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

From: Eric Uhrhane <ericu@google.com>
Date: Thu, 16 Sep 2010 14:50:18 -0700
Message-ID: <AANLkTikg-NU_tc1REpqKfGNPU9PuvWnEEfQGLM8Wtesi@mail.gmail.com>
To: Kinuko Yasuda <kinuko@chromium.org>
Cc: ifette@google.com, Web Applications Working Group WG <public-webapps@w3.org>
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.

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

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.

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 21:51:04 UTC

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