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recovery.rs
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recovery.rs
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// Tracking of sent packets and detecting their loss.
#![deny(clippy::pedantic)]
use std::cmp::{max, min};
use std::collections::BTreeMap;
use std::convert::TryFrom;
use std::mem;
use std::ops::RangeInclusive;
use std::time::{Duration, Instant};
use smallvec::{smallvec, SmallVec};
use neqo_common::{qdebug, qinfo, qlog::NeqoQlog, qtrace, qwarn};
use crate::ackrate::AckRate;
use crate::cid::ConnectionIdEntry;
use crate::crypto::CryptoRecoveryToken;
use crate::packet::PacketNumber;
use crate::path::{Path, PathRef};
use crate::qlog::{self, QlogMetric};
use crate::quic_datagrams::DatagramTracking;
use crate::rtt::RttEstimate;
use crate::send_stream::SendStreamRecoveryToken;
use crate::stats::{Stats, StatsCell};
use crate::stream_id::{StreamId, StreamType};
use crate::tracking::{AckToken, PacketNumberSpace, PacketNumberSpaceSet, SentPacket};
pub(crate) const PACKET_THRESHOLD: u64 = 3;
/// `ACK_ONLY_SIZE_LIMIT` is the minimum size of the congestion window.
/// If the congestion window is this small, we will only send ACK frames.
pub(crate) const ACK_ONLY_SIZE_LIMIT: usize = 256;
/// The number of packets we send on a PTO.
/// And the number to declare lost when the PTO timer is hit.
pub const PTO_PACKET_COUNT: usize = 2;
/// The preferred limit on the number of packets that are tracked.
/// If we exceed this number, we start sending `PING` frames sooner to
/// force the peer to acknowledge some of them.
pub(crate) const MAX_OUTSTANDING_UNACK: usize = 200;
/// Disable PING until this many packets are outstanding.
pub(crate) const MIN_OUTSTANDING_UNACK: usize = 16;
/// The scale we use for the fast PTO feature.
pub const FAST_PTO_SCALE: u8 = 100;
#[derive(Debug, Clone)]
#[allow(clippy::module_name_repetitions)]
pub enum StreamRecoveryToken {
Stream(SendStreamRecoveryToken),
ResetStream {
stream_id: StreamId,
},
StopSending {
stream_id: StreamId,
},
MaxData(u64),
DataBlocked(u64),
MaxStreamData {
stream_id: StreamId,
max_data: u64,
},
StreamDataBlocked {
stream_id: StreamId,
limit: u64,
},
MaxStreams {
stream_type: StreamType,
max_streams: u64,
},
StreamsBlocked {
stream_type: StreamType,
limit: u64,
},
}
#[derive(Debug, Clone)]
#[allow(clippy::module_name_repetitions)]
pub enum RecoveryToken {
Stream(StreamRecoveryToken),
Ack(AckToken),
Crypto(CryptoRecoveryToken),
HandshakeDone,
KeepAlive, // Special PING.
NewToken(usize),
NewConnectionId(ConnectionIdEntry<[u8; 16]>),
RetireConnectionId(u64),
AckFrequency(AckRate),
Datagram(DatagramTracking),
}
/// `SendProfile` tells a sender how to send packets.
#[derive(Debug)]
pub struct SendProfile {
/// The limit on the size of the packet.
limit: usize,
/// Whether this is a PTO, and what space the PTO is for.
pto: Option<PacketNumberSpace>,
/// What spaces should be probed.
probe: PacketNumberSpaceSet,
/// Whether pacing is active.
paced: bool,
}
impl SendProfile {
pub fn new_limited(limit: usize) -> Self {
// When the limit is too low, we only send ACK frames.
// Set the limit to `ACK_ONLY_SIZE_LIMIT - 1` to ensure that
// ACK-only packets are still limited in size.
Self {
limit: max(ACK_ONLY_SIZE_LIMIT - 1, limit),
pto: None,
probe: PacketNumberSpaceSet::default(),
paced: false,
}
}
pub fn new_paced() -> Self {
// When pacing, we still allow ACK frames to be sent.
