Comment by kazinator

But "Tue" is not at the fourth byte in the example, which has:

   %%CreationDate: (Tue Mar 3 19:47:42 2009)

Something munged he the data. Perhaps some step which removes all characters after %%, except those in parentheses?

   %%(Tue Mar 3 ...)

Now we're at the fourth byte. Another hypothesis is that the second incorrect match is kicking in. That is to say, some fields are added above %% CreationDate such that the Tue lands on position 79. The bug that was fixed in the magic database is this:

  -+4	string	Tue Jan 22 14:32:44 MET 1991	Erlang JAM file - version 4.2 
  -+79	string	Tue Jan 22 14:32:44 MET 1991	Erlang JAM file - version 4.2
  ++4	string	Tue\ Jan\ 22\ 14:32:44\ MET\ 1991	Erlang JAM file - version 4.2
  ++79	string	Tue\ Jan\ 22\ 14:32:44\ MET\ 1991	Erlang JAM file - version 4.2

(This is a patch of a patch: a fix to a an incorrect patch.) There are two matches for this special date which identifies JAM files: one at offset 4, but a possible other one at offset 79 which will cause the same problem.

The real bug here is arguably the CUPS script. It should identify the file's type before munging it. And it shouldn't use a completely general, highly configurable utility whose data-driven file classification system is a moving target from release to release! This is a print script, so there is no reason to suspect that an input file is a Doom WAD file, or a Sun OS 4 MC68000 executable. The possibilities are quite limited, and can be handled with a bit of custom logic.

Did Brother people write this? If so, I'm not surprised.

Nobody should ever write code whose correct execution depends on the "file" utility classifying something. That is, not unless you write your own "magic" file and use only that file; then you're taking proper ownership of the classification logic, such that any bugs are likely to be your own.

The fact that file got something wrong here is a red herring; the file utility is wrong once in a while, as anyone knows who has been using various versions of it regularly regularly for a few decades. Installations of the utility are only suitable for one-off interactive use. You got a mystery file from out of the blue, and need a clue as to what it is. Run file on it to get an often useful opinion. It is only usable in an advisory role, not in an authoritative role.