ant_quic/connection/
paths.rs

1use std::{cmp, net::SocketAddr};
2
3use tracing::trace;
4
5use super::{
6    mtud::MtuDiscovery,
7    pacing::Pacer,
8    spaces::{PacketSpace, SentPacket},
9};
10use crate::{Duration, Instant, TIMER_GRANULARITY, TransportConfig, congestion, packet::SpaceId};
11
12#[cfg(feature = "__qlog")]
13use qlog::events::quic::MetricsUpdated;
14
15/// Description of a particular network path
16pub(super) struct PathData {
17    pub(super) remote: SocketAddr,
18    pub(super) rtt: RttEstimator,
19    /// Whether we're enabling ECN on outgoing packets
20    pub(super) sending_ecn: bool,
21    /// Congestion controller state
22    pub(super) congestion: Box<dyn congestion::Controller>,
23    /// Pacing state
24    pub(super) pacing: Pacer,
25    pub(super) challenge: Option<u64>,
26    pub(super) challenge_pending: bool,
27    /// Whether we're certain the peer can both send and receive on this address
28    ///
29    /// Initially equal to `use_stateless_retry` for servers, and becomes false again on every
30    /// migration. Always true for clients.
31    pub(super) validated: bool,
32    /// Total size of all UDP datagrams sent on this path
33    pub(super) total_sent: u64,
34    /// Total size of all UDP datagrams received on this path
35    pub(super) total_recvd: u64,
36    /// The state of the MTU discovery process
37    pub(super) mtud: MtuDiscovery,
38    /// Packet number of the first packet sent after an RTT sample was collected on this path
39    ///
40    /// Used in persistent congestion determination.
41    pub(super) first_packet_after_rtt_sample: Option<(SpaceId, u64)>,
42    pub(super) in_flight: InFlight,
43    /// Number of the first packet sent on this path
44    ///
45    /// Used to determine whether a packet was sent on an earlier path. Insufficient to determine if
46    /// a packet was sent on a later path.
47    first_packet: Option<u64>,
48
49    /// Snapshot of the qlog recovery metrics
50    #[cfg(feature = "__qlog")]
51    congestion_metrics: CongestionMetrics,
52}
53
54impl PathData {
55    pub(super) fn new(
56        remote: SocketAddr,
57        allow_mtud: bool,
58        peer_max_udp_payload_size: Option<u16>,
59        now: Instant,
60        config: &TransportConfig,
61    ) -> Self {
62        let congestion = config
63            .congestion_controller_factory
64            .clone()
65            .build(now, config.get_initial_mtu());
66        Self {
67            remote,
68            rtt: RttEstimator::new(config.initial_rtt),
69            sending_ecn: true,
70            pacing: Pacer::new(
71                config.initial_rtt,
72                congestion.initial_window(),
73                config.get_initial_mtu(),
74                now,
75            ),
76            congestion,
77            challenge: None,
78            challenge_pending: false,
79            validated: false,
80            total_sent: 0,
81            total_recvd: 0,
82            mtud: config
83                .mtu_discovery_config
84                .as_ref()
85                .filter(|_| allow_mtud)
86                .map_or(
87                    MtuDiscovery::disabled(config.get_initial_mtu(), config.min_mtu),
88                    |mtud_config| {
89                        MtuDiscovery::new(
90                            config.get_initial_mtu(),
91                            config.min_mtu,
92                            peer_max_udp_payload_size,
93                            mtud_config.clone(),
94                        )
95                    },
96                ),
97            first_packet_after_rtt_sample: None,
98            in_flight: InFlight::new(),
99            first_packet: None,
100            #[cfg(feature = "__qlog")]
101            congestion_metrics: CongestionMetrics::default(),
102        }
103    }
104
105    pub(super) fn from_previous(remote: SocketAddr, prev: &Self, now: Instant) -> Self {
106        let congestion = prev.congestion.clone_box();
107        let smoothed_rtt = prev.rtt.get();
108        Self {
109            remote,
110            rtt: prev.rtt,
111            pacing: Pacer::new(smoothed_rtt, congestion.window(), prev.current_mtu(), now),
112            sending_ecn: true,
113            congestion,
114            challenge: None,
115            challenge_pending: false,
116            validated: false,
117            total_sent: 0,
118            total_recvd: 0,
119            mtud: prev.mtud.clone(),
120            first_packet_after_rtt_sample: prev.first_packet_after_rtt_sample,
121            in_flight: InFlight::new(),
122            first_packet: None,
123            #[cfg(feature = "__qlog")]
124            congestion_metrics: prev.congestion_metrics.clone(),
125        }
126    }
127
128    /// Resets RTT, congestion control and MTU states.
