Official PDF URLs for X Specs

Glynn Clements glynn at
Fri Apr 25 00:51:05 PDT 2008

Alexander E. Patrakov wrote:

> > with PS being a real langiage, and pdf never having that capability.
> IMHO, PS being a real language capable of emulating a Turing machine is a 
> critical bug, and PDF is a step in the right direction (although it also has 
> drawbacks). Reason:
> The print spooler (e.g., CUPS) blindly sends the user-generated PS to the 
> printer without checking whether the program will terminate at all. Worse, it is 
> impossible to determine algorithmically. Thus, we have a DOS attack, just run 
> this command:
> echo -e '%!PS\n{ } loop' | lpr

I don't know about using CUPS and Ghostscript to emulate a PostScript
printer, but every real PostScript printer I've encountered imposes
some form of timeout.

Turing-completeness is a red herring. There's no meaningful difference
between a PostScript program which never terminates and one which
terminates after a year of execution. Either way, any sane
implementation will abort the job within a matter of minutes.

Glynn Clements <glynn at>

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