staticaddr/loopin: add listening for sweep request

This commit adds the listening for sweep requests from the server.
On a sweep request the loopin manager will fetch the loop in from the
db, do sanity and safety checks and then sign the psbt for the input
and send it back to the server.

Author: sputn1ck

staticaddr/loopin/interface.go

@@ -9,6 +9,7 @@ import (
 	"github.com/lightninglabs/loop/staticaddr/address"
 	"github.com/lightninglabs/loop/staticaddr/deposit"
 	"github.com/lightninglabs/loop/staticaddr/script"
+	"github.com/lightninglabs/loop/swapserverrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/zpay32"
@@ -74,3 +75,11 @@ type QuoteGetter interface {
 		routeHints [][]zpay32.HopHint,
 		initiator string, numDeposits uint32) (*loop.LoopInQuote, error)
 }
+
+type NotificationManager interface {
+	// SubscribeStaticLoopInSweepRequests subscribes to the static loop in
+	// sweep requests. These are sent by the server to the client to request
+	// a sweep of a static loop in that has been finished.
+	SubscribeStaticLoopInSweepRequests(ctx context.Context,
+	) <-chan *swapserverrpc.ServerStaticLoopInSweepRequest
+}

staticaddr/loopin/manager.go

@@ -1,17 +1,24 @@
 package loopin
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"sync/atomic"
 	"time"
 
+	"github.com/btcsuite/btcd/btcec/v2/schnorr/musig2"
+	"github.com/btcsuite/btcd/btcutil/psbt"
 	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/txscript"
+	"github.com/btcsuite/btcd/wire"
 	"github.com/lightninglabs/lndclient"
 	"github.com/lightninglabs/loop"
 	"github.com/lightninglabs/loop/fsm"
 	"github.com/lightninglabs/loop/labels"
 	"github.com/lightninglabs/loop/staticaddr/deposit"
+	"github.com/lightninglabs/loop/swapserverrpc"
 	looprpc "github.com/lightninglabs/loop/swapserverrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/routing/route"
@@ -63,6 +70,10 @@ type Config struct {
 	// loop-in related records.
 	Store StaticAddressLoopInStore
 
+	// NotificationManager is the manager that handles the notification
+	// subscriptions.
+	NotificationManager NotificationManager
+
 	// ValidateLoopInContract validates the contract parameters against our
 	// request.
 	ValidateLoopInContract ValidateLoopInContract
@@ -150,6 +161,12 @@ func (m *Manager) Run(ctx context.Context, currentHeight uint32) error {
 		return err
 	}
 
+	// Register for notifications of loop-in sweep requests.
+	sweepReqs := m.cfg.NotificationManager.
+		SubscribeStaticLoopInSweepRequests(
+			ctx,
+		)
+
 	// Communicate to the caller that the address manager has completed its
 	// initialization.
 	close(m.initChan)
@@ -189,12 +206,169 @@ func (m *Manager) Run(ctx context.Context, currentHeight uint32) error {
 				return ctx.Err()
 			}
 
+		case sweepReq := <-sweepReqs:
+			err = m.handleLoopInSweepReq(ctx, sweepReq)
+			if err != nil {
+				log.Errorf("Error handling loop-in sweep request: %v",
+					err)
+			}
+
 		case <-ctx.Done():
 			return ctx.Err()
 		}
 	}
 }
 
