Save 1 allocation in shadowsocks

common/alloc/buffer.go

@@ -63,13 +63,8 @@ func (b *Buffer) Append(data []byte) *Buffer {
 // Prepend prepends bytes in front of the buffer. Caller must ensure total bytes prepended is
 // no more than 16 bytes.
 func (b *Buffer) Prepend(data []byte) *Buffer {
-	newoffset := b.offset - len(data)
-	if newoffset < 0 {
-		newoffset = 0
-	}
-	copy(b.head[newoffset:], data)
-	b.Value = b.head[newoffset : b.offset+len(b.Value)]
-	b.offset = newoffset
+	b.SliceBack(len(data))
+	copy(b.Value, data)
 	return b
 }
 
@@ -89,6 +84,16 @@ func (b *Buffer) SliceFrom(from int) *Buffer {
 	return b
 }
 
+func (b *Buffer) SliceBack(offset int) *Buffer {
+	newoffset := b.offset - offset
+	if newoffset < 0 {
+		newoffset = 0
+	}
+	b.Value = b.head[newoffset : b.offset+len(b.Value)]
+	b.offset = newoffset
+	return b
+}
+
 // Len returns the length of the buffer content.
 func (b *Buffer) Len() int {
 	return len(b.Value)