Use multiple LibP2P topics

We still need a peering protocol... Hopefully, we can read peers off of the
Substrate node's DHT.

coordinator/src/p2p.rs

@@ -58,6 +58,16 @@ pub enum P2pMessageKind {
 }
 
 impl P2pMessageKind {
+  fn genesis(&self) -> Option<[u8; 32]> {
+    match self {
+      P2pMessageKind::KeepAlive => None,
+      P2pMessageKind::Tributary(genesis) => Some(*genesis),
+      P2pMessageKind::Heartbeat(genesis) => Some(*genesis),
+      P2pMessageKind::Block(genesis) => Some(*genesis),
+      P2pMessageKind::CosignedBlock => None,
+    }
+  }
+
   fn serialize(&self) -> Vec<u8> {
     match self {
       P2pMessageKind::KeepAlive => vec![0],
@@ -119,14 +129,17 @@ pub struct Message<P: P2p> {
 pub trait P2p: Send + Sync + Clone + fmt::Debug + TributaryP2p {
   type Id: Send + Sync + Clone + Copy + fmt::Debug;
 
-  async fn send_raw(&self, to: Self::Id, msg: Vec<u8>);
-  async fn broadcast_raw(&self, msg: Vec<u8>);
+  async fn subscribe(&self, genesis: [u8; 32]);
+  async fn unsubscribe(&self, genesis: [u8; 32]);
+
+  async fn send_raw(&self, to: Self::Id, genesis: Option<[u8; 32]>, msg: Vec<u8>);
+  async fn broadcast_raw(&self, genesis: Option<[u8; 32]>, msg: Vec<u8>);
   async fn receive_raw(&self) -> (Self::Id, Vec<u8>);
 
   async fn send(&self, to: Self::Id, kind: P2pMessageKind, msg: Vec<u8>) {
     let mut actual_msg = kind.serialize();
     actual_msg.extend(msg);
-    self.send_raw(to, actual_msg).await;
+    self.send_raw(to, kind.genesis(), actual_msg).await;
   }
   async fn broadcast(&self, kind: P2pMessageKind, msg: Vec<u8>) {
     let mut actual_msg = kind.serialize();
@@ -143,7 +156,7 @@ pub trait P2p: Send + Sync + Clone + fmt::Debug + TributaryP2p {
       }
     );
     */
-    self.broadcast_raw(actual_msg).await;
+    self.broadcast_raw(kind.genesis(), actual_msg).await;
   }
   async fn receive(&self) -> Message<Self> {
     let (sender, kind, msg) = loop {
@@ -185,10 +198,11 @@ struct Behavior {
 
 #[allow(clippy::type_complexity)]
 #[derive(Clone)]
-pub struct LibP2p(
-  Arc<Mutex<mpsc::UnboundedSender<Vec<u8>>>>,
-  Arc<Mutex<mpsc::UnboundedReceiver<(PeerId, Vec<u8>)>>>,
-);
+pub struct LibP2p {
+  subscribe: Arc<Mutex<mpsc::UnboundedSender<(bool, [u8; 32])>>>,
+  broadcast: Arc<Mutex<mpsc::UnboundedSender<(Option<[u8; 32]>, Vec<u8>)>>>,
+  receive: Arc<Mutex<mpsc::UnboundedReceiver<(PeerId, Vec<u8>)>>>,
+}
 impl fmt::Debug for LibP2p {
   fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
     fmt.debug_struct("LibP2p").finish_non_exhaustive()
@@ -240,8 +254,7 @@ impl LibP2p {
         )
         .unwrap();
 
-        // Uses a single topic to prevent being a BTC validator only connected to ETH validators,
-        // unable to communicate with other BTC validators
+        // Subscribe to the base topic
         let topic = IdentTopic::new(LIBP2P_TOPIC);
         gossipsub.subscribe(&topic).unwrap();
 
