The initial version of the /etc./magic file used by the file(1) command (opens in new tab)

It's really about the assumption that the past was like the present, only older. Unix didn't have version control when `file(1)` was written, unless you count last week's backup tapes. (Granted, ‘backup tapes with fancy labels’ is also the working model of git.)

It's not portable because nobody else adopted it. Had DOS and Unix also embraced the concept this would be a solved problem. Microsoft does actually have something on NTFS that works similarly, which is how Windows knows when something has been downloaded from the internet and warns you that it might be dangerous.

Having a standard to separate your data from your metadata isn't necessarily incompatible with streams. It would be something you would IOCTL on an open stream if you cared.

    int fd;
    fd = open("the_file", O_RDONLY);
    if ( fd < 0 )
    {
      perror("the_file");
      return -1;
    }
    char* filetype = NULL;
    ioctl(fd, FDRESGET, "FILETYPE", &filetype);
    if ( filetype != NULL )
    {
      printf("%s has a filetype of %s\n", "the_file", filetype);
    }

You could also have a version FNRESGET that operates on file names instead of file descriptors. Also a setter. There's still obviously a lot of details to work out, but nothing about this should be all that difficult. It even simplifies some other parts of the system, for example if you have a network socket the socket metadata like the remote IP address and port numbers could be in the resource fork of the socket itself.

macOS has xattrs too (had them very early actually), and supports resource forks through them (it’s the same concept), though they are not used anymore except in some fringe cases.

Yes those are the very epitome of hacks.

Wait, macOS still doss this? So you still have to use stuffit for a platform agnostic transfer? Don't get me wrong, hacking everything with resedit and the like almost makes me reach for the rose glasses.

I have scads of macOS footprints all over my NAS from a Mac I used a decade ago.