fix(gossipsub): use the protobuf max message size

#5868 introduced the customization of message size and mesh parameters per topic.
When decoding a message if no max size is defined per topic we should not use the default which is not customizable, we should just no-op as we are already covered by the max protobuf size passed to `GossipsubDecoder`, the respective tests are also not required.
Sorry I overlook this when reviewing #5868.
Cc @elijahhampton

Pull-Request: #5983.

Author: jxs

protocols/gossipsub/src/behaviour/tests.rs

@@ -6567,202 +6567,6 @@ fn test_publish_large_message_with_specific_transmit_size_config() {
     );
 }
 
-#[test]
-fn test_validation_error_message_size_too_large_default() {
-    let config = ConfigBuilder::default()
-        .validation_mode(ValidationMode::None)
-        .build()
-        .unwrap();
-
-    let (mut gs, peers, _, topic_hashes) = inject_nodes1()
-        .peer_no(1)
-        .topics(vec![String::from("test")])
-        .to_subscribe(true)
-        .gs_config(config)
-        .create_network();
-
-    let data = vec![0u8; Config::default_max_transmit_size() + 1];
-    let raw_message = RawMessage {
-        source: Some(peers[0]),
-        data,
-        sequence_number: Some(1u64),
-        topic: topic_hashes[0].clone(),
-        signature: None,
-        key: None,
-        validated: false,
-    };
-
-    gs.on_connection_handler_event(
-        peers[0],
-        ConnectionId::new_unchecked(0),
-        HandlerEvent::Message {
-            rpc: Rpc {
-                messages: vec![raw_message],
-                subscriptions: vec![],
-                control_msgs: vec![],
-            },
-            invalid_messages: vec![],
-        },
-    );
-
-    let event = gs.events.pop_front().expect("Event should be generated");
-    match event {
-        ToSwarm::GenerateEvent(Event::Message {
-            propagation_source,
-            message_id: _,
-            message,
-        }) => {
-            assert_eq!(propagation_source, peers[0]);
-            assert_eq!(message.data.len(), Config::default_max_transmit_size() + 1);
-        }
-        ToSwarm::NotifyHandler { peer_id, .. } => {
-            assert_eq!(peer_id, peers[0]);
-        }
-        _ => panic!("Unexpected event"),
-    }
-
-    // Simulate a peer sending a message exceeding the default max_transmit_size + 1 (65537 bytes).
-    // The codec's max_length is set high to allow encoding/decoding the RPC, while
-    // max_transmit_sizes enforces the per-topic limit (in this case the default).
-    let mut codec = GossipsubCodec::new(
-        Config::default_max_transmit_size() * 2,
-        ValidationMode::Strict,
-        HashMap::new(),
-    );
-    let mut buf = BytesMut::new();
-    let rpc = proto::RPC {
-        publish: vec![proto::Message {
-            from: Some(peers[0].to_bytes()),
-            data: Some(vec![0u8; Config::default_max_transmit_size() + 1]),
-            seqno: Some(1u64.to_be_bytes().to_vec()),
-            topic: topic_hashes[0].to_string(),
-            signature: None,
-            key: None,
-        }],
-        subscriptions: vec![],
-        control: None,
-    };
-    codec.encode(rpc, &mut buf).unwrap();
-
-    let decoded = codec.decode(&mut buf).unwrap().unwrap();
-    match decoded {
-        HandlerEvent::Message {
-            rpc,
-            invalid_messages,
-        } => {
-            assert!(
-                rpc.messages.is_empty(),
-                "No valid messages should be present"
-            );
-            assert_eq!(invalid_messages.len(), 1, "One message should be invalid");
-            let (invalid_msg, error) = &invalid_messages[0];
-            assert_eq!(
-                invalid_msg.data.len(),
-                Config::default_max_transmit_size() + 1
-            );
-            assert_eq!(error, &ValidationError::MessageSizeTooLargeForTopic);
-        }
-        _ => panic!("Unexpected event"),
-    }
-}
-
-#[test]
-fn test_validation_message_size_within_default() {
-    let config = ConfigBuilder::default()
-        .validation_mode(ValidationMode::None)
-        .build()
-        .unwrap();
-
-    let (mut gs, peers, _, topic_hashes) = inject_nodes1()
-        .peer_no(1)
-        .topics(vec![String::from("test")])
-        .to_subscribe(true)
-        .gs_config(config)
-        .create_network();
-
-    let data = vec![0u8; Config::default_max_transmit_size() - 100];
-    let raw_message = RawMessage {
-        source: Some(peers[0]),
-        data,
-        sequence_number: Some(1u64),
-        topic: topic_hashes[0].clone(),
-        signature: None,
-        key: None,
-        validated: false,
-    };
-
-    gs.on_connection_handler_event(
-        peers[0],
-        ConnectionId::new_unchecked(0),
-        HandlerEvent::Message {
-            rpc: Rpc {
-                messages: vec![raw_message],
-                subscriptions: vec![],
-                control_msgs: vec![],
-            },
-            invalid_messages: vec![],
-        },
-    );
-
-    let event = gs.events.pop_front().expect("Event should be generated");
-    match event {
-        ToSwarm::GenerateEvent(Event::Message {
-            propagation_source,
-            message_id: _,
-            message,
-        }) => {
-            assert_eq!(propagation_source, peers[0]);
-            assert_eq!(
-                message.data.len(),
-                Config::default_max_transmit_size() - 100
-            );
-        }
-        ToSwarm::NotifyHandler { peer_id, .. } => {
-            assert_eq!(peer_id, peers[0]);
-        }
-        _ => panic!("Unexpected event"),
-    }
-
-    // Simulate a peer sending a message within the default max_transmit_size (65536 bytes).
-    // The codec's max_length allows encoding/decoding the RPC, and max_transmit_sizes confirms
-    // the message size is acceptable.
-    let mut codec = GossipsubCodec::new(
-        Config::default_max_transmit_size() * 2,
-        ValidationMode::None,
-        HashMap::new(),
-    );
-    let mut buf = BytesMut::new();
-    let rpc = proto::RPC {
-        publish: vec![proto::Message {
-            from: Some(peers[0].to_bytes()),
-            data: Some(vec![0u8; Config::default_max_transmit_size() - 100]),
-            seqno: Some(1u64.to_be_bytes().to_vec()),
-            topic: topic_hashes[0].to_string(),
-            signature: None,
-            key: None,
-        }],
-        subscriptions: vec![],
-        control: None,
-    };
-    codec.encode(rpc, &mut buf).unwrap();
-
-    let decoded = codec.decode(&mut buf).unwrap().unwrap();
-    match decoded {
-        HandlerEvent::Message {
-            rpc,
-            invalid_messages,
-        } => {
-            assert_eq!(rpc.messages.len(), 1, "One valid message should be present");
-            assert!(invalid_messages.is_empty(), "No messages should be invalid");
-            assert_eq!(
-                rpc.messages[0].data.len(),
-                Config::default_max_transmit_size() - 100
-            );
-        }
-        _ => panic!("Unexpected event"),
-    }
-}
-
 #[test]
 fn test_validation_error_message_size_too_large_topic_specific() {
     let topic = Topic::new("test");

