routerrpc: inject clock for testable expiry validation

Refactors payment request expiry validation to use an injected clock
dependency instead of calling time.Now() directly.

lnrpc/routerrpc/router_backend.go

@@ -15,6 +15,7 @@ import (
 	"github.com/btcsuite/btcd/wire"
 	sphinx "github.com/lightningnetwork/lightning-onion"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/clock"
 	"github.com/lightningnetwork/lnd/feature"
 	"github.com/lightningnetwork/lnd/fn/v2"
 	"github.com/lightningnetwork/lnd/htlcswitch"
@@ -118,6 +119,10 @@ type RouterBackend struct {
 	// ShouldSetExpEndorsement returns a boolean indicating whether the
 	// experimental endorsement bit should be set.
 	ShouldSetExpEndorsement func() bool
+
+	// Clock is the clock used to validate payment requests expiry.
+	// It is useful for testing.
+	Clock clock.Clock
 }
 
 // MissionControl defines the mission control dependencies of routerrpc.
@@ -980,7 +985,7 @@ func (r *RouterBackend) extractIntentFromSendRequest(
 		}
 
 		// Next, we'll ensure that this payreq hasn't already expired.
-		err = ValidatePayReqExpiry(payReq)
+		err = ValidatePayReqExpiry(r.Clock, payReq)
 		if err != nil {
 			return nil, err
 		}
@@ -1370,10 +1375,10 @@ func UnmarshalFeatures(
 
 // ValidatePayReqExpiry checks if the passed payment request has expired. In
 // the case it has expired, an error will be returned.
-func ValidatePayReqExpiry(payReq *zpay32.Invoice) error {
+func ValidatePayReqExpiry(clock clock.Clock, payReq *zpay32.Invoice) error {
 	expiry := payReq.Expiry()
 	validUntil := payReq.Timestamp.Add(expiry)
-	if time.Now().After(validUntil) {
+	if clock.Now().After(validUntil) {
 		return fmt.Errorf("invoice expired. Valid until %v", validUntil)
 	}
 

lnrpc/routerrpc/router_backend_test.go

@@ -5,9 +5,11 @@ import (
 	"context"
 	"encoding/hex"
 	"testing"
+	"time"
 
 	"github.com/btcsuite/btcd/btcutil"
 	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/lightningnetwork/lnd/lnmock"
 	"github.com/lightningnetwork/lnd/lnrpc"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
@@ -509,6 +511,9 @@ func TestExtractIntentFromSendRequest(t *testing.T) {
 	target, err := route.NewVertexFromBytes(destNodeBytes)
 	require.NoError(t, err)
 
+	mockClock := &lnmock.MockClock{}
+	mockClock.On("Now").Return(time.Date(2025, 3, 1, 13, 0, 0, 0, time.UTC))
+
 	testCases := []extractIntentTestCase{
 		{
 			name:    "Time preference out of range",
@@ -706,6 +711,7 @@ func TestExtractIntentFromSendRequest(t *testing.T) {
 					return false
 				},
 				ActiveNetParams: &chaincfg.RegressionNetParams,
+				Clock:           mockClock,
 			},
 			sendReq: &SendPaymentRequest{
 				Amt:            int64(paymentAmount),