[webkit-dev] localStorage quota limit

Maciej Stachowiak mjs at apple.com
Wed Dec 2 22:20:37 PST 2009

On Dec 2, 2009, at 9:07 PM, Darin Fisher wrote:

> On Wed, Dec 2, 2009 at 8:44 PM, Maciej Stachowiak <mjs at apple.com>  
> wrote:
> On Dec 2, 2009, at 8:14 PM, Darin Fisher wrote:
>> What about Maciej's comment.  JS strings are often use to store  
>> binary values.  Obviously, if people stick to octets, then it  
>> should be fine, but perhaps some folks leverage all 16 bits?
> I think some people do use JavaScript strings this way, though not  
> necessarily with LocalStorage. This kind of use will probably become  
> obsolete when we add a proper way to store binary data from the  
> platform.
> Most Web-related APIs are fully accepting of JavaScript strings that  
> are not proper UTF-16. I don't see a strong reason to make  
> LocalStorage an exception. It does make sense for WebSocket to be an  
> exception, since in that case charset transcoding is required by the  
> protocol, and since it is desirable in that case to prevent any  
> funny business that may trip up the server..
> Also, looking at UTF-16 more closely, it seems like all UTF-16 can  
> be transcoded to UTF-8 and round-tripped if one is willing to allow  
> technically invalid UTF-8 that encodes unpaired characters in the  
> surrogate range as if they were characters. It's not clear to me why  
> Firefox or IE choose to reject instead of doing this. This also  
> removes my original objection to storing strings as UTF-8.
> I think it is typical for UTF-16 to UTF-8 conversion to involve the  
> intermediate step of forming a Unicode code point.  If that cannot  
> be done, then conversion fails.  This may actually be a security  
> thing.  If something expects UTF-8, it is safer to ensure that it  
> gets valid UTF-8 (even if that involves loss of information).

These security considerations seem important for WebSocket where the  
protocol uses UTF-8 per spec, but not for the internal storage  
representation of JavaScript strings in LocalStorage (where observable  
input and output are both possibly-invalid UTF-16).


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