code: func Concat(bss ...[]byte) []byte {
  	offset := 0
  	for _, bs := range bss {
  		offset += len(bs)
  	}
  	bytes := make([]byte, offset)
  	offset = 0
  	for _, bs := range bss {
  		for i, b := range bs {
  			bytes[offset+i] = b
  		}
  		offset += len(bs)
  	}
  	return bytes
  }
docs: // Concatenate multiple byte slices without unnecessary copying