utils.go

package withdrawals

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/accounts/abi"
	"github.com/ethereum/go-ethereum/accounts/abi/bind"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/crypto"
	"github.com/ethereum/go-ethereum/ethclient/gethclient"

	"github.com/ethereum-optimism/optimism/op-bindings/predeploys"
	"github.com/ethereum-optimism/optimism/op-node/bindings"
	bindingspreview "github.com/ethereum-optimism/optimism/op-node/bindings/preview"
)

var MessagePassedTopic = crypto.Keccak256Hash([]byte("MessagePassed(uint256,address,address,uint256,uint256,bytes,bytes32)"))

type ProofClient interface {
	GetProof(context.Context, common.Address, []string, *big.Int) (*gethclient.AccountResult, error)
}

type ReceiptClient interface {
	TransactionReceipt(context.Context, common.Hash) (*types.Receipt, error)
}

type BlockClient interface {
	BlockByNumber(context.Context, *big.Int) (*types.Block, error)
}

// ProvenWithdrawalParameters is the set of parameters to pass to the ProveWithdrawalTransaction
// and FinalizeWithdrawalTransaction functions
type ProvenWithdrawalParameters struct {
	Nonce           *big.Int
	Sender          common.Address
	Target          common.Address
	Value           *big.Int
	GasLimit        *big.Int
	L2OutputIndex   *big.Int
	Data            []byte
	OutputRootProof bindings.TypesOutputRootProof
	WithdrawalProof [][]byte // List of trie nodes to prove L2 storage
}

// ProveWithdrawalParameters calls ProveWithdrawalParametersForBlock with the most recent L2 output after the given header.
func ProveWithdrawalParameters(ctx context.Context, proofCl ProofClient, l2ReceiptCl ReceiptClient, l2BlockCl BlockClient, txHash common.Hash, header *types.Header, l2OutputOracleContract *bindings.L2OutputOracleCaller) (ProvenWithdrawalParameters, error) {
	l2OutputIndex, err := l2OutputOracleContract.GetL2OutputIndexAfter(&bind.CallOpts{}, header.Number)
	if err != nil {
		return ProvenWithdrawalParameters{}, fmt.Errorf("failed to get l2OutputIndex: %w", err)
	}
	l2BlockNumber := header.Number
	return ProveWithdrawalParametersForBlock(ctx, proofCl, l2ReceiptCl, l2BlockCl, txHash, l2BlockNumber, l2OutputIndex)
}

// ProveWithdrawalParametersFPAC calls ProveWithdrawalParametersForBlock with the most recent L2 output after the latest game.
func ProveWithdrawalParametersFPAC(ctx context.Context, proofCl ProofClient, l2ReceiptCl ReceiptClient, l2BlockCl BlockClient, txHash common.Hash, disputeGameFactoryContract *bindings.DisputeGameFactoryCaller, optimismPortal2Contract *bindingspreview.OptimismPortal2Caller) (ProvenWithdrawalParameters, error) {
	latestGame, err := FindLatestGame(ctx, disputeGameFactoryContract, optimismPortal2Contract)
	if err != nil {
		return ProvenWithdrawalParameters{}, fmt.Errorf("failed to find latest game: %w", err)
	}

	l2BlockNumber := new(big.Int).SetBytes(latestGame.ExtraData[0:32])
	l2OutputIndex := latestGame.Index
	return ProveWithdrawalParametersForBlock(ctx, proofCl, l2ReceiptCl, l2BlockCl, txHash, l2BlockNumber, l2OutputIndex)
}

// ProveWithdrawalParametersForBlock queries L1 & L2 to generate all withdrawal parameters and proof necessary to prove a withdrawal on L1.
// The header provided is very important. It should be a block (timestamp) for which there is a submitted output in the L2 Output Oracle
// contract. If not, the withdrawal will fail as it the storage proof cannot be verified if there is no submitted state root.
func ProveWithdrawalParametersForBlock(ctx context.Context, proofCl ProofClient, l2ReceiptCl ReceiptClient, l2BlockCl BlockClient, txHash common.Hash, l2BlockNumber, l2OutputIndex *big.Int) (ProvenWithdrawalParameters, error) {
	// Transaction receipt
	receipt, err := l2ReceiptCl.TransactionReceipt(ctx, txHash)
	if err != nil {
		return ProvenWithdrawalParameters{}, err
	}
	// Parse the receipt
	ev, err := ParseMessagePassed(receipt)
	if err != nil {
		return ProvenWithdrawalParameters{}, err
	}
	// Generate then verify the withdrawal proof
	withdrawalHash, err := WithdrawalHash(ev)
	if !bytes.Equal(withdrawalHash[:], ev.WithdrawalHash[:]) {
		return ProvenWithdrawalParameters{}, errors.New("Computed withdrawal hash incorrectly")
	}
	if err != nil {
		return ProvenWithdrawalParameters{}, err
	}
	slot := StorageSlotOfWithdrawalHash(withdrawalHash)

