code: func pkcs7decode(buf []byte, blockSize int) []byte {
  	if len(buf) == 0 {
  		panic("Cannot decode a PKCS7 buffer of zero length")
  	}
  	n := len(buf)
  	last := buf[n-1]
  	n -= int(last)
  	return buf[:n]
  }
docs: // pkcs7decode is used to decode a buffer that has been padded