fix(gossipsub): respect already received IDONTWANT when handling IWANT

This PR ensures that the node respects `IDONTWANT` messages that have already been received, when handling `IWANT`.

Pull-Request: #5901.

Author: ackintosh

protocols/gossipsub/CHANGELOG.md

@@ -5,6 +5,9 @@
 - Improve `max_messages_per_rpc` consistency by ensuring RPC control messages also adhere to the existing limits.
   See [PR 5826](https://github.com/libp2p/rust-libp2p/pull/5826)
 
+- Respect already received IDONTWANT messages when handling IWANT.
+  See [PR 5901](https://github.com/libp2p/rust-libp2p/pull/5901)
+
 ## 0.48.0
 
 - Allow broadcasting `IDONTWANT` messages when publishing to avoid downloading data that is already available.

protocols/gossipsub/src/behaviour.rs

@@ -1344,6 +1344,13 @@ where
                         "IWANT: Peer has asked for message too many times; ignoring request"
                     );
                 } else {
+                    if let Some(peer) = self.connected_peers.get_mut(peer_id) {
+                        if peer.dont_send.contains_key(&id) {
+                            tracing::debug!(%peer_id, message=%id, "Peer already sent IDONTWANT for this message");
+                            continue;
+                        }
+                    }
+
                     tracing::debug!(peer=%peer_id, "IWANT: Sending cached messages to peer");
                     self.send_message(
                         *peer_id,

protocols/gossipsub/src/behaviour/tests.rs

@@ -1199,6 +1199,59 @@ fn test_handle_iwant_msg_not_cached() {
     );
 }
 
+#[test]
+fn test_handle_iwant_msg_but_already_sent_idontwant() {
+    let (mut gs, peers, receivers, _) = inject_nodes1()
+        .peer_no(20)
+        .topics(Vec::new())
+        .to_subscribe(true)
+        .create_network();
+
+    let raw_message = RawMessage {
+        source: Some(peers[11]),
+        data: vec![1, 2, 3, 4],
+        sequence_number: Some(1u64),
+        topic: TopicHash::from_raw("topic"),
+        signature: None,
+        key: None,
+        validated: true,
+    };
+
+    // Transform the inbound message
+    let message = &gs
+        .data_transform
+        .inbound_transform(raw_message.clone())
+        .unwrap();
+
+    let msg_id = gs.config.message_id(message);
+    gs.mcache.put(&msg_id, raw_message);
+
+    // Receive IDONTWANT from Peer 1.
+    let rpc = Rpc {
+        messages: vec![],
+        subscriptions: vec![],
+        control_msgs: vec![ControlAction::IDontWant(IDontWant {
+            message_ids: vec![msg_id.clone()],
+        })],
+    };
+    gs.on_connection_handler_event(
+        peers[1],
+        ConnectionId::new_unchecked(0),
+        HandlerEvent::Message {
+            rpc,
+            invalid_messages: vec![],
+        },
+    );
+
+    // Receive IWANT from Peer 1.
+    gs.handle_iwant(&peers[1], vec![msg_id.clone()]);
+
+    // Check that no messages are sent.
+    receivers.iter().for_each(|(_, receiver)| {
+        assert!(receiver.non_priority.get_ref().is_empty());
+    });
+}
+
 /// tests that an event is created when a peer shares that it has a message we want
 #[test]
 fn test_handle_ihave_subscribed_and_msg_not_cached() {