Self {
limit: ACK_ONLY_SIZE_LIMIT - 1,
pto: None,
probe: PacketNumberSpaceSet::default(),
paced: true,
}
}
pub fn new_pto(pn_space: PacketNumberSpace, mtu: usize, probe: PacketNumberSpaceSet) -> Self {
debug_assert!(mtu > ACK_ONLY_SIZE_LIMIT);
debug_assert!(probe[pn_space]);
Self {
limit: mtu,
pto: Some(pn_space),
probe,
paced: false,
}
}
/// Whether probing this space is helpful. This isn't necessarily the space
/// that caused the timer to pop, but it is helpful to send a PING in a space
/// that has the PTO timer armed.
pub fn should_probe(&self, space: PacketNumberSpace) -> bool {
self.probe[space]
}
/// Determine whether an ACK-only packet should be sent for the given packet
/// number space.
/// Send only ACKs either: when the space available is too small, or when a PTO
/// exists for a later packet number space (which should get the most space).
pub fn ack_only(&self, space: PacketNumberSpace) -> bool {
self.limit < ACK_ONLY_SIZE_LIMIT || self.pto.map_or(false, |sp| space < sp)
}
pub fn paced(&self) -> bool {
self.paced
}
pub fn limit(&self) -> usize {
self.limit
}
}
#[derive(Debug)]
pub(crate) struct LossRecoverySpace {
space: PacketNumberSpace,
largest_acked: Option<PacketNumber>,
largest_acked_sent_time: Option<Instant>,
/// The time used to calculate the PTO timer for this space.
/// This is the time that the last ACK-eliciting packet in this space
/// was sent. This might be the time that a probe was sent.
last_ack_eliciting: Option<Instant>,
/// The number of outstanding packets in this space that are in flight.
/// This might be less than the number of ACK-eliciting packets,
/// because PTO packets don't count.
in_flight_outstanding: usize,
sent_packets: BTreeMap<u64, SentPacket>,
/// The time that the first out-of-order packet was sent.
/// This is `None` if there were no out-of-order packets detected.
/// When set to `Some(T)`, time-based loss detection should be enabled.
first_ooo_time: Option<Instant>,
}
impl LossRecoverySpace {
pub fn new(space: PacketNumberSpace) -> Self {
Self {
space,
largest_acked: None,
largest_acked_sent_time: None,
last_ack_eliciting: None,
in_flight_outstanding: 0,
sent_packets: BTreeMap::default(),
first_ooo_time: None,
}
}
#[must_use]
pub fn space(&self) -> PacketNumberSpace {
self.space
}
/// Find the time we sent the first packet that is lower than the
/// largest acknowledged and that isn't yet declared lost.
/// Use the value we prepared earlier in `detect_lost_packets`.
#[must_use]
pub fn loss_recovery_timer_start(&self) -> Option<Instant> {
self.first_ooo_time
}
pub fn in_flight_outstanding(&self) -> bool {
self.in_flight_outstanding > 0
}
pub fn pto_packets(&mut self, count: usize) -> impl Iterator<Item = &SentPacket> {
self.sent_packets
.iter_mut()
.filter_map(|(pn, sent)| {
if sent.pto() {
qtrace!("PTO: marking packet {} lost ", pn);
Some(&*sent)
} else {
None
}
})
.take(count)
}
pub fn pto_base_time(&self) -> Option<Instant> {
if self.in_flight_outstanding() {
debug_assert!(self.last_ack_eliciting.is_some());
self.last_ack_eliciting
} else if self.space == PacketNumberSpace::ApplicationData {
None
} else {
// Nasty special case to prevent handshake deadlocks.
// A client needs to keep the PTO timer armed to prevent a stall
// of the handshake. Technically, this has to stop once we receive
// an ACK of Handshake or 1-RTT, or when we receive HANDSHAKE_DONE,
// but a few extra probes won't hurt.
// It only means that we fail anti-amplification tests.
