multi: move Input interface and related code

This commit is a step to split the lnwallet package. It puts the Input
interface and implementations in a separate package along with all their
dependencies from lnwallet.

input/txout.go

@@ -0,0 +1,46 @@
+package input
+
+import (
+	"encoding/binary"
+	"io"
+
+	"github.com/btcsuite/btcd/wire"
+)
+
+// writeTxOut serializes a wire.TxOut struct into the passed io.Writer stream.
+func writeTxOut(w io.Writer, txo *wire.TxOut) error {
+	var scratch [8]byte
+
+	binary.BigEndian.PutUint64(scratch[:], uint64(txo.Value))
+	if _, err := w.Write(scratch[:]); err != nil {
+		return err
+	}
+
+	if err := wire.WriteVarBytes(w, 0, txo.PkScript); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// readTxOut deserializes a wire.TxOut struct from the passed io.Reader stream.
+func readTxOut(r io.Reader, txo *wire.TxOut) error {
+	var scratch [8]byte
+
+	if _, err := io.ReadFull(r, scratch[:]); err != nil {
+		return err
+	}
+	value := int64(binary.BigEndian.Uint64(scratch[:]))
+
+	pkScript, err := wire.ReadVarBytes(r, 0, 80, "pkScript")
+	if err != nil {
+		return err
+	}
+
+	*txo = wire.TxOut{
+		Value:    value,
+		PkScript: pkScript,
+	}
+
+	return nil
+}