129    ///
130    /// This is useful when it is known the underlying path has changed.
131    pub(super) fn reset(&mut self, now: Instant, config: &TransportConfig) {
132        self.rtt = RttEstimator::new(config.initial_rtt);
133        self.congestion = config
134            .congestion_controller_factory
135            .clone()
136            .build(now, config.get_initial_mtu());
137        self.mtud.reset(config.get_initial_mtu(), config.min_mtu);
138    }
139
140    /// Indicates whether we're a server that hasn't validated the peer's address and hasn't
141    /// received enough data from the peer to permit sending `bytes_to_send` additional bytes
142    pub(super) fn anti_amplification_blocked(&self, bytes_to_send: u64) -> bool {
143        !self.validated && self.total_recvd * 3 < self.total_sent + bytes_to_send
144    }
145
146    /// Returns the path's current MTU
147    pub(super) fn current_mtu(&self) -> u16 {
148        self.mtud.current_mtu()
149    }
150
151    /// Account for transmission of `packet` with number `pn` in `space`
152    pub(super) fn sent(&mut self, pn: u64, packet: SentPacket, space: &mut PacketSpace) {
153        self.in_flight.insert(&packet);
154        if self.first_packet.is_none() {
155            self.first_packet = Some(pn);
156        }
157        self.in_flight.bytes -= space.sent(pn, packet);
158    }
159
160    /// Remove `packet` with number `pn` from this path's congestion control counters, or return
161    /// `false` if `pn` was sent before this path was established.
162    pub(super) fn remove_in_flight(&mut self, pn: u64, packet: &SentPacket) -> bool {
163        if self.first_packet.map_or(true, |first| first > pn) {
164            return false;
165        }
166        self.in_flight.remove(packet);
167        true
168    }
169
170    #[cfg(feature = "__qlog")]
171    pub(super) fn qlog_congestion_metrics(&mut self, pto_count: u32) -> Option<MetricsUpdated> {
172        let controller_metrics = self.congestion.metrics();
173
174        let metrics = CongestionMetrics {
175            min_rtt: Some(self.rtt.min),
176            smoothed_rtt: Some(self.rtt.get()),
177            latest_rtt: Some(self.rtt.latest),
178            rtt_variance: Some(self.rtt.var),
179            pto_count: Some(pto_count),
180            bytes_in_flight: Some(self.in_flight.bytes),
181            packets_in_flight: Some(self.in_flight.ack_eliciting),
182
183            congestion_window: Some(controller_metrics.congestion_window),
184            ssthresh: controller_metrics.ssthresh,
185            pacing_rate: controller_metrics.pacing_rate,
186        };
187
188        let event = metrics.to_qlog_event(&self.congestion_metrics);
189        self.congestion_metrics = metrics;
190        event
191    }
192}
193
194/// Congestion metrics as described in [`recovery_metrics_updated`].
195///
196/// [`recovery_metrics_updated`]: https://datatracker.ietf.org/doc/html/draft-ietf-quic-qlog-quic-events.html#name-recovery_metrics_updated
197#[cfg(feature = "__qlog")]
198#[derive(Default, Clone, PartialEq)]
199#[non_exhaustive]
200struct CongestionMetrics {
201    pub min_rtt: Option<Duration>,
202    pub smoothed_rtt: Option<Duration>,
203    pub latest_rtt: Option<Duration>,
204    pub rtt_variance: Option<Duration>,
205    pub pto_count: Option<u32>,
206    pub bytes_in_flight: Option<u64>,
207    pub packets_in_flight: Option<u64>,
208    pub congestion_window: Option<u64>,
209    pub ssthresh: Option<u64>,
210    pub pacing_rate: Option<u64>,
211}
212
213#[cfg(feature = "__qlog")]
214impl CongestionMetrics {
215    /// Retain only values that have been updated since the last snapshot.
