Re: new mime detection approach

[Brian Nitz <Brian Nitz Sun COM>]

Alexander,

  I haven't looked at this gnome-vfs code in a while, but I suspect 
that you have to use regex and filename hints along with sniffing to 
differentiate some OpenOffice/Staroffice documents from zip files.

Also I'm not sure it is possible to determine whether a .jar file is a 
Java library, data, or an executable without unpacking and looking in 
META-INF/MANIFEST.MF

Do you have any suggestions on handling these cases?

We will probably always need a mixture of sniffing and filetype/regex 
for legacy documents but wouldn't it be possible to write meta-data into 
a cache for all gnome documents written via gnome-vfs?

A directory would contain a .vfs-meta file with something like this:
   Number of files: 3
   Number of files type-checked by gnome-vfs: 3
   myfile.jpg    type:image/jpeg     launchwith:gimp
   myfile.mov   type:video/mpeg4     launchwith:totem
   myfile.xxx   type:unknown         launchwith:undefined

If the .vfs-meta file doesn't exist or the number of files in a 
directory doesn't match the number typechecked by gnome-vfs, you'd know 
you have to do some sniffing.  Wouldn't this speed up thumbnailing, 
launching and directory browing for all gnome created files?

If only this had been done right back in 1980 :(

-------------
application/winvirus
      regex,2: \.doc\.scr
      regex,2: \.jpg\.exe...


Alexander Larsson wrote:
> On Thu, 2004-01-15 at 05:43, Peter Harvey wrote:
>
>
> > I have no idea how the magic mime-type detection code works, but would
> > it be made faster by using the extensions of a file as a hint? ie. if
> > you are trying to determine the type of a file with .jpg extension,
> > first check the JPEG magic entry? This should only involve reading the
> > first few characters of the file.
>
>
> This doesn't help. The slow part about sniffing is reading the first few
> bytes of the file. You have to do several seeks on the hard-drive, and
> each seek is delayed by the HD seek time and on average half a
> rotational delay. This adds up to about 10-15 msecs per file, and faster
> harddrives don't really make this better. In fact, Alan Cox claimed that
> opening a new file takes about the same time as reading another 8 meg
> from a continuous file (on modern disks). 
>
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>  Alexander Larsson                                            Red Hat, Inc 
>                    alexl redhat com    alla lysator liu se 
> He's an oversexed crooked stage actor whom everyone believes is mad. She's a 
> hard-bitten antique-collecting archaeologist with her own daytime radio talk 
> show. They fight crime! 
>
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