channeldb+routing: persist first hop custom data for route

Author: guggero

channeldb/payments.go

@@ -1096,6 +1096,25 @@ func serializeHTLCAttemptInfo(w io.Writer, a *HTLCAttemptInfo) error {
 		return err
 	}
 
+	// Merge the fixed/known records together with the custom records to
+	// serialize them as a single blob. We can't do this in SerializeRoute
+	// because we're in the middle of the byte stream there. We can only do
+	// TLV serialization at the end of the stream, since EOF is allowed for
+	// a stream if no more data is expected.
+	producers := []tlv.RecordProducer{
+		&a.Route.FirstHopAmount,
+	}
+	tlvData, err := lnwire.MergeAndEncode(
+		producers, nil, a.Route.FirstHopWireCustomRecords,
+	)
+	if err != nil {
+		return err
+	}
+
+	if _, err := w.Write(tlvData); err != nil {
+		return err
+	}
+
 	return nil
 }
 
@@ -1133,6 +1152,22 @@ func deserializeHTLCAttemptInfo(r io.Reader) (*HTLCAttemptInfo, error) {
 
 	a.Hash = &hash
 
+	// Read any remaining data (if any) and parse it into the known records
+	// and custom records.
+	extraData, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	customRecords, _, _, err := lnwire.ParseAndExtractCustomRecords(
+		extraData, &a.Route.FirstHopAmount,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	a.Route.FirstHopWireCustomRecords = customRecords
+
 	return a, nil
 }
 
@@ -1398,6 +1433,8 @@ func SerializeRoute(w io.Writer, r route.Route) error {
 		}
 	}
 
+	// Any new/extra TLV data is encoded in serializeHTLCAttemptInfo!
+
 	return nil
 }
 
@@ -1431,5 +1468,7 @@ func DeserializeRoute(r io.Reader) (route.Route, error) {
 	}
 	rt.Hops = hops
 
+	// Any new/extra TLV data is decoded in deserializeHTLCAttemptInfo!
+
 	return rt, nil
 }

channeldb/payments_test.go

@@ -16,6 +16,7 @@ import (
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/routing/route"
+	"github.com/lightningnetwork/lnd/tlv"
 	"github.com/stretchr/testify/require"
 )
 
@@ -149,20 +150,34 @@ func TestSentPaymentSerialization(t *testing.T) {
 	require.NoError(t, err, "deserialize")
 	require.Equal(t, c, newCreationInfo)
 
+	b.Reset()
 	require.NoError(t, serializeHTLCAttemptInfo(&b, s), "serialize")
 
 	newWireInfo, err := deserializeHTLCAttemptInfo(&b)
 	require.NoError(t, err, "deserialize")
-	newWireInfo.AttemptID = s.AttemptID
 
-	// First we verify all the records match up properly, as they aren't
-	// able to be properly compared using reflect.DeepEqual.
-	err = assertRouteEqual(&s.Route, &newWireInfo.Route)
-	require.NoError(t, err)
+	// First we verify all the records match up properly.
+	require.Equal(t, s.Route, newWireInfo.Route)
+
+	// We now add the new fields and custom records to the route and
+	// serialize it again.
+	b.Reset()
+	s.Route.FirstHopAmount = tlv.NewRecordT[tlv.TlvType0](
+		tlv.NewBigSizeT(lnwire.MilliSatoshi(1234)),
+	)
+	s.Route.FirstHopWireCustomRecords = lnwire.CustomRecords{
+		lnwire.MinCustomRecordsTlvType + 3: []byte{4, 5, 6},
+	}
+	require.NoError(t, serializeHTLCAttemptInfo(&b, s), "serialize")
+
+	newWireInfo, err = deserializeHTLCAttemptInfo(&b)
+	require.NoError(t, err, "deserialize")
+	require.Equal(t, s.Route, newWireInfo.Route)
 
 	// Clear routes to allow DeepEqual to compare the remaining fields.
 	newWireInfo.Route = route.Route{}
 	s.Route = route.Route{}
+	newWireInfo.AttemptID = s.AttemptID
 
 	// Call session key method to set our cached session key so we can use
 	// DeepEqual, and assert that our key equals the original key.

routing/route/route.go

@@ -488,6 +488,26 @@ type Route struct {
 	// Hops contains details concerning the specific forwarding details at
 	// each hop.
 	Hops []*Hop
+
+	// FirstHopAmount is the amount that should actually be sent to the
+	// first hop in the route. This is only different from TotalAmount above
+	// for custom channels where the on-chain amount doesn't necessarily
+	// reflect all the value of an outgoing payment.
+	FirstHopAmount tlv.RecordT[
+		tlv.TlvType0, tlv.BigSizeT[lnwire.MilliSatoshi],
+	]
+
+	// FirstHopWireCustomRecords is a set of custom records that should be
+	// included in the wire message sent to the first hop. This is only set
+	// on custom channels and is used to include additional information
+	// about the actual value of the payment.
+	//
+	// NOTE: Since these records already represent TLV records, and we
+	// enforce them to be in the custom range (e.g. >= 65536), we don't use
+	// another parent record type here. Instead, when serializing the Route
+	// we merge the TLV records together with the custom records and encode
+	// everything as a single TLV stream.
+	FirstHopWireCustomRecords lnwire.CustomRecords
 }
 
 // Copy returns a deep copy of the Route.