From 9d498044299f7d0c1caeb3b09ab9633cc5a4bd5b Mon Sep 17 00:00:00 2001
From: sputn1ck <kon@kon.ninja>
Date: Wed, 22 Jan 2025 09:54:59 +0100
Subject: [PATCH] assetclient: fix wrong fee limit

---
 assets/client.go      | 34 +++++++++++++++++++---
 assets/client_test.go | 67 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+), 4 deletions(-)
 create mode 100644 assets/client_test.go

diff --git a/assets/client.go b/assets/client.go
index 4024e30b..9a80547e 100644
--- a/assets/client.go
+++ b/assets/client.go
@@ -16,6 +16,7 @@ import (
 	"github.com/lightninglabs/taproot-assets/taprpc/tapchannelrpc"
 	"github.com/lightninglabs/taproot-assets/taprpc/universerpc"
 	"github.com/lightningnetwork/lnd/lnrpc"
+	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/macaroons"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials"
@@ -105,9 +106,12 @@ func (c *TapdClient) GetRfqForAsset(ctx context.Context,
 	expiry int64, feeLimitMultiplier float64) (
 	*rfqrpc.PeerAcceptedSellQuote, error) {
 
-	feeLimit, err := lnrpc.UnmarshallAmt(
-		int64(satAmount)+int64(satAmount.MulF64(feeLimitMultiplier)), 0,
-	)
+	// paymentMaxAmt is the maximum amount we are willing to pay for the
+	// payment.
+	// E.g. on a 250k sats payment we'll multiply the sat amount by 1.2.
+	// The resulting maximum amount we're willing to pay is 300k sats.
+	// The response asset amount will be for those 300k sats.
+	paymentMaxAmt, err := getPaymentMaxAmount(satAmount, feeLimitMultiplier)
 	if err != nil {
 		return nil, err
 	}
@@ -120,7 +124,7 @@ func (c *TapdClient) GetRfqForAsset(ctx context.Context,
 				},
 			},
 			PeerPubKey:     peerPubkey,
-			PaymentMaxAmt:  uint64(feeLimit),
+			PaymentMaxAmt:  uint64(paymentMaxAmt),
 			Expiry:         uint64(expiry),
 			TimeoutSeconds: uint32(c.cfg.RFQtimeout.Seconds()),
 		})
@@ -180,6 +184,28 @@ func (c *TapdClient) GetAssetName(ctx context.Context,
 	return assetName, nil
 }
 
+// getPaymentMaxAmount returns the milisat amount we are willing to pay for the
+// payment.
+func getPaymentMaxAmount(satAmount btcutil.Amount, feeLimitMultiplier float64) (
+	lnwire.MilliSatoshi, error) {
+
+	if satAmount == 0 {
+		return 0, fmt.Errorf("satAmount cannot be zero")
+	}
+	if feeLimitMultiplier < 1 {
+		return 0, fmt.Errorf("feeLimitMultiplier must be at least 1")
+	}
+
+	// paymentMaxAmt is the maximum amount we are willing to pay for the
+	// payment.
+	// E.g. on a 250k sats payment we'll multiply the sat amount by 1.2.
+	// The resulting maximum amount we're willing to pay is 300k sats.
+	// The response asset amount will be for those 300k sats.
+	return lnrpc.UnmarshallAmt(
+		int64(satAmount.MulF64(feeLimitMultiplier)), 0,
+	)
+}
+
 func getClientConn(config *TapdConfig) (*grpc.ClientConn, error) {
 	// Load the specified TLS certificate and build transport credentials.
 	creds, err := credentials.NewClientTLSFromFile(config.TLSPath, "")
diff --git a/assets/client_test.go b/assets/client_test.go
new file mode 100644
index 00000000..d783b9d5
--- /dev/null
+++ b/assets/client_test.go
@@ -0,0 +1,67 @@
+package assets
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/btcutil"
+	"github.com/lightningnetwork/lnd/lnwire"
+)
+
+func TestGetPaymentMaxAmount(t *testing.T) {
+	tests := []struct {
+		satAmount          btcutil.Amount
+		feeLimitMultiplier float64
+		expectedAmount     lnwire.MilliSatoshi
+		expectError        bool
+	}{
+		{
+			satAmount:          btcutil.Amount(250000),
+			feeLimitMultiplier: 1.2,
+			expectedAmount:     lnwire.MilliSatoshi(300000000),
+			expectError:        false,
+		},
+		{
+			satAmount:          btcutil.Amount(100000),
+			feeLimitMultiplier: 1.5,
+			expectedAmount:     lnwire.MilliSatoshi(150000000),
+			expectError:        false,
+		},
+		{
+			satAmount:          btcutil.Amount(50000),
+			feeLimitMultiplier: 2.0,
+			expectedAmount:     lnwire.MilliSatoshi(100000000),
+			expectError:        false,
+		},
+		{
+			satAmount:          btcutil.Amount(0),
+			feeLimitMultiplier: 1.2,
+			expectedAmount:     lnwire.MilliSatoshi(0),
+			expectError:        true,
+		},
+		{
+			satAmount:          btcutil.Amount(250000),
+			feeLimitMultiplier: 0.8,
+			expectedAmount:     lnwire.MilliSatoshi(0),
+			expectError:        true,
+		},
+	}
+
+	for _, test := range tests {
+		result, err := getPaymentMaxAmount(
+			test.satAmount, test.feeLimitMultiplier,
+		)
+		if test.expectError {
+			if err == nil {
+				t.Fatalf("expected error but got none")
+			}
+		} else {
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if result != test.expectedAmount {
+				t.Fatalf("expected %v, got %v",
+					test.expectedAmount, result)
+			}
+		}
+	}
+}