[File] [PATCH] Magdir/archive for Ai32 archive *.ai

[Christos Zoulas]

Committed, thanks!

christos

> On Jan 12, 2023, at 5:29 PM, Jörg Jenderek <joerg.jen.der.ek at gmx.net> wrote:
> 
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> Hello,
> 
> some times ago i tried to add extension for PostScript document text,
> but i had some difficulties. Some samples with suffix AI are
> PostScript files for which normally the suffix PS is used.
> Unfortunately the suffix AI is also used for other file formats.
> One is for compressed files.
> 
> When running running file command version 5.44 on such compressed
> files i get an output like:
> 
> lmhosts-m3-solid.ai: Ai32 archive data
> readme-m4.ai:        Ai32 archive data
> test-Ai-1.ai:        Ai archive data
> test-Ai-2.ai:        Ai archive data
> 
> With option -i only generic application/octet-stream is shown.
> Furthermore with --extension option only ??? is displayed.
> 
> For comparison reason i run the file format identification utility
> TrID ( See https://mark0.net/soft-trid-e.html). The samples which are
> described by file commandas "Ai32" are described here as "Ai
> Archivator compressed archive" with correct suffix AI by
> ark-ai.trid.xml (See appended trid-v-ai.txt.gz).
> 
> For comparison reason i also run the file format identification
> utility DROID ( See https://sourceforge.net/projects/droid/). Here
> all AI examples described wrong as "Adobe Illustrator" by PUID
> fmt/421	based on file name extension.
> 
> With the help of TrID out put i found pages on file formats archive
> team web site. That informations are expressed by comment lines like:
> # URL:		http://fileformats.archiveteam.org/wiki/Ai_Archiver
> # Reference:	http://mark0.net/download/triddefs_xml.7z
> #		defs/a/ark-ai.trid.xml
> 
> The current description happens in side Magdir/archive. There exist 4
> similar entries for such compressed files. The forth entry consist of
> just one line like:
> 0	string	Ai\2\1 Ai32 archive data
> So i add afterwards 2 line for mime type and file name suffix like
> !:mime	application/x-compress-ai
> !:ext	ai
> Instead of generic mime type application/octet-stream i choose an
> user defined. At offset 10 apparently the name of original
> uncompressed file is stored. At offset 8 apparently the length of
> this name is stored as 2 byte little endian integer. So show this
> information by additional line like:
>> 8	pstring/h x	"%s"
> 
> According to TrID the next 3 bytes after start pattern are nil, but i
> do not know if this is always true. So in case of unexpected values
> i show this by lines like:
>> 5	ubyte	!0	\b, at 5 %#x
>> 6	ubyte	!0	\b, at 6 %#x
>> 7	ubyte	!0	\b, at 7 %#x
> 
> According to documentation and also found in my examples the fourth
> byte with value 0x01 is probably a flag for "solid" mode. So show
> this by additional line
>> 3	ubyte	=0x01	\b, solid mode
> 
> Then do the same modification for third entry which consist of 1 line
> like:
> 0	string	Ai\2\0 Ai32 archive data
> The only difference here is that at offset 3 byte field has value 0,
> which apparently means "non solid". That is the default mode when
> compressing files with ai tool. So this information can be
> expressed by line like:
> #>3	ubyte	=0x00	\b, unsolid mode
> 
> The first and second entry are apparently for other older versions.
> That was expressed by lines like:
> 0	string	Ai\1\1\0 Ai archive data
> 0	string	Ai\1\0\0 Ai archive data
> Unfortunately i found no real samples for these versions. So i only
> add same lines for mime type and file name suffix.
> 
> After applying the above mentioned modifications by patch
> file-5.44-archive-ai.diff then all such inspected AI compressed files
> are still described, but with more details. This now looks like:
> 
> lmhosts-m3-solid.ai: Ai32 archive data "lmhosts.sam", solid mode
> readme-m4.ai:        Ai32 archive data "readme.txt"
> test-Ai-1.ai:        Ai archive data
> test-Ai-2.ai:        Ai archive 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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