216    fn retain_updated(&self, previous: &Self) -> Self {
217        macro_rules! keep_if_changed {
218            ($name:ident) => {
219                if previous.$name == self.$name {
220                    None
221                } else {
222                    self.$name
223                }
224            };
225        }
226
227        Self {
228            min_rtt: keep_if_changed!(min_rtt),
229            smoothed_rtt: keep_if_changed!(smoothed_rtt),
230            latest_rtt: keep_if_changed!(latest_rtt),
231            rtt_variance: keep_if_changed!(rtt_variance),
232            pto_count: keep_if_changed!(pto_count),
233            bytes_in_flight: keep_if_changed!(bytes_in_flight),
234            packets_in_flight: keep_if_changed!(packets_in_flight),
235            congestion_window: keep_if_changed!(congestion_window),
236            ssthresh: keep_if_changed!(ssthresh),
237            pacing_rate: keep_if_changed!(pacing_rate),
238        }
239    }
240
241    /// Emit a `MetricsUpdated` event containing only updated values
242    fn to_qlog_event(&self, previous: &Self) -> Option<MetricsUpdated> {
243        let updated = self.retain_updated(previous);
244
245        if updated == Self::default() {
246            return None;
247        }
248
249        Some(MetricsUpdated {
250            min_rtt: updated.min_rtt.map(|rtt| rtt.as_secs_f32()),
251            smoothed_rtt: updated.smoothed_rtt.map(|rtt| rtt.as_secs_f32()),
252            latest_rtt: updated.latest_rtt.map(|rtt| rtt.as_secs_f32()),
253            rtt_variance: updated.rtt_variance.map(|rtt| rtt.as_secs_f32()),
254            pto_count: updated
255                .pto_count
256                .map(|count| count.try_into().unwrap_or(u16::MAX)),
257            bytes_in_flight: updated.bytes_in_flight,
258            packets_in_flight: updated.packets_in_flight,
259            congestion_window: updated.congestion_window,
260            ssthresh: updated.ssthresh,
261            pacing_rate: updated.pacing_rate,
262        })
263    }
264}
265
266/// RTT estimation for a particular network path
267#[derive(Copy, Clone)]
268pub struct RttEstimator {
269    /// The most recent RTT measurement made when receiving an ack for a previously unacked packet
270    latest: Duration,
271    /// The smoothed RTT of the connection, computed as described in RFC6298
272    smoothed: Option<Duration>,
273    /// The RTT variance, computed as described in RFC6298
274    var: Duration,
275    /// The minimum RTT seen in the connection, ignoring ack delay.
276    min: Duration,
277}
278
279impl RttEstimator {
280    fn new(initial_rtt: Duration) -> Self {
281        Self {
282            latest: initial_rtt,
283            smoothed: None,
284            var: initial_rtt / 2,
285            min: initial_rtt,
286        }
287    }
288
289    /// The current best RTT estimation.
290    pub fn get(&self) -> Duration {
291        self.smoothed.unwrap_or(self.latest)
292    }
293
294    /// Conservative estimate of RTT
295    ///
296    /// Takes the maximum of smoothed and latest RTT, as recommended
297    /// in 6.1.2 of the recovery spec (draft 29).
298    pub fn conservative(&self) -> Duration {
299        self.get().max(self.latest)
300    }
301
302    /// Minimum RTT registered so far for this estimator.
303    pub fn min(&self) -> Duration {
304        self.min
305    }
306
307    // PTO computed as described in RFC9002#6.2.1
308    pub(crate) fn pto_base(&self) -> Duration {
309        self.get() + cmp::max(4 * self.var, TIMER_GRANULARITY)
310    }
311
312    pub(crate) fn update(&mut self, ack_delay: Duration, rtt: Duration) {
313        self.latest = rtt;
314        // min_rtt ignores ack delay.
315        self.min = cmp::min(self.min, self.latest);
316        // Based on RFC6298.
