2 files changed, 33 insertions, 13 deletions

diff --git a/crates/tor-guardmgr/src/vanguards.rs b/crates/tor-guardmgr/src/vanguards.rs
index 12925686f..5d8f5d401 100644
--- a/crates/tor-guardmgr/src/vanguards.rs
+++ b/crates/tor-guardmgr/src/vanguards.rs
@@ -460,13 +460,15 @@ impl<R: Runtime> VanguardMgr<R> {
         netdir_provider: &Arc<dyn NetDirProvider>,
         now: SystemTime,
     ) -> Result<Option<Duration>, VanguardMgrError> {
-        info!("Rotating vanguards");
-
         let mut inner = self.inner.write().expect("poisoned lock");
         let inner = &mut *inner;
 
         let vanguard_sets = &mut inner.vanguard_sets;
-        vanguard_sets.remove_expired(now);
+        let expired_count = vanguard_sets.remove_expired(now);
+
+        if expired_count > 0 {
+            info!("Rotating vanguards");
+        }
 
         if let Some(netdir) = Self::timely_netdir(netdir_provider)? {
             // If we have a NetDir, replenish the vanguard sets that don't have enough vanguards.
@@ -548,7 +550,7 @@ impl Inner {
         match self.mode {
             VanguardMode::Lite | VanguardMode::Disabled => Ok(()),
             VanguardMode::Full => {
-                debug!("The vanguards have changed; flushing vanguards to vanguard state file");
+                debug!("The vanguards may have changed; flushing to vanguard state file");
                 Ok(storage.store(&self.vanguard_sets)?)
             }
         }
diff --git a/crates/tor-guardmgr/src/vanguards/set.rs b/crates/tor-guardmgr/src/vanguards/set.rs
index f650d70cf..8170f9b51 100644
--- a/crates/tor-guardmgr/src/vanguards/set.rs
+++ b/crates/tor-guardmgr/src/vanguards/set.rs
@@ -106,9 +106,13 @@ impl VanguardSets {
     }
 
     /// Remove the vanguards that are expired at the specified timestamp.
-    pub(super) fn remove_expired(&mut self, now: SystemTime) {
-        self.l2_vanguards.remove_expired(now);
-        self.l3_vanguards.remove_expired(now);
+    ///
+    /// Returns the number of vanguards that were removed.
+    pub(super) fn remove_expired(&mut self, now: SystemTime) -> usize {
+        let l2_expired = self.l2_vanguards.remove_expired(now);
+        let l3_expired = self.l3_vanguards.remove_expired(now);
+
+        l2_expired + l3_expired
     }
 
     /// Remove the vanguards that are no longer listed in `netdir`.
@@ -305,8 +309,10 @@ impl VanguardSet {
     }
 
     /// Remove the vanguards that are no longer listed in `netdir`
-    fn remove_unlisted(&mut self, netdir: &NetDir) {
-        self.vanguards.retain(|v| {
+    ///
+    /// Returns the number of vanguards that were unlisted.
+    fn remove_unlisted(&mut self, netdir: &NetDir) -> usize {
+        self.retain(|v| {
             let cond = netdir.ids_listed(&v.id) != Some(false);
 
             if !cond {
@@ -314,12 +320,14 @@ impl VanguardSet {
             }
 
             cond
-        });
+        })
     }
 
     /// Remove the vanguards that are expired at the specified timestamp.
-    fn remove_expired(&mut self, now: SystemTime) {
-        self.vanguards.retain(|v| {
+    ///
+    /// Returns the number of vanguards that expired.
+    fn remove_expired(&mut self, now: SystemTime) -> usize {
+        self.retain(|v| {
             let cond = v.when > now;
 
             if !cond {
@@ -327,7 +335,17 @@ impl VanguardSet {
             }
 
             cond
-        });
+        })
+    }
+
+    /// A wrapper around [`Vec::retain`] that returns the number of discarded elements.
+    fn retain<F>(&mut self, f: F) -> usize
+    where
+        F: FnMut(&TimeBoundVanguard) -> bool,
+    {
+        let old_len = self.vanguards.len();
+        self.vanguards.retain(f);
+        old_len - self.vanguards.len()
     }
 
     /// Find the timestamp of the vanguard that is due to expire next.