protocols/gossipsub/src/protocol.rs

@@ -38,7 +38,7 @@ use crate::{
         ControlAction, Graft, IDontWant, IHave, IWant, MessageId, PeerInfo, PeerKind, Prune,
         RawMessage, Rpc, Subscription, SubscriptionAction,
     },
-    Config, ValidationError,
+    ValidationError,
 };
 
 pub(crate) const SIGNING_PREFIX: &[u8] = b"libp2p-pubsub:";
@@ -194,12 +194,9 @@ impl GossipsubCodec {
         }
     }
 
-    /// Get the max transmit size for a given topic, falling back to the default.
-    fn max_transmit_size_for_topic(&self, topic: &TopicHash) -> usize {
-        self.max_transmit_sizes
-            .get(topic)
-            .copied()
-            .unwrap_or(Config::default_max_transmit_size())
+    /// Get the max transmit size for a given topic if it exists.
+    fn max_transmit_size_for_topic(&self, topic: &TopicHash) -> Option<usize> {
+        self.max_transmit_sizes.get(topic).copied()
     }
 
     /// Verifies a gossipsub message. This returns either a success or failure. All errors
@@ -285,7 +282,10 @@ impl Decoder for GossipsubCodec {
             let topic = TopicHash::from_raw(&message.topic);
 
             // Check the message size to ensure it doesn't bypass the configured max.
-            if message.get_size() > self.max_transmit_size_for_topic(&topic) {
+            if self
+                .max_transmit_size_for_topic(&topic)
+                .is_some_and(|max| message.get_size() > max)
+            {
                 let message = RawMessage {
                     source: None, // don't bother inform the application
                     data: message.data.unwrap_or_default(),