ubuntu-phone team mailing list archive

[Jamie Strandboge <jamie@xxxxxxxxxxxxx>]

On 10/24/2013 06:26 PM, Robert Schroll wrote:
> Hi all,
> 
> Since my previous questions about the content hub didn't get me anywhere, I must
> have been asking stupid questions.  Allow me to back up to a more basic topic.

I doubt that was the case-- probably simply that people got quite busy with
13.10's release.

> This is the workflow I wish to enable:
> 
> 1) The user copies (via rsync or Ubuntu One folder or whatever) files to their
> home directory or subdirectory thereof of their device.
> 
> 2) The user uses my app to display the contents of those files.
> 
> 3) Optionally, my app can download more files of a similar type to the same
> location, so that the user can rsync (or whatever) these files back to their
> computer.
> 
> Is this possible with click apps in from the app store?  If so, how?
> 

It is possible for files stored in the writable locations of your app. In
practice, that means one of these directories (or a subdirectory):

APP_PKGNAME="com.ubuntu.developer.username.foo"
@{HOME}/.cache/@{APP_PKGNAME}/*
@{HOME}/.local/share/@{APP_PKGNAME}/*

Application confinement necessarily blocks access to arbitrary files in $HOME
because of Ubuntu's trust model[1]. If your goal is to be able to sync arbitrary
files in $HOME outside of the above app-specific directories across multiple
devices, this is not currently supported and content-hub in its current form
isn't going to be particularly helpful. Ie, right now, there isn't a 'file
picking' content provider for your app to use with content-hub to prompt the
user for a list of files. This will need to be supported for the converged
device, but even when it becomes available, your app would only get a copy of
the file in the app-specific directory but no way to sync the file back out to
its original location (in the future, we should/may also support passing a file
descriptor instead of a full copy-- but this is an implementation detail that
won't help your use case). To support your use case, we need to somehow support
persistent file access through content-hub or some other means (ie, allow the
user to expand file access in a controlled manner). A very simplistic solution
would be to expand content-hub to support hardlinking and then have your app use
a (system) file picking content provider to choose which files to hardlink into
place. This has a number of limitations (not least of which, security policy is
not updated so it is difficult to know what files the app now has access to) but
*may* be good enough depending on the implementation-- a more proper
implementation requires apparmor user profiles, which is a desired feature but
not something that is planned to be delivered for 14.04 or 14.10. Bottom line,
this is an extremely security sensitive topic, difficult to get right and needs
to be carefully implemented.

In short, your use case falls into the category of 'backup software' and backup
software is not supported by the appstore at this time.

[1]http://developer.ubuntu.com/publish/apps/security-policy-for-click-packages/

-- 
Jamie Strandboge                 http://www.ubuntu.com/

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