// A server shouldn't arm its PTO timer this way. The server sends
// ack-eliciting, in-flight packets immediately so this only
// happens when the server has nothing outstanding. If we had
// client authentication, this might cause some extra probes,
// but they would be harmless anyway.
self.last_ack_eliciting
}
}
pub fn on_packet_sent(&mut self, sent_packet: SentPacket) {
if sent_packet.ack_eliciting() {
self.last_ack_eliciting = Some(sent_packet.time_sent);
self.in_flight_outstanding += 1;
} else if self.space != PacketNumberSpace::ApplicationData
&& self.last_ack_eliciting.is_none()
{
// For Initial and Handshake spaces, make sure that we have a PTO baseline
// always. See `LossRecoverySpace::pto_base_time()` for details.
self.last_ack_eliciting = Some(sent_packet.time_sent);
}
self.sent_packets.insert(sent_packet.pn, sent_packet);
}
/// If we are only sending ACK frames, send a PING frame after 2 PTOs so that
/// the peer sends an ACK frame. If we have received lots of packets and no ACK,
/// send a PING frame after 1 PTO. Note that this can't be within a PTO, or
/// we would risk setting up a feedback loop; having this many packets
/// outstanding can be normal and we don't want to PING too often.
pub fn should_probe(&self, pto: Duration, now: Instant) -> bool {
let n_pto = if self.sent_packets.len() >= MAX_OUTSTANDING_UNACK {
1
} else if self.sent_packets.len() >= MIN_OUTSTANDING_UNACK {
2
} else {
return false;
};
self.last_ack_eliciting
.map_or(false, |t| now > t + (pto * n_pto))
}
fn remove_packet(&mut self, p: &SentPacket) {
if p.ack_eliciting() {
debug_assert!(self.in_flight_outstanding > 0);
self.in_flight_outstanding -= 1;
if self.in_flight_outstanding == 0 {
qtrace!("remove_packet outstanding == 0 for space {}", self.space);
}
}
}
/// Remove all acknowledged packets.
/// Returns all the acknowledged packets, with the largest packet number first.
/// ...and a boolean indicating if any of those packets were ack-eliciting.
/// This operates more efficiently because it assumes that the input is sorted
/// in the order that an ACK frame is (from the top).
fn remove_acked<R>(&mut self, acked_ranges: R, stats: &mut Stats) -> (Vec<SentPacket>, bool)
where
R: IntoIterator<Item = RangeInclusive<u64>>,
R::IntoIter: ExactSizeIterator,
{
let acked_ranges = acked_ranges.into_iter();
let mut keep = Vec::with_capacity(acked_ranges.len());
let mut acked = Vec::new();
let mut eliciting = false;
for range in acked_ranges {
let first_keep = *range.end() + 1;
if let Some((&first, _)) = self.sent_packets.range(range).next() {
let mut tail = self.sent_packets.split_off(&first);
if let Some((&next, _)) = tail.range(first_keep..).next() {
keep.push(tail.split_off(&next));
}
for (_, p) in tail.into_iter().rev() {
self.remove_packet(&p);
eliciting |= p.ack_eliciting();
if p.lost() {
stats.late_ack += 1;
}
if p.pto_fired() {
stats.pto_ack += 1;
}
acked.push(p);
}
}
}
for mut k in keep.into_iter().rev() {
self.sent_packets.append(&mut k);
}
(acked, eliciting)
}
/// Remove all tracked packets from the space.
/// This is called by a client when 0-RTT packets are dropped, when a Retry is received
/// and when keys are dropped.
fn remove_ignored(&mut self) -> impl Iterator<Item = SentPacket> {
self.in_flight_outstanding = 0;
mem::take(&mut self.sent_packets).into_values()
}
/// Remove the primary path marking on any packets this is tracking.
fn migrate(&mut self) {
for pkt in self.sent_packets.values_mut() {
pkt.clear_primary_path();
}
}
/// Remove old packets that we've been tracking in case they get acknowledged.
/// We try to keep these around until a probe is sent for them, so it is
/// important that `cd` is set to at least the current PTO time; otherwise we
/// might remove all in-flight packets and stop sending probes.
