channeldb: Serialize/deserialize AMP struct in hop

The AMP struct in a hop was never being set when deserizlied. Also,
the AMP TLV record was not being added when the hop was serialized.
This sets the TLV record when serializing and correctly sets the
AMP struct on the hop when that record is present.

Co-authored-by: BitcoinCoderBob <90647227+BitcoinCoderBob@users.noreply.github.com>
Co-authored-by: Tee8z <tee8z@protonmail.com>

channeldb/payments.go

@@ -1157,6 +1157,10 @@ func serializeHop(w io.Writer, h *route.Hop) error {
 		))
 	}
 
+	if h.AMP != nil {
+		records = append(records, h.AMP.Record())
+	}
+
 	if h.Metadata != nil {
 		records = append(records, record.NewMetadataRecord(&h.Metadata))
 	}
@@ -1301,7 +1305,23 @@ func deserializeHop(r io.Reader) (*route.Hop, error) {
 		}
 	}
 
-	// If the metatdata type is present, remove it from the tlv map and
+	ampType := uint64(record.AMPOnionType)
+	if ampBytes, ok := tlvMap[ampType]; ok {
+		delete(tlvMap, ampType)
+
+		var (
+			amp    = &record.AMP{}
+			ampRec = amp.Record()
+			r      = bytes.NewReader(ampBytes)
+		)
+		err := ampRec.Decode(r, uint64(len(ampBytes)))
+		if err != nil {
+			return nil, err
+		}
+		h.AMP = amp
+	}
+
+	// If the metadata type is present, remove it from the tlv map and
 	// populate directly on the hop.
 	metadataType := uint64(record.MetadataOnionType)
 	if metadata, ok := tlvMap[metadataType]; ok {

channeldb/payments_test.go

@@ -44,11 +44,25 @@ var (
 		LegacyPayload:    true,
 	}
 
+	testHop3 = &route.Hop{
+		PubKeyBytes:      route.NewVertex(pub),
+		ChannelID:        12345,
+		OutgoingTimeLock: 111,
+		AmtToForward:     555,
+		CustomRecords: record.CustomSet{
+			65536: []byte{},
+			80001: []byte{},
+		},
+		AMP:      record.NewAMP([32]byte{0x69}, [32]byte{0x42}, 1),
+		Metadata: []byte{1, 2, 3},
+	}
+
 	testRoute = route.Route{
 		TotalTimeLock: 123,
 		TotalAmount:   1234567,
 		SourcePubKey:  vertex,
 		Hops: []*route.Hop{
+			testHop3,
 			testHop2,
 			testHop1,
 		},

docs/release-notes/release-notes-0.18.0.md

@@ -53,6 +53,8 @@
   walletrpc endpoint `RemoveTransaction` is introduced which let one easily
   remove unconfirmed transaction manually.
 
+* The AMP struct in payment hops will [now be populated](https://github.com/lightningnetwork/lnd/pull/7976) when the AMP TLV is set.
+
 # New Features
 ## Functional Enhancements
 
@@ -203,6 +205,7 @@
 
 * Amin Bashiri
 * Andras Banki-Horvath
+* BitcoinerCoderBob
 * Carla Kirk-Cohen
 * Elle Mouton
 * ErikEk
@@ -210,6 +213,8 @@
 * Marcos Fernandez Perez
 * Matt Morehouse
 * Slyghtning
+* Tee8z
 * Turtle
 * Ononiwu Maureen Chiamaka
+* w3irdrobot
 * Yong Yu