(result).to.eq(test.result)
+      }
+    })
+  })
+})