lnwire: add type CustomRecords

This commit introduces the `CustomRecords` type in the `lnwire` package,
designed to hold arbitrary byte slices. Each entry in this map can
associate with TLV type values that are greater than or equal to 65536.

lnwire/custom_records.go

@@ -0,0 +1,176 @@
+package lnwire
+
+import (
+	"bytes"
+	"fmt"
+	"sort"
+
+	"github.com/lightningnetwork/lnd/tlv"
+)
+
+const (
+	// MinCustomRecordsTlvType is the minimum custom records TLV type as
+	// defined in BOLT 01.
+	MinCustomRecordsTlvType = 65536
+)
+
+// CustomRecords stores a set of custom key/value pairs. Map keys are TLV types
+// which must be greater than or equal to MinCustomRecordsTlvType.
+type CustomRecords map[uint64][]byte
+
+// NewCustomRecords creates a new CustomRecords instance from a
+// tlv.TypeMap.
+func NewCustomRecords(tlvMap tlv.TypeMap) (CustomRecords, error) {
+	// Make comparisons in unit tests easy by returning nil if the map is
+	// empty.
+	if len(tlvMap) == 0 {
+		return nil, nil
+	}
+
+	customRecords := make(CustomRecords, len(tlvMap))
+	for k, v := range tlvMap {
+		customRecords[uint64(k)] = v
+	}
+
+	// Validate the custom records.
+	err := customRecords.Validate()
+	if err != nil {
+		return nil, fmt.Errorf("custom records from tlv map "+
+			"validation error: %w", err)
+	}
+
+	return customRecords, nil
+}
+
+// ParseCustomRecords creates a new CustomRecords instance from a tlv.Blob.
+func ParseCustomRecords(b tlv.Blob) (CustomRecords, error) {
+	stream, err := tlv.NewStream()
+	if err != nil {
+		return nil, fmt.Errorf("error creating stream: %w", err)
+	}
+
+	typeMap, err := stream.DecodeWithParsedTypes(bytes.NewReader(b))
+	if err != nil {
+		return nil, fmt.Errorf("error decoding HTLC record: %w", err)
+	}
+
+	return NewCustomRecords(typeMap)
+}
+
+// Validate checks that all custom records are in the custom type range.
+func (c CustomRecords) Validate() error {
+	if c == nil {
+		return nil
+	}
+
+	for key := range c {
+		if key < MinCustomRecordsTlvType {
+			return fmt.Errorf("custom records entry with TLV "+
+				"type below min: %d", MinCustomRecordsTlvType)
+		}
+	}
+
+	return nil
+}
+
+// Copy returns a copy of the custom records.
+func (c CustomRecords) Copy() CustomRecords {
+	if c == nil {
+		return nil
+	}
+
+	customRecords := make(CustomRecords, len(c))
+	for k, v := range c {
+		customRecords[k] = v
+	}
+
+	return customRecords
+}
+
+// ExtendRecordProducers extends the given records slice with the custom
+// records. The resultant records slice will be sorted if the given records
+// slice contains TLV types greater than or equal to MinCustomRecordsTlvType.
+func (c CustomRecords) ExtendRecordProducers(
+	producers []tlv.RecordProducer) ([]tlv.RecordProducer, error) {
+
+	// If the custom records are nil or empty, there is nothing to do.
+	if len(c) == 0 {
+		return producers, nil
+	}
+
+	// Validate the custom records.
+	err := c.Validate()
+	if err != nil {
+		return nil, err
+	}
+
+	// Ensure that the existing records slice TLV types are not also present
+	// in the custom records. If they are, the resultant extended records
+	// slice would erroneously contain duplicate TLV types.
+	for _, rp := range producers {
+		record := rp.Record()
+		recordTlvType := uint64(record.Type())
+
+		_, foundDuplicateTlvType := c[recordTlvType]
+		if foundDuplicateTlvType {
+			return nil, fmt.Errorf("custom records contains a TLV "+
+				"type that is already present in the "+
+				"existing records: %d", recordTlvType)
+		}
+	}
+
+	// Convert the custom records map to a TLV record producer slice and
+	// append them to the exiting records slice.
+	crRecords := tlv.MapToRecords(c)
+	for _, record := range crRecords {
+		r := recordProducer{record}
+		producers = append(producers, &r)
+	}
+
+	// If the records slice which was given as an argument included TLV
+	// values greater than or equal to the minimum custom records TLV type
+	// we will sort the extended records slice to ensure that it is ordered
+	// correctly.
+	sort.Slice(producers, func(i, j int) bool {
+		recordI := producers[i].Record()
+		recordJ := producers[j].Record()
+		return recordI.Type() < recordJ.Type()
+	})
+
+	return producers, nil
+}
+
+// RecordProducers returns a slice of record producers for the custom records.
+func (c CustomRecords) RecordProducers() []tlv.RecordProducer {
+	// If the custom records are nil or empty, return an empty slice.
+	if len(c) == 0 {
+		return nil
+	}
+
+	// Convert the custom records map to a TLV record producer slice.
+	records := tlv.MapToRecords(c)
+
+	// Convert the records to record producers.
+	producers := make([]tlv.RecordProducer, len(records))
+	for i, record := range records {
+		producers[i] = &recordProducer{record}
+	}
+
+	return producers
+}
+
+// Serialize serializes the custom records into a byte slice.
+func (c CustomRecords) Serialize() ([]byte, error) {
+	records := tlv.MapToRecords(c)
+	stream, err := tlv.NewStream(records...)
+	if err != nil {
+		return nil, fmt.Errorf("error creating stream: %w", err)
+	}
+
+	var b bytes.Buffer
+	if err := stream.Encode(&b); err != nil {
+		return nil, fmt.Errorf("error encoding custom records: %w", err)
+	}
+
+	return b.Bytes(), nil
+}