refactor(irtt-stats): extract IPDV tracking module

crates/irtt-stats/src/ipdv.rs

@@ -0,0 +1,263 @@
+use std::{
+    collections::{HashMap, HashSet, VecDeque},
+    time::{Duration, Instant},
+};
+
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) struct IpdvSample {
+    pub(crate) seq: u32,
+    pub(crate) rtt_primary_ns: i128,
+    pub(crate) client_send_mono: Instant,
+    pub(crate) client_receive_mono: Instant,
+    pub(crate) client_send_wall_ns: Option<i128>,
+    pub(crate) client_receive_wall_ns: Option<i128>,
+    pub(crate) server_receive_mono_ns: Option<i64>,
+    pub(crate) server_send_mono_ns: Option<i64>,
+    pub(crate) server_receive_wall_ns: Option<i64>,
+    pub(crate) server_send_wall_ns: Option<i64>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) struct IpdvTracker {
+    samples: HashMap<u32, IpdvSample>,
+    sample_order: VecDeque<u32>,
+    completed_pairs: HashSet<u32>,
+    sequence_limit: Option<usize>,
+}
+
+impl IpdvTracker {
+    pub(crate) fn new(sequence_limit: Option<usize>) -> Self {
+        Self {
+            samples: HashMap::new(),
+            sample_order: VecDeque::new(),
+            completed_pairs: HashSet::new(),
+            sequence_limit,
+        }
+    }
+
+    pub(crate) fn insert(&mut self, sample: IpdvSample) -> Vec<CompletedIpdvPair> {
+        let seq = sample.seq;
+        if self.samples.insert(seq, sample).is_some() {
+            return Vec::new();
+        }
+
+        self.sample_order.push_back(seq);
+        self.enforce_sequence_limit();
+
+        let mut pairs = Vec::with_capacity(2);
+        if let Some(pair) = self.try_pair(seq) {
+            pairs.push(pair);
+        }
+        if let Some(next) = seq.checked_add(1) {
+            if let Some(pair) = self.try_pair(next) {
+                pairs.push(pair);
+            }
+        }
+        pairs
+    }
+
+    fn enforce_sequence_limit(&mut self) {
+        let Some(limit) = self.sequence_limit else {
+            return;
+        };
+        while self.samples.len() > limit {
+            let Some(seq) = self.sample_order.pop_front() else {
+                break;
+            };
+            if self.samples.remove(&seq).is_some() {
+                self.completed_pairs.remove(&seq);
+                if let Some(next) = seq.checked_add(1) {
+                    self.completed_pairs.remove(&next);
+                }
+            }
+        }
+    }
+
+    fn try_pair(&mut self, current_seq: u32) -> Option<CompletedIpdvPair> {
+        let previous_seq = current_seq.checked_sub(1)?;
+
+        if !self.completed_pairs.insert(current_seq) {
+            return None;
+        }
+
+        let Some(previous) = self.samples.get(&previous_seq) else {
+            self.completed_pairs.remove(&current_seq);
+            return None;
+        };
+
+        let Some(current) = self.samples.get(&current_seq) else {
+            self.completed_pairs.remove(&current_seq);
+            return None;
+        };
+
+        Some(CompletedIpdvPair {
+            previous_seq,
+            current_seq,
+            rtt_ipdv_ns: abs_i128_ns(current.rtt_primary_ns - previous.rtt_primary_ns),
+            send_ipdv_ns: send_ipdv_ns(previous, current).map(abs_i128_ns),
+            receive_ipdv_ns: receive_ipdv_ns(previous, current).map(abs_i128_ns),
+        })
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct CompletedIpdvPair {
+    pub(crate) previous_seq: u32,
+    pub(crate) current_seq: u32,
+    pub(crate) rtt_ipdv_ns: i128,
+    pub(crate) send_ipdv_ns: Option<i128>,
+    pub(crate) receive_ipdv_ns: Option<i128>,
+}
+
+fn send_ipdv_ns(previous: &IpdvSample, current: &IpdvSample) -> Option<i128> {
+    if let (Some(prev_server), Some(cur_server)) = (
+        previous.server_receive_mono_ns,
+        current.server_receive_mono_ns,
+    ) {
+        return Some(
+            i128::from(cur_server)
+                - i128::from(prev_server)
+                - instant_diff_ns(current.client_send_mono, previous.client_send_mono),
+        );
+    }
+    if let (Some(prev_server), Some(cur_server), Some(prev_client), Some(cur_client)) = (
+        previous.server_receive_wall_ns,
+        current.server_receive_wall_ns,
+        previous.client_send_wall_ns,
+        current.client_send_wall_ns,
+    ) {