+// handleLoopInSweepReq handles a loop-in sweep request from the server.
+// It first checks if the requested loop-in is finished as expected and if
+// yes will send signature to the server for the provided psbt.
+func (m *Manager) handleLoopInSweepReq(ctx context.Context,
+	req *swapserverrpc.ServerStaticLoopInSweepRequest) error {
+
+	// First we'll check if the loop-ins are known to us and in
+	// the expected state.
+	swapHash, err := lntypes.MakeHash(req.SwapHash)
+	if err != nil {
+		return err
+	}
+
+	// Fetch the loop-in from the store.
+	loopIn, err := m.cfg.Store.FetchLoopInByHash(ctx, swapHash)
+	if err != nil {
+		return err
+	}
+
+	// If the loop-in is not in the Succeeded state we return an
+	// error.
+	if loopIn.state != Succeeded {
+		return fmt.Errorf("loop-in %v not in Succeeded state",
+			swapHash)
+	}
+
+	reader := bytes.NewReader(req.SweepTxPsbt)
+	sweepPacket, err := psbt.NewFromRawBytes(reader, false)
+	if err != nil {
+		return err
+	}
+
+	sweepTx := sweepPacket.UnsignedTx
+
+	// Perform a sanity check on the number of unsigned tx inputs and
+	// prevout info.
+	if len(sweepTx.TxIn) != len(req.PrevoutInfo) {
+		return fmt.Errorf("expected %v inputs, got %v",
+			len(req.PrevoutInfo), len(sweepTx.TxIn))
+	}
+
+	prevoutMap := make(map[wire.OutPoint]*wire.TxOut)
+	var depositOutpoint *wire.OutPoint
+
+	for i := range req.PrevoutInfo {
+		prevout := req.PrevoutInfo[i]
+
+		txid, err := chainhash.NewHash(prevout.TxidBytes)
+		if err != nil {
+			return err
+		}
+
+		if i == int(req.OutputIndex) {
+			depositOutpoint = &wire.OutPoint{
+				Hash:  *txid,
+				Index: prevout.OutputIndex,
+			}
+		}
+
+		prevoutMap[wire.OutPoint{
+			Hash:  *txid,
+			Index: prevout.OutputIndex,
+		}] = &wire.TxOut{
+			Value:    int64(req.PrevoutInfo[i].Value),
+			PkScript: req.PrevoutInfo[i].PkScript,
+		}
+	}
+
+	// Check if the deposit outpoint is part of the loop-in.
+	if depositOutpoint == nil {
+		return fmt.Errorf("deposit outpoint not part of loop-in")
+	}
+
+	foundDeposit := false
+	for _, loopInDeposit := range loopIn.DepositOutpoints {
+		if loopInDeposit == fmt.Sprintf("%v:%v",
+			depositOutpoint.Hash, depositOutpoint.Index) {
+			foundDeposit = true
+		}
+	}
+
+	if !foundDeposit {
+		return fmt.Errorf("deposit outpoint not part of loop-in")
+	}
+
+	prevOutputFetcher := txscript.NewMultiPrevOutFetcher(
+		prevoutMap,
+	)
+
+	sigHashes := txscript.NewTxSigHashes(
+		sweepPacket.UnsignedTx, prevOutputFetcher,
+	)
+
+	taprootSigHash, err := txscript.CalcTaprootSignatureHash(
+		sigHashes, txscript.SigHashDefault, sweepPacket.UnsignedTx,
+		int(req.OutputIndex), prevOutputFetcher,
+	)
+	if err != nil {
+		return err
+	}
+
+	var (
+		serverNonce [musig2.PubNonceSize]byte
+		sigHash     [32]byte
+	)
+
+	copy(serverNonce[:], req.Nonce)
+	musig2Session, err := loopIn.createMusig2Session(ctx, m.cfg.Signer)
+	if err != nil {
+		return err
+	}
+
+	haveAllNonces, err := m.cfg.Signer.MuSig2RegisterNonces(
+		ctx, musig2Session.SessionID,
+		[][musig2.PubNonceSize]byte{serverNonce},
+	)
+	if err != nil {
+		return err
+	}
+
+	if !haveAllNonces {
+		return fmt.Errorf("expected all nonces to be registered")
+	}
+
+	copy(sigHash[:], taprootSigHash)
+
+	// Since our MuSig2 session has all nonces, we can now create
+	// the local partial signature by signing the sig hash.
+	sig, err := m.cfg.Signer.MuSig2Sign(
+		ctx, musig2Session.SessionID, sigHash, false,
+	)
+	if err != nil {
+		return err
+	}
+
+	txHash := sweepTx.TxHash()
+
+	// We'll now push the signature to the server.
+	_, err = m.cfg.Server.PushStaticAddressSweeplessSigs(
+		ctx, &looprpc.PushStaticAddressSweeplessSigsRequest{
+			TxHash:      txHash[:],
+			SwapHash:    loopIn.SwapHash[:],
+			OutputIndex: req.OutputIndex,
+			Nonce:       musig2Session.PublicNonce[:],
+			Sig:         sig,
+		},
+	)
+	return err
+}
+
 // recover stars a loop-in state machine for each non-final loop-in to pick up
 // work where it was left off before the restart.
 func (m *Manager) recoverLoopIns(ctx context.Context) error {