Tor v3 support #18884

Meta issue to track Tor v3 support. It needs:

• Finalize BIP155:
  • Get this merged: #907 BIP155: include changes from followup discussions
  • Get this merged: #967 BIP155: clarify variable integer format and change time to fixed 32 bit
  • Decide how to signal for addrv2 support - protocol version bump (as in the BIP), service bit or a new p2p message (as in the WIP implementation). Integrate that decision into the BIP (either via the above PR or separately). Done: https://github.com/bitcoin/bips/pull/907#issuecomment-641145777
  • Flip the BIP from Status: Draft to Status: Final
• Implement BIP155
  • Rebase pull#16748 [WIP] Add support for addrv2 (BIP155)
  • Get all unit tests to pass (pull#16748)
  • Get all functional tests to pass (if they don't) (pull#16748)
  • Address review suggestions (pull#16748)
  • Create a new PR from above (ready for review). Done: pull#19031 Implement ADDRv2 support (part of BIP155)
  • Split pull#19031 in smaller, digestible PRs, targeting each one to have 100% code coverage of modified code (see details on the PR page):
    • Preparation changes
    • Change CNetAddr::ip to have flexible size
    • Implement addrv2 (un)serializing
    • Advertise support for addrv2 and start sending such messages to peers
  • Document addrv2 next to addr (https://github.com/bitcoin-dot-org/developer.bitcoin.org/pull/99)
• Implement Tor v3 on top of that (#19954).

Related: issue#2091 Binding to multiple anonymous networks (esp. I2P) issue#9214 ensure ADD_ONION implementation is compatible with upstream changes, next generation onion addresses issue#18254 setting externalip=<version 3 onion address> results in error

From #bitcoin-core-dev:

19:05 < dongcarl> According to the tor-dev mailing list, Tor plans to deprecate v2 with 0.4.4.x (Sept. 15th, 2020) and obsolete it in 0.4.6.x (July 15th, 2021) 19:05 < dongcarl> More details here: https://lists.torproject.org/pipermail/tor-dev/2020-June/014365.html

#19031 (or #19360) would benefit from some more code review.

cc @laanwj @MarcoFalke @dongcarl @naumenkogs @TheBlueMatt

Can be closed, as the doc updates regard other repositories?

Indeed