String with both length and padding

[katzuv]

Let's say I have this kind of struct: 1 byte of string length, then the ASCII string itself, then padding up to 255 (the padding's length is 255-string length), and then some 3-byte value. So it looks like this:

data = b"\x08mystring\xff\xff\xff\xff\xff\xff\xff ... xab\xcd"

I thought of building this struct with a PaddedString, but another requirement I need is to be able to use .sizeof() on it (for another use in a bigger library I am writing). This is not possible with PaddedString because the size of it can't be determined.

Is there some solution from construct for this? Obviously, I could simply use Byte[255] and slice the string myself, but I was wondering whether construct could do it on its own, while still having a fixed-sized struct.
Thanks!

[arekbulski]

I would recommend using a custom adapter or parsing class. Simply.