code: func (c *CipherReader) Read(p []byte) (n int, err error) {
  	n, err = c.r.Read(p)
  	ws.Cipher(p[:n], c.mask, c.pos)
  	c.pos += n
  	return
  }
docs: // Read implements io.Reader interface. It applies mask given during
  // initialization to every read byte.