On 27 Feb 2013, at 01:00, Gwynne Raskind <gwy...@darkrainfall.org> wrote:
> On Feb 26, 2013, at 12:47 PM, Gerriet M. Denkmann <gerr...@mdenkmann.de>
> wrote:
>> My investigations regarding archiving on OS X:
>>
>> 1. NSArchiver stores all strings in Utf-8.
>> This is inefficient for strings which contain mainly non-european
>> characters (e.g. Chinese or Thai) as one character will use 3 bytes (Utf-16
>> would use only 2).
>> Corollary: It cannot store strings which contain illegal Unicode chars.
>
> And then in UTF-16, strings which contain mostly ASCII/European characters
> are wasting 2x space. Six of one, half dozen of the other. This is a very old
> debate and I'm grateful that Apple chose UTF-8 for storage, as UTF-16 makes
> things much more complicated.
Or one could (as NSKeyedArchiver seems to do) choose the shortest
representation,
>> 2. NSKeyedArchiver seems to be ok.
>> But it does create unnecessary data. E.g. in the case of an array
>> containing identical objects, like:
>> NSArray *a = @[ @"a", @"a", ...., @"a"];
>> With 1 000 000 items it creates 10,000,395 bytes - my version creates
>> only 1 000 332 bytes
>> and the output is still readable by NSKeyedUnarchiver.
>
> Are you sure this is happening? NSKeyedArchiver is documented as doing
> deduplication of objects. If this is true, it's definitely a bug and there is
> no reason Apple wouldn't want it fixed.
Just try it yourself:
#define NBR 1000000
NSMutableArray *m = [ NSMutableArray array ];
for ( NSUInteger i = 0; i < NBR; i++ ) [ m addObject: @"a" ];
NSData *dataKeyed = [ NSKeyedArchiver
archivedDataWithRootObject: m ];
NSLog(@"%s NSKeyedArchiver created %10lu bytes ", __FUNCTION__,
[dataKeyed length]);
Then change NBR to 1000001 and compare.
>
>> 3, NSKeyedUnarchiver has several bugs.
>> The string $null is converted to nil.
>> Very harmful if this string is part of a collection (like array, set or
>> dictionary).
>
> It should have already been mangled by NSKeyedArchiver.
Strings (other than keys) do NOT get mangled by NSKeyedArchiver.
>
>> If the key in: encodeXXX:forKey: starts with an "$" NSKeyedArchiver
>> correctly mangles this by prefixing
>> another "$". But NSKeyedUnarchiver does not find these mangled keys and
>> returns nil or 0.
>
> You can, as a workaround, consider keys prefixed by $ as reserved, however
> this is certainly a bug. The fact that no one has reported it/gotten it fixed
> in so much time shows that it's probably not a major issue, though.
>
>> I have not reported these bugs, as I am convinced that Apple has no interest
>> in fixing these problems.
>
> This is the exact attitude that causes Apple to be perceived as not having
> interest. Please file the bugs - the engineers reading this list can't give
> high priority to things that developers don't report, as much as they'd
> probably like to.
I have filed the $null bug. Got back as duplicate with a very low id-number.
Meaning: this bug is known to Apple since several years. Still no fix.
Gerriet.
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