[tor-bugs] #15775 [Tor]: Add IPv4 Fallback Directory List to tor, active by default

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#15775: Add IPv4 Fallback Directory List to tor, active by default
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     Reporter:  teor         |      Owner:  teor
         Type:  enhancement  |     Status:  accepted
     Priority:  major        |  Milestone:  Tor: 0.2.7.x-final
    Component:  Tor          |    Version:  Tor: 0.2.4.7-alpha
   Resolution:               |   Keywords:  tor-dist, 027-triaged-1-in
Actual Points:               |  Parent ID:  #15228
       Points:               |
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Comment (by teor):

 I have made the following changes to weasel's script:
 * Changed output to C comments and strings
  * removed potentially harmful characters to avoid injection attacks
 * Remove relays that have ever had a `BadExit` flag
  * No FallbackDirs currently have a `BadExit` flag
 * Remove relays that are not running a `recommended_version` (22/353)
  * every FallbackDir reports a version
 * Added IPv6 for #8374
  * 44/353 FallbackDirs have at least one IPv6 address
  * It's not clear what additional work needs to be done for IPv6 directory
 fetches (#6027), but the ipv6 lines can easily be removed if we decide
 they're better left out. I think they'd make getting #6027 working easier
 if they were left in.
 * Implemented stable sorting of secondary orport addresses, so that we
 always choose the same IP addresses, even if OnionOO changes the order it
 returns them in (the secondary address order is documented as arbitrary)
  * This affects IPv6 addresses (44/353), and IPv4 addresses where we fall
 back to a secondary ORPort address because the IP addresses of the DirPort
 and primary ORPort address don't match (none at present).
 * Implemented last-modified-date to reduce load on OnionOO
  * cache the files on the local filesystem (100MB) and only re-download
 them when they change

 This leaves 331 default FallbackDirs. Is this about what we were
 expecting?

 I'll attach the modified script and the candidate include file to this
 task after this comment goes through. The patch will include them both.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/15775#comment:16>
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