Path: utzoo!attcan!uunet!wyse!vsi1!apple!rutgers!columbia!douglass!dupuy
From: dupuy@douglass.columbia.edu (Alexander Dupuy)
Newsgroups: comp.sources.bugs
Subject: Re: v05i028: /etc/magic lines for compress
Message-ID: <6021@columbia.edu>
Date: 16 Nov 88 21:46:50 GMT
References: <1033@investor.UUCP> <454@auspex.UUCP> <7714@boring.cwi.nl>
Sender: news@columbia.edu
Reply-To: dupuy@douglass.columbia.edu (Alexander Dupuy)
Followup-To: comp.sources.bugs
Organization: Columbia University Computer Science Dept.
Lines: 32

In article <454@auspex.UUCP> guy@auspex.UUCP (Guy Harris) writes:
> Unfortunately, "strings" in "/etc/magic" cannot, in the standard S5
> version, contain C-language escapes, so you can't do this:
> 
> 	0	string		\037\235	compressed data
> 
> which the SunOS version of the S5 'file" supports; this obviates the need
> for byte-order-dependent versions of "/etc/magic".

In article <7714@boring.cwi.nl> dik@cwi.nl (Dik T. Winter) replies:
> Wouldn't it be better to allow specification like AR16W, AR32W and
> AR32WR as happens in so many places in SysV (COFF comes to mind)?
> Then each system can specify in its favourite order its own /etc/magic
> part.

Not only is this better, but the "strings" in even the SunOS version of magic
can't contain null bytes (well actually, they can, but it doesn't do what you
want), and can't be masked in the way which SunOS allows you to mask numbers.

While I find AR32WR pretty incomprehensible (is it network order, or reversed?)
it should be possible to write a file which converts the numbers and masks
specified in /etc/magic into network order before doing any comparisons, and
converts values read from the file into local byte order before performing %d
substitutions on the descriptions in the /etc/magic file.  If needed, special
printf macros could be used to indicate substitutions for which the bytes
needed to be swapped before the ntohl conversion was done.  This should provide
a portable file(1).

@alex
-- 
inet: dupuy@columbia.edu
uucp: ...!rutgers!columbia!dupuy