Implements another part of #23713.

Implements part of #23713.

Implements #25448.

The filter is applicable to both bridges and relays. It uses basic
string operations to extract the operating system from the platform line
of descriptors.

Fixes: #6946

A missing descriptor directory has caused an IllegalStateException
when we attempted to write our parse history files. Let's be more
careful about this case and skip this history file if there is no such
directory.

Fixes #26711.

Indexes are created for relays with no known country code or
autonomous system number using the special values "xz" and "AS0"
respectively.

No changes are made to the summary or details documents.

Fixes: #26665

This commit adds two new fields: {un,}verified_host_names.

Whereas previously InetAddress was used to resolve reverse domain
names, this instead changes the lookup mechanism to use JNDI allowing
for a deeper view into the DNS. It also accounts for the fact that
multiple PTR records are not forbidden in the DNS specification and are
often used in shared hosting scenarios.

A host name is considered verified if it has a matching forward record.
If a PTR value is found to have multiple A records, it will be
considered verified if any one of the A records matches the original
address. If no matching record is found, it will be reported as an
unverified host name.

Previously, unverified host names were discarded internally by the
InetAddress lookup mechanism and so this data could not be used.

To maintain "bug compatibility" with the previous implementation of the
"host_name" field, which will now be deprecated, the IP address is
returned when a lookup fails.

The host_name field continues to be used, but now will consider all
verified and unverified host names. If finer grained filtering is
needed, then a seperate ticket could be filed for that, but it is
unclear that it is useful enough to justify the work.

Fixes: #18342

Update metrics-lib dependency to 2.4.0.

Adapt touched logging statements to our standards.

Implements #25848.

Fixes #25332.

Also adapt tests to check the new functionality.
Implements task-25740.

Fixes #25700.

Implements #24256.

Add a utility method for only un-escaping valid utf and supply a test
as well as test data for this issue.

Fixes task-22594.

Part of task-25002.

Rather than on system time we're now depending on the last time a
relay or bridge was seen in a consensus or status to determine when
history ends for this relay.

This has the advantage of making the write step deterministic, and it
produces the exact same graph intervals for the different documents of
a given relay or bridge.

A minor downside is that we're now depending on node statuses _and_
another status file in order to produce a history document. Should be
okay.

Define graph end as last full data point before the relay/bridge was
last seen.

Also make sure that graphs end at that defined graph end and do not
continue just because there's more history available. This is mostly
to exclude falsely-reported statistics.

Implements #16513.

Add a "recommended_version" parameter to return only relays and
bridges running a Tor software version that is recommended or not
recommended by the directory authorities.

Implements #23544.

Add a "recommended_version" field to bridge details documents based on
whether the directory authorities recommend the bridge's version.

Implements #21827.

Extend the "version" parameter to also return bridges with the given
version or version prefix.

Implements #23962.

Add a "version" field to relay details documents with the Tor software
version listed in the consensus and similarly to bridge details
documents with the Tor software version found in the server
descriptor.

Implements #22488.

Implements #21637.

Implements #16553.

With this patch, the "search" parameter does not only accept unquoted
qualified search terms like `search=contact:John Doe` where "John"
would be looked up in the contact line and "Doe" in the nickname or
base64-encoded fingerprint. It also accepts quoted qualified search
terms like `search=contact:"John Doe"` where "John Doe" would be
looked up in the contact line. It further accepts escaped double
quotes (\") within quoted qualified search terms.

Implements #21366.

There's a relay running an alternate Tor version that produces
descriptors without "uptime" line, and the directory authorities don't
include a "v" line for that relay, likely because its platform string
does not include the magic word "Tor".

Fixes #24012.

Implements task-23778.

When we set this field in the update process, we only looked whether
the bridge is contained in the last known bridge network status. We
also need to check whether it has the "Running" flag assigned there.

This is different from relays, because the consensus only lists relays
with the "Running" flag since a couple of years, whereas the bridge
network status lists all known bridges.

Fixes #23467. Spotted by nusenu.