#[allow(clippy::option_if_let_else)] // Hard enough to read as-is.
fn remove_old_lost(&mut self, now: Instant, cd: Duration) {
let mut it = self.sent_packets.iter();
// If the first item is not expired, do nothing.
if it.next().map_or(false, |(_, p)| p.expired(now, cd)) {
// Find the index of the first unexpired packet.
let to_remove = if let Some(first_keep) =
it.find_map(|(i, p)| if p.expired(now, cd) { None } else { Some(*i) })
{
// Some packets haven't expired, so keep those.
let keep = self.sent_packets.split_off(&first_keep);
mem::replace(&mut self.sent_packets, keep)
} else {
// All packets are expired.
mem::take(&mut self.sent_packets)
};
for (_, p) in to_remove {
self.remove_packet(&p);
}
}
}
/// Detect lost packets.
/// `loss_delay` is the time we will wait before declaring something lost.
/// `cleanup_delay` is the time we will wait before cleaning up a lost packet.
pub fn detect_lost_packets(
&mut self,
now: Instant,
loss_delay: Duration,
cleanup_delay: Duration,
lost_packets: &mut Vec<SentPacket>,
) {
// Housekeeping.
self.remove_old_lost(now, cleanup_delay);
qtrace!(
"detect lost {}: now={:?} delay={:?}",
self.space,
now,
loss_delay,
);
self.first_ooo_time = None;
let largest_acked = self.largest_acked;
// Lost for retrans/CC purposes
let mut lost_pns = SmallVec::<[_; 8]>::new();
for (pn, packet) in self
.sent_packets
.iter_mut()
// BTreeMap iterates in order of ascending PN
.take_while(|(&k, _)| Some(k) < largest_acked)
{
// Packets sent before now - loss_delay are deemed lost.
if packet.time_sent + loss_delay <= now {
qtrace!(
"lost={}, time sent {:?} is before lost_delay {:?}",
pn,
packet.time_sent,
loss_delay
);
} else if largest_acked >= Some(*pn + PACKET_THRESHOLD) {
qtrace!(
"lost={}, is >= {} from largest acked {:?}",
pn,
PACKET_THRESHOLD,
largest_acked
);
} else {
self.first_ooo_time = Some(packet.time_sent);
// No more packets can be declared lost after this one.
break;
};
if packet.declare_lost(now) {
lost_pns.push(*pn);
}
}
lost_packets.extend(lost_pns.iter().map(|pn| self.sent_packets[pn].clone()));
}
}
#[derive(Debug)]
pub(crate) struct LossRecoverySpaces {
/// When we have all of the loss recovery spaces, this will use a separate
/// allocation, but this is reduced once the handshake is done.
spaces: SmallVec<[LossRecoverySpace; 1]>,
}
impl LossRecoverySpaces {
fn idx(space: PacketNumberSpace) -> usize {
match space {
PacketNumberSpace::ApplicationData => 0,
PacketNumberSpace::Handshake => 1,
PacketNumberSpace::Initial => 2,
}
}
/// Drop a packet number space and return all the packets that were
/// outstanding, so that those can be marked as lost.
/// # Panics
/// If the space has already been removed.
pub fn drop_space(&mut self, space: PacketNumberSpace) -> impl IntoIterator<Item = SentPacket> {
let sp = match space {
PacketNumberSpace::Initial => self.spaces.pop(),
PacketNumberSpace::Handshake => {
let sp = self.spaces.pop();
self.spaces.shrink_to_fit();
sp
}
PacketNumberSpace::ApplicationData => panic!("discarding application space"),
};
let mut sp = sp.unwrap();
assert_eq!(sp.space(), space, "dropping spaces out of order");
sp.remove_ignored()
}
pub fn get(&self, space: PacketNumberSpace) -> Option<&LossRecoverySpace> {
self.spaces.get(Self::idx(space))
}
pub fn get_mut(&mut self, space: PacketNumberSpace) -> Option<&mut LossRecoverySpace> {
self.spaces.get_mut(Self::idx(space))
}
fn iter(&self) -> impl Iterator<Item = &LossRecoverySpace> {
self.spaces.iter()
}
fn iter_mut(&mut self) -> impl Iterator<Item = &mut LossRecoverySpace> {
self.spaces.iter_mut()
}
}
impl Default for LossRecoverySpaces {
fn default() -> Self {
Self {
spaces: smallvec![
LossRecoverySpace::new(PacketNumberSpace::ApplicationData),
LossRecoverySpace::new(PacketNumberSpace::Handshake),
LossRecoverySpace::new(PacketNumberSpace::Initial),
],
}
}
}
#[derive(Debug)]
struct PtoState {
/// The packet number space that caused the PTO to fire.
