[tor-bugs] #16387 [Core Tor/Tor]: Improve reachability of hidden services on mobile phones

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#16387: Improve reachability of hidden services on mobile phones
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 Reporter:  asn           |          Owner:
     Type:  enhancement   |         Status:  new
 Priority:  Medium        |      Milestone:  Tor: 0.2.???
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:  tor-hs        |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:  SponsorR-can
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Comment (by timonh):

 Replying to [comment:11 teor]:
 > It's worth noting that Tor clients also have some of these issues on
 mobile, whether accessing hidden services or exits. So general
 improvements that improve tor's response to broken circuits will also help
 with hidden services on mobile.

 To detect broken circuits earlier Tor could use TCP keepalive or use own
 keepalive messages. If Tor would use the keepalive messages to detect
 broken connections (and through that circuits) it would be necessary to
 negotiate the interval (so the other end knows when keepalive messages
 should arrive and when the connection expired). Right now keepalive
 messages are only used to keep firewalls from expiring connections and the
 interval is set by KeepalivePeriod.

 I don't know how easy it is to use TCP keepalive in a platform-independent
 manner. Another question is if this might violate the privacy of a user.
 If a user uses a different interval than the majority he might stand out.

 Also on Linux there is a nice option called TCP_USER_TIMEOUT which allows
 to set a "maximum amount of time in milliseconds that transmitted data may
 remain unacknowledged before TCP will forcibly close the corresponding
 connection". So this would improve the situation where an IP sends a
 RELAY_COMMAND_INTRODUCE2 to a HS which isn't reachable anymore. The IP
 would detect earlier (depending on TCP_USER_TIMEOUT) that the connection
 is broken.
 For idle connections it would still be necessary to use a keepalive
 mechanism.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16387#comment:12>
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