loopd: fractional static address swap amount

cmd/loop/staticaddr.go

@@ -458,6 +458,13 @@ var staticAddressLoopInCommand = cli.Command{
 				"The client can retry the swap with adjusted " +
 				"parameters after the payment timed out.",
 		},
+		cli.IntFlag{
+			Name: "amount",
+			Usage: "the number of satoshis that should be " +
+				"swapped from the selected deposits. If there" +
+				"is change it is sent back to the static " +
+				"address.",
+		},
 		lastHopFlag,
 		labelFlag,
 		routeHintsFlag,
@@ -552,6 +559,7 @@ func staticAddressLoopIn(ctx *cli.Context) error {
 	}
 
 	quoteReq := &looprpc.QuoteRequest{
+		Amt:              ctx.Int64("amount"),
 		LoopInRouteHints: hints,
 		LoopInLastHop:    lastHop,
 		Private:          ctx.Bool(privateFlag.Name),
@@ -564,15 +572,6 @@ func staticAddressLoopIn(ctx *cli.Context) error {
 
 	limits := getInLimits(quote)
 
-	// populate the quote request with the sum of selected deposits and
-	// prompt the user for acceptance.
-	quoteReq.Amt, err = sumDeposits(
-		depositOutpoints, depositList.FilteredDeposits,
-	)
-	if err != nil {
-		return err
-	}
-
 	if !(ctx.Bool("force") || ctx.Bool("f")) {
 		err = displayInDetails(quoteReq, quote, ctx.Bool("verbose"))
 		if err != nil {
@@ -585,6 +584,7 @@ func staticAddressLoopIn(ctx *cli.Context) error {
 	}
 
 	req := &looprpc.StaticAddressLoopInRequest{
+		Amount:                quoteReq.Amt,
 		Outpoints:             depositOutpoints,
 		MaxSwapFeeSatoshis:    int64(limits.maxSwapFee),
 		LastHop:               lastHop,
@@ -617,26 +617,6 @@ func containsDuplicates(outpoints []string) bool {
 	return false
 }
 
-func sumDeposits(outpoints []string, deposits []*looprpc.Deposit) (int64,
-	error) {
-
-	var sum int64
-	depositMap := make(map[string]*looprpc.Deposit)
-	for _, deposit := range deposits {
-		depositMap[deposit.Outpoint] = deposit
-	}
-
-	for _, outpoint := range outpoints {
-		if _, ok := depositMap[outpoint]; !ok {
-			return 0, fmt.Errorf("deposit %v not found", outpoint)
-		}
-
-		sum += depositMap[outpoint].Value
-	}
-
-	return sum, nil
-}
-
 func depositsToOutpoints(deposits []*looprpc.Deposit) []string {
 	outpoints := make([]string, 0, len(deposits))
 	for _, deposit := range deposits {

loopd/swapclient_server.go

@@ -34,8 +34,10 @@ import (
 	"github.com/lightninglabs/loop/swap"
 	"github.com/lightninglabs/loop/swapserverrpc"
 	"github.com/lightninglabs/taproot-assets/rfqmath"
+	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
 	"github.com/lightningnetwork/lnd/lntypes"
+	"github.com/lightningnetwork/lnd/lnwallet"
 	"github.com/lightningnetwork/lnd/queue"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/zpay32"
@@ -845,21 +847,30 @@ func (s *swapClientServer) GetLoopInQuote(ctx context.Context,
 	log.Infof("Loop in quote request received")
 
 	var (
-		numDeposits = uint32(len(req.DepositOutpoints))
-		err         error
+		selectedAmount        = btcutil.Amount(req.Amt)
+		selectedDepositAmount btcutil.Amount
+		numDeposits           = len(req.DepositOutpoints)
+		err                   error
 	)
 
