[whatwg] Any way to submit only those parts of a form that havechanged?

[dolphinling]

Greg Kilwein wrote:
> dolphinling wrote:
> 
>> Ian Hickson wrote:
>>
>>> On Sun, 12 Dec 2004, Ben Meadowcroft wrote:
>>>
>>>>>> I don't feel like doing a detailed readthrough of the spec again 
>>>>>> (though I did glance at parts that looked relevant), but is there 
>>>>>> anything in WF2 that allows only parts of a form that have changed 
>>>>>> from their default value to be submitted?
>>>>>
>>>>> There isn't; what would the use case be?
>>>>
>>>> Seriously though I recently had to frig this by adding hidden form 
>>>> elements using Javascript to the form on an onchange handler 
>>>> indicating when a field had been changed so you don't have to do 
>>>> lookups on the backend data first to decide if there has been a 
>>>> change or not.
>>>
>>> Be very careful with this -- you should always assume that the 
>>> client-provided data is hostile, and not trusted.
>>
>> Once again, if the data's not submitted, it can't be hostile.
> 
> Yes, it can be, say, on a required field on a form.

But in that case the data /is/ submitted (and you do validity checking, 
etc. on it). This is for data that's /not/ submitted, and is assumed by 
the server to be the default. It's logically impossible for that data to 
be hostile unless the default is hostile.

>>> (Note that there is also the problem of how to handle checkboxes that 
>>> I mentioned earlier. Any proposal for how to handle this would have 
>>> to address that issue first.)
>>
>> Which problem is this?
>
> When a checkbox is not checked, the UA does not submit the value of the 
> checkbox with the form.  Therefore, how is the server supposed to 
> differentiate between when the checkbox has been unchecked by the user 
> and when the UA is not submitting it because the field has not changed?
> 
> This also creates other problems.  Given a situation where a user is 
> editing a "comments" textarea, assume the user wants to erase the 
> comments.  How can the server differentiate between the user 
> legitimately erasing the comments and the UA not submitting it because 
> the field has not changed?

As far as I can tell, for textareas (and input type='text', etc.) The 
value of '' (i.e., empty) is submitted normally, so that wouldn't be a 
problem.

For an easy workaround for the checkbox problem, input type='checkbox', 
'radio', and select (any others?) could just always be submitted. Anyone 
else have a better solution?