space: PacketNumberSpace,
/// The number of probes that we have sent.
count: usize,
packets: usize,
/// The complete set of packet number spaces that can have probes sent.
probe: PacketNumberSpaceSet,
}
impl PtoState {
pub fn new(space: PacketNumberSpace, probe: PacketNumberSpaceSet) -> Self {
debug_assert!(probe[space]);
Self {
space,
count: 1,
packets: PTO_PACKET_COUNT,
probe,
}
}
pub fn pto(&mut self, space: PacketNumberSpace, probe: PacketNumberSpaceSet) {
debug_assert!(probe[space]);
self.space = space;
self.count += 1;
self.packets = PTO_PACKET_COUNT;
self.probe = probe;
}
pub fn count(&self) -> usize {
self.count
}
pub fn count_pto(&self, stats: &mut Stats) {
stats.add_pto_count(self.count);
}
/// Generate a sending profile, indicating what space it should be from.
/// This takes a packet from the supply if one remains, or returns `None`.
pub fn send_profile(&mut self, mtu: usize) -> Option<SendProfile> {
if self.packets > 0 {
// This is a PTO, so ignore the limit.
self.packets -= 1;
Some(SendProfile::new_pto(self.space, mtu, self.probe))
} else {
None
}
}
}
#[derive(Debug)]
pub(crate) struct LossRecovery {
/// When the handshake was confirmed, if it has been.
confirmed_time: Option<Instant>,
pto_state: Option<PtoState>,
spaces: LossRecoverySpaces,
qlog: NeqoQlog,
stats: StatsCell,
/// The factor by which the PTO period is reduced.
/// This enables faster probing at a cost in additional lost packets.
fast_pto: u8,
}
impl LossRecovery {
pub fn new(stats: StatsCell, fast_pto: u8) -> Self {
Self {
confirmed_time: None,
pto_state: None,
spaces: LossRecoverySpaces::default(),
qlog: NeqoQlog::default(),
stats,
fast_pto,
}
}
pub fn largest_acknowledged_pn(&self, pn_space: PacketNumberSpace) -> Option<PacketNumber> {
self.spaces.get(pn_space).and_then(|sp| sp.largest_acked)
}
pub fn set_qlog(&mut self, qlog: NeqoQlog) {
self.qlog = qlog;
}
pub fn drop_0rtt(&mut self, primary_path: &PathRef, now: Instant) -> Vec<SentPacket> {
// The largest acknowledged or loss_time should still be unset.
// The client should not have received any ACK frames when it drops 0-RTT.
assert!(self
.spaces
.get(PacketNumberSpace::ApplicationData)
.unwrap()
.largest_acked
.is_none());
let mut dropped = self
.spaces
.get_mut(PacketNumberSpace::ApplicationData)
.unwrap()
.remove_ignored()
.collect::<Vec<_>>();
let mut path = primary_path.borrow_mut();
for p in &mut dropped {
path.discard_packet(p, now);
}
dropped
}
pub fn on_packet_sent(&mut self, path: &PathRef, mut sent_packet: SentPacket) {
let pn_space = PacketNumberSpace::from(sent_packet.pt);
qdebug!([self], "packet {}-{} sent", pn_space, sent_packet.pn);
if let Some(space) = self.spaces.get_mut(pn_space) {
path.borrow_mut().packet_sent(&mut sent_packet);
space.on_packet_sent(sent_packet);
} else {
qwarn!(
[self],
"ignoring {}-{} from dropped space",
pn_space,
sent_packet.pn
);
}
}
pub fn should_probe(&self, pto: Duration, now: Instant) -> bool {
self.spaces
.get(PacketNumberSpace::ApplicationData)
.unwrap()
.should_probe(pto, now)
}
/// Record an RTT sample.
