Re: New draft of FileSystem API posted

On Fri, Aug 13, 2010 at 10:58 AM, Eric Uhrhane <ericu@google.com> wrote:

> On Thu, Aug 12, 2010 at 11:08 PM, Kinuko Yasuda <kinuko@chromium.org>
> wrote:
> > Hi Eric,
> > Thanks for your reply.
> > Actually after sending that email I had started to think that caching
> isFile
> > / isDirectory information in memory would be ok if user could get an
> > informative error code when an entry becomes stale -- and seems like
> that's
> > the case.  So I'm almost convinced :)
> > One thing I'm not fully convinced yet about FileEntry / DirectoryEntry is
> > if we really want to make FileEntry a subclass of File.
> > To me it looks like they have slightly different semantics - File is an
> > immutable snapshot of file content, while Entry is more like a handle for
> > meta-level operations that actually modify the underlying disk image.
> > File's size attribute and slice() method assume its snapshot doesn't
> change
> > after it was captured, but FileEntry has createWriter method and it will
> > likely change the file content.  It brings several questions: if
> FileEntry
> > == File in what timing are UAs supposed to capture a snapshot?  Do we
> want
> > to have a synchronous size attribute on a mutable Entry?  If we move an
> > Entry to another name, does its File.type need to change according to its
> > new name?
>
> You're quite right.  A mutable FileEntry shouldn't have a synchronous
> size member, and slice() and type are likewise problematic.
>
> How about if we add a getFile() method that returns a File object,
> snapshotted at the time of the call?  Hmm...that name's going to be a
> bit confusing, though, since there's a getFile on DirectoryEntry that
> does something completely different.  Perhaps just file()?  It should
> definitely be a method, not a member, to make clear that it's making
> calls to the underlying filesystem.


file() sounds good to me.

(Oh yes we have getFile on DirectoryEntry...)


