feat(gossipsub): Allow setting a size threshold for IDONTWANT messages

protocols/gossipsub/CHANGELOG.md

@@ -1,4 +1,6 @@
 ## 0.48.0
+- Add configurable `idontwant_message_size_threshold` parameter.
+  See [PR 5770](https://github.com/libp2p/rust-libp2p/pull/5770)
 
 - Introduce Gossipsub v1.2 [spec](https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.2.md).
   See [PR 5697](https://github.com/libp2p/rust-libp2p/pull/5697)

protocols/gossipsub/src/behaviour.rs

@@ -1739,9 +1739,6 @@ where
         // Calculate the message id on the transformed data.
         let msg_id = self.config.message_id(&message);
 
-        // Broadcast IDONTWANT messages.
-        self.send_idontwant(&raw_message, &msg_id, propagation_source);
-
         // Check the validity of the message
         // Peers get penalized if this message is invalid. We don't add it to the duplicate cache
         // and instead continually penalize peers that repeatedly send this message.
@@ -1757,6 +1754,12 @@ where
             self.mcache.observe_duplicate(&msg_id, propagation_source);
             return;
         }
+
+        // Broadcast IDONTWANT messages
+        if raw_message.raw_protobuf_len() > self.config.idontwant_message_size_threshold() {
+            self.send_idontwant(&raw_message, &msg_id, propagation_source);
+        }
+
         tracing::debug!(
             message=%msg_id,
             "Put message in duplicate_cache and resolve promises"

protocols/gossipsub/src/behaviour/tests.rs

@@ -5288,7 +5288,7 @@ fn sends_idontwant() {
 
     let message = RawMessage {
         source: Some(peers[1]),
-        data: vec![12],
+        data: vec![12u8; 1024],
         sequence_number: Some(0),
         topic: topic_hashes[0].clone(),
         signature: None,
@@ -5314,6 +5314,48 @@ fn sends_idontwant() {
     );
 }
 
+#[test]
+fn doesnt_sends_idontwant_for_lower_message_size() {
+    let (mut gs, peers, receivers, topic_hashes) = inject_nodes1()
+        .peer_no(5)
+        .topics(vec![String::from("topic1")])
+        .to_subscribe(true)
+        .gs_config(Config::default())
+        .explicit(1)
+        .peer_kind(PeerKind::Gossipsubv1_2)
+        .create_network();
+
+    let local_id = PeerId::random();
+
+    let message = RawMessage {
+        source: Some(peers[1]),
+        data: vec![12],
+        sequence_number: Some(0),
+        topic: topic_hashes[0].clone(),
+        signature: None,
+        key: None,
+        validated: true,
+    };
+
+    gs.handle_received_message(message.clone(), &local_id);
+    assert_eq!(
+        receivers
+            .into_iter()
+            .fold(0, |mut idontwants, (peer_id, c)| {
+                let non_priority = c.non_priority.get_ref();
+                while !non_priority.is_empty() {
+                    if let Ok(RpcOut::IDontWant(_)) = non_priority.try_recv() {
+                        assert_ne!(peer_id, peers[1]);
+                        idontwants += 1;
+                    }
+                }
+                idontwants
+            }),
+        0,
+        "IDONTWANT was sent"
+    );
+}
+
 /// Test that a node doesn't send IDONTWANT messages to the mesh peers
 /// that don't run Gossipsub v1.2.
 #[test]

protocols/gossipsub/src/config.rs

@@ -98,6 +98,7 @@ pub struct Config {
     connection_handler_queue_len: usize,
     connection_handler_publish_duration: Duration,
     connection_handler_forward_duration: Duration,
+    idontwant_message_size_threshold: usize,
 }
 
 impl Config {
@@ -371,6 +372,16 @@ impl Config {
     pub fn forward_queue_duration(&self) -> Duration {
         self.connection_handler_forward_duration
     }
+
+    // The message size threshold for which IDONTWANT messages are sent.
+    // Sending IDONTWANT messages for small messages can have a negative effect to the overall
+    // traffic and CPU load. This acts as a lower bound cutoff for the message size to which
+    // IDONTWANT won't be sent to peers. Only works if the peers support Gossipsub1.2
+    // (see https://github.com/libp2p/specs/blob/master/pubsub/gossipsub/gossipsub-v1.2.md#idontwant-message)
+    // default is 1kB
+    pub fn idontwant_message_size_threshold(&self) -> usize {
+        self.idontwant_message_size_threshold
+    }
 }
 
 impl Default for Config {
@@ -443,6 +454,7 @@ impl Default for ConfigBuilder {
                 connection_handler_queue_len: 5000,
                 connection_handler_publish_duration: Duration::from_secs(5),
                 connection_handler_forward_duration: Duration::from_secs(1),
+                idontwant_message_size_threshold: 1000,
             },
             invalid_protocol: false,
         }
@@ -899,6 +911,10 @@ impl std::fmt::Debug for Config {
             "published_message_ids_cache_time",
             &self.published_message_ids_cache_time,
         );
+        let _ = builder.field(
+            "idontwant_message_size_threhold",
+            &self.idontwant_message_size_threshold,
+        );
         builder.finish()
     }
 }