nim-eth/eth/p2p/discoveryv5/ip_vote.nim

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2.5 KiB
Nim

# nim-eth - Node Discovery Protocol v5
# Copyright (c) 2021 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
#
## IP:port address votes implemented similarly as in
## https://github.com/sigp/discv5
##
## This allows the selection of a node its own public IP based on address
## information that is received from other nodes.
## This can be used in conjuction with discovery v5 ping-pong request responses
## that provide this information.
## To select the right address, a majority count is done. This is done over a
## sort of moving window as votes expire after `IpVoteTimeout`.
{.push raises: [Defect].}
import
std/[tables, options],
chronos,
./node
export options
const IpVoteTimeout = 5.minutes ## Duration until a vote expires
type
IpVote* = object
votes: Table[NodeId, tuple[address: Address, expiry: chronos.Moment]]
threshold: uint ## Minimum threshold to allow for a majority to count
func init*(T: type IpVote, threshold: uint = 10): T =
## Initialize IpVote.
##
## If provided threshold is lower than 2 it will be set to 2.
if threshold < 2:
IpVote(threshold: 2)
else:
IpVote(threshold: threshold)
proc insert*(ipvote: var IpVote, key: NodeId, address: Address) =
## Insert a vote for an address coming from a specific `NodeId`. A `NodeId`
## can only hold 1 vote.
ipvote.votes[key] = (address, now(chronos.Moment) + IpVoteTimeout)
proc majority*(ipvote: var IpVote): Option[Address] =
## Get the majority of votes on an address. Pruning of votes older than
## `IpVoteTime` will be done before the majority count.
## Note: When there is a draw the selected "majority" will depend on whichever
## address comes first in the CountTable. This seems acceptable as there is no
## other criteria to make a selection.
let now = now(chronos.Moment)
var
pruneList: seq[NodeId]
ipCount: CountTable[Address]
for k, v in ipvote.votes:
if now > v.expiry:
pruneList.add(k)
else:
ipCount.inc(v.address)
for id in pruneList:
ipvote.votes.del(id)
if ipCount.len <= 0:
return none(Address)
let (address, count) = ipCount.largest()
if uint(count) >= ipvote.threshold:
some(address)
else:
none(Address)