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Re: FileSystem API - overwrite flag for copy/move?

From: Kinuko Yasuda <kinuko@chromium.org>
Date: Thu, 16 Sep 2010 15:55:05 -0700
Message-ID: <AANLkTin79T39vNCeWoA3Jq_P4DtofgtwE_ko4+iDyq5K@mail.gmail.com>
To: Eric Uhrhane <ericu@google.com>
Cc: ifette@google.com, Web Applications Working Group WG <public-webapps@w3.org>
On Thu, Sep 16, 2010 at 2:50 PM, Eric Uhrhane <ericu@google.com> wrote:
> How about this?
>
> For a move/copy of a file on top of existing file, or a directory on
> top of an existing empty directory, you get an automatic overwrite.
> A move/copy of a file on top of an existing directory, or of a
> directory on top of an existing file, will always fail.
> A move/copy of a file or directory on top of an existing non-empty
> directory will always fail.

This sounds good to me.
I think sticking to the compatibility with Posix would make sense to
developers too.

> That matches Posix[1] rename behavior, and should cover most or all of
> the normal use cases.
> If necessary, we can consider adding a "don't overwrite" flag, but
> that may be difficult to implement without race conditions on all
> platforms.

We can achieve this in a safer way by combining getFile/getDirectory
with exclusive flag and move/copy, so I think it's reasonable not to
have "don't overwrite" flag.

> Regarding recursive deletion of directories:
>
> One option is to add a flag to remove(); that flag will be ignored if
> the Entry is a file, so it's not as clean as it might be, but it keeps
> the interface small.
> Another is to add a removeRecursively() method to DirectoryEntry; this
> makes it really clear what's going on, and might prevent some
> accidental deletions.

I have no strong opinion on this but removeRecursively might be error prone?
(Recursive remove can be very destructive and it should be triggered
with an explicit intention.)

Thanks,

> Which do you prefer?
>
> [1] http://www.opengroup.org/onlinepubs/009695399/functions/rename.html
>
> 2010/9/9 Kinuko Yasuda <kinuko@chromium.org>:
>> On Thu, Sep 9, 2010 at 12:37 AM, Ian Fette (イアンフェッティ) <ifette@google.com>
>> wrote:
>>>
>>> I think recursive copy/remove is a very valid use case. As for overwrite,
>>> is a flag necessary? On most OSes you already get overwrite as the default
>>> behaviour (at least from APIs, many interactive UAs such as Explorer on
>>> windows will prompt), is there a compelling argument why it should be
>>> different for a web api?
>>
>> Making overwriting mode default for copy/move sounds reasonable to me too.
>>  Especially if we allow recursive remove (and I think there would be more
>> need for this one) it'd look more consistent.
>> As for providing options, I was a bit concerned about the complexity in
>> programming with nested callbacks, but in this case it's not a big deal
>> (we'll need only two) and wouldn't be a problem.
>> I'm more concerned with recursive remove though.  The js code to do that
>> isn't very pretty.
>>
>>> On Thu, Sep 9, 2010 at 12:22 AM, Kinuko Yasuda <kinuko@chromium.org>
>>> wrote:
>>>>
>>>> On Thu, Sep 9, 2010 at 12:12 AM, Kinuko Yasuda <kinuko@chromium.org>
>>>> wrote:
>>>>>
>>>>> On Tue, Sep 7, 2010 at 6:12 PM, Eric Uhrhane <ericu@google.com> wrote:
>>>>>>
>>>>>> On Mon, Aug 30, 2010 at 9:27 PM, Kinuko Yasuda <kinuko@chromium.org>
>>>>>> wrote:
>>>>>> > Hi,
>>>>>> > I have a question about Entry.moveTo/copyTo behavior defined in
>>>>>> > the File API: Directories and System [1].
>>>>>> > Currently the API doesn't specify how Entry.moveTo() and copyTo()
>>>>>> > should
>>>>>> > behave
>>>>>> > when a source entry is a file and there's *already* a file at the
>>>>>> > destination path.
>>>>>> > Should UAs overwrite the existing file at the destination path or
>>>>>> > not?
>>>>>> > Or maybe we should add an 'overwrite' flag to indicate if the script
>>>>>> > wants
>>>>>> > to overwrite an existing file or not?
>>>>>>
>>>>>> I'm open to a flag.  We're already up to 4 parameters to each of those
>>>>>> methods, though...5 is a bit ungainly.  I'm concerned that we might
>>>>>> find another flag to add at some point, and we'd then be up to 6.
>>>>>> What about adding an flags object, as in getFile, to allow for
>>>>>> expansion?
>>>>>
>>>>> Adding a flag or flags object (suppose the other thread about Flags will
>>>>> be settled) sounds good to me.
>>>>> Or I think it's also ok to explicitly disallow overwriting copy/move,
>>>>> i.e. specify that 'it is an error to copy or move a file or directory if
>>>>> there's already an entry'.  In this case it might be better to have another
>>>>> error code like ENTRY_EXISTS_ERR so that the user script can act
>>>>> differently.  (But in general having a handy option would make programming
>>>>> much easier in async context where every operation requires one or two
>>>>> callbacks.)
>>>>> If we're going to add 'overwrite' flag, there'll be a few more things to
>>>>> be made clear.
>>>>> For example I wonder how the overwriting copy/move should behave when
>>>>> there's already a **directory** at the destination path/name.
>>>>> Should the UA remove the existing directory and create a new entry at
>>>>> the same path?
>>>>> This sounds reasonable but it'll also provide a handy alternative way to
>>>>> remove a directory recursively.
>>>>
>>>> By the way how do you think about recursive remove?
>>>> Is there a reason (or past discussion) not to have recursive option in
>>>> remove?  (I mean, other than the fact that adding more and more options to
>>>> every method doesn't look very clean.)
>>>> I found that it's not very easy to remove a directory when there're
>>>> children in it -- it requires multiple DirectoryReader.readEntries and
>>>> Entry.remove in a nested way.
>>>> Thanks,
>>>>>
>>>>> Or should the UA create a new entry *under* the directory?
>>>>> This behavior doesn't sound like 'overwriting'.  The resulting path will
>>>>> be like 'destParentPath/name/name' which doesn't sound quite consistent with
>>>>> the spec either.
>>>>>
>>>>>> > Similarly I wondered if we'd want to have a 'recursive' flag for
>>>>>> > moveTo/copyTo.
>>>>>> > I think for directories we can simply assume that the user wants to
>>>>>> > move/copy
>>>>>> > them recursively, but it might be good to add some notion about that
>>>>>> > in the
>>>>>> > spec.
>>>>>>
>>>>>> How about I add a note indicating that directory copies are always
>>>>>> recursive?
>>>>>> I don't think we need anything for move.
>>>>>
>>>>> This sounds good to me.  Thanks!
>>>>>
>>>>>
>>>>>>
>>>>>> > Thanks,
>>>>>> > [1] http://dev.w3.org/2009/dap/file-system/file-dir-sys.html
>>>>>> >
>>>>>
>>>>
>>>
>>
>>
>
Received on Thursday, 16 September 2010 22:56:03 GMT

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