[tor-bugs] #24050 [Core Tor/Tor]: We still do client-side caching. We just don't use the cache.

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#24050: We still do client-side caching. We just don't use the cache.
------------------------------+--------------------
     Reporter:  arma          |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------
 In Tor 0.2.4.7-alpha, we said {{{Turn off the client-side DNS cache by
 default.}}} (Proposal 205, #7570)

 But actually, in {{{port_cfg_new()}}} we say
 {{{
   cfg->entry_cfg.cache_ipv4_answers = 1;
 }}}
 And similarly in {{{parse_port_config()}}} we say
 {{{
       cache_ipv4 = 1,
 }}}

 Now, fortunately, there is a bonus surprise field named
 {{{use_cached_ipv4}}} and that is left to 0. You can read more in commit
 ac990aa44a which removes the line
 {{{
 -  cfg->use_cached_ipv4_answers = 1;
 }}}

 Now, that's all well and good -- we keep a client-side dns cache but we
 don't use it. I hacked up my Tor client to confirm, and it's really true.

 But then there's commit bbad23b, which says {{{No, client-side DNS
 cacheing should not be on by default.}}} and its patch to
 {{{parse_unix_socket_config()}}} is
 {{{
 -        port->entry_cfg.cache_ipv4_answers = 1;
 -        port->entry_cfg.cache_ipv6_answers = 1;
 +        port->entry_cfg.cache_ipv4_answers = 0;
 +        port->entry_cfg.cache_ipv6_answers = 0;
 }}}

 But then in commit 485fdcf82 we took out that whole
 {{{parse_unix_socket_config()}}} concept, unifying stuff back to the "yes,
 keep the client-side dns cache" default.

 Do we want to set the cache to default to off? Since we don't use it? Does
 anything need it to be on? It would seem that anything that relies on it
 is a bug (and a surprise) at this point.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24050>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online

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