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refundtx.go
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refundtx.go
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package dlc
import (
"errors"
"fmt"
"github.com/btcsuite/btcd/btcec"
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
)
// RefundTx creates refund tx
// refund transaction
// input:
// [0]:fund transaction output[0]
// Sequence (0xfeffffff LE)
// output:
// [0]:p2wpkh a
// [1]:p2wpkh b
// locktime:
// Value decided by contract.
func (d *DLC) RefundTx() (*wire.MsgTx, error) {
tx, err := d.newRedeemTx()
if err != nil {
return nil, err
}
// use locktime
tx.TxIn[fundTxInAt].Sequence-- // max(0xffffffff-0x01)
tx.LockTime = d.Conds.RefundLockTime
// txouts
for _, p := range []Contractor{FirstParty, SecondParty} {
txout, err := d.distTxOut(p, d.Conds.FundAmts[p])
if err != nil {
fmt.Printf("err in closing tx out: %+v\n", err)
return nil, err
}
tx.AddTxOut(txout)
}
return tx, nil
}
// SignRefundTx creates signature for a refund tx, sets it, and returns it
func (b *Builder) SignRefundTx() ([]byte, error) {
tx, err := b.Contract.RefundTx()
if err != nil {
return nil, err
}
sig, err := b.witsigForFundScript(tx)
if err != nil {
return nil, err
}
b.Contract.RefundSigs[b.party] = sig
return sig, nil
}
// SignedRefundTx returns a refund tx with its witness signature
func (d *DLC) SignedRefundTx() (*wire.MsgTx, error) {
tx, err := d.RefundTx()
if err != nil {
return nil, err
}
wt, err := d.witnessForRefundTx()
if err != nil {
return nil, err
}
tx.TxIn[0].Witness = wt
return tx, nil
}
func (d *DLC) witnessForRefundTx() (wire.TxWitness, error) {
sc, err := d.fundScript()
if err != nil {
return nil, err
}
sig1 := d.RefundSigs[FirstParty]
if sig1 == nil {
return nil, errors.New("First party must sign refund tx")
}
sig2 := d.RefundSigs[SecondParty]
if sig2 == nil {
return nil, errors.New("Second party must sign refund tx")
}
wt := wire.TxWitness{[]byte{}, sig1, sig2, sc}
return wt, nil
}
// AcceptRefundTxSignature verifies couterparty's given signature is valid and then
func (b *Builder) AcceptRefundTxSignature(sig []byte) error {
p := counterparty(b.party)
err := b.Contract.VerifyRefundTx(sig, b.Contract.Pubs[p])
if err != nil {
return err
}
// accept verified signature
b.Contract.RefundSigs[p] = sig
return nil
}
// VerifyRefundTx verifies the refund transaction signature.
// Returns nil if the passed signature is valid and corresponds to the passed
// in public key, and an error if it isnt.
func (d *DLC) VerifyRefundTx(sig []byte, pub *btcec.PublicKey) error {
// parse signature
s, err := btcec.ParseDERSignature(sig, btcec.S256())
if err != nil {
return err
}
// verify
script, err := d.fundScript()
if err != nil {
return err
}
if script == nil {
return fmt.Errorf("fund script not found ")
}
tx, err := d.RefundTx()
if err != nil {
return err
}
sighashes := txscript.NewTxSigHashes(tx)
fundtx, err := d.FundTx()
if err != nil {
return err
}
amt := fundtx.TxOut[0].Value
hash, err := txscript.CalcWitnessSigHash(script, sighashes, txscript.SigHashAll,
tx, 0, amt)
if err != nil {
return err
}
verify := s.Verify(hash, pub)
if !verify {
return fmt.Errorf("verify fail : %v", verify)
}
return nil
}
// SendRefundTx sends refund tx
func (b *Builder) SendRefundTx() error {
tx, err := b.Contract.SignedRefundTx()
if err != nil {
return err
}
_, err = b.wallet.SendRawTransaction(tx)
return err
}