// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package netutil
import (
"time"
"github.com/dexon-foundation/dexon/common/mclock"
)
// IPTracker predicts the external endpoint, i.e. IP address and port, of the local host
// based on statements made by other hosts.
type IPTracker struct {
window time.Duration
contactWindow time.Duration
minStatements int
clock mclock.Clock
statements map[string]ipStatement
contact map[string]mclock.AbsTime
lastStatementGC mclock.AbsTime
lastContactGC mclock.AbsTime
}
type ipStatement struct {
endpoint string
time mclock.AbsTime
}
// NewIPTracker creates an IP tracker.
//
// The window parameters configure the amount of past network events which are kept. The
// minStatements parameter enforces a minimum number of statements which must be recorded
// before any prediction is made. Higher values for these parameters decrease 'flapping' of
// predictions as network conditions change. Window duration values should typically be in
// the range of minutes.
func NewIPTracker(window, contactWindow time.Duration, minStatements int) *IPTracker {
return &IPTracker{
window: window,
contactWindow: contactWindow,
statements: make(map[string]ipStatement),
minStatements: minStatements,
contact: make(map[string]mclock.AbsTime),
clock: mclock.System{},
}
}
// PredictFullConeNAT checks whether the local host is behind full cone NAT. It predicts by
// checking whether any statement has been received from a node we didn't contact before
// the statement was made.
func (it *IPTracker) PredictFullConeNAT() bool {
now := it.clock.Now()
it.gcContact(now)
it.gcStatements(now)
for host, st := range it.statements {
if c, ok := it.contact[host]; !ok || c > st.time {
return true
}
}
return false
}
// PredictEndpoint returns the current prediction of the external endpoint.
func (it *IPTracker) PredictEndpoint() string {
it.gcStatements(it.clock.Now())
// The current strategy is simple: find the endpoint with most statements.
counts := make(map[string]int)
maxcount, max := 0, ""
for _, s := range it.statements {
c := counts[s.endpoint] + 1
counts[s.endpoint] = c
if c > maxcount && c >= it.minStatements {
maxcount, max = c, s.endpoint
}
}
return max
}
// AddStatement records that a certain host thinks our external endpoint is the one given.
func (it *IPTracker) AddStatement(host, endpoint string) {
now := it.clock.Now()
it.statements[host] = ipStatement{endpoint, now}
if time.Duration(now-it.lastStatementGC) >= it.window {
it.gcStatements(now)
}
}
// AddContact records that a packet containing our endpoint information has been sent to a
// certain host.
func (it *IPTracker) AddContact(host string) {
now := it.clock.Now()
it.contact[host] = now
if time.Duration(now-it.lastContactGC) >= it.contactWindow {
it.gcContact(now)
}
}
func (it *IPTracker) gcStatements(now mclock.AbsTime) {
it.lastStatementGC = now
cutoff := now.Add(-it.window)
for host, s := range it.statements {
if s.time < cutoff {
delete(it.statements, host)
}
}
}
func (it *IPTracker) gcContact(now mclock.AbsTime) {
it.lastContactGC = now
cutoff := now.Add(-it.contactWindow)
for host, ct := range it.contact {
if ct < cutoff {
delete(it.contact, host)
}
}
}
