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Re: FengAndy@aol.com

From: Jim Luther <luther.j@apple.com>
Date: Wed, 17 Mar 2004 13:45:50 -0800
Message-Id: <753B2BAA-785C-11D8-816B-000A95DC65E0@apple.com>
Cc: FengAndy@aol.com
To: w3c-dist-auth@w3.org

On a Macintosh, thumbnails icons for directories are stored in a  
special file inside the directory (Mac OS 8 through 9 and Mac OS X use  
different techniques for that file). Thumbnails icons for files are  
stored in a file's resource fork (the Macintosh file system supports  
two file forks -- See  
<http://developer.apple.com/documentation/mac/Files/Files-14.html>).

To store a file's data fork and the file's resource fork and other  
Macintosh-specific metadata on volume formats (like WebDAV) which don't  
support Macintosh-style resources forks or metadata, the file is stored  
in AppleDouble format (it's funny but the only place I can find the  
AppleDouble documentation isn't on Apple web site -- it's at  
<http://www.lazerware.com/formats/Specs/AppleSingle_AppleDouble.pdf>.  
The AppleDouble formatted file is stored as two files. The data for the  
file is stored in the "AppleDouble Data file" which has the file's  
name. The resource fork and other Macintosh-specific metadata is stored  
in the "AppleDouble Header file" which has the file's name with the  
characters "._" prepended.

So, if you look at a WebDAV server that has files stored by Mac OS X  
clients, you'll probably see files with names beginning with "._" --  
that's where the thumbnail icons (if any) are stored.

If a non-Macintosh client wanted to display those icons, it would be a  
lot of work. That client would have to know how to:

1 - Parse the AppleDouble Header file to get the Macintosh Finder  
information (the metadata which contains a flag indicating the presence  
of a custom thumbnail icon) and the resource fork.

2 - Interpret the resource fork to get to the custom icon resources  
(see  
http://developer.apple.com/documentation/mac/MoreToolbox/MoreToolbox 
-99.html for the resoruce file format).

3 - Display the icon resources (they are bitmaps (see  
http://developer.apple.com/documentation/mac/Toolbox/Toolbox-448.html),  
'icns' resources (see  
http://developer.apple.com/documentation/Carbon/Conceptual/ 
Icon_Service_nd_Utilities/02concepts/chapter_2_section_4.html), or in  
PICT format (see  
http://developer.apple.com/documentation/mac/QuickDraw/QuickDraw 
-458.html) -- they aren't jpeg or gif).

So... a bunch of work just for thumbnails.

- Jim Luther

On Mar 17, 2004, at 11:23 AM, Julian Reschke wrote:

>
> FengAndy@aol.com wrote:
>> Folks,
>>  Have anyone tried to enable thumbnails via WebDAV clients? Apple's  
>> iDisk enables such features. All other WebDAV clients don't seem to  
>> have such support. For example, in Windows, you could not select a  
>> WebFolder to have a thumbnail view.
>>  Any suggestion? Thanks in advance.
>
> There's no specific support for that in WebDAV. Do you know what  
> Apple's iDisk is doing here?
>
> Regards, Julian
>
>
> -- 
> <green/>bytes GmbH -- http://www.greenbytes.de -- tel:+492512807760
>
Received on Wednesday, 17 March 2004 16:46:25 UTC

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