Allow IPv6 extend cells

As part of #33817 (moved), we want to allow IPv6 extend cells.

We want clients and relays to send:

• dual-stack EXTEND2 cells
• IPv6-only EXTEND2 cells

We want relays to parse:

• dual-stack EXTEND2 cells
• IPv6-only EXTEND2 cells

changed milestone to %Tor: 0.4.4.x-final

Trac:
Parent Ticket: #33048 (moved)

added actualpoints::0.5 component::core tor/tor ipv6 milestone::Tor: 0.4.4.x-final owner::teor parent::33048 points::0.5 priority::medium prop311 resolution::fixed reviewer::ahf severity::normal sponsor::55-must status::closed type::enhancement labels

See my PR:

• master: https://github.com/torproject/tor/pull/1863

The unit tests cover the two major cases:

• dual-stack EXTEND2 cells
• IPv6-only EXTEND2 cells

The tests also cover cell parsing and cell encoding.

They don't cover the edge cases of all-zero IP addresses or ports. I'm not particularly worried about those cases.

Trac:
Reviewer: N/A to ahf
Status: assigned to needs_review

I considered moving create_cell_parse() and extend_cell_parse() (and the functions they call) to a new feature/relay/onion_relay.c file.

But there are lots of dependencies between parsing and formatting. (Clients and relays format, only relays parse.)

ahf, nickm, what do you think?

Trac:
Cc: N/A to ahf, nickm

Trac:
Parent: #33817 (moved) to #33220 (moved)

I think we should review this code along with #33817 (moved).

Trac:
Parent: #33220 (moved) to #33817 (moved)
Status: needs_review to closed
Resolution: N/A to fixed

Trac:
Parent: #33817 (moved) to #33048 (moved)

closed

changed time estimate to 4h

added 4h of time spent

mentioned in issue #33048 (moved)

mentioned in issue tpo/core/tor#33818 (closed)

moved to tpo/core/tor#33901 (closed)