[tor-bugs] #20778 [Applications/Tor Browser Sandbox]: Check and download updates in the background.

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#20778: Check and download updates in the background.
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 Reporter:  yawning                           |          Owner:  yawning
     Type:  enhancement                       |         Status:  accepted
 Priority:  High                              |      Milestone:
Component:  Applications/Tor Browser Sandbox  |        Version:
 Severity:  Normal                            |     Resolution:
 Keywords:  Yawning201612                     |  Actual Points:
Parent ID:                                    |         Points:
 Reviewer:                                    |        Sponsor:
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Comment (by yawning):

 Ok, so my plan as far as Tor Browser UI integration of the sandboxed
 update goes is:
  1. Introduce a new env var `TOR_SANDBOX` that my implementation will set
 to `linux-v0`.
  2. Modify the `sandboxed-tor-browser` control port surrogate to add:
     * `_TBB_CHECKUPDATE`, a command which will trigger (or display if
 already in progress) the `sandboxed-tor-browser` update check.
     * `_TBB_UPDATE`, an event that will fire if there is a browser update
 pending.
  3. Modify torbutton to (all actions assuming the new env var is set
 appropriately):
     * Send the `_TBB_CHECKUPDATE` command from
 `torbutton_check_for_update()` instead of calling into the prompter.
     * Register for the `_TBB_UPDATE` event, and set
 `extensions.torbutton.updateNeeded` to `true` if it fires.

 I believe this mostly preserves the existing UX.  I'm not sure what the
 right thing to do when the browser doesn't support integration would be,
 though I doubt my current strategy of "pop up a modal dialog box every 5
 mins asking if the user wants to udpate" is the correct behavior.

 nb: Since the new command and event are entirely synthetic and never hit
 the actual tor daemon, I'm not going to bother with a `control-spec.txt`
 patch (and since the surrogate doesn't allow `events/names` as a `GETINFO`
 query, the right way to check if this behavior should happen is "is the
 env var set to what I said I will set it to".

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20778#comment:10>
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