[tor-bugs] #17543 [Tor]: Bring some clarity to behavior of net_is_disabled() vs DisableNetwork vs we_are_hibernating()

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#17543: Bring some clarity to behavior of net_is_disabled() vs DisableNetwork vs
we_are_hibernating()
------------------------+--------------------------------
     Reporter:  nickm   |      Owner:
         Type:  defect  |     Status:  new
     Priority:  Medium  |  Milestone:  Tor: 0.2.8.x-final
    Component:  Tor     |    Version:
     Severity:  Normal  |   Keywords:
Actual Points:          |  Parent ID:  #2149
       Points:          |    Sponsor:
------------------------+--------------------------------
 We have at least three ways to say "no network for us, please":
 `net_is_disabled()` vs `options->DisableNetwork` vs
 `we_are_hibernating()`.

 Currently, `net_is_disabled()` is true if either of the other is true.
 `DisableNetwork` can be set like any other option.  And
 `we_are_hibernating()` is true if we are currently in any hibernation
 state other than "live and alert" -- for example, if we are entering
 hibernation in a little while, or if we are shutting down cleanly.

 They have the following behavior:


 net_is_disabled() --
    - makes us not continue pending pt configuration. ##
    - stops reachability tests ##
    - stops retrying listeners
    - stops constructing predicted circuits.
    - stops uploading info about HS descriptors
    - stops launching/checking port-forwarding app
    - stops warning about unreachable orport/dirport
    - stops us from warning if we mark ourself as down.
    - means that our dirport is unreachable.
    - means that our dirport shouldn't be advertised.

 DisableNetwork --
    - close all noncontroller stuff and note that circuits won't work,
      immediately, during options_act_reversible (?)
    - Used to decide whether to launch ClientTransportPlugins and
      ServerTransportPlugins. ##
    - Affects discriptor.
    - Categorically prevents any outgoing socket.
    - Categorically prevents any outgoing DNS resolve.
    - Categorically prevents DNS testing and probing.
    - Prevents any descriptor upload.
    - Prevents fetching bridge descriptors.
    - Stops checking for need for new descriptor.
    - Stops launching upness checks
    - stops testing reachability
    - Stops updating ns downloads at all
    - Causes dir fetches to get delayed
    - Causes descriptor downloads not to get updated.

 we_are_hibernating() --
    - makes all create cells get destroyed.
    - causes all BEGIN cells to get closed.
    - makes us recommendation-ignore bootstrap problems. ##
    - makes us decide that we are down, to dirserv_set_router_is_running.
 ##
    - makes us expire unused OR connections.
    - makes us suppress reachability tests.
    - makes us advertise no capacity, and say that we're hibernating.

 complex:
    - we_are_hibernating() and DisableNetwork are used together in
      options_act_reversible to decide how and why to call
      retry_all_listeners()

 These may all be correct, but we should try to make it so their function
 is more obvious, and there's a more clear division of what we do when.

 Motivation: For #2149 we want to add yet another way for Tor to 'turn
 itself off'.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17543>
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