node: Track peer latency

This is useful for a bunch of different network optimizations we're
going to be working on.

radicle-node/src/service.rs

@@ -78,6 +78,8 @@ pub const PRUNE_INTERVAL: LocalDuration = LocalDuration::from_mins(30);
 pub const STALE_CONNECTION_TIMEOUT: LocalDuration = LocalDuration::from_mins(2);
 /// How much time should pass after a peer was last active for a *ping* to be sent.
 pub const KEEP_ALIVE_DELTA: LocalDuration = LocalDuration::from_mins(1);
+/// Maximum number of latency values to keep for a session.
+pub const MAX_LATENCIES: usize = 16;
 /// Maximum time difference between the local time, and an announcement timestamp.
 pub const MAX_TIME_DELTA: LocalDuration = LocalDuration::from_mins(60);
 /// Maximum attempts to connect to a peer before we give up.
@@ -1653,10 +1655,24 @@ where
                     },
                 );
             }
-            (session::State::Connected { ping, .. }, Message::Pong { zeroes }) => {
+            (
-                if let session::PingState::AwaitingResponse(ponglen) = *ping {
+                session::State::Connected {
+                    ping, latencies, ..
+                },
+                Message::Pong { zeroes },
+            ) => {
+                if let session::PingState::AwaitingResponse {
+                    len: ponglen,
+                    since,
+                } = *ping
+                {
                     if (ponglen as usize) == zeroes.len() {
                         *ping = session::PingState::Ok;
+                        // Keep track of peer latency.
+                        latencies.push_back(self.clock - since);
+                        if latencies.len() > MAX_LATENCIES {
+                            latencies.pop_front();
+                        }
                     }
                 }
             }
@@ -2036,7 +2052,7 @@ where
             .filter(|(_, session)| *now - session.last_active >= KEEP_ALIVE_DELTA)
             .map(|(_, session)| session);
         for session in inactive_sessions {
-            session.ping(&mut self.outbox).ok();
+            session.ping(self.clock, &mut self.outbox).ok();
         }
     }
 

radicle-node/src/service/session.rs

@@ -1,4 +1,4 @@
-use std::collections::HashSet;
+use std::collections::{HashSet, VecDeque};
 use std::fmt;
 
 use crate::node::config::Limits;
@@ -119,6 +119,7 @@ impl Session {
                 since: time,
                 ping: PingState::default(),
                 fetching: HashSet::default(),
+                latencies: VecDeque::default(),
             },
             link: Link::Inbound,
             subscribe: None,
@@ -212,6 +213,7 @@ impl Session {
             since,
             ping: PingState::default(),
             fetching: HashSet::default(),
+            latencies: VecDeque::default(),
         };
     }
 
@@ -231,11 +233,13 @@ impl Session {
         self.state = State::Initial;
     }
 
-    pub fn ping(&mut self, reactor: &mut Outbox) -> Result<(), Error> {
+    pub fn ping(&mut self, since: LocalTime, reactor: &mut Outbox) -> Result<(), Error> {
         if let State::Connected { ping, .. } = &mut self.state {
             let msg = message::Ping::new(&mut self.rng);
-            *ping = PingState::AwaitingResponse(msg.ponglen);
+            *ping = PingState::AwaitingResponse {
-
+                len: msg.ponglen,
+                since,
+            };
             reactor.write(self, Message::Ping(msg));
         }
         Ok(())

radicle/src/node.rs

@@ -11,7 +11,7 @@ pub mod policy;
 pub mod routing;
 pub mod seed;
 
-use std::collections::{BTreeSet, HashMap, HashSet};
+use std::collections::{BTreeSet, HashMap, HashSet, VecDeque};
 use std::io::{BufRead, BufReader};
 use std::ops::{ControlFlow, Deref};
 use std::os::unix::net::UnixStream;
@@ -21,7 +21,7 @@ use std::{fmt, io, net, thread, time};
 
 use amplify::WrapperMut;
 use cyphernet::addr::NetAddr;
-use localtime::LocalTime;
+use localtime::{LocalDuration, LocalTime};
 use serde::de::DeserializeOwned;
 use serde::{Deserialize, Serialize};
 use serde_json as json;
@@ -73,7 +73,12 @@ pub enum PingState {
     /// The peer has not been sent a ping.
     None,
     /// A ping has been sent and is waiting on the peer's response.
-    AwaitingResponse(u16),
+    AwaitingResponse {
+        /// Length of pong payload expected.
+        len: u16,
+        /// Since when are we waiting.
+        since: LocalTime,
+    },
     /// The peer was successfully pinged.
     Ok,
 }
@@ -97,6 +102,9 @@ pub enum State {
         ping: PingState,
         /// Ongoing fetches.
         fetching: HashSet<RepoId>,
+        /// Measured latencies for this peer.
+        #[serde(skip)]
+        latencies: VecDeque<LocalDuration>,
     },
     /// When a peer is disconnected.
     #[serde(rename_all = "camelCase")]
@@ -1177,6 +1185,7 @@ mod test {
                 since: LocalTime::now(),
                 ping: Default::default(),
                 fetching: Default::default(),
+                latencies: VecDeque::default(),
             }))
             .unwrap(),
         )