watchtower/wtdb/breach_hint: adds BreachHint, txid prefix

watchtower/wtdb/breach_hint.go

@@ -0,0 +1,27 @@
+package wtdb
+
+import (
+	"encoding/hex"
+
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+)
+
+// BreachHintSize is the length of the txid prefix used to identify remote
+// commitment broadcasts.
+const BreachHintSize = 16
+
+// BreachHint is the first 16-bytes of the txid belonging to a revoked
+// commitment transaction.
+type BreachHint [BreachHintSize]byte
+
+// NewBreachHintFromHash creates a breach hint from a transaction ID.
+func NewBreachHintFromHash(hash *chainhash.Hash) BreachHint {
+	var hint BreachHint
+	copy(hint[:], hash[:BreachHintSize])
+	return hint
+}
+
+// String returns a hex encoding of the breach hint.
+func (h BreachHint) String() string {
+	return hex.EncodeToString(h[:])
+}