multi: add session to swap kit

loopin.go

@@ -9,6 +9,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/btcsuite/btcd/btcec/v2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/mempool"
@@ -19,6 +20,7 @@ import (
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnrpc/invoicesrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwallet/chainfee"
@@ -248,9 +250,17 @@ func newLoopInSwap(globalCtx context.Context, cfg *swapConfig,
 		},
 	}
 
+	// TODO - add nonce to server reponse and add to session
+	session, err := swap.NewMusig2Session(
+		globalCtx, cfg.lnd, keyDesc, swapResp.receiverKey,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	swapKit := newSwapKit(
 		swapHash, swap.TypeIn,
-		cfg, &contract.SwapContract,
+		cfg, &contract.SwapContract, session,
 	)
 
 	swapKit.lastUpdateTime = initiationTime
@@ -349,16 +359,34 @@ func awaitProbe(ctx context.Context, lnd lndclient.LndServices,
 
 // resumeLoopInSwap returns a swap object representing a pending swap that has
 // been restored from the database.
-func resumeLoopInSwap(_ context.Context, cfg *swapConfig,
+func resumeLoopInSwap(ctx context.Context, cfg *swapConfig,
 	pend *loopdb.LoopIn) (*loopInSwap, error) {
 
 	hash := lntypes.Hash(sha256.Sum256(pend.Contract.Preimage[:]))
 
 	log.Infof("Resuming loop in swap %v", hash)
 
+	pubkey, err := btcec.ParsePubKey(pend.Contract.SenderKey[:])
+	if err != nil {
+		return nil, err
+	}
+
+	keyDesc := &keychain.KeyDescriptor{
+		PubKey: pubkey,
+		// TODO - NB! get locator for key, otherwise we won't resume
+		// session with the right key.
+		KeyLocator: keychain.KeyLocator{},
+	}
+	session, err := swap.NewMusig2Session(
+		ctx, cfg.lnd, keyDesc, pend.Contract.ReceiverKey,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	swapKit := newSwapKit(
 		hash, swap.TypeIn, cfg,
-		&pend.Contract.SwapContract,
+		&pend.Contract.SwapContract, session,
 	)
 
 	swap := &loopInSwap{

loopout.go

@@ -10,6 +10,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/btcsuite/btcd/wire"
@@ -20,6 +22,7 @@ import (
 	"github.com/lightninglabs/loop/sweep"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/keychain"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/zpay32"
@@ -153,6 +156,22 @@ func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 		confs = loopdb.DefaultLoopOutHtlcConfirmations
 	}
 
+	// Create a musig session using the key and nonce shared from the
+	// server.
+	var serverNonce [musig2.PubNonceSize]byte
+	copy(serverNonce[:], swapResp.nonce[:])
+
+	opt := lndclient.MusigNonceOpt([][musig2.PubNonceSize]byte{
+		serverNonce,
+	})
+
+	session, err := swap.NewMusig2Session(
+		globalCtx, cfg.lnd, keyDesc, swapResp.senderKey, opt,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	// Instantiate a struct that contains all required data to start the
 	// swap.
 	initiationTime := time.Now()
@@ -184,7 +203,7 @@ func newLoopOutSwap(globalCtx context.Context, cfg *swapConfig,
 
 	swapKit := newSwapKit(
 		swapHash, swap.TypeOut,
-		cfg, &contract.SwapContract,
+		cfg, &contract.SwapContract, session,
 	)
 
 	swapKit.lastUpdateTime = initiationTime
@@ -238,9 +257,27 @@ func resumeLoopOutSwap(reqContext context.Context, cfg *swapConfig,
 
 	log.Infof("Resuming loop out swap %v", hash)
 
+	pubkey, err := btcec.ParsePubKey(pend.Contract.ReceiverKey[:])
+	if err != nil {
+		return nil, err
+	}
+
+	keyDesc := &keychain.KeyDescriptor{
+		PubKey: pubkey,
+		// TODO - get key locator or we will resume with the wrong
+		// key!!
+		KeyLocator: keychain.KeyLocator{},
+	}
+	session, err := swap.NewMusig2Session(
+		reqContext, cfg.lnd, keyDesc, pend.Contract.SenderKey,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	swapKit := newSwapKit(
 		hash, swap.TypeOut, cfg,
-		&pend.Contract.SwapContract,
+		&pend.Contract.SwapContract, session,
 	)
 
 	// Create the htlc.

swap.go

@@ -28,10 +28,13 @@ type swapKit struct {
 	swapType swap.Type
 
 	swapConfig
+
+	musig2Session *lndclient.MuSig2Session
 }
 
 func newSwapKit(hash lntypes.Hash, swapType swap.Type, cfg *swapConfig,
-	contract *loopdb.SwapContract) *swapKit {
+	contract *loopdb.SwapContract,
+	session *lndclient.MuSig2Session) *swapKit {
 
 	log := &swap.PrefixLog{
 		Hash:   hash,
@@ -45,6 +48,7 @@ func newSwapKit(hash lntypes.Hash, swapType swap.Type, cfg *swapConfig,
 		state:         loopdb.StateInitiated,
 		contract:      contract,
 		swapType:      swapType,
+		musig2Session: session,
 	}
 }
 

swap/musig2.go

@@ -0,0 +1,29 @@
+package swap
+
+import (
+	"context"
+
+	"github.com/btcsuite/btcd/btcec/v2"
+	"github.com/btcsuite/btcd/btcec/v2/schnorr"
+	"github.com/lightninglabs/lndclient"
+	"github.com/lightningnetwork/lnd/keychain"
+)
+
+// NewMuSig2Session creates a new musig session.
+func NewMusig2Session(ctx context.Context, lnd *lndclient.LndServices,
+	ourKey *keychain.KeyDescriptor, theirKey [33]byte,
+	opts ...lndclient.MuSigSessionOpts) (*lndclient.MuSig2Session, error) {
+
+	theirPubkey, err := btcec.ParsePubKey(theirKey[:])
+	if err != nil {
+		return nil, err
+	}
+
+	signers := make([][32]byte, 2)
+	copy(signers[0][:], schnorr.SerializePubKey(ourKey.PubKey))
+	copy(signers[1][:], schnorr.SerializePubKey(theirPubkey))
+
+	return lnd.Signer.NewMuSig2Session(
+		ctx, &ourKey.KeyLocator, signers, opts...,
+	)
+}