Allow Relay Searches for Additional Flags

[teor]

I just tried to search for all the FallbackDirs on Relay Search to find out if they had been updated.

But I didn't get any results with a simple search: "flag:FallbackDir".
And the Advanced Search doesn't have the additional flags as options.

[irl]

Currently these are generated by Relay Search. We should move these into Onionoo so that other clients can benefit from them (e.g. metrics-bot) and so that searching works too.

[karsten]

Fallback directories are a special case, because Onionoo doesn't even have this data. We'd have to add the data first before adding this additional flag to search parameters.

The other additional flags would be easier. Would you mind adding a list and precise specification for each of them here?

[irl]

I'll add a list and outline a plan for making individual tickets for these.

[irl]

The following flags are synthesised by Relay Search:

Flag	Description
NotRecommended	This relay is running a version of tor that is not recommended by the directory authorities
Unmeasured	This relay has not been measured by at least 3 bwauths
Hibernating	This relay indicated that it is hibernating in its last known descriptor
FallbackDir	This relay is listed as a fallback directory in the tor source code
ReachableIPv6	This relay has been confirmed as reachable via IPv6 in the consensus
UnreachableIPv4	This relay was not reachable on at least one IPv4 address published in the server descriptor
UnreachableIPv6	This relay was not reachable on at least one IPv6 address published in the server descriptor
IPv6 Exit	This relay allows exit connections to IPv6 hosts

The relevant code in Relay Search is:

/* Synthetic Additional Flags */
var additional_flags = []
if (!((typeof relay.recommended_version !== 'undefined') ? relay.recommended_version : true)) additional_flags.push("Not Recommended");
if (!((typeof relay.measured !== 'undefined') ? relay.measured : true)) additional_flags.push("Unmeasured");
if (((typeof relay.hibernating !== 'undefined') ? relay.hibernating : false)) additional_flags.push("Hibernating");
if (IsFallbackDir(relay.fingerprint)) additional_flags.push("FallbackDir");
if (relay.or_v6_addresses.length > 0) additional_flags.push("ReachableIPv6");
if (relay.unreachable_or_v4_addresses.length > 0) additional_flags.push("UnreachableIPv4");
if (relay.unreachable_or_v6_addresses.length > 0) additional_flags.push("UnreachableIPv6");
if (relay.exit_policy_v6_summary !== null) additional_flags.push("IPv6 Exit");

For the Onionoo protocol, I would prefer it if these flags are kept separate from the dir-spec flags in a new "additional_flags" field, but for searching it would be good to still have "flag:X" work. I don't know if this introduces a lot more complexity in Onionoo though.

Things that would need to be done as I understand it:

• Add a new "additional_flags" field to Onionoo's relay details documents
• Extend the "flag" parameter to also search in this new field, as well as the existing "flags" field
• Synthesise each of the flags:
  • NotRecommended, Hibernating and Unmeasured are all based on boolean values already in the document
  • ReachableIPv6, UnreachableIPv4 and UnreachableIPv6 will require checking the "or_addresses" and "unreachable_or_addresses" fields
  • IPv6 Exit will require checking the exit policies
  • FallbackDir will depend on #24436

[karsten]

I just commented on #24436 that we might not have to block on CollecTor providing fallback directory information.

Two more ideas I had when reading this ticket today:

• We should also add a new "fallback_directory" (or similarly named) field in details documents, rather than just the entry in "additional_flags".
• Rather than extending the "flag" parameter, which would require a major protocol update, we could as well introduce a new "additional_flag" parameter that searches just additional flags. Users would then have to know whether a flag is one set by the directory authorities or by Onionoo, but that's not necessarily a bad requirement. And we wouldn't need a major protocol update.