feat(sdk): support legacy withdraws after Bedrock (#4119)

Adds support for finalizing legacy withdrawals after the Bedrock
migration. Cleans up some SDK code at the same time.

.changeset/four-mugs-taste.md

+---
+'@eth-optimism/core-utils': minor
+'@eth-optimism/sdk': minor
+---
+
+Add suppory for finalizing legacy withdrawals after the Bedrock migration

packages/contracts-bedrock/scripts/differential-testing.ts

@@ -22,7 +22,7 @@ const command = args[0]
   switch (command) {
     case 'decodeVersionedNonce': {
       const input = BigNumber.from(args[1])
-      const [nonce, version] = decodeVersionedNonce(input)
+      const { nonce, version } = decodeVersionedNonce(input)
 
       const output = utils.defaultAbiCoder.encode(
         ['uint256', 'uint256'],

packages/core-utils/src/optimism/encoding.ts

@@ -10,9 +10,6 @@ const nonceMask = BigNumber.from(
   '0x0000ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff'
 )
 
-export const big0 = BigNumber.from(0)
-export const big1 = BigNumber.from(1)
-
 /**
  * Encodes the version into the nonce.
  *
@@ -34,8 +31,16 @@ export const encodeVersionedNonce = (
  *
  * @param nonce
  */
-export const decodeVersionedNonce = (nonce: BigNumber): BigNumber[] => {
-  return [nonce.and(nonceMask), nonce.shr(240)]
+export const decodeVersionedNonce = (
+  nonce: BigNumber
+): {
+  version: BigNumber
+  nonce: BigNumber
+} => {
+  return {
+    version: nonce.shr(240),
+    nonce: nonce.and(nonceMask),
+  }
 }
 
 /**
@@ -104,10 +109,10 @@ export const encodeCrossDomainMessage = (
   gasLimit: BigNumber,
   data: string
 ) => {
-  const [, version] = decodeVersionedNonce(nonce)
-  if (version.eq(big0)) {
+  const { version } = decodeVersionedNonce(nonce)
+  if (version.eq(0)) {
     return encodeCrossDomainMessageV0(target, sender, data, nonce)
-  } else if (version.eq(big1)) {
+  } else if (version.eq(1)) {
     return encodeCrossDomainMessageV1(
       nonce,
       sender,

packages/core-utils/src/optimism/hashing.ts

@@ -6,8 +6,6 @@ import {
   decodeVersionedNonce,
   encodeCrossDomainMessageV0,
   encodeCrossDomainMessageV1,
-  big0,
-  big1,
 } from './encoding'
 
 /**
@@ -34,6 +32,7 @@ export interface OutputRootProof {
  * Bedrock proof data required to finalize an L2 to L1 message.
  */
 export interface BedrockCrossChainMessageProof {
+  l2OutputIndex: number
   outputRootProof: OutputRootProof
   withdrawalProof: string[]
 }
@@ -65,10 +64,10 @@ export const hashCrossDomainMessage = (
   gasLimit: BigNumber,
   data: string
 ) => {
-  const [, version] = decodeVersionedNonce(nonce)
-  if (version.eq(big0)) {
+  const { version } = decodeVersionedNonce(nonce)
+  if (version.eq(0)) {
     return hashCrossDomainMessagev0(target, sender, data, nonce)
-  } else if (version.eq(big1)) {
+  } else if (version.eq(1)) {
     return hashCrossDomainMessagev1(
       nonce,
       sender,

packages/sdk/src/interfaces/types.ts

@@ -203,6 +203,12 @@ export interface CrossChainMessage extends CoreCrossChainMessage {
   transactionHash: string
 }
 
+/**
+ * Describes messages sent inside the L2ToL1MessagePasser on L2. Happens to be the same structure
+ * as the CoreCrossChainMessage so we'll reuse the type for now.
+ */
+export type LowLevelMessage = CoreCrossChainMessage
+
 /**
  * Describes a token withdrawal or deposit, along with the underlying raw cross chain message
  * behind the deposit or withdrawal.

packages/sdk/src/utils/index.ts

@@ -4,3 +4,4 @@ export * from './type-utils'
 export * from './misc-utils'
 export * from './merkle-utils'
 export * from './chain-constants'
+export * from './message-utils'

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

+import { hashWithdrawal } from '@eth-optimism/core-utils'
+
+import { LowLevelMessage } from '../interfaces'
+
+/**
+ * Utility for hashing a LowLevelMessage object.
+ *
+ * @param message LowLevelMessage object to hash.
+ * @returns Hash of the given LowLevelMessage.
+ */
+export const hashLowLevelMessage = (message: LowLevelMessage): string => {
+  return hashWithdrawal(
+    message.messageNonce,
+    message.sender,
+    message.target,
+    message.value,
+    message.minGasLimit,
+    message.message
+  )
+}