update area

arena/arena.go

@@ -3,26 +3,28 @@ package arena
 type Arena struct {
 	buf []byte
 
-	size int
+	offset int
 }
 
 func NewArena(size int) *Arena {
 	a := new(Arena)
 
-	a.size = size
 	a.buf = make([]byte, size, size)
+	a.offset = 0
 
 	return a
 }
 
 func (a *Arena) Make(size int) []byte {
-	if a.size < size {
+	if len(a.buf) < size || len(a.buf)-a.offset < size {
 		return make([]byte, size)
-	} else if len(a.buf) < size {
-		a.buf = make([]byte, a.size)
 	}
 
-	b := a.buf[0:size]
-	a.buf = a.buf[size:]
+	b := a.buf[a.offset : size+a.offset]
+	a.offset += size
 	return b
 }
+
+func (a *Arena) Reset() {
+	a.offset = 0
+}