feat(sdk): implement withdrawETH

This commit implements the SDK's withdrawETH function which allows users
to withdraw an amount of ETH (specified in wei) from L2 to L1.

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

@@ -4,6 +4,7 @@ import {
   TransactionRequest,
   TransactionResponse,
 } from '@ethersproject/abstract-provider'
+import { predeploys } from '@eth-optimism/contracts'
 
 import {
   CrossChainMessageRequest,
@@ -85,7 +86,9 @@ export class CrossChainMessenger implements ICrossChainMessenger {
     amount: NumberLike,
     overrides?: Overrides
   ): Promise<TransactionResponse> {
-    throw new Error('Not implemented')
+    return this.l2Signer.sendTransaction(
+      await this.populateTransaction.withdrawETH(amount, overrides)
+    )
   }
 
   populateTransaction = {
@@ -163,7 +166,13 @@ export class CrossChainMessenger implements ICrossChainMessenger {
       amount: NumberLike,
       overrides?: Overrides
     ): Promise<TransactionRequest> => {
-      throw new Error('Not implemented')
+      return this.provider.contracts.l2.L2StandardBridge.populateTransaction.withdraw(
+        predeploys.OVM_ETH,
+        amount,
+        0, // No need to supply gas here
+        '0x', // No data,
+        overrides || {}
+      )
     },
   }
 
@@ -212,7 +221,8 @@ export class CrossChainMessenger implements ICrossChainMessenger {
       amount: NumberLike,
       overrides?: Overrides
     ): Promise<BigNumber> => {
-      throw new Error('Not implemented')
+      const tx = await this.populateTransaction.withdrawETH(amount, overrides)
+      return this.provider.l2Provider.estimateGas(tx)
     },
   }
 }

packages/sdk/test/contracts/MockBridge.sol

@@ -132,4 +132,23 @@ contract MockBridge {
             _data
         );
     }
+
+    function withdraw(
+        address _l2Token,
+        uint256 _amount,
+        uint32 _l1Gas,
+        bytes calldata _data
+    )
+        public
+        payable
+    {
+        emit WithdrawalInitiated(
+            address(0),
+            _l2Token,
+            msg.sender,
+            msg.sender,
+            _amount,
+            _data
+        );
+    }
 }

packages/sdk/test/cross-chain-messenger.spec.ts

 import { Contract } from 'ethers'
 import { ethers } from 'hardhat'
+import { predeploys } from '@eth-optimism/contracts'
 
 import { expect } from './setup'
 import {
@@ -255,4 +256,50 @@ describe('CrossChainMessenger', () => {
         )
     })
   })
+
+  describe('withdrawETH', () => {
+    let l2Messenger: Contract
+    let l2Bridge: Contract
+    let provider: CrossChainProvider
+    let messenger: CrossChainMessenger
+    beforeEach(async () => {
+      l2Messenger = (await (
+        await ethers.getContractFactory('MockMessenger')
+      ).deploy()) as any
+      l2Bridge = (await (
+        await ethers.getContractFactory('MockBridge')
+      ).deploy(l2Messenger.address)) as any
+
+      provider = new CrossChainProvider({
+        l1Provider: ethers.provider,
+        l2Provider: ethers.provider,
+        l1ChainId: 31337,
+        contracts: {
+          l2: {
+            L2CrossDomainMessenger: l2Messenger.address,
+            L2StandardBridge: l2Bridge.address,
+          },
+        },
+      })
+
+      messenger = new CrossChainMessenger({
+        provider,
+        l1Signer,
+        l2Signer,
+      })
+    })
+
+    it('should trigger the deposit ETH function with the given amount', async () => {
+      await expect(messenger.withdrawETH(100000))
+        .to.emit(l2Bridge, 'WithdrawalInitiated')
+        .withArgs(
+          ethers.constants.AddressZero,
+          predeploys.OVM_ETH,
+          await l2Signer.getAddress(),
+          await l2Signer.getAddress(),
+          100000,
+          '0x'
+        )
+    })
+  })
 })