[File] [PATCH] Magdir/archive Atari MSA archive misidentifies setup.skin

[Christos Zoulas]

Added, thanks!

christos

> On May 24, 2022, at 6:38 PM, Jörg Jenderek <joerg.jen.der.ek at gmx.net> wrote:
> 
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> 
> Hello,
> 
> some days ago i handle some skin examples. When running file
> command version 5.41 some such SKIN examples and related files i
> get an output like:
> 
> PDATS578.msa: Atari MSA archive data,
> 	      9 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 79
> XXX_INT.MSA:  Atari MSA archive data,
> 	      10 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 81
> adr_1.msa:    Atari MSA archive data,
> 	      10 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 80
> maggie4a.msa: Atari MSA archive data,
> 	      10 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 39
> setup.skin:   Atari MSA archive data,
> 	      -11636 sectors per track,
> 	      starting track: 22332, ending track: 3470
> 
> 
> With option -i only generic application/octet-stream is shown. With
> option --extension only 3 byte sequence ??? is shown.
> 
> For comparison reason i run the file format identification utility
> TrID ( See https://mark0.net/soft-trid-e.html). It identifies the
> Atari examples as "Atari MSA Disk Image" by msa.trid.xml. It does not
> misidentifies example setup.skin as MSA but i was not able to
> recognise it (described as "Unknown!" see appended trid-v-msa.txt.gz)
> .
> 
> Luckily TrID tool with option -v shows used file name extension.
> With this information i was able to find a page about
> MSA (Magic Shadow Archiver) on file formats archive team web site.
> There also a link to Atari Image File Formats Specifications is
> listed. That information is added inside Magdir/archive by comment
> lines like:
> 
> # URL:		http://fileformats.archiveteam.org/
> #		wiki/MSA_(Magic_Shadow_Archiver)
> # Reference:	http://info-coach.fr
> #		atari/documents/_mydoc/FD_Image_File_Format.pdf
> #		http://mark0.net/download/triddefs_xml.7z
> #		defs/m/msa.trid.xml
> 
> On mentioned site download links for examples and tools are
> listed. I verified information partly by decoding tool deark (See
> appended deark-l-msa.txt)  by command lines like:
> 	deark -l -m msa -d2 PDATS578.msa
> Here also example setup.skin is not misidentified.
> 
> The detection happens inside Magdir/archive by lines like:
> # Atari MSA archive - Teemu Hukkanen <tjhukkan at iki.fi>
> 0	beshort 0x0e0f		Atari MSA archive data
> 
> So only 2 bytes are used for detection and obviously this
> recognition method is not strong enough. Additional information is
> shown by additional lines like:
>> 2	beshort x		\b, %d sectors per track
>> 6	beshort x		\b, starting track: %d
>> 8	beshort x		\b, ending track: %d
> 
> For real MSA examples i get low values:
> 	9 10		sectors per track
> 	0		starting track
> 	39 79 80 81	ending track
> For bad example like setup.skin i get unrealistic high numbers or
> numbers are so high that these are interpreted as negative value.
> So i could use that values as additional test, but there is a
> problem to define or research the limits for what is valid or wrong.
> 
> The sides value minus one is stored as 2 byte integer value in big
> endian format. So only value zero or one can occur here. That
> information is shown by lines like:
>> 4	beshort 0		\b, 1 sided
>> 4	beshort 1		\b, 2 sided
> 
> So i use that reliable information and recognition now starts with
> lines like:
> 0	beshort 0x0e0f
>> 4	ubeshort <2		Atari MSA archive data
> !:mime	application/x-atari-msa
> !:ext	msa
> So now bad example setup.skin is skipped. Instead of generic mime
> type application/octet-stream for such binary files i apply an user
> defined one.
> 
> After applying the above mentioned modifications by patch
> file-5.41-archive-msa.diff then all my inspected MSA examples are
> still described but misidentification vanish. This now looks like:
> 
> PDATS578.msa: Atari MSA archive data,
> 	      9 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 79
> XXX_INT.MSA:  Atari MSA archive data,
> 	      10 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 81
> adr_1.msa:    Atari MSA archive data,
> 	      10 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 80
> maggie4a.msa: Atari MSA archive data,
> 	      10 sectors per track, 2 sided,
> 	      starting track: 0, ending track: 39
> setup.skin:   data
> 
> I hope my diff file can be applied in future version of file
> utility.
> 
> With best wishes,
> Jörg Jenderek
> - --
> Jörg Jenderek
> 
> 
> 
> 
> 
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> <Nachrichtenteil als Anhang.DEFANGED-16758><file-5_41-archive-msa_diff.DEFANGED-16759><file-5_41-archive-msa_diff_sig.DEFANGED-16760><deark-l-msa.txt.gz><trid-v-msa.txt.gz>--
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