Re: FengAndy@aol.com

Jim, 
I noticed that Windows XP could display the thumbnail for iDisk  stored 
pictures. However, it's not be able to display thumbnails. 
Any explanation?
Andy
In a message dated 3/17/2004 1:46:11 PM Pacific Standard Time,  
luther.j@apple.com writes:

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  isstored  
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/arbon/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
>


Andy Feng 
_AOL Storage &  Personalization Architecture_ 
(http://blues.netscape.com/users/afeng/publish/)