* Whenever a node downloads a new VL, send it to all peers that
haven't already sent or received it. It also saves it to the
database_dir as a Json text file named "cache." plus the public key of
the list signer. Any files that exist for public keys provided in
[validator_list_keys] will be loaded and processed if any download
from [validator_list_sites] fails or no [validator_list_sites] are
configured.
* Whenever a node receives a broadcast VL message, it treats it as if
it had downloaded it on it's own, broadcasting to other peers as
described above.
* Because nodes normally download the VL once every 5 minutes, a single
node downloading a VL with an updated sequence number could
potentially propagate across a large part of a well-connected network
before any other nodes attempt to download, decreasing the amount of
time that different parts of the network are using different VLs.
* Send all of our current valid VLs to new peers on connection.
This is probably the "noisiest" part of this change, but will give
poorly connected or poorly networked nodes the best chance of syncing
quickly. Nodes which have no http(s) access configured or available
can get a VL with no extra effort.
* Requests on the peer port to the /vl/<pubkey> endpoint will return
that VL in the same JSON format as is used to download now, IF the
node trusts and has a valid instance of that VL.
* Upgrade protocol version to 2.1. VLs will only be sent to 2.1 and
higher nodes.
* Resolves#2953
* Adds local file:// URL support to the [validator_list_sites] stanza.
The file:// URL must not contain a hostname. Allows a rippled node
operator to "sideload" a new list if their node is unable to reach
a validator list's web site before an old list expires. Lists
loaded from a file will be validated in the same way a downloaded
list is validated.
* Generalize file/dir "guards" from Config test so they can be reused
in other tests.
* Check for error when reading validators.txt. Saves some parsing and
checking of an empty string, and will give a more meaningful error.
* Completes RIPD-1674.