+        return Some(i128::from(cur_server) - i128::from(prev_server) - (cur_client - prev_client));
+    }
+    None
+}
+
+fn receive_ipdv_ns(previous: &IpdvSample, current: &IpdvSample) -> Option<i128> {
+    if let (Some(prev_server), Some(cur_server)) =
+        (previous.server_send_mono_ns, current.server_send_mono_ns)
+    {
+        return Some(
+            instant_diff_ns(current.client_receive_mono, previous.client_receive_mono)
+                - (i128::from(cur_server) - i128::from(prev_server)),
+        );
+    }
+    if let (Some(prev_server), Some(cur_server), Some(prev_client), Some(cur_client)) = (
+        previous.server_send_wall_ns,
+        current.server_send_wall_ns,
+        previous.client_receive_wall_ns,
+        current.client_receive_wall_ns,
+    ) {
+        return Some(
+            (cur_client - prev_client) - (i128::from(cur_server) - i128::from(prev_server)),
+        );
+    }
+    None
+}
+
+fn instant_diff_ns(current: Instant, previous: Instant) -> i128 {
+    if let Some(diff) = current.checked_duration_since(previous) {
+        duration_ns_i128(diff)
+    } else {
+        -duration_ns_i128(previous.duration_since(current))
+    }
+}
+
+fn duration_ns_i128(duration: Duration) -> i128 {
+    i128::try_from(duration.as_nanos()).unwrap_or(i128::MAX)
+}
+
+fn abs_i128_ns(value: i128) -> i128 {
+    value.saturating_abs()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn ipdv_sample(seq: u32, rtt_primary_ns: i128) -> IpdvSample {
+        let now = Instant::now();
+        IpdvSample {
+            seq,
+            rtt_primary_ns,
+            client_send_mono: now,
+            client_receive_mono: now,
+            client_send_wall_ns: None,
+            client_receive_wall_ns: None,
+            server_receive_mono_ns: None,
+            server_send_mono_ns: None,
+            server_receive_wall_ns: None,
+            server_send_wall_ns: None,
+        }
+    }
+
+    #[test]
+    fn ipdv_tracker_completes_adjacent_pair() {
+        let mut tracker = IpdvTracker::new(None);
+        assert!(tracker.insert(ipdv_sample(0, 10)).is_empty());
+
+        let pairs = tracker.insert(ipdv_sample(1, 14));
+
+        assert_eq!(
+            pairs,
+            vec![CompletedIpdvPair {
+                previous_seq: 0,
+                current_seq: 1,
+                rtt_ipdv_ns: 4,
+                send_ipdv_ns: None,
+                receive_ipdv_ns: None,
+            }]
+        );
+    }
+
+    #[test]
+    fn ipdv_tracker_gap_fill_completes_both_adjacent_pairs() {
+        let mut tracker = IpdvTracker::new(None);
+        assert!(tracker.insert(ipdv_sample(0, 10)).is_empty());
+        assert!(tracker.insert(ipdv_sample(2, 20)).is_empty());
+
+        let pairs = tracker.insert(ipdv_sample(1, 13));
+
+        assert_eq!(
+            pairs,
+            vec![
+                CompletedIpdvPair {
+                    previous_seq: 0,
+                    current_seq: 1,
+                    rtt_ipdv_ns: 3,
+                    send_ipdv_ns: None,
+                    receive_ipdv_ns: None,
+                },
+                CompletedIpdvPair {
+                    previous_seq: 1,
+                    current_seq: 2,
+                    rtt_ipdv_ns: 7,
+                    send_ipdv_ns: None,
+                    receive_ipdv_ns: None,
+                },
+            ]
+        );
+    }
+
+    #[test]
+    fn ipdv_tracker_duplicate_sequence_does_not_emit_pair_again() {
+        let mut tracker = IpdvTracker::new(None);
+        assert!(tracker.insert(ipdv_sample(0, 10)).is_empty());
+        assert_eq!(tracker.insert(ipdv_sample(1, 14)).len(), 1);
+
+        assert!(tracker.insert(ipdv_sample(1, 18)).is_empty());
+    }
+
+    #[test]
+    fn ipdv_tracker_bounded_mode_evicts_old_sequence_state() {
+        let mut tracker = IpdvTracker::new(Some(2));
+        assert!(tracker.insert(ipdv_sample(0, 10)).is_empty());
+        assert_eq!(tracker.insert(ipdv_sample(1, 14)).len(), 1);
+
+        let pairs = tracker.insert(ipdv_sample(2, 20));
+
+        assert_eq!(pairs.len(), 1);
+        assert!(!tracker.samples.contains_key(&0));
+        assert!(!tracker.completed_pairs.contains(&0));
+        assert!(!tracker.completed_pairs.contains(&1));
+        assert!(tracker.completed_pairs.contains(&2));
+    }
+}