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We're going to be modifying tor's address detection and reachability code for an upcoming sponsor. To help us debug, we should log the following info when tor starts up:

IPv4:

• the Address torrc option
  • and whether it is an IP address, or a DNS name
• the local hostname
  • and whether it is an IP address, or a DNS name
• the local network interface addresses

See resolve_my_address() for details.

IPv6:

• the IPv6 address of the first IPv6 ORPort torrc option

See router_build_fresh_descriptor() and router_get_advertised_ipv6_or_ap() (in #32588 (moved)) for details.

When (or if) we use them as part of address detection, we should also log the following info:

IPv4 and IPv6:

• the Address torrc option
  • and whether it is an IP address, or a DNS name
• the IPv4 and IPv6 addresses of the first ORPort torrc option of each address family
• the local hostname
  • and whether it is an IP address, or a DNS name
• the local network interface addresses

Notes:

• We'll need a proposal to decide if ORPort or hostname should come first
• We'll probably want a summary at notice level, and then detailed logs at info level
• If all these methods fail, relays use X-Your-Address-Is: headers from directory authorities. They are out of scope, because they are not available at startup.
• Similarly, we won't print address reachability self-testing info, because it's not available at startup.
• We may want to print similar log messages (including X-Your-Address-Is: and reachability info) as part of tor's regular heartbeat messages. But that deserves a separate ticket.

I don't think we'll use (or log):

• the addresses of any DirPort torrc options
• the addresses of multiple ORPort torrc options