[whatwg] RFC: Alternatives to storage mutex for cookies and localStorage

[Jonas Sicking]

On Tue, Sep 8, 2009 at 1:33 AM, Aaron Boodman<aa at google.com> wrote:
> On Tue, Sep 8, 2009 at 1:20 AM, Jonas Sicking<jonas at sicking.cc> wrote:
>> On Tue, Sep 8, 2009 at 1:18 AM, Aaron Boodman<aa at google.com> wrote:
>>> On Tue, Sep 8, 2009 at 1:13 AM, Jonas Sicking<jonas at sicking.cc> wrote:
>>>> On Tue, Sep 8, 2009 at 1:07 AM, Aaron Boodman<aa at google.com> wrote:
>>>>> On Tue, Sep 8, 2009 at 12:54 AM, Jonas Sicking<jonas at sicking.cc> wrote:
>>>>>> On Tue, Sep 8, 2009 at 12:00 AM, Aaron Boodman<aa at google.com> wrote:
>>>>>>> On Fri, Sep 4, 2009 at 12:02 AM, Chris Jones<cjones at mozilla.com> wrote:
>>>>>>>> I propose adding the functions
>>>>>>>>
>>>>>>>>  window.localStorage.beginTransaction()
>>>>>>>>  window.localStorage.commitTransaction()
>>>>>>>> or
>>>>>>>>  window.beginTransaction()
>>>>>>>>  window.commitTransaction()
>>>>>>>
>>>>>>> I think this is a good idea! I would modify it to follow the pattern
>>>>>>> set by the current SQLDatabase proposal, to have a callback, like
>>>>>>> this:
>>>>>>>
>>>>>>> window.localStorage.transaction(function() {
>>>>>>>  // use local storage here
>>>>>>> });
>>>>>>
>>>>>> We have discussed similar APIs in the past. Something like a:
>>>>>>
>>>>>> window.getLocalStorage(function (storage) {
>>>>>>  ...use storage...
>>>>>> });
>>>>>>
>>>>>> This is nice because it can be expanded to something like:
>>>>>> window.getSharedItems(window.SHARED_ITEM_LOCALSTORAGE |
>>>>>> window.SHARED_ITEM_COOKIES, function (...) { ... });
>>>>>>
>>>>>> to let you access both cookies and localStorage safely at the same time.
>>>>>
>>>>> I think worrying about safely accessing cookies is a bit of
>>>>> over-design. As has been pointed out, cookies don't work correctly
>>>>> today and the wheels haven't fallen off yet.
>>>>>
>>>>> I think a solution for localStorage that doesn't fix cookies is fine.
>>>>>
>>>>>> However, this requires breaking compatibility with existing syntax,
>>>>>> something that seems impossible at this point given that Microsoft has
>>>>>> shipped localStorage. I know Hixie has asked them in the past about
>>>>>> how they plan to deal with the mutex problem, but I'm not sure if an
>>>>>> answer has been received as of yet.
>>>>>
>>>>> I addressed this at the end of my last message. Specifically, I suggest:
>>>>>
>>>>> interface LocalStorageTransactionCallback {
>>>>>  void handleEvent();  // note: no arguments!
>>>>> };
>>>>>
>>>>> interface LocalStorage {
>>>>>  ...
>>>>>  // LocalStorage can only be accessed inside this callback. Access outside
>>>>>  // of it will raise an exception, except in some browsers that support such
>>>>>  // behavior for legacy reasons.
>>>>>  void transaction(LocalStorageTransactionCallback callback);
>>>>>  ...
>>>>> };
>>>>>
>>>>> With this, there is no need to change anything about the current API.
>>>>> The only change is the addition of the new transaction() method.
>>>>
>>>> While this keeps existing IDL intact, it still breaks any existing
>>>> pages, which is the real concern for any browser vendor I would think.
>>>
>>> Not necessarily.
>>>
>>> The second half of my proposal is that vendors who currently implement
>>> local storage can choose to continue to allow access to it outside of
>>> the transaction() callback. It seems like this would work fine for
>>> single-event-loop browsers, right?
>>
>> But that results in code that works in one browser, but not another,
>> defeating the whole point of having a standard.
>>
>> Would you be fine with having pages that work fine in Firefox and IE,
>> break in Chrome?
>
> I don't really see another option. People on the Chrome team are
> saying it may be impractical to implement the spec as-is. Presumably
> Firefox is unwillingly to break backward compatibility. If both of
> these are true, we are headed for a split.
>
> In this case, I don't think it is a big deal. My proposed API change
> is so minor that it is trivial to handle in code:
>
> function doStorageStuff() {
>  ... use window.localStorage ...
> }
>
> if (localStorage.transaction)
>  localStorage.transaction(doStorageStuff);
> else
>  doStorageStuff();

I think Firefox would be willing to break compat. The question is if
microsoft is. Which we need to ask them.

/ Jonas