5 files changed, 119 insertions, 0 deletions
diff --git a/src/state/peer.rs b/src/state/peer.rs
index e0cea7e..857c29d 100644
--- a/src/state/peer.rs
+++ b/src/state/peer.rs
@@ -370,6 +370,18 @@ impl PeerState {
             .map(|(bytes, _)| bytes)
     }
 
+    /// The machine slept for `gap` (`swarm::suspend`): heard from, added, and awaiting
+    /// an answer that much earlier, as the monotonic clock stood still meanwhile.
+    pub(crate) fn aged(&mut self, gap: Duration) {
+        let earlier = |at: Instant| at.checked_sub(gap).unwrap_or(at);
+        self.last_seen = self.last_seen.map(earlier);
+        self.added_at = earlier(self.added_at);
+        if let Some(awaiting) = &mut self.awaiting_answer {
+            awaiting.ask_again_at = awaiting.ask_again_at.map(earlier);
+            awaiting.unreached_at = earlier(awaiting.unreached_at);
+        }
+    }
+
     fn quiet_for(&self, now: Instant) -> Duration {
         now.saturating_duration_since(self.last_seen.unwrap_or(self.added_at))
     }
diff --git a/src/swarm/mod.rs b/src/swarm/mod.rs
index 071f00e..ac62c64 100644
--- a/src/swarm/mod.rs
+++ b/src/swarm/mod.rs
@@ -19,6 +19,7 @@ pub(crate) mod source;
 pub(crate) mod stability;
 pub(crate) mod state_file;
 pub(crate) mod stats;
+pub(crate) mod suspend;
 pub(crate) mod sync;
 pub(crate) mod throughput;
 pub(crate) mod topology;
diff --git a/src/swarm/peer/worker.rs b/src/swarm/peer/worker.rs
index 7a0b502..b6f55cd 100644
--- a/src/swarm/peer/worker.rs
+++ b/src/swarm/peer/worker.rs
@@ -65,9 +65,13 @@ pub(crate) async fn run_peer_worker(state: AppState) {
     let mut last_forget_check: Option<Instant> = None;
     let mut forgets_applied = AppliedForgets::new();
     let mut was_ready = false;
+    let mut awake = crate::swarm::suspend::Awake::default();
 
     loop {
         state.peers_due.passing();
+        if let Some(gap) = awake.check() {
+            crate::swarm::suspend::asleep(&state, gap).await;
+        }
         let mut next = Instant::now() + FORGET_CHECK_INTERVAL;
 
         // While joining, keep handshakes fast; dormancy would slow probes to minutes.
diff --git a/src/swarm/stability.rs b/src/swarm/stability.rs
index 1ee308f..8163e06 100644
--- a/src/swarm/stability.rs
+++ b/src/swarm/stability.rs
@@ -148,6 +148,15 @@ pub(crate) fn note_away(state: &AppState, away: Option<Duration>) {
     }
 }
 
+/// The machine slept for `gap` (`swarm::suspend`): observed, and not connected. The
+/// monotonic clock `record` goes by stopped meanwhile, so it doesn't see it.
+pub(crate) fn away(state: &AppState, gap: Duration) {
+    let mut stability = lock(state);
+    if let Some(bucket) = stability.buckets.back_mut() {
+        bucket.observed += gap.min(WINDOW);
+    }
+}
+
 /// Measures, and updates our tier in the registry when it should change. Called every
 /// few seconds by the peer worker.
 pub(crate) async fn tick(state: &AppState) {
diff --git a/src/swarm/suspend.rs b/src/swarm/suspend.rs
new file mode 100644
index 0000000..87a13ab
--- /dev/null
+++ b/src/swarm/suspend.rs
@@ -0,0 +1,93 @@
+//! Whether the machine was suspended (a laptop's lid closed). The monotonic clock every
+//! timer here runs on (`tokio::time::Instant`: `CLOCK_MONOTONIC` on Linux, likewise
+//! elsewhere) stops while the machine sleeps, so after eight hours asleep every peer
+//! looks heard from minutes ago, and the hours count as connected. A clock that runs
+//! on (`CLOCK_BOOTTIME`, as `/proc/uptime` gives it, on Linux; the wall clock
+//! elsewhere, which a correction of the clock may move too) tells how long it was:
+//! what it moved beyond the monotonic clock between two looks. The peer worker looks on
+//! every pass (`Awake::check`), and on waking ages what judges silence by that much
+//! (`asleep`).
+
+use std::time::{Duration, Instant};
+
+use tracing::warn;
+
+use crate::state::AppState;
+
+/// Less than this between the clocks is no suspension (a pass that took long, a small
+/// correction of the wall clock).
+const AT_LEAST: Duration = Duration::from_secs(30);
+
+/// The clocks at the last look.
+#[derive(Default)]
+pub(crate) struct Awake {
+    last: Option<(Instant, Duration)>,
+}
+
+impl Awake {
+    /// How long the machine was suspended since the last look, if at least `AT_LEAST`.
+    pub(crate) fn check(&mut self) -> Option<Duration> {
+        let now = (Instant::now(), running()?);
+        let (monotonic, running) = self.last.replace(now)?;
+        gap(
+            now.0.saturating_duration_since(monotonic),
+            now.1.saturating_sub(running),
+        )
+    }
+}
+
+/// How long the machine slept between two looks `monotonic` and `running` apart by
+/// the two clocks, if at least `AT_LEAST`.
+fn gap(monotonic: Duration, running: Duration) -> Option<Duration> {
+    let gap = running.saturating_sub(monotonic);
+    (gap >= AT_LEAST).then_some(gap)
+}
+
+/// A clock that runs on while the machine sleeps.
+fn running() -> Option<Duration> {
+    #[cfg(target_os = "linux")]
+    {
+        // Seconds since boot, suspension included, with two decimals.
+        let uptime = std::fs::read_to_string("/proc/uptime").ok()?;
+        let seconds: f64 = uptime.split_whitespace().next()?.parse().ok()?;
+        Some(Duration::from_secs_f64(seconds))
+    }
+    #[cfg(not(target_os = "linux"))]
+    {
+        std::time::SystemTime::now()
+            .duration_since(std::time::SystemTime::UNIX_EPOCH)
+            .ok()
+    }
+}
+
+/// The machine slept for `gap`: peers count as silent that much longer (they are held
+/// dormant, and greeted again, as after an absence that long: they may have moved on),
+/// and the time counts as not connected (`swarm::stability`).
+pub(crate) async fn asleep(state: &AppState, gap: Duration) {
+    warn!(
+        secs = gap.as_secs(),
+        "The machine was suspended; peers count as silent for that long"
+    );
+    crate::swarm::stability::away(state, gap);
+    for (_, peer_state) in state.peers_snapshot().await {
+        let mut peer_state = peer_state.lock().await;
+        peer_state.aged(gap);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// A gap is what the running clock moved beyond the monotonic one, from `AT_LEAST`.
+    #[test]
+    fn a_gap_between_the_clocks_is_a_suspension() {
+        let s = Duration::from_secs;
+        assert_eq!(gap(s(5), s(5)), None);
+        assert_eq!(gap(s(5), s(20)), None);
+        assert_eq!(gap(s(5), s(3605)), Some(s(3600)));
+        // The monotonic clock ahead (paused time in tests): none.
+        assert_eq!(gap(s(3600), s(5)), None);
+        assert!(running().is_some());
+    }
+}