Re: [Afpfs-ng-devel] precompose and decompose

[HAT <ha...@fa...>]

Mac OS X don't use bare precomopsition and bare decomosition.
NFC and NFD are implemented. These are complete normalization.
The processes of NFC and NFD are as follows.

    NFC
    decompose(including singleton) -> ordering -> precompose

    NFD
    decompose(including singleton) -> ordering

NFC and NFD are irreversible conversions.
If the table of decomposition have a term "X -> Y",

   NFC
   X -> Y
   Y -> Y

   NFD
   X -> Y
   Y -> Y

"X" doesn't exist in HFS+. It is saved as "Y".

Maybe, the problem will not occur even if afpfs-ng imprement or not
because Mac OS X 10.2 and later implement NFC and NFD perfectly.

Netatalk don't implement Singleton. I think that it's ideal.
Netatalk use not HFS+ but general UNIX filesystem.
"X" and "Y" might exist in one directory.
It is not ideal that netatalk report to the clients, "I have Y and Y".
It's better reporting "I have X and Y".
This is not a perfect method. But I think it's better.

If afpfs-ng implement singleton and netatalk have X only...
   Netatalk says "I have X"
   Afpfs-ng convert from X to Y.
   Afpfs-ng says "Please give me Y"
   Netatalk says "I have no Y"

Therefore, I think that afpfs-ng should not implement Singleton.

AFP server might have to act like a HFS+ as much as possible.
But afpfs-ng should act like a UNIX filesystem.
Afpfs-ng need not perfectly implement NFC and NFD.

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Mac OS X 10.0/10.1's NFC and NFD are imprefect because it's besed on
Unicode 2.x.
The decompose() and ordering() are necessary for Mac OS X 10.0/10.1's
imperfect filenames.

	  decompose(excluding singleton) -> ordering -> precompose

However, A complete Mac OS X 10.0/10.1 support will be impossible maybe.
It is unstable that Mac OS X 10.2/10.3/10.4 connect to 10.0/10.1.

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At first, afpfs-ng should implement bare UCS4precompose() that having
perfect table[] for Mac OS X 10.2 and later.

The Mac OS X 10.0/10.1 support is the next step.

-- 
HAT