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package sctp
import (
"math"
"sync"
"time"
)
const (
rtoInitial float64 = 3.0 * 1000 // msec
rtoMin float64 = 1.0 * 1000 // msec
rtoMax float64 = 60.0 * 1000 // msec
rtoAlpha float64 = 0.125
rtoBeta float64 = 0.25
maxInitRetrans uint = 8
pathMaxRetrans uint = 5
noMaxRetrans uint = 0
)
// rtoManager manages Rtx timeout values.
// This is an implementation of RFC 4960 sec 6.3.1.
type rtoManager struct {
srtt float64
rttvar float64
rto float64
noUpdate bool
mutex sync.RWMutex
}
// newRTOManager creates a new rtoManager.
func newRTOManager() *rtoManager {
return &rtoManager{
rto: rtoInitial,
}
}
// setNewRTT takes a newly measured RTT then adjust the RTO in msec.
func (m *rtoManager) setNewRTT(rtt float64) float64 {
m.mutex.Lock()
defer m.mutex.Unlock()
if m.noUpdate {
return m.srtt
}
if m.srtt == 0 {
// First measurement
m.srtt = rtt
m.rttvar = rtt / 2
} else {
// Subsequent rtt measurement
m.rttvar = (1-rtoBeta)*m.rttvar + rtoBeta*(math.Abs(m.srtt-rtt))
m.srtt = (1-rtoAlpha)*m.srtt + rtoAlpha*rtt
}
m.rto = math.Min(math.Max(m.srtt+4*m.rttvar, rtoMin), rtoMax)
return m.srtt
}
// getRTO simply returns the current RTO in msec.
func (m *rtoManager) getRTO() float64 {
m.mutex.RLock()
defer m.mutex.RUnlock()
return m.rto
}
// reset resets the RTO variables to the initial values.
func (m *rtoManager) reset() {
m.mutex.Lock()
defer m.mutex.Unlock()
if m.noUpdate {
return
}
m.srtt = 0
m.rttvar = 0
m.rto = rtoInitial
}
// set RTO value for testing
func (m *rtoManager) setRTO(rto float64, noUpdate bool) {
m.mutex.Lock()
defer m.mutex.Unlock()
m.rto = rto
m.noUpdate = noUpdate
}
// rtxTimerObserver is the inteface to a timer observer.
// NOTE: Observers MUST NOT call start() or stop() method on rtxTimer
// from within these callbacks.
type rtxTimerObserver interface {
onRetransmissionTimeout(timerID int, n uint)
onRetransmissionFailure(timerID int)
}
// rtxTimer provides the retnransmission timer conforms with RFC 4960 Sec 6.3.1
type rtxTimer struct {
id int
observer rtxTimerObserver
maxRetrans uint
stopFunc stopTimerLoop
closed bool
mutex sync.RWMutex
}
type stopTimerLoop func()
// newRTXTimer creates a new retransmission timer.
// if maxRetrans is set to 0, it will keep retransmitting until stop() is called.
// (it will never make onRetransmissionFailure() callback.
func newRTXTimer(id int, observer rtxTimerObserver, maxRetrans uint) *rtxTimer {
return &rtxTimer{
id: id,
observer: observer,
maxRetrans: maxRetrans,
}
}
// start starts the timer.
func (t *rtxTimer) start(rto float64) bool {
t.mutex.Lock()
defer t.mutex.Unlock()
// this timer is already closed
if t.closed {
return false
}
// this is a noop if the timer is always running
if t.stopFunc != nil {
return false
}
// Note: rto value is intentionally not capped by RTO.Min to allow
// fast timeout for the tests. Non-test code should pass in the
// rto generated by rtoManager getRTO() method which caps the
// value at RTO.Min or at RTO.Max.
var nRtos uint
cancelCh := make(chan struct{})
go func() {
canceling := false
for !canceling {
timeout := calculateNextTimeout(rto, nRtos)
timer := time.NewTimer(time.Duration(timeout) * time.Millisecond)
select {
case <-timer.C:
nRtos++
if t.maxRetrans == 0 || nRtos <= t.maxRetrans {
t.observer.onRetransmissionTimeout(t.id, nRtos)
} else {
t.stop()
t.observer.onRetransmissionFailure(t.id)
}
case <-cancelCh:
canceling = true
timer.Stop()
}
}
}()
t.stopFunc = func() {
close(cancelCh)
}
return true
}
// stop stops the timer.
func (t *rtxTimer) stop() {
t.mutex.Lock()
defer t.mutex.Unlock()
if t.stopFunc != nil {
t.stopFunc()
t.stopFunc = nil
}
}
// closes the timer. this is similar to stop() but subsequent start() call
// will fail (the timer is no longer usable)
func (t *rtxTimer) close() {
t.mutex.Lock()
defer t.mutex.Unlock()
if t.stopFunc != nil {
t.stopFunc()
t.stopFunc = nil
}
t.closed = true
}
// isRunning tests if the timer is running.
// Debug purpose only
func (t *rtxTimer) isRunning() bool {
t.mutex.RLock()
defer t.mutex.RUnlock()
return (t.stopFunc != nil)
}
func calculateNextTimeout(rto float64, nRtos uint) float64 {
// RFC 4096 sec 6.3.3. Handle T3-rtx Expiration
// E2) For the destination address for which the timer expires, set RTO
// <- RTO * 2 ("back off the timer"). The maximum value discussed
// in rule C7 above (RTO.max) may be used to provide an upper bound
// to this doubling operation.
if nRtos < 31 {
m := 1 << nRtos
return math.Min(rto*float64(m), rtoMax)
}
return rtoMax
}
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