fn rtt_sample(
&mut self,
rtt: &mut RttEstimate,
send_time: Instant,
now: Instant,
ack_delay: Duration,
) {
let confirmed = self.confirmed_time.map_or(false, |t| t < send_time);
if let Some(sample) = now.checked_duration_since(send_time) {
rtt.update(&mut self.qlog, sample, ack_delay, confirmed, now);
}
}
/// Returns (acked packets, lost packets)
pub fn on_ack_received<R>(
&mut self,
primary_path: &PathRef,
pn_space: PacketNumberSpace,
largest_acked: u64,
acked_ranges: R,
ack_delay: Duration,
now: Instant,
) -> (Vec<SentPacket>, Vec<SentPacket>)
where
R: IntoIterator<Item = RangeInclusive<u64>>,
R::IntoIter: ExactSizeIterator,
{
qdebug!(
[self],
"ACK for {} - largest_acked={}.",
pn_space,
largest_acked
);
let Some(space) = self.spaces.get_mut(pn_space) else {
qinfo!("ACK on discarded space");
return (Vec::new(), Vec::new());
};
let (acked_packets, any_ack_eliciting) =
space.remove_acked(acked_ranges, &mut self.stats.borrow_mut());
if acked_packets.is_empty() {
// No new information.
return (Vec::new(), Vec::new());
}
// Track largest PN acked per space
let prev_largest_acked = space.largest_acked_sent_time;
if Some(largest_acked) > space.largest_acked {
space.largest_acked = Some(largest_acked);
// If the largest acknowledged is newly acked and any newly acked
// packet was ack-eliciting, update the RTT. (-recovery 5.1)
let largest_acked_pkt = acked_packets.first().expect("must be there");
space.largest_acked_sent_time = Some(largest_acked_pkt.time_sent);
if any_ack_eliciting && largest_acked_pkt.on_primary_path() {
self.rtt_sample(
primary_path.borrow_mut().rtt_mut(),
largest_acked_pkt.time_sent,
now,
ack_delay,
);
}
}
// Perform loss detection.
// PTO is used to remove lost packets from in-flight accounting.
// We need to ensure that we have sent any PTO probes before they are removed
// as we rely on the count of in-flight packets to determine whether to send
// another probe. Removing them too soon would result in not sending on PTO.
let loss_delay = primary_path.borrow().rtt().loss_delay();
let cleanup_delay = self.pto_period(primary_path.borrow().rtt(), pn_space);
let mut lost = Vec::new();
self.spaces.get_mut(pn_space).unwrap().detect_lost_packets(
now,
loss_delay,
cleanup_delay,
&mut lost,
);
self.stats.borrow_mut().lost += lost.len();
// Tell the congestion controller about any lost packets.
// The PTO for congestion control is the raw number, without exponential
// backoff, so that we can determine persistent congestion.
primary_path
.borrow_mut()
.on_packets_lost(prev_largest_acked, pn_space, &lost);
// This must happen after on_packets_lost. If in recovery, this could
// take us out, and then lost packets will start a new recovery period
// when it shouldn't.
primary_path
.borrow_mut()
.on_packets_acked(&acked_packets, now);
self.pto_state = None;
(acked_packets, lost)
}
/// When receiving a retry, get all the sent packets so that they can be flushed.
/// We also need to pretend that they never happened for the purposes of congestion control.
pub fn retry(&mut self, primary_path: &PathRef, now: Instant) -> Vec<SentPacket> {
self.pto_state = None;
let mut dropped = self
.spaces
.iter_mut()
.flat_map(LossRecoverySpace::remove_ignored)
.collect::<Vec<_>>();
let mut path = primary_path.borrow_mut();
for p in &mut dropped {
path.discard_packet(p, now);
}
dropped
}
fn confirmed(&mut self, rtt: &RttEstimate, now: Instant) {
debug_assert!(self.confirmed_time.is_none());
self.confirmed_time = Some(now);
// Up until now, the ApplicationData space has been ignored for PTO.
// So maybe fire a PTO.
if let Some(pto) = self.pto_time(rtt, PacketNumberSpace::ApplicationData) {
if pto < now {
let probes = PacketNumberSpaceSet::from(&[PacketNumberSpace::ApplicationData]);
self.fire_pto(PacketNumberSpace::ApplicationData, probes);
}
}
}
/// This function is called when the connection migrates.
/// It marks all packets that are outstanding as having being sent on a non-primary path.
