refactor(gossipsub): improve code legibility

As part of working on the [generalized `gossipsub` strategies](libp2p/specs#664) I have been cleaning up code, here follows some of the improvements

Pull-Request: #5991.

Author: jxs

protocols/gossipsub/src/behaviour.rs

@@ -969,12 +969,6 @@ where
     fn join(&mut self, topic_hash: &TopicHash) {
         tracing::debug!(topic=%topic_hash, "Running JOIN for topic");
 
-        // if we are already in the mesh, return
-        if self.mesh.contains_key(topic_hash) {
-            tracing::debug!(topic=%topic_hash, "JOIN: The topic is already in the mesh, ignoring JOIN");
-            return;
-        }
-
         let mut added_peers = HashSet::new();
         let mesh_n = self.config.mesh_n_for_topic(topic_hash);
         if let Some(m) = self.metrics.as_mut() {
@@ -1015,9 +1009,9 @@ where
             self.fanout_last_pub.remove(topic_hash);
         }
 
-        let fanaout_added = added_peers.len();
+        let fanout_added = added_peers.len();
         if let Some(m) = self.metrics.as_mut() {
-            m.peers_included(topic_hash, Inclusion::Fanout, fanaout_added)
+            m.peers_included(topic_hash, Inclusion::Fanout, fanout_added)
         }
 
         // check if we need to get more peers, which we randomly select
@@ -1045,7 +1039,7 @@ where
             mesh_peers.extend(new_peers);
         }
 
-        let random_added = added_peers.len() - fanaout_added;
+        let random_added = added_peers.len() - fanout_added;
         if let Some(m) = self.metrics.as_mut() {
             m.peers_included(topic_hash, Inclusion::Random, random_added)
         }
@@ -1251,14 +1245,6 @@ where
 
         let mut iwant_ids = HashSet::new();
 
-        let want_message = |id: &MessageId| {
-            if self.duplicate_cache.contains(id) {
-                return false;
-            }
-
-            !self.gossip_promises.contains(id)
-        };
-
         for (topic, ids) in ihave_msgs {
             // only process the message if we are subscribed
             if !self.mesh.contains_key(&topic) {
@@ -1269,7 +1255,13 @@ where
                 continue;
             }
 
-            for id in ids.into_iter().filter(want_message) {
+            for id in ids.into_iter().filter(|id| {
+                if self.duplicate_cache.contains(id) {
+                    return false;
+                }
+
+                !self.gossip_promises.contains(id)
+            }) {
                 // have not seen this message and are not currently requesting it
                 if iwant_ids.insert(id) {
                     // Register the IWANT metric
@@ -2158,7 +2150,7 @@ where
                     topic=%topic_hash,
                     "HEARTBEAT: Mesh low. Topic contains: {} needs: {}",
                     peers.len(),
-                    mesh_n_low
+                    self.config.mesh_n()
                 );
                 // not enough peers - get mesh_n - current_length more
                 let desired_peers = mesh_n - peers.len();
@@ -2185,9 +2177,9 @@ where
             if peers.len() > mesh_n_high {
                 tracing::debug!(
                     topic=%topic_hash,
-                    "HEARTBEAT: Mesh high. Topic contains: {} needs: {}",
+                    "HEARTBEAT: Mesh high. Topic contains: {} will reduce to: {}",
                     peers.len(),
-                    mesh_n_high
+                    self.config.mesh_n()
                 );
                 let excess_peer_no = peers.len() - mesh_n;