+	if selectedAmount == 0 && numDeposits == 0 {
+		return nil, fmt.Errorf("amount and deposit outpoints " +
+			"cannot both be zero")
+	}
+
 	htlcConfTarget, err := validateLoopInRequest(
-		req.ConfTarget, req.ExternalHtlc, numDeposits, req.Amt,
+		req.ConfTarget, req.ExternalHtlc, uint32(numDeposits), req.Amt,
 	)
 	if err != nil {
 		return nil, err
 	}
 
 	// Retrieve deposits to calculate their total value.
 	var depositList *looprpc.ListStaticAddressDepositsResponse
-	amount := btcutil.Amount(req.Amt)
-	if len(req.DepositOutpoints) > 0 {
+
+	// If deposits are selected, we need to retrieve them to calculate the
+	// total value which we request a quote for. If a
+	if numDeposits > 0 {
 		depositList, err = s.ListStaticAddressDeposits(
 			ctx, &looprpc.ListStaticAddressDepositsRequest{
 				Outpoints: req.DepositOutpoints,
@@ -874,20 +885,34 @@ func (s *swapClientServer) GetLoopInQuote(ctx context.Context,
 				"deposit outpoints")
 		}
 
-		// The requested amount should be 0 here if the request
-		// contained deposit outpoints.
-		if amount != 0 && len(depositList.FilteredDeposits) > 0 {
-			return nil, fmt.Errorf("amount should be 0 for " +
-				"deposit quotes")
+		if numDeposits != len(depositList.FilteredDeposits) {
+			return nil, fmt.Errorf("expected %d deposits, got %d",
+				numDeposits, len(depositList.FilteredDeposits))
 		}
 
 		// In case we quote for deposits we send the server both the
-		// total value and the number of deposits. This is so the server
-		// can probe the total amount and calculate the per input fee.
-		if amount == 0 && len(depositList.FilteredDeposits) > 0 {
-			for _, deposit := range depositList.FilteredDeposits {
-				amount += btcutil.Amount(deposit.Value)
-			}
+		// selected value and the number of deposits. This is so the
+		// server can probe the selected value and calculate the per
+		// input fee.
+		for _, deposit := range depositList.FilteredDeposits {
+			selectedDepositAmount += btcutil.Amount(
+				deposit.Value,
+			)
+		}
+
+		// If the selected amount would leave a dust change output or
+		// exceeds the total deposits value, we return an error.
+		dustLimit := lnwallet.DustLimitForSize(input.P2TRSize)
+		if selectedDepositAmount-selectedAmount < dustLimit {
+			return nil, fmt.Errorf("selected amount %v leaves "+
+				"dust or exceeds total deposit value %v",
+				selectedAmount, selectedDepositAmount)
+		}
+
+		// If the client didn't select an amount we quote for the total
+		// deposits value.
+		if selectedAmount == 0 {
+			selectedAmount = selectedDepositAmount
 		}
 	}
 
@@ -914,14 +939,14 @@ func (s *swapClientServer) GetLoopInQuote(ctx context.Context,
 	}
 
 	quote, err := s.impl.LoopInQuote(ctx, &loop.LoopInQuoteRequest{
-		Amount:         amount,
+		Amount:         selectedAmount,
 		HtlcConfTarget: htlcConfTarget,
 		ExternalHtlc:   req.ExternalHtlc,
 		LastHop:        lastHop,
 		RouteHints:     routeHints,
 		Private:        req.Private,
 		Initiator:      defaultLoopdInitiator,
-		NumDeposits:    numDeposits,
+		NumDeposits:    uint32(numDeposits),
 	})
 	if err != nil {
 		return nil, err
@@ -1764,6 +1789,7 @@ func (s *swapClientServer) StaticAddressLoopIn(ctx context.Context,
 	}
 
 	req := &loop.StaticAddressLoopInRequest{
+		SelectedAmount:        btcutil.Amount(in.Amount),
 		DepositOutpoints:      in.Outpoints,
 		MaxSwapFee:            btcutil.Amount(in.MaxSwapFeeSatoshis),
 		Label:                 in.Label,