	// Fetch the block from the L2 node
	l2Block, err := l2BlockCl.BlockByNumber(ctx, l2BlockNumber)
	if err != nil {
		return ProvenWithdrawalParameters{}, fmt.Errorf("failed to get l2Block: %w", err)
	}

	p, err := proofCl.GetProof(ctx, predeploys.L2ToL1MessagePasserAddr, []string{slot.String()}, l2Block.Number())
	if err != nil {
		return ProvenWithdrawalParameters{}, err
	}
	if len(p.StorageProof) != 1 {
		return ProvenWithdrawalParameters{}, errors.New("invalid amount of storage proofs")
	}

	err = VerifyProof(l2Block.Root(), p)
	if err != nil {
		return ProvenWithdrawalParameters{}, err
	}

	// Encode it as expected by the contract
	trieNodes := make([][]byte, len(p.StorageProof[0].Proof))
	for i, s := range p.StorageProof[0].Proof {
		trieNodes[i] = common.FromHex(s)
	}

	return ProvenWithdrawalParameters{
		Nonce:         ev.Nonce,
		Sender:        ev.Sender,
		Target:        ev.Target,
		Value:         ev.Value,
		GasLimit:      ev.GasLimit,
		L2OutputIndex: l2OutputIndex,
		Data:          ev.Data,
		OutputRootProof: bindings.TypesOutputRootProof{
			Version:                  [32]byte{}, // Empty for version 1
			StateRoot:                l2Block.Root(),
			MessagePasserStorageRoot: p.StorageHash,
			LatestBlockhash:          l2Block.Hash(),
		},
		WithdrawalProof: trieNodes,
	}, nil
}

// FindLatestGame finds the latest game in the DisputeGameFactory contract.
func FindLatestGame(ctx context.Context, disputeGameFactoryContract *bindings.DisputeGameFactoryCaller, optimismPortal2Contract *bindingspreview.OptimismPortal2Caller) (*bindings.IDisputeGameFactoryGameSearchResult, error) {
	respectedGameType, err := optimismPortal2Contract.RespectedGameType(&bind.CallOpts{})
	if err != nil {
		return nil, fmt.Errorf("failed to get respected game type: %w", err)
	}

	gameCount, err := disputeGameFactoryContract.GameCount(&bind.CallOpts{})
	if err != nil {
		return nil, fmt.Errorf("failed to get game count: %w", err)
	}
	if gameCount.Cmp(common.Big0) == 0 {
		return nil, errors.New("no games")
	}

	searchStart := new(big.Int).Sub(gameCount, common.Big1)
	latestGames, err := disputeGameFactoryContract.FindLatestGames(&bind.CallOpts{}, respectedGameType, searchStart, common.Big1)
	if err != nil {
		return nil, fmt.Errorf("failed to get latest games: %w", err)
	}
	if len(latestGames) == 0 {
		return nil, errors.New("no latest games")
	}

	latestGame := latestGames[0]
	return &latestGame, nil
}

// Standard ABI types copied from golang ABI tests
var (
	Uint256Type, _ = abi.NewType("uint256", "", nil)
	BytesType, _   = abi.NewType("bytes", "", nil)
	AddressType, _ = abi.NewType("address", "", nil)
)

// WithdrawalHash computes the hash of the withdrawal that was stored in the L2toL1MessagePasser
// contract state.
// TODO:
//   - I don't like having to use the ABI Generated struct
//   - There should be a better way to run the ABI encoding
//   - These needs to be fuzzed against the solidity
func WithdrawalHash(ev *bindings.L2ToL1MessagePasserMessagePassed) (common.Hash, error) {
	//  abi.encode(nonce, msg.sender, _target, msg.value, _gasLimit, _data)
	args := abi.Arguments{
		{Name: "nonce", Type: Uint256Type},
		{Name: "sender", Type: AddressType},
		{Name: "target", Type: AddressType},
		{Name: "value", Type: Uint256Type},
		{Name: "gasLimit", Type: Uint256Type},
		{Name: "data", Type: BytesType},
	}
	enc, err := args.Pack(ev.Nonce, ev.Sender, ev.Target, ev.Value, ev.GasLimit, ev.Data)
	if err != nil {
		return common.Hash{}, fmt.Errorf("failed to pack for withdrawal hash: %w", err)
	}
	return crypto.Keccak256Hash(enc), nil
}

// ParseMessagePassed parses MessagePassed events from
// a transaction receipt. It does not support multiple withdrawals
// per receipt.
func ParseMessagePassed(receipt *types.Receipt) (*bindings.L2ToL1MessagePasserMessagePassed, error) {
	contract, err := bindings.NewL2ToL1MessagePasser(common.Address{}, nil)
	if err != nil {
		return nil, err
	}

	for _, log := range receipt.Logs {
		if len(log.Topics) == 0 || log.Topics[0] != MessagePassedTopic {
			continue
		}

		ev, err := contract.ParseMessagePassed(*log)
		if err != nil {
			return nil, fmt.Errorf("failed to parse log: %w", err)
		}
		return ev, nil
	}
	return nil, errors.New("Unable to find MessagePassed event")
}

// StorageSlotOfWithdrawalHash determines the storage slot of the L2ToL1MessagePasser contract to look at
// given a WithdrawalHash
func StorageSlotOfWithdrawalHash(hash common.Hash) common.Hash {
	// The withdrawals mapping is the 0th storage slot in the L2ToL1MessagePasser contract.
	// To determine the storage slot, use keccak256(withdrawalHash ++ p)
	// Where p is the 32 byte value of the storage slot and ++ is concatenation
	buf := make([]byte, 64)
	copy(buf, hash[:])
	return crypto.Keccak256Hash(buf)
}