317        if let Some(smoothed) = self.smoothed {
318            let adjusted_rtt = if self.min + ack_delay <= self.latest {
319                self.latest - ack_delay
320            } else {
321                self.latest
322            };
323            let var_sample = if smoothed > adjusted_rtt {
324                smoothed - adjusted_rtt
325            } else {
326                adjusted_rtt - smoothed
327            };
328            self.var = (3 * self.var + var_sample) / 4;
329            self.smoothed = Some((7 * smoothed + adjusted_rtt) / 8);
330        } else {
331            self.smoothed = Some(self.latest);
332            self.var = self.latest / 2;
333            self.min = self.latest;
334        }
335    }
336}
337
338#[derive(Default)]
339pub(crate) struct PathResponses {
340    pending: Vec<PathResponse>,
341}
342
343impl PathResponses {
344    pub(crate) fn push(&mut self, packet: u64, token: u64, remote: SocketAddr) {
345        /// Arbitrary permissive limit to prevent abuse
346        const MAX_PATH_RESPONSES: usize = 16;
347        let response = PathResponse {
348            packet,
349            token,
350            remote,
351        };
352        let existing = self.pending.iter_mut().find(|x| x.remote == remote);
353        if let Some(existing) = existing {
354            // Update a queued response
355            if existing.packet <= packet {
356                *existing = response;
357            }
358            return;
359        }
360        if self.pending.len() < MAX_PATH_RESPONSES {
361            self.pending.push(response);
362        } else {
363            // We don't expect to ever hit this with well-behaved peers, so we don't bother dropping
364            // older challenges.
365            trace!("ignoring excessive PATH_CHALLENGE");
366        }
367    }
368
369    pub(crate) fn pop_off_path(&mut self, remote: SocketAddr) -> Option<(u64, SocketAddr)> {
370        let response = *self.pending.last()?;
371        if response.remote == remote {
372            // We don't bother searching further because we expect that the on-path response will
373            // get drained in the immediate future by a call to `pop_on_path`
374            return None;
375        }
376        self.pending.pop();
377        Some((response.token, response.remote))
378    }
379
380    pub(crate) fn pop_on_path(&mut self, remote: SocketAddr) -> Option<u64> {
381        let response = *self.pending.last()?;
382        if response.remote != remote {
383            // We don't bother searching further because we expect that the off-path response will
384            // get drained in the immediate future by a call to `pop_off_path`
385            return None;
386        }
387        self.pending.pop();
388        Some(response.token)
389    }
390
391    pub(crate) fn is_empty(&self) -> bool {
392        self.pending.is_empty()
393    }
394}
395
396#[derive(Copy, Clone)]
397struct PathResponse {
398    /// The packet number the corresponding PATH_CHALLENGE was received in
399    packet: u64,
400    token: u64,
401    /// The address the corresponding PATH_CHALLENGE was received from
402    remote: SocketAddr,
403}
404
405/// Summary statistics of packets that have been sent on a particular path, but which have not yet
406/// been acked or deemed lost
407pub(super) struct InFlight {
408    /// Sum of the sizes of all sent packets considered "in flight" by congestion control
409    ///
410    /// The size does not include IP or UDP overhead. Packets only containing ACK frames do not
411    /// count towards this to ensure congestion control does not impede congestion feedback.
412    pub(super) bytes: u64,
413    /// Number of packets in flight containing frames other than ACK and PADDING
414    ///
415    /// This can be 0 even when bytes is not 0 because PADDING frames cause a packet to be
416    /// considered "in flight" by congestion control. However, if this is nonzero, bytes will always
417    /// also be nonzero.
418    pub(super) ack_eliciting: u64,
419}
420
421impl InFlight {
422    fn new() -> Self {
423        Self {
424            bytes: 0,
425            ack_eliciting: 0,
426        }
427    }
428
429    fn insert(&mut self, packet: &SentPacket) {
430        self.bytes += u64::from(packet.size);
431        self.ack_eliciting += u64::from(packet.ack_eliciting);
432    }
433
434    /// Update counters to account for a packet becoming acknowledged, lost, or abandoned
435    fn remove(&mut self, packet: &SentPacket) {
436        self.bytes -= u64::from(packet.size);
437        self.ack_eliciting -= u64::from(packet.ack_eliciting);
438    }
439}
ant_quic/connection/paths.rs

ant_quic/connection/
paths.rs
