1 files changed, 27 insertions, 9 deletions

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.