Add coder/decoder size to coder

encoding/coder.go

@@ -5,4 +5,6 @@ import "bytes"
 type Coder interface {
 	Encode(s *string, buf *bytes.Buffer) error
 	Decode(buf *bytes.Buffer) (string, error)
-}
+	EncodesInto(s *string) int
+	DecodesInto(buf *bytes.Buffer) int
+}