From e1f1077f4426fdde2cf01e8183c629af6280884c Mon Sep 17 00:00:00 2001
From: Boris Nagaev <bnagaev@gmail.com>
Date: Wed, 15 Apr 2026 00:29:08 -0500
Subject: [PATCH] loop+test: add loop-in route hint regression

---
 loopin_test.go        | 71 +++++++++++++++++++++++++++++++++++++++++++
 server_mock_test.go   | 10 +++---
 test/invoices_mock.go | 10 ++++--
 3 files changed, 85 insertions(+), 6 deletions(-)

diff --git a/loopin_test.go b/loopin_test.go
index 156f1d60..a1a09584 100644
--- a/loopin_test.go
+++ b/loopin_test.go
@@ -10,6 +10,7 @@ import (
 	"github.com/btcsuite/btcd/wire"
 	"github.com/lightninglabs/lndclient"
 	"github.com/lightninglabs/loop/loopdb"
+	"github.com/lightninglabs/loop/swap"
 	"github.com/lightninglabs/loop/test"
 	"github.com/lightninglabs/loop/utils"
 	"github.com/lightningnetwork/lnd/chainntnfs"
@@ -17,6 +18,7 @@ import (
 	invpkg "github.com/lightningnetwork/lnd/invoices"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/lightningnetwork/lnd/zpay32"
 	"github.com/stretchr/testify/require"
 )
 
@@ -124,6 +126,39 @@ func TestLoopInSuccess(t *testing.T) {
 	})
 }
 
+// TestLoopInSwapInvoiceRouteHintsMatchProbe asserts that explicit route hints
+// are preserved on both loop-in invoices. The probe invoice already keeps the
+// requested hints, while the swap invoice currently loses them via the
+// lndclient AddInvoice wrapper.
+func TestLoopInSwapInvoiceRouteHintsMatchProbe(t *testing.T) {
+	t.Parallel()
+
+	ctx := newLoopInTestContext(t)
+	cfg := newSwapConfig(
+		&ctx.lnd.LndServices, ctx.store, ctx.server, nil,
+		clock.NewTestClock(time.Unix(123, 0)),
+	)
+
+	req := testLoopInRequest
+	req.RouteHints = testLoopInRouteHints()
+
+	_, err := newLoopInSwap(t.Context(), cfg, 600, &req)
+	require.NoError(t, err)
+
+	_, swapRouteHints, _, _, err := swap.DecodeInvoice(
+		ctx.lnd.ChainParams, ctx.server.swapInvoice,
+	)
+	require.NoError(t, err)
+
+	_, probeRouteHints, _, _, err := swap.DecodeInvoice(
+		ctx.lnd.ChainParams, ctx.server.probeInvoice,
+	)
+	require.NoError(t, err)
+
+	test.RequireRouteHintsEqual(t, req.RouteHints, probeRouteHints)
+	test.RequireRouteHintsEqual(t, probeRouteHints, swapRouteHints)
+}
+
 func testLoopInSuccess(t *testing.T) {
 	defer test.Guard(t)()
 
@@ -233,6 +268,42 @@ func testLoopInSuccess(t *testing.T) {
 	require.NoError(t, <-errChan)
 }
 
+// testLoopInRouteHints returns deterministic explicit route hints that can be
+// encoded into loop-in invoices for regression tests.
+func testLoopInRouteHints() [][]zpay32.HopHint {
+	_, pubKey1 := test.CreateKey(11)
+	_, pubKey2 := test.CreateKey(12)
+	_, pubKey3 := test.CreateKey(13)
+
+	return [][]zpay32.HopHint{
+		{
+			{
+				NodeID:                    pubKey1,
+				ChannelID:                 1,
+				FeeBaseMSat:               10,
+				FeeProportionalMillionths: 20,
+				CLTVExpiryDelta:           30,
+			},
+			{
+				NodeID:                    pubKey2,
+				ChannelID:                 2,
+				FeeBaseMSat:               11,
+				FeeProportionalMillionths: 21,
+				CLTVExpiryDelta:           31,
+			},
+		},
+		{
+			{
+				NodeID:                    pubKey3,
+				ChannelID:                 3,
+				FeeBaseMSat:               12,
+				FeeProportionalMillionths: 22,
+				CLTVExpiryDelta:           32,
+			},
+		},
+	}
+}
+
 // TestLoopInTimeout tests scenarios where the server doesn't sweep the htlc
 // and the client is forced to reclaim the funds using the timeout tx.
 func TestLoopInTimeout(t *testing.T) {
diff --git a/server_mock_test.go b/server_mock_test.go
index 4baceb64..0e8c029b 100644
--- a/server_mock_test.go
+++ b/server_mock_test.go
@@ -40,9 +40,10 @@ type serverMock struct {
 
 	height int32
 
-	swapInvoice string
-	swapHash    lntypes.Hash
-	prepayHash  lntypes.Hash
+	swapInvoice  string
+	probeInvoice string
+	swapHash     lntypes.Hash
+	prepayHash   lntypes.Hash
 
 	// preimagePush is a channel that preimage pushes are sent into.
 	preimagePush chan lntypes.Preimage
@@ -157,7 +158,7 @@ func getInvoice(hash lntypes.Hash, amt btcutil.Amount, memo string) (string, err
 }
 
 func (s *serverMock) NewLoopInSwap(_ context.Context, swapHash lntypes.Hash,
-	amount btcutil.Amount, _, _ [33]byte, swapInvoice, _ string,
+	amount btcutil.Amount, _, _ [33]byte, swapInvoice, probeInvoice string,
 	_ *route.Vertex, _ string) (*newLoopInResponse, error) {
 
 	_, receiverKey := test.CreateKey(101)
@@ -175,6 +176,7 @@ func (s *serverMock) NewLoopInSwap(_ context.Context, swapHash lntypes.Hash,
 	)
 
 	s.swapInvoice = swapInvoice
+	s.probeInvoice = probeInvoice
 	s.swapHash = swapHash
 
 	// Simulate the server paying the probe invoice and expect the client to
diff --git a/test/invoices_mock.go b/test/invoices_mock.go
index 0174a925..7b0f309d 100644
--- a/test/invoices_mock.go
+++ b/test/invoices_mock.go
@@ -83,11 +83,17 @@ func (s *mockInvoices) AddHoldInvoice(ctx context.Context,
 	// Create and encode the payment request as a bech32 (zpay32) string.
 	creationDate := time.Now()
 
-	payReq, err := zpay32.NewInvoice(
-		s.lnd.ChainParams, *hash, creationDate,
+	options := []func(*zpay32.Invoice){
 		zpay32.Description(in.Memo),
 		zpay32.CLTVExpiry(in.CltvExpiry),
 		zpay32.Amount(in.Value),
+	}
+	for _, routeHint := range in.RouteHints {
+		options = append(options, zpay32.RouteHint(routeHint))
+	}
+
+	payReq, err := zpay32.NewInvoice(
+		s.lnd.ChainParams, *hash, creationDate, options...,
 	)
 	if err != nil {
 		return "", err