code: func (enc *Encoder) EncodeFixedOpaque(v []byte) (err error) {
  	l := len(v)
  	pad := (4 - (l % 4)) % 4
  	size := l + pad
  
  	if len(enc.data) > maxInt-size {
  		err = marshalError("EncodeFixedOpaque", ErrOverflow, errMaxSlice, size)
  		return
  	}
  
  	enc.data = append(enc.data, v...)
  	if pad > 0 {
  		b := make([]byte, pad, pad)
  		for i := 0; i < pad; i++ {
  			b[i] = 0
  		}
  		enc.data = append(enc.data, b...)
  	}
  	return
  }
docs: // RFC Section 4.8 -  Quadruple-Precision Floating Point
  // 128-bit quadruple-precision floating point
  // Not Implemented
  // EncodeFixedOpaque treats the passed byte slice as opaque data of a fixed
  // size and appends the XDR encoded representation of it to the Encoder's data.
  //
  // A MarshalError is returned if appending the data would overflow the
  // internal data slice.
  //
  // Reference:
  // 	RFC Section 4.9 - Fixed-Length Opaque Data
  // 	Fixed-length uninterpreted data zero-padded to a multiple of four