>  > On Wed, Aug 11, 2010 at 1:25 PM, Eric Uhrhane <ericu@google.com> wrote:
> >>
> >> My apologies for the slow response; I'm now back from my vacation.
> >>
> >> On Tue, Jul 20, 2010 at 6:27 PM, Kinuko Yasuda <kinuko@google.com>
> wrote:
> >> > Hi Eric,
> >> > Thanks for brushing up the draft.
> >> > We had some internal discussion about the API details and came up with
> a
> >> > question regarding is{File,Directory} attributes of Entry interface.
> >> > It seems like user agent needs to be able to tell if a given entry is
> >> > file
> >> > or directory synchronously (or from its cache), but we wonder what
> >> > should
> >> > happen if the underlying file object is changed later.  For example,
> we
> >> > may
> >> > have a situation like this:
> >> > 1. a user code gets (or creates) a file entry.
> >> > 2. another flow of the code (or another code in the same
> origin) removes
> >> > the
> >> > same entry and creates a *directory* at the same path.
> >> > 3. the original code refers isFile attribute of the entry. -- should
> it
> >> > be
> >> > true or false?
> >>
> >> My intention was that the UA would look up that information when first
> >> creating the Entry and keep it cached.  It's not the kind of thing
> >> that changes very often, so I didn't think we needed it to be a live
> >> query every time.  If the user tries to write to a file that's become
> >> a directory, or vice-versa, that's what INVALID_STATE_ERROR is for.
> >>
> >> This is an unusual error, thus it's appropriate that it be handled via
> >> exception.
> >>
> >> > If an Entry is just a reference (i.e. a pathname) of a system file
> >> > entity,
> >> > it would look natural that it is resolved at run-time thus returns
> false
> >> > in
> >> > the above case.   But if so we'll have two problems: 1) we'll need to
> >> > make
> >> > synchronous stat calls to get the attribute values, and 2) as we have
> >> > different interfaces for file and directory, we may end up with having
> >> > invalid FileEntry objects for directories - or vice versa.
> >> > Would it be possible to have a single unified interface for file and
> >> > directory and let scripts figure out the info at runtime (e.g. in each
> >> > asynchronous filesystem operation)?
> >>
> >> Do you mean, allow all file operations and directory operation, and
> >> fail if you use the wrong one?  UAs already have to fail on operations
> >> that don't make sense [or fail in the underlying implementation],
> >> whether or not we keep a unified interface, so I think that would just
> >> clutter up each subtype with the others' methods.
> >
> >
> >>
> >> If I'm misunderstanding you, please give an example of your proposed
> >> interface and a situation which it would improve.
> >
> > You're not misunderstanding me.   I meant if UAs didn't cache the
> > information that an entry is file or directory it would be natural to
> make
> > wrong operations fail at run-time, but otherwise I fully agree that
> > cluttering up subtypes with irrelevant methods is not a good idea.
> >>
> >> > On Wed, Jul 7, 2010 at 6:50 PM, Eric Uhrhane <ericu@google.com>
> wrote:
> >> >>
> >> >> I've posted a new draft of File API: Directories and System [1].  In
> >> >> this draft I've rolled in quite a bit of feedback that I received
> >> >> since first posting it on DAP--many apologies for the delay.  This is
> >> >> the first draft produced since we agreed to move this spec from DAP
> to
> >> >> WebApps; I hope those of you who have time will give it a look and
> let
> >> >> me know what you think.
> >> >>
> >> >> In general I've tried to address any comment I was sent and had not
> >> >> already addressed via email.  The few that didn't make it in, I've
> >> >> responded to below.
> >> >>
> >> >> My thanks to Robin Berjon and Mike Clement for all their feedback.
> >> >>
> >> >> Robin:
> >> >>  - "data stored there by the application should not be deleted by the
> >> >> UA without user intervention", "UA should require permission from the
> >> >> user", "The application may of course delete it at will" -> these
> >> >> sound like real conformance statements, therefore SHOULD, SHOULD NOT,
> >> >> and MAY.
> >> >>
> >> >> Those are in a non-normative section; is that language still
> >> >> appropriate
> >> >> there?
> >> >>
> >> >> Robin:
> >> >> [discussion about speccing the URI format]
> >> >>
> >> >> Left as an open issue.
> >> >>
> >> >> Mike:
> >> >> [discussion about multiple sandboxes per origin]
> >> >>
> >> >> I think that would be very easy and clean to add later if desired,
> and
> >> >> in the mean time, one can use subdirectories.
> >> >>
> >> >> Mike:
> >> >> getFile/getDirectory are a bit overloaded.  How about including
> >> >> methods like exists(), createFile() and createDirectory()?  Though
> >> >> these methods are easily implemented in terms of
> getFile/getDirectory,
> >> >> I always prefer more direct API methods that help make the code
> easier
> >> >> to understand.  I expect, though, that you are attempting to be a low
> >> >> level as possible here.
> >> >>
> >> >> As Robin pointed out, adding extra round-trips will slow things down.
> >> >> Also, it can encourage race conditions.  These are easy for libraries
> >> >> to implement via wrappers.
> >> >>
> >> >> Mike:
> >> >> [request for creation time in getMetadata]
> >> >>
> >> >> It may be hard to support reliably cross-platform [2].
> >> >>
> >> >> Robin:
> >> >> [specifying a single locale everywhere]
> >> >>
> >> >> I don't think that'll make folks very happy if it's not their locale.
> >> >> If I e.g. try to force my locale on Turkish Windows users, they're
> >> >> going to see some interesting errors trying to share files with apps
> >> >> outside the browser, or for that matter even saving certain groups of
> >> >> files from inside the browser.
> >> >>
> >> >>    Eric
> >> >>
> >> >> [1] http://dev.w3.org/2009/dap/file-system/file-dir-sys.html
> >> >> [2] http://en.wikipedia.org/wiki/MAC_times
> >> >>
> >> >
> >> >
> >
> >
>