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

[Aaron Boodman]

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();

- a