/// This way failure to deliver on the old path doesn't count against the congestion
/// control state on the new path and the RTT measurements don't apply either.
pub fn migrate(&mut self) {
for space in self.spaces.iter_mut() {
space.migrate();
}
}
/// Discard state for a given packet number space.
pub fn discard(&mut self, primary_path: &PathRef, space: PacketNumberSpace, now: Instant) {
qdebug!([self], "Reset loss recovery state for {}", space);
let mut path = primary_path.borrow_mut();
for p in self.spaces.drop_space(space) {
path.discard_packet(&p, now);
}
// We just made progress, so discard PTO count.
// The spec says that clients should not do this until confirming that
// the server has completed address validation, but ignore that.
self.pto_state = None;
if space == PacketNumberSpace::Handshake {
self.confirmed(path.rtt(), now);
}
}
/// Calculate when the next timeout is likely to be. This is the earlier of the loss timer
/// and the PTO timer; either or both might be disabled, so this can return `None`.
pub fn next_timeout(&mut self, rtt: &RttEstimate) -> Option<Instant> {
let loss_time = self.earliest_loss_time(rtt);
let pto_time = self.earliest_pto(rtt);
qtrace!(
[self],
"next_timeout loss={:?} pto={:?}",
loss_time,
pto_time
);
match (loss_time, pto_time) {
(Some(loss_time), Some(pto_time)) => Some(min(loss_time, pto_time)),
(Some(loss_time), None) => Some(loss_time),
(None, Some(pto_time)) => Some(pto_time),
_ => None,
}
}
/// Find when the earliest sent packet should be considered lost.
fn earliest_loss_time(&self, rtt: &RttEstimate) -> Option<Instant> {
self.spaces
.iter()
.filter_map(LossRecoverySpace::loss_recovery_timer_start)
.min()
.map(|val| val + rtt.loss_delay())
}
/// Simple wrapper for the PTO calculation that avoids borrow check rules.
fn pto_period_inner(
rtt: &RttEstimate,
pto_state: Option<&PtoState>,
pn_space: PacketNumberSpace,
fast_pto: u8,
) -> Duration {
// This is a complicated (but safe) way of calculating:
// base_pto * F * 2^pto_count
// where F = fast_pto / FAST_PTO_SCALE (== 1 by default)
let pto_count = pto_state.map_or(0, |p| u32::try_from(p.count).unwrap_or(0));
rtt.pto(pn_space)
.checked_mul(
u32::from(fast_pto)
.checked_shl(pto_count)
.unwrap_or(u32::MAX),
)
.map_or(Duration::from_secs(3600), |p| p / u32::from(FAST_PTO_SCALE))
}
/// Get the current PTO period for the given packet number space.
/// Unlike calling `RttEstimate::pto` directly, this includes exponential backoff.
fn pto_period(&self, rtt: &RttEstimate, pn_space: PacketNumberSpace) -> Duration {
Self::pto_period_inner(rtt, self.pto_state.as_ref(), pn_space, self.fast_pto)
}
// Calculate PTO time for the given space.
fn pto_time(&self, rtt: &RttEstimate, pn_space: PacketNumberSpace) -> Option<Instant> {
if self.confirmed_time.is_none() && pn_space == PacketNumberSpace::ApplicationData {
None
} else {
self.spaces.get(pn_space).and_then(|space| {
space
.pto_base_time()
.map(|t| t + self.pto_period(rtt, pn_space))
})
}
}
/// Find the earliest PTO time for all active packet number spaces.
/// Ignore Application if either Initial or Handshake have an active PTO.
fn earliest_pto(&self, rtt: &RttEstimate) -> Option<Instant> {
if self.confirmed_time.is_some() {
self.pto_time(rtt, PacketNumberSpace::ApplicationData)
} else {
self.pto_time(rtt, PacketNumberSpace::Initial)
.iter()
.chain(self.pto_time(rtt, PacketNumberSpace::Handshake).iter())
.min()
.copied()
}
}
fn fire_pto(&mut self, pn_space: PacketNumberSpace, allow_probes: PacketNumberSpaceSet) {
if let Some(st) = &mut self.pto_state {
st.pto(pn_space, allow_probes);
} else {
self.pto_state = Some(PtoState::new(pn_space, allow_probes));
}
self.pto_state
.as_mut()
.unwrap()
.count_pto(&mut self.stats.borrow_mut());
qlog::metrics_updated(
&mut self.qlog,
&[QlogMetric::PtoCount(
self.pto_state.as_ref().unwrap().count(),
)],
);
}
/// This checks whether the PTO timer has fired and fires it if needed.
