protocols/gossipsub: Do not overwrite msg's peers if put again into mcache (#2493)

Co-authored-by: Max Inden <mail@max-inden.de>

protocols/gossipsub/CHANGELOG.md

@@ -8,14 +8,17 @@
 
 - Emit gossip of all non empty topics (see [PR 2481]).
 
-- Merge NetworkBehaviour's inject_\* paired methods (see PR 2445).
+- Merge NetworkBehaviour's inject_\* paired methods (see [PR 2445]).
 
 - Revert to wasm-timer (see [PR 2506]).
 
+- Do not overwrite msg's peers if put again into mcache (see [PR 2493]).
+
 [PR 2442]: https://github.com/libp2p/rust-libp2p/pull/2442
 [PR 2481]: https://github.com/libp2p/rust-libp2p/pull/2481
 [PR 2445]: https://github.com/libp2p/rust-libp2p/pull/2445
 [PR 2506]: https://github.com/libp2p/rust-libp2p/pull/2506
+[PR 2493]: https://github.com/libp2p/rust-libp2p/pull/2493
 
 # 0.35.0 [2022-01-27]
 

protocols/gossipsub/src/mcache.rs

@@ -22,6 +22,7 @@ use crate::topic::TopicHash;
 use crate::types::{MessageId, RawGossipsubMessage};
 use libp2p_core::PeerId;
 use log::{debug, trace};
+use std::collections::hash_map::Entry;
 use std::fmt::Debug;
 use std::{
     collections::{HashMap, HashSet},
@@ -73,22 +74,22 @@ impl MessageCache {
     ///
     /// Returns true if the message didn't already exist in the cache.
     pub fn put(&mut self, message_id: &MessageId, msg: RawGossipsubMessage) -> bool {
-        trace!("Put message {:?} in mcache", message_id);
+        match self.msgs.entry(message_id.clone()) {
+            Entry::Occupied(_) => {
+                // Don't add duplicate entries to the cache.
+                false
+            }
+            Entry::Vacant(entry) => {
                 let cache_entry = CacheEntry {
                     mid: message_id.clone(),
                     topic: msg.topic.clone(),
                 };
-
-        if self
-            .msgs
-            .insert(message_id.clone(), (msg, HashSet::new()))
-            .is_none()
-        {
-            // Don't add duplicate entries to the cache.
+                entry.insert((msg, HashSet::default()));
                 self.history[0].push(cache_entry);
-            return true;
-        } else {
-            return false;
+
+                trace!("Put message {:?} in mcache", message_id);
+                true
+            }
         }
     }