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

From: Eric Uhrhane <ericu@google.com>
Date: Thu, 16 Sep 2010 16:00:44 -0700
Message-ID: <AANLkTi=CLjoGbjfGPZUPyRVfTR0j_w1gYEXs7ngW4cTX@mail.gmail.com>
To: Kinuko Yasuda <kinuko@chromium.org>
Cc: ifette@google.com, Web Applications Working Group WG <public-webapps@w3.org>
2010/9/16 Kinuko Yasuda <kinuko@chromium.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.)

Which do you think is more error-prone, a method called
removeRecursively, or a boolean flag to remove?

>> 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 23:01:29 UTC

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