Also add misbehaving relays to updateFallbackDirs.py blacklist,
but leave them commented out in case it's a transient issue,
or it's been resolved by the download check fixes. (These
relays hang stem's downloader. It's unlikely they'll ever help
clients.)
Allow fallback directories which have been stable for 30 days
to work around #18050, which causes relays to submit descriptors
with 0 DirPorts when restarted. (Particularly during Tor version
upgrades.)
Ignore low fallback directory count in alpha builds.
"Tor has included a feature to fetch the initial consensus from nodes
other than the authorities for a while now. We just haven't shipped a
list of alternate locations for clients to go to yet.
Reasons why we might want to ship tor with a list of additional places
where clients can find the consensus is that it makes authority
reachability and BW less important.
We want them to have been around and using their current key, address,
and port for a while now (120 days), and have been running, a guard,
and a v2 directory mirror for most of that time."
Features:
* whitelist and blacklist for an opt-in/opt-out trial.
* excludes BadExits, tor versions that aren't recommended, and low
consensus weight directory mirrors.
* reduces the weighting of Exits to avoid overloading them.
* places limits on the weight of any one fallback.
* includes an IPv6 address and orport for each FallbackDir, as
implemented in #17327. (Tor won't bootstrap using IPv6 fallbacks
until #17840 is merged.)
* generated output includes timestamps & Onionoo URL for traceability.
* unit test ensures that we successfully load all included default
fallback directories.
Closes ticket #15775. Patch by "teor".
OnionOO script by "weasel", "teor", "gsathya", and "karsten".
