lnwire: add attribution data helpers

We add some simple helpers for the purpose of parsing the attribution
data from and to the wire format.

Author: GeorgeTsagk

lnwire/attr_data.go

@@ -0,0 +1,40 @@
+package lnwire
+
+import "github.com/lightningnetwork/lnd/tlv"
+
+// AttrDataTlvType  is the TlvType that hosts the attribution data in the
+// update_fail_htlc wire message.
+var AttrDataTlvType tlv.TlvType101
+
+// AttrDataTlvTypeVal is the value of the type of the TLV record for the
+// attribution data.
+var AttrDataTlvTypeVal = AttrDataTlvType.TypeVal()
+
+// AttrDataToExtraData converts the provided attribution data to the extra
+// opaque data to be included in the wire message.
+func AttrDataToExtraData(attrData []byte) (ExtraOpaqueData, error) {
+	attrRecs := make(tlv.TypeMap)
+
+	attrType := AttrDataTlvType.TypeVal()
+
+	attrRecs[attrType] = attrData
+
+	return NewExtraOpaqueData(attrRecs)
+}
+
+// ExtraDataToAttrData takes the extra opaque data of the wire message and tries
+// to extract the attribution data.
+func ExtraDataToAttrData(extraData ExtraOpaqueData) ([]byte, error) {
+	extraRecords, err := extraData.ExtractRecords()
+	if err != nil {
+		return nil, err
+	}
+
+	attrType := AttrDataTlvTypeVal
+	var attrData []byte
+	if value, ok := extraRecords[attrType]; ok {
+		attrData = value
+	}
+
+	return attrData, nil
+}