/// When it has, mark a few packets as "lost" for the purposes of having frames
/// regenerated in subsequent packets. The packets aren't truly lost, so
/// we have to clone the `SentPacket` instance.
fn maybe_fire_pto(&mut self, rtt: &RttEstimate, now: Instant, lost: &mut Vec<SentPacket>) {
let mut pto_space = None;
// The spaces in which we will allow probing.
let mut allow_probes = PacketNumberSpaceSet::default();
for pn_space in PacketNumberSpace::iter() {
if let Some(t) = self.pto_time(rtt, *pn_space) {
allow_probes[*pn_space] = true;
if t <= now {
qdebug!([self], "PTO timer fired for {}", pn_space);
let space = self.spaces.get_mut(*pn_space).unwrap();
lost.extend(space.pto_packets(PTO_PACKET_COUNT).cloned());
pto_space = pto_space.or(Some(*pn_space));
}
}
}
// This has to happen outside the loop. Increasing the PTO count here causes the
// pto_time to increase which might cause PTO for later packet number spaces to not fire.
if let Some(pn_space) = pto_space {
qtrace!([self], "PTO {}, probing {:?}", pn_space, allow_probes);
self.fire_pto(pn_space, allow_probes);
}
}
pub fn timeout(&mut self, primary_path: &PathRef, now: Instant) -> Vec<SentPacket> {
qtrace!([self], "timeout {:?}", now);
let loss_delay = primary_path.borrow().rtt().loss_delay();
let mut lost_packets = Vec::new();
for space in self.spaces.iter_mut() {
let first = lost_packets.len(); // The first packet lost in this space.
let pto = Self::pto_period_inner(
primary_path.borrow().rtt(),
self.pto_state.as_ref(),
space.space(),
self.fast_pto,
);
space.detect_lost_packets(now, loss_delay, pto, &mut lost_packets);
primary_path.borrow_mut().on_packets_lost(
space.largest_acked_sent_time,
space.space(),
&lost_packets[first..],
);
}
self.stats.borrow_mut().lost += lost_packets.len();
self.maybe_fire_pto(primary_path.borrow().rtt(), now, &mut lost_packets);
lost_packets
}
/// Check how packets should be sent, based on whether there is a PTO,
/// what the current congestion window is, and what the pacer says.
#[allow(clippy::option_if_let_else)]
pub fn send_profile(&mut self, path: &Path, now: Instant) -> SendProfile {
qdebug!([self], "get send profile {:?}", now);
let sender = path.sender();
let mtu = path.mtu();
if let Some(profile) = self
.pto_state
.as_mut()
.and_then(|pto| pto.send_profile(mtu))
{
profile
} else {
let limit = min(sender.cwnd_avail(), path.amplification_limit());
if limit > mtu {
// More than an MTU available; we might need to pace.
if sender
.next_paced(path.rtt().estimate())
.map_or(false, |t| t > now)
{
SendProfile::new_paced()
} else {
SendProfile::new_limited(mtu)
}
} else if sender.recovery_packet() {
// After entering recovery, allow a packet to be sent immediately.
// This uses the PTO machinery, probing in all spaces. This will
// result in a PING being sent in every active space.
SendProfile::new_pto(PacketNumberSpace::Initial, mtu, PacketNumberSpaceSet::all())
} else {
SendProfile::new_limited(limit)
}
}
}
}
impl ::std::fmt::Display for LossRecovery {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
write!(f, "LossRecovery")
}
}
#[cfg(test)]
mod tests {
use super::{
LossRecovery, LossRecoverySpace, PacketNumberSpace, SendProfile, SentPacket, FAST_PTO_SCALE,
};
use crate::cc::CongestionControlAlgorithm;