itx.go

package itx

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

	"github.com/ChainSafe/chainbridge-core/chains/evm/calls/transactor"
	"github.com/ethereum/go-ethereum/accounts/abi"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/crypto"
)

var (
	DefaultTransactionOptions = transactor.TransactOptions{
		GasLimit: 400000,
		GasPrice: big.NewInt(1),
		Priority: 1, // slow
		Value:    big.NewInt(0),
	}
)

// itx only supports priority as string - we use uint8 to save on data
// currently we support only "slow" and "fast" - that's why 2 (medium) defaults to slow
var ItxTxPriorities = map[uint8]string{
	1: "slow",
	2: "slow",
	3: "fast",
}

type RelayTx struct {
	to   common.Address
	data []byte
	opts transactor.TransactOptions
}

type SignedRelayTx struct {
	*RelayTx
	txID common.Hash
	sig  []byte
}

type RelayCaller interface {
	CallContext(ctx context.Context, result interface{}, method string, args ...interface{}) error
}

type Forwarder interface {
	ForwarderAddress() common.Address
	ChainId() *big.Int
	UnsafeNonce() (*big.Int, error)
	UnsafeIncreaseNonce()
	LockNonce()
	UnlockNonce()
	ForwarderData(to *common.Address, data []byte, opts transactor.TransactOptions) ([]byte, error)
}

type Signer interface {
	CommonAddress() common.Address
	Sign(digestHash []byte) ([]byte, error)
}

type ITXTransactor struct {
	forwarder   Forwarder
	relayCaller RelayCaller
	signer      Signer
}

func NewITXTransactor(relayCaller RelayCaller, forwarder Forwarder, signer Signer) *ITXTransactor {
	return &ITXTransactor{
		relayCaller: relayCaller,
		forwarder:   forwarder,
		signer:      signer,
	}
}

// Transact packs tx into a forwarded transaction, signs it and sends the relayed transaction to Infura ITX
func (itx *ITXTransactor) Transact(to *common.Address, data []byte, opts transactor.TransactOptions) (*common.Hash, error) {
	err := transactor.MergeTransactionOptions(&opts, &DefaultTransactionOptions)
	if err != nil {
		return nil, err
	}
	opts.ChainID = itx.forwarder.ChainId()

	defer itx.forwarder.UnlockNonce()
	itx.forwarder.LockNonce()

	nonce, err := itx.forwarder.UnsafeNonce()
	if err != nil {
		return nil, err
	}
	opts.Nonce = nonce

	forwarderData, err := itx.forwarder.ForwarderData(to, data, opts)
	if err != nil {
		return nil, err
	}

	// increase gas limit because of forwarder overhead
	opts.GasLimit = opts.GasLimit * 11 / 10
	signedTx, err := itx.signRelayTx(&RelayTx{
		to:   itx.forwarder.ForwarderAddress(),
		data: forwarderData,
		opts: opts,
	})
	if err != nil {
		return nil, err
	}

	h, err := itx.sendTransaction(context.Background(), signedTx)
	if err != nil {
		return nil, err
	}

	itx.forwarder.UnsafeIncreaseNonce()
	return &h, nil
}

func (itx *ITXTransactor) signRelayTx(tx *RelayTx) (*SignedRelayTx, error) {
	uint256Type, _ := abi.NewType("uint256", "uint256", nil)
	addressType, _ := abi.NewType("address", "address", nil)
	bytesType, _ := abi.NewType("bytes", "bytes", nil)
	stringType, _ := abi.NewType("string", "string", nil)
	arguments := abi.Arguments{
		{Type: addressType},
		{Type: bytesType},
		{Type: uint256Type},
		{Type: uint256Type},
		{Type: stringType},
	}
	packed, err := arguments.Pack(
		tx.to,
		tx.data,
		big.NewInt(int64(tx.opts.GasLimit)),
		tx.opts.ChainID,
		ItxTxPriorities[tx.opts.Priority],
	)
	if err != nil {
		return nil, err
	}

	txID := crypto.Keccak256Hash(packed)
	msg := fmt.Sprintf("\x19Ethereum Signed Message:\n%d%s", len(txID), string(txID.Bytes()))
	hash := crypto.Keccak256Hash([]byte(msg))
	sig, err := itx.signer.Sign(hash.Bytes())
	if err != nil {
		return nil, err
	}

	return &SignedRelayTx{
		RelayTx: tx,
		sig:     sig,
		txID:    txID,
	}, nil
}

func (itx *ITXTransactor) sendTransaction(ctx context.Context, signedTx *SignedRelayTx) (common.Hash, error) {
	sig := "0x" + common.Bytes2Hex(signedTx.sig)
	txArg := map[string]interface{}{
		"to":       &signedTx.to,
		"data":     "0x" + common.Bytes2Hex(signedTx.data),
		"gas":      fmt.Sprint(signedTx.opts.GasLimit),
		"schedule": ItxTxPriorities[signedTx.opts.Priority],
	}

	resp := struct {
		RelayTransactionHash hexutil.Bytes
	}{}
	err := itx.relayCaller.CallContext(ctx, &resp, "relay_sendTransaction", txArg, sig)
	if err != nil {
		return common.Hash{}, err
	}

	return common.HexToHash(resp.RelayTransactionHash.String()), nil
}