Don't request indirect ping to same addr

If a member changed its identity while being probed there was
a chance foca would try to ask the new identity to ping
the old one on its behalf

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## UNRELEASED
+
+- Bugfix: when restarting members, there was a chance foca would
+  ask a member to ping its own previous identity.
+  No harm done to the cluster state, but would lead to noise in
+  the form of `Error::DataFromOurselves` in the member logs
+  See: https://github.com/caio/foca/issues/34
+
 ## v0.17.0 - 2024-03-20
 
 This release contains significant changes aimed at freeing users

src/lib.rs

@@ -646,6 +646,17 @@ where
                     return Ok(());
                 }
 
+                if !self.members.is_active(&probed_id) {
+                    // Probed member is not active anymore
+                    // Nothing else to be done this probe cycle
+                    #[cfg(feature = "tracing")]
+                    tracing::debug!(
+                        probed_id = tracing::field::debug(&probed_id),
+                        "Probed member isn't active anymore"
+                    );
+                    return Ok(());
+                }
+
                 self.member_buf.clear();
                 self.members.choose_active_members(
                     self.config.num_indirect_probes.get(),
@@ -4246,4 +4257,32 @@ mod tests {
             assert!(runtime.is_empty());
         }
     }
+
+    #[test]
+    fn no_indirect_cycle_if_probed_disappears() {
+        // ref https://github.com/caio/foca/issues/34
+
+        let (mut foca, probed, send_indirect_probe) = craft_probing_foca(1, config());
+        let mut runtime = AccumulatingRuntime::new();
+        assert_eq!(1, foca.num_members());
+
+        // while `foca` is probing `probed`, it learns
+        // that it changed its identity for whatever reason
+        let renewed = probed.bump();
+        assert_eq!(Ok(()), foca.apply(Member::alive(renewed), &mut runtime));
+        assert_eq!(1, foca.num_members());
+        runtime.clear();
+
+        // So when the indirect part of the cycle fires
+        assert_eq!(Ok(()), foca.handle_timer(send_indirect_probe, &mut runtime));
+
+        // Since `renewed` and `probed` are technically the same
+        assert_eq!(renewed.addr(), probed.addr());
+        assert!(renewed.win_addr_conflict(&probed));
+        assert!(!probed.win_addr_conflict(&renewed));
+
+        // Foca must not request `renewed` to probe `probed`
+        // on its behalf
+        assert!(runtime.take_all_data().is_empty());
+    }
 }

src/member.rs

@@ -276,6 +276,12 @@ where
         self.inner.iter().filter(|m| m.is_active())
     }
 
+    pub(crate) fn is_active(&self, id: &T) -> bool {
+        self.inner
+            .iter()
+            .any(|member| &member.id == id && member.is_active())
+    }
+
     pub(crate) fn apply_existing_if<F: Fn(&Member<T>) -> bool>(
         &mut self,
         mut update: Member<T>,