[Bug 1541787] Re: Printing from legacy apps on the pocket desktop

[Stephen M. Webb]

** Changed in: libertine (Ubuntu)
       Status: New => Triaged

** Changed in: libertine (Ubuntu)
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/1541787

Title:
  Printing from legacy apps on the pocket desktop

Status in avahi package in Ubuntu:
  New
Status in cups-filters package in Ubuntu:
  New
Status in libertine package in Ubuntu:
  Triaged

Bug description:
  I have worked out a concept on how to introduce printing support to
  the phone (tablet, mobile devices) keeping the resource consumption
  low, starting the needed daemons on-demand.

  The daemons needed for printing are avahi-daemon, cups-browsed, and
  CUPS. avahi-daemon discovers printers on the network, cups-browsed
  creates local CUPS queues pointing to the remote printers and CUPS
  does the actual printing.

  CUPS is started socket-activated by Upstart and stops by itself when
  it gets idle. So CUPS for example starts when cups-browsed tries to
  create a print queue or an app sends a job to be printed. avahi-daemon
  and cups-browsed will be started by the print dialog of Ubuntu Touch,
  right before the dialog opens, making available printers on the
  network appear within seconds in the dialog. When the dialog closes,
  either because the user sent the print job or because he has
  cancelled, it kills avahi-daemon. cups-browsed and CUPS terminate
  automatically then as soon as the user's job is printed (plus a
  timeout).

  If you connect a monitor to the pone and so fire up the pocket desktop
  you are able to run legacy apps (apps designed for a conventional PC)
  which have print functionalities but their print dialogs do not start
  and kill daemons, they assume that all daemons and print queues are
  readily available. CUPS would be fired up automatically by any app's
  print functionality due to the socket activation, but then we would
  not have print queues on our phone as avahi-daemon and cups-browsed
  are not running.

  So what has to be made sure is that cups-browsed and avahi-daemon are
  running if at least one of

   - the native print dialog of Ubuntu Touch
   - any legacy app

  are running. So when one of these get started the two daemons need to
  get started and if all of these terminate avahi-daemon needs to get
  killed, so that the rest of the printing stack shuts down when all
  jobs get done.

  We assume that ubuntu-app-launch is the place where this should be
  done, please re-assign if this is not correct. I also add cups-filters
  (source of cups-browsed) and avahi-daemon tasks for the case that
  perhaps here something needs to get done, too.

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