feat: add Reverse Swaps

README.md

@@ -1 +1,7 @@
-# boltz-lnd
+# Boltz LND
+
+The LND node to which this daemon connects to, has to be version `v0.10.0-beta` or higher. Also, LND needs to be compiled with these build flags (binaries from the official releases already include them):
+
+- `routerrpc` (multi path payments)
+- `chainrpc` (block listener)
+- `walletrpc` (fee estimations)

boltz/api.go

@@ -55,7 +55,11 @@ type SwapStatusRequest struct {
 }
 
 type SwapStatusResponse struct {
-	Status string `json:"status"`
+	Status      string `json:"status"`
+	Transaction struct {
+		Id  string `json:"id"`
+		Hex string `json:"hex"`
+	} `json:"transaction"`
 
 	Error string `json:"error"`
 }
@@ -93,12 +97,32 @@ type CreateSwapRequest struct {
 
 type CreateSwapResponse struct {
 	Id                 string `json:"id"`
+	Bip21              string `json:"bip21"`
+	Address            string `json:"address"`
+	RedeemScript       string `json:"redeemScript"`
 	AcceptZeroConf     bool   `json:"acceptZeroConf"`
 	ExpectedAmount     int    `json:"expectedAmount"`
 	TimeoutBlockHeight int    `json:"timeoutBlockHeight"`
-	Address            string `json:"address"`
-	Bip21              string `json:"bip21"`
+
+	Error string `json:"error"`
+}
+
+type CreateReverseSwapRequest struct {
+	Type           string `json:"type"`
+	PairId         string `json:"pairId"`
+	OrderSide      string `json:"orderSide"`
+	InvoiceAmount  int    `json:"invoiceAmount"`
+	PreimageHash   string `json:"preimageHash"`
+	ClaimPublicKey string `json:"claimPublicKey"`
+}
+
+type CreateReverseSwapResponse struct {
+	Id                 string `json:"id"`
+	Invoice            string `json:"invoice"`
+	OnchainAmount      int    `json:"onchainAmount"`
 	RedeemScript       string `json:"redeemScript"`
+	LockupAddress      string `json:"lockupAddress"`
+	TimeoutBlockHeight int    `json:"TimeoutBlockHeight"`
 
 	Error string `json:"error"`
 }
@@ -186,6 +210,17 @@ func (boltz *Boltz) CreateSwap(request CreateSwapRequest) (*CreateSwapResponse,
 	return &response, err
 }
 
+func (boltz *Boltz) CreateReverseSwap(request CreateReverseSwapRequest) (*CreateReverseSwapResponse, error) {
+	var response CreateReverseSwapResponse
+	err := boltz.sendPostRequest("/createswap", request, &response)
+
+	if response.Error != "" {
+		return nil, errors.New(response.Error)
+	}
+
+	return &response, err
+}
+
 func (boltz *Boltz) sendGetRequest(endpoint string, response interface{}) error {
 	res, err := http.Get(boltz.URL + endpoint)
 

boltz/events.go

@@ -48,6 +48,7 @@ var swapUpdateEventStrings = map[string]SwapUpdateEvent{
 var CompletedStatus = []string{
 	SwapRefunded.String(),
 	SwapAbandoned.String(),
+	InvoiceSettled.String(),
 	TransactionClaimed.String(),
 }
 

boltz/scripts.go

@@ -10,6 +10,8 @@ import (
 	"strings"
 )
 
+var invalidRedeemScript = errors.New("invalid redeem script")
+
 func CheckSwapScript(redeemScript, preimageHash []byte, refundKey *btcec.PrivateKey, timeoutBlockHeight int) error {
 	disassembledScript, err := txscript.DisasmString(redeemScript)
 
