1 files changed, 42 insertions, 0 deletions

diff --git a/src/api/peers.rs b/src/api/peers.rs
index 6662a55..b00593f 100644
--- a/src/api/peers.rs
+++ b/src/api/peers.rs
@@ -74,6 +74,34 @@ pub(crate) struct PeerStatus {
     /// How far its clock is ahead of ours, give or take (`Transport::clock_offset`);
     /// absent before a PONG from it.
     pub(crate) clock: Option<ClockOffset>,
+    /// How long its sync messages take to come (`swarm::hop`); absent before one came
+    /// while we knew its clock.
+    pub(crate) hop_delay: Option<HopDelayInfo>,
+}
+
+/// How long a peer's sync messages take to come, by its clock and ours, its offset
+/// taken off: good to half the round trip (the offset's error), the same for every
+/// message while the offset stands, so the minutes' means show a trend exactly.
+#[derive(Debug, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct HopDelayInfo {
+    /// Messages measured since we started.
+    pub(crate) count: u64,
+    pub(crate) mean_ms: u64,
+    /// The bucket bounds by which half, and 99%, came (`/admin/stats`' propagation
+    /// buckets); absent if beyond the last.
+    pub(crate) half_within_ms: Option<u64>,
+    pub(crate) p99_within_ms: Option<u64>,
+    /// Messages that took less than nothing by the clocks: the offset's error was larger
+    /// (counted as 0 above).
+    pub(crate) below_zero: u64,
+    /// The mean of each of the last 15 minutes, oldest first (the last is the current
+    /// one); null for a minute without messages. May be negative, as `belowZero`.
+    pub(crate) by_minute_ms: Vec<Option<i64>>,
+    /// Half the round trip to it now, from PINGs (which wait behind nothing): what a
+    /// message would take with nothing waiting anywhere; what the delay takes beyond it
+    /// waits in queues (and is the offset's error). Absent without a recent round trip.
+    pub(crate) half_rtt_ms: Option<u64>,
 }
 
 #[derive(Debug, Serialize)]
@@ -163,6 +191,19 @@ pub(crate) async fn peer_list(state: &AppState) -> PeerListResponse {
         let addresses = state.transport.addresses_of(&peer);
         let destination = state.transport.destination(&peer);
         let clock = state.transport.clock_offset(&peer);
+        let hops = &ps.hop_delays;
+        let hop_delay = (hops.all.count > 0).then(|| HopDelayInfo {
+            count: hops.all.count,
+            mean_ms: hops.all.sum_ms / hops.all.count,
+            half_within_ms: hops.all.within(0.5),
+            p99_within_ms: hops.all.within(0.99),
+            below_zero: hops.all.ahead,
+            by_minute_ms: hops.by_minute(now),
+            half_rtt_ms: state
+                .lock_rtt()
+                .effective(&peer, now, state.timing.rtt_fresh_for())
+                .map(|rtt| rtt.as_millis() as u64 / 2),
+        });
         peers.insert(
             peer,
             PeerStatus {
@@ -192,6 +233,7 @@ pub(crate) async fn peer_list(state: &AppState) -> PeerListResponse {
                 incidents: ps.incidents,
                 sync_throughput,
                 clock,
+                hop_delay,
             },
         );
     }