code: func PutCloseFrameBody(p []byte, code StatusCode, reason string) {
  	_ = p[1+len(reason)]
  	binary.BigEndian.PutUint16(p, uint16(code))
  	copy(p[2:], reason)
  }
docs: // PutCloseFrameBody encodes code and reason into buf.
  //
  // It will panic if the buffer is too small to accommodate a code or a reason.
  //
  // PutCloseFrameBody does not check buffer to be RFC compliant, but note that
  // by RFC it must be at most MaxControlFramePayloadSize.