fix(kad): close progress whenever closer in range

protocols/kad/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.45.3 - unreleased
+- Close progress whenever closer in range, instead of having to be the closest.
+  See [PR 4596](https://github.com/libp2p/rust-libp2p/pull/4934).
+
 ## 0.45.2
 
 - Ensure `Multiaddr` handled and returned by `Behaviour` are `/p2p` terminated.

protocols/kad/src/query/peers/closest.rs

@@ -175,6 +175,17 @@ impl ClosestPeersIter {
             },
         }
 
+        let mut cur_range = distance;
+        let mut index = 0;
+        for (dist, _state) in self.closest_peers.iter() {
+            if index < self.config.num_results.get() {
+                index += 1;
+                cur_range = *dist;
+            } else {
+                break;
+            }
+        }
+
         let num_closest = self.closest_peers.len();
         let mut progress = false;
 
@@ -187,11 +198,10 @@ impl ClosestPeersIter {
                 state: PeerState::NotContacted,
             };
             self.closest_peers.entry(distance).or_insert(peer);
-            // The iterator makes progress if the new peer is either closer to the target
-            // than any peer seen so far (i.e. is the first entry), or the iterator did
-            // not yet accumulate enough closest peers.
-            progress = self.closest_peers.keys().next() == Some(&distance)
-                || num_closest < self.config.num_results.get();
+            // The iterator makes progress if either any of the new peer is among the `num_results`
+            // closest peers to the target seen so far,
+            // or the iterator did not yet accumulate enough closest peers.
+            progress = distance < cur_range || num_closest < self.config.num_results.get();
         }
 
         // Update the iterator state.
@@ -316,8 +326,9 @@ impl ClosestPeersIter {
                     if let Some(ref mut cnt) = result_counter {
                         *cnt += 1;
                         // If `num_results` successful results have been delivered for the
-                        // closest peers, the iterator is done.
-                        if *cnt >= self.config.num_results.get() {
+                        // closest peers, AND there is no `waiting on result` peer so far,
+                        // the iterator is done.
+                        if *cnt >= self.config.num_results.get() && result_counter.is_some() {
                             self.state = State::Finished;
                             return PeersIterState::Finished;
                         }