code: func (v *Surface) GetMimeData(mimeType MimeType) []byte {
  	cstr := C.CString(string(mimeType))
  	defer C.free(unsafe.Pointer(cstr))
  	var data *C.uchar
  	var length C.ulong
  	C.cairo_surface_get_mime_data(v.native(), cstr, &data, &length)
  	return C.GoBytes(unsafe.Pointer(data), C.int(length))
  }
docs: // TODO(jrick) SetMimeData (depends on DestroyFunc)
  // GetMimeData is a wrapper around cairo_surface_get_mime_data().  The
  // returned mimetype data is returned as a Go byte slice.