routing: make msg and index optional

This is later used to handle their nil values.

routing/missioncontrol.go

@@ -845,10 +845,15 @@ func newPaymentFailure(sourceIdx *int,
 	}
 
 	info := paymentFailureInfo{
-		sourceIdx: tlv.NewPrimitiveRecord[tlv.TlvType0](
-			uint8(*sourceIdx),
+		sourceIdx: tlv.SomeRecordT(
+			tlv.NewPrimitiveRecord[tlv.TlvType0](
+				uint8(*sourceIdx),
+			)),
+		msg: tlv.SomeRecordT(
+			tlv.NewRecordT[tlv.TlvType1](
+				failureMessage{failureMsg},
+			),
 		),
-		msg: tlv.NewRecordT[tlv.TlvType1](failureMessage{failureMsg}),
 	}
 
 	return &paymentFailure{
@@ -921,8 +926,15 @@ func decodePaymentFailure(r io.Reader, val interface{}, _ *[8]byte,
 
 // paymentFailureInfo holds additional information about a payment failure.
 type paymentFailureInfo struct {
-	sourceIdx tlv.RecordT[tlv.TlvType0, uint8]
-	msg       tlv.RecordT[tlv.TlvType1, failureMessage]
+	// sourceIdx is the hop the error was reported from. In order to be able
+	// to decrypt the error message, we need to know the source, which is
+	// why an error message can only be present if the source is known.
+	sourceIdx tlv.OptionalRecordT[tlv.TlvType0, uint8]
+
+	// msg is the error why a payment failed. If we identify the failure of
+	// a certain hop at the above index, but aren't able to decode the
+	// failure message we indicate this by not setting this field.
+	msg tlv.OptionalRecordT[tlv.TlvType1, failureMessage]
 }
 
 // Record returns a TLV record that can be used to encode/decode a
@@ -948,9 +960,27 @@ func (r *paymentFailureInfo) Record() tlv.Record {
 
 func encodePaymentFailureInfo(w io.Writer, val interface{}, _ *[8]byte) error {
 	if v, ok := val.(*paymentFailureInfo); ok {
+		var recordProducers []tlv.RecordProducer
+
+		v.sourceIdx.WhenSome(
+			func(r tlv.RecordT[tlv.TlvType0, uint8]) {
+				recordProducers = append(
+					recordProducers, &r,
+				)
+			},
+		)
+
+		v.msg.WhenSome(
+			func(r tlv.RecordT[tlv.TlvType1, failureMessage]) {
+				recordProducers = append(
+					recordProducers, &r,
+				)
+			},
+		)
+
 		return lnwire.EncodeRecordsTo(
 			w, lnwire.ProduceRecordsSorted(
-				&v.sourceIdx, &v.msg,
+				recordProducers...,
 			),
 		)
 	}
@@ -964,14 +994,26 @@ func decodePaymentFailureInfo(r io.Reader, val interface{}, _ *[8]byte,
 	if v, ok := val.(*paymentFailureInfo); ok {
 		var h paymentFailureInfo
 
-		_, err := lnwire.DecodeRecords(
+		sourceIdx := tlv.ZeroRecordT[tlv.TlvType0, uint8]()
+		msg := tlv.ZeroRecordT[tlv.TlvType1, failureMessage]()
+
+		typeMap, err := lnwire.DecodeRecords(
 			r,
-			lnwire.ProduceRecordsSorted(&h.sourceIdx, &h.msg)...,
+			lnwire.ProduceRecordsSorted(&sourceIdx, &msg)...,
 		)
+
 		if err != nil {
 			return err
 		}
 
+		if _, ok := typeMap[h.sourceIdx.TlvType()]; ok {
+			h.sourceIdx = tlv.SomeRecordT(sourceIdx)
+		}
+
+		if _, ok := typeMap[h.msg.TlvType()]; ok {
+			h.msg = tlv.SomeRecordT(msg)
+		}
+
 		*v = h
 
 		return nil

routing/result_interpretation.go

@@ -138,8 +138,17 @@ func (i *interpretedResult) processFail(rt *mcRoute, failure paymentFailure) {
 
 	failure.info.WhenSome(
 		func(r tlv.RecordT[tlv.TlvType0, paymentFailureInfo]) {
-			idx = int(r.Val.sourceIdx.Val)
-			failMsg = r.Val.msg.Val.FailureMessage
+			r.Val.sourceIdx.WhenSome(
+				func(r tlv.RecordT[tlv.TlvType0, uint8]) {
+					idx = int(r.Val)
+				},
+			)
+
+			r.Val.msg.WhenSome(
+				func(r tlv.RecordT[tlv.TlvType1, failureMessage]) {
+					failMsg = r.Val.FailureMessage
+				},
+			)
 		},
 	)