@@ -33,7 +35,40 @@ func CheckSwapScript(redeemScript, preimageHash []byte, refundKey *btcec.Private
 	}
 
 	if disassembledScript != strings.Join(expectedScript, " ") {
-		return errors.New("invalid redeem script")
+		return invalidRedeemScript
+	}
+
+	return nil
+}
+
+func CheckReverseSwapScript(redeemScript, preimageHash []byte, claimKey *btcec.PrivateKey, timeoutBlockHeight int) error {
+	disassembledScript, err := txscript.DisasmString(redeemScript)
+
+	if err != nil {
+		return err
+	}
+
+	expectedScript := []string{
+		"OP_SIZE",
+		"20",
+		"OP_EQUAL",
+		"OP_IF",
+		"OP_HASH160",
+		hex.EncodeToString(input.Ripemd160H(preimageHash)),
+		"OP_EQUALVERIFY",
+		hex.EncodeToString(claimKey.PubKey().SerializeCompressed()),
+		"OP_ELSE",
+		"OP_DROP",
+		formatHeight(timeoutBlockHeight),
+		"OP_CHECKLOCKTIMEVERIFY",
+		"OP_DROP",
+		strings.Split(disassembledScript, " ")[13],
+		"OP_ENDIF",
+		"OP_CHECKSIG",
+	}
+
+	if disassembledScript != strings.Join(expectedScript, " ") {
+		return invalidRedeemScript
 	}
 
 	return nil

boltz/scripts_test.go

@@ -27,6 +27,25 @@ func TestCheckSwapScript(t *testing.T) {
 	assert.Equal(t, err, CheckSwapScript(redeemScript, preimageHash, refundKey, 0))
 }
 
+func TestCheckReverseSwapScript(t *testing.T) {
+	redeemScript, _ := hex.DecodeString("8201208763a9147ba0ab22fcffda41fd324aba4b5ce192ba9ec5dd882102e82694032768e49526972307874d868b67c87c37e9256c05a2c5c0474e7395e3677502f800b175210247d7443123302272524c9754b44a6e7e6e1236719e9f468e15927aa4ea26301168ac")
+	preimageHash, _ := hex.DecodeString("fa9ef1d253d34e9e44da97b00c6ec6a95058f646de35ddb7649fc3313ac6fc61")
+
+	key, _ := hex.DecodeString("dddc90e33843662631fb8c3833c4743ffd8f00a94715735633bf178e62eb291c")
+	claimKey, _ := btcec.PrivKeyFromBytes(btcec.S256(), key)
+
+	timeoutBlockHeight := 248
+
+	assert.Nil(t, CheckReverseSwapScript(redeemScript, preimageHash, claimKey, timeoutBlockHeight))
+
+	err := errors.New("invalid redeem script")
+	newKey, _ := btcec.NewPrivateKey(btcec.S256())
+
+	assert.Equal(t, err, CheckReverseSwapScript(redeemScript, []byte{}, claimKey, timeoutBlockHeight))
+	assert.Equal(t, err, CheckReverseSwapScript(redeemScript, preimageHash, newKey, timeoutBlockHeight))
+	assert.Equal(t, err, CheckReverseSwapScript(redeemScript, preimageHash, claimKey, 0))
+}
+
 func TestFormatHeight(t *testing.T) {
 	assert.Equal(t, "0400", formatHeight(4))
 	assert.Equal(t, "36a7", formatHeight(632630))

boltz/transaction.go

@@ -39,9 +39,9 @@ func ConstructTransaction(outputs []OutputDetails, outputAddress btcutil.Address
 	}
 
 	witnessSize := noFeeTransaction.SerializeSize() - noFeeTransaction.SerializeSizeStripped()
-	vByte := int64(noFeeTransaction.SerializeSizeStripped()) + int64(math.Ceil(float64(witnessSize) / 4))
+	vByte := int64(noFeeTransaction.SerializeSizeStripped()) + int64(math.Ceil(float64(witnessSize)/4))
 
-	return constructTransaction(outputs, outputAddress, vByte * satPerVbyte)
+	return constructTransaction(outputs, outputAddress, vByte*satPerVbyte)
 }
 
 func constructTransaction(outputs []OutputDetails, outputAddress btcutil.Address, fee int64) (*wire.MsgTx, error) {