client: LoopOutQuote to support estimate using v3 htlc

client.go

@@ -499,7 +499,23 @@ func (s *Client) LoopOutQuote(ctx context.Context,
 
 	log.Infof("Offchain swap destination: %x", quote.SwapPaymentDest)
 
-	swapFee := quote.SwapFee
+	minerFee, err := s.getLoopOutSweepFee(ctx, request.SweepConfTarget)
+	if err != nil {
+		return nil, err
+	}
+
+	return &LoopOutQuote{
+		SwapFee:         quote.SwapFee,
+		MinerFee:        minerFee,
+		PrepayAmount:    quote.PrepayAmount,
+		SwapPaymentDest: quote.SwapPaymentDest,
+	}, nil
+}
+
+// getLoopOutSweepFee is a helper method to estimate the loop out htlc sweep
+// fee to a p2wsh address.
+func (s *Client) getLoopOutSweepFee(ctx context.Context, confTarget int32) (
+	btcutil.Amount, error) {
 
 	// Generate dummy p2wsh address for fee estimation. The p2wsh address
 	// type is chosen because it adds the most weight of all output types
@@ -509,23 +525,21 @@ func (s *Client) LoopOutQuote(ctx context.Context,
 		wsh[:], s.lndServices.ChainParams,
 	)
 	if err != nil {
-		return nil, err
+		return 0, err
 	}
 
-	minerFee, err := s.sweeper.GetSweepFee(
+	scriptVersion := GetHtlcScriptVersion(
-		ctx, swap.QuoteHtlc.AddSuccessToEstimator,
+		loopdb.CurrentProtocolVersion(),
-		p2wshAddress, request.SweepConfTarget,
 	)
-	if err != nil {
+
-		return nil, err
+	htlc := swap.QuoteHtlcP2TR
+	if scriptVersion != swap.HtlcV3 {
+		htlc = swap.QuoteHtlcP2WSH
 	}
 
-	return &LoopOutQuote{
+	return s.sweeper.GetSweepFee(
-		SwapFee:         swapFee,
+		ctx, htlc.AddSuccessToEstimator, p2wshAddress, confTarget,
-		MinerFee:        minerFee,
+	)
-		PrepayAmount:    quote.PrepayAmount,
-		SwapPaymentDest: quote.SwapPaymentDest,
-	}, nil
 }
 
 // LoopOutTerms returns the terms on which the server executes swaps.

swap/htlc.go

@@ -108,17 +108,30 @@ type Htlc struct {
 }
 
 var (
-	quoteKey [33]byte
+	// dummyPubKey is a valid public key use for the quote htlc
+	// construction.
+	dummyPubKey = [33]byte{
+		0x03, 0x26, 0x89, 0xc7, 0xc2, 0xda, 0xb1, 0x33, 0x09, 0xfb,
+		0x14, 0x3e, 0x0e, 0x8f, 0xe3, 0x96, 0x34, 0x25, 0x21, 0x88,
+		0x7e, 0x97, 0x66, 0x90, 0xb6, 0xb4, 0x7f, 0x5b, 0x2a, 0x4b,
+		0x7d, 0x44, 0x8e,
+	}
 
+	// quoteHash is an empty hash used for the quote htlc construction.
 	quoteHash lntypes.Hash
 
-	// QuoteHtlc is a template script just used for fee estimation. It uses
+	// QuoteHtlcP2WSH is a template script just used for sweep fee
-	// the maximum value for cltv expiry to get the maximum (worst case)
+	// estimation.
-	// script size.
+	QuoteHtlcP2WSH, _ = NewHtlc(
-	QuoteHtlc, _ = NewHtlc(
+		HtlcV2, ^int32(0), dummyPubKey, dummyPubKey, quoteHash,
-		HtlcV2,
+		HtlcP2WSH, &chaincfg.MainNetParams,
-		^int32(0), quoteKey, quoteKey, quoteHash, HtlcP2WSH,
+	)
-		&chaincfg.MainNetParams,
+
+	// QuoteHtlcP2TR is a template script just used for sweep fee
+	// estimation.
+	QuoteHtlcP2TR, _ = NewHtlc(
+		HtlcV3, ^int32(0), dummyPubKey, dummyPubKey, quoteHash,
+		HtlcP2TR, &chaincfg.MainNetParams,
 	)
 
 	// ErrInvalidScriptVersion is returned when an unknown htlc version