[tor-bugs] #17623 [Tor]: Improve not-a-server behavior of server-only timer callbacks

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#17623: Improve not-a-server behavior of server-only timer callbacks
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 Reporter:  nickm   |          Owner:
     Type:  defect  |         Status:  new
 Priority:  Low     |      Milestone:  Tor: 0.2.???
Component:  Tor     |        Version:
 Severity:  Minor   |     Resolution:
 Keywords:          |  Actual Points:
Parent ID:          |         Points:
  Sponsor:          |
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Comment (by teor):

 We could be clever about this and activate callbacks only on the kinds of
 servers which use them:
 * Relays, including Bridge Relays: `server_mode()`
   * check_descriptor
   * check_for_reachability_bw
 * Relays, including Bridge Relays, and Single Onion Servers (prop 252):
 `server_mode() || ???`
   * rotate_onion_key
   * check_ed_keys
   * expire_old_ciruits_serverside
 * Exits: `server_mode() && !router_my_exit_policy_is_reject_star()`
   * retry_dns_callback
   * check_dns_honesty
 * Bridge Relays: `get_options()->BridgeRelay`
   * record_bridge_stats
 * Authorities: `authdir_mode_any_nonhidserv()`
   * launch_reachability_tests
 * V3 Authorities: `authdir_mode_v3(get_options())`
   * check_authority_cert
 * Bridge Authorities: `get_options()->BridgeAuthoritativeDir`
   * write_bridge_ns

 Every time the config changes, we may have to deactivate/reactivate some
 of these callbacks.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/17623#comment:3>
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