feat: broadcasting idontwant for published messages

This PR introduces an optimisation to preemptively broadcast `IDONTWANT` for published messages, preventing redundant downloads of the same message received over gossip. This feature is opt-in and respects the existing `idontwant_message_size_threshold`. By default, `IDONTWANT` messages will only be sent for published messages larger than 1000 bytes.

reference PRs:
[spec](libp2p/specs#642)

Pull-Request: #5773.

Author: hopinheimer

protocols/gossipsub/CHANGELOG.md

@@ -1,4 +1,8 @@
 ## 0.48.0
+
+- Allow broadcasting `IDONTWANT` messages when publishing to avoid downloading data that is already available.
+  See [PR 5773](https://github.com/libp2p/rust-libp2p/pull/5773)
+
 - Add configurable `idontwant_message_size_threshold` parameter.
   See [PR 5770](https://github.com/libp2p/rust-libp2p/pull/5770)
 

protocols/gossipsub/src/behaviour.rs

@@ -757,6 +757,13 @@ where
             return Err(PublishError::AllQueuesFull(recipient_peers.len()));
         }
 
+        // Broadcast IDONTWANT messages
+        if raw_message.raw_protobuf_len() > self.config.idontwant_message_size_threshold()
+            && self.config.idontwant_on_publish()
+        {
+            self.send_idontwant(&raw_message, &msg_id, raw_message.source.as_ref());
+        }
+
         tracing::debug!(message=%msg_id, "Published message");
 
         if let Some(metrics) = self.metrics.as_mut() {
@@ -1741,7 +1748,7 @@ where
 
         // Broadcast IDONTWANT messages
         if raw_message.raw_protobuf_len() > self.config.idontwant_message_size_threshold() {
-            self.send_idontwant(&raw_message, &msg_id, propagation_source);
+            self.send_idontwant(&raw_message, &msg_id, Some(propagation_source));
         }
 
         // Check the validity of the message
@@ -2600,7 +2607,7 @@ where
         &mut self,
         message: &RawMessage,
         msg_id: &MessageId,
-        propagation_source: &PeerId,
+        propagation_source: Option<&PeerId>,
     ) {
         let Some(mesh_peers) = self.mesh.get(&message.topic) else {
             return;
@@ -2611,8 +2618,8 @@ where
         let recipient_peers: Vec<PeerId> = mesh_peers
             .iter()
             .chain(iwant_peers.iter())
-            .filter(|peer_id| {
-                *peer_id != propagation_source && Some(*peer_id) != message.source.as_ref()
+            .filter(|&peer_id| {
+                Some(peer_id) != propagation_source && Some(peer_id) != message.source.as_ref()
             })
             .cloned()
             .collect();

protocols/gossipsub/src/config.rs

@@ -99,6 +99,7 @@ pub struct Config {
     connection_handler_publish_duration: Duration,
     connection_handler_forward_duration: Duration,
     idontwant_message_size_threshold: usize,
+    idontwant_on_publish: bool,
 }
 
 impl Config {
@@ -373,15 +374,22 @@ impl Config {
         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
+    /// 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
     }
+
+    /// Send IDONTWANT messages after publishing message on gossip. This is an optimisation
+    /// to avoid bandwidth consumption by downloading the published message over gossip.
+    /// By default it is false.
+    pub fn idontwant_on_publish(&self) -> bool {
+        self.idontwant_on_publish
+    }
 }
 
 impl Default for Config {
@@ -455,6 +463,7 @@ impl Default for ConfigBuilder {
                 connection_handler_publish_duration: Duration::from_secs(5),
                 connection_handler_forward_duration: Duration::from_secs(1),
                 idontwant_message_size_threshold: 1000,
+                idontwant_on_publish: false,
             },
             invalid_protocol: false,
         }
@@ -841,17 +850,25 @@ impl ConfigBuilder {
         self
     }
 
-    // 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
+    /// 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(&mut self, size: usize) -> &mut Self {
         self.config.idontwant_message_size_threshold = size;
         self
     }
 
+    /// Send IDONTWANT messages after publishing message on gossip. This is an optimisation
+    /// to avoid bandwidth consumption by downloading the published message over gossip.
+    /// By default it is false.
+    pub fn idontwant_on_publish(&mut self, idontwant_on_publish: bool) -> &mut Self {
+        self.config.idontwant_on_publish = idontwant_on_publish;
+        self
+    }
+
     /// Constructs a [`Config`] from the given configuration and validates the settings.
     pub fn build(&self) -> Result<Config, ConfigBuilderError> {
         // check all constraints on config
@@ -926,6 +943,7 @@ impl std::fmt::Debug for Config {
             "idontwant_message_size_threhold",
             &self.idontwant_message_size_threshold,
         );
+        let _ = builder.field("idontwant_on_publish", &self.idontwant_on_publish);
         builder.finish()
     }
 }