@@ -274,6 +287,11 @@ impl LibP2p {
 
     let (broadcast_send, mut broadcast_recv) = mpsc::unbounded_channel();
     let (receive_send, receive_recv) = mpsc::unbounded_channel();
+    let (subscribe_send, mut subscribe_recv) = mpsc::unbounded_channel();
+
+    fn topic_for_genesis(genesis: [u8; 32]) -> IdentTopic {
+      IdentTopic::new(format!("{LIBP2P_TOPIC}-{}", hex::encode(genesis)))
+    }
 
     tokio::spawn({
       let mut time_of_last_p2p_message = Instant::now();
@@ -282,12 +300,19 @@ impl LibP2p {
       async fn broadcast_raw(
         p2p: &mut Swarm<Behavior>,
         time_of_last_p2p_message: &mut Instant,
+        genesis: Option<[u8; 32]>,
         msg: Vec<u8>,
       ) {
         // Update the time of last message
         *time_of_last_p2p_message = Instant::now();
 
-        match p2p.behaviour_mut().gossipsub.publish(IdentTopic::new(LIBP2P_TOPIC), msg.clone()) {
+        let topic = if let Some(genesis) = genesis {
+          topic_for_genesis(genesis)
+        } else {
+          IdentTopic::new(LIBP2P_TOPIC)
+        };
+
+        match p2p.behaviour_mut().gossipsub.publish(topic, msg.clone()) {
           Err(PublishError::SigningError(e)) => panic!("signing error when broadcasting: {e}"),
           Err(PublishError::InsufficientPeers) => {
             log::warn!("failed to send p2p message due to insufficient peers")
@@ -307,12 +332,32 @@ impl LibP2p {
           tokio::select! {
             biased;
 
+            // Subscribe to any new topics
+            topic = subscribe_recv.recv() => {
+              let (subscribe, topic) = topic.expect("subscribe_recv closed. are we shutting down?");
+              if subscribe {
+                swarm
+                  .behaviour_mut()
+                  .gossipsub
+                  .subscribe(&topic_for_genesis(topic))
+                  .unwrap();
+              } else {
+                swarm
+                  .behaviour_mut()
+                  .gossipsub
+                  .unsubscribe(&topic_for_genesis(topic))
+                  .unwrap();
+              }
+            }
+
             // Handle any queued outbound messages
             msg = broadcast_recv.recv() => {
+              let (genesis, msg) = msg.expect("broadcast_recv closed. are we shutting down?");
               broadcast_raw(
                 &mut swarm,
                 &mut time_of_last_p2p_message,
-                msg.expect("broadcast_recv closed. are we shutting down?")
+                genesis,
+                msg,
               ).await;
             }
 
@@ -363,6 +408,7 @@ impl LibP2p {
               broadcast_raw(
                 &mut swarm,
                 &mut time_of_last_p2p_message,
+                None,
                 P2pMessageKind::KeepAlive.serialize()
               ).await;
             }
@@ -371,7 +417,11 @@ impl LibP2p {
       }
     });
 
-    LibP2p(Arc::new(Mutex::new(broadcast_send)), Arc::new(Mutex::new(receive_recv)))
+    LibP2p {
+      subscribe: Arc::new(Mutex::new(subscribe_send)),
+      broadcast: Arc::new(Mutex::new(broadcast_send)),
+      receive: Arc::new(Mutex::new(receive_recv)),
+    }
   }
 }
 
@@ -379,18 +429,41 @@ impl LibP2p {
 impl P2p for LibP2p {
   type Id = PeerId;
 
-  async fn send_raw(&self, _: Self::Id, msg: Vec<u8>) {
-    self.broadcast_raw(msg).await;
+  async fn subscribe(&self, genesis: [u8; 32]) {
+    self
+      .subscribe
+      .lock()
+      .await
+      .send((true, genesis))
+      .expect("subscribe_send closed. are we shutting down?");
   }
 
-  async fn broadcast_raw(&self, msg: Vec<u8>) {
-    self.0.lock().await.send(msg).expect("broadcast_send closed. are we shutting down?");
+  async fn unsubscribe(&self, genesis: [u8; 32]) {
+    self
+      .subscribe
+      .lock()
+      .await
+      .send((false, genesis))
+      .expect("subscribe_send closed. are we shutting down?");
+  }
+
+  async fn send_raw(&self, _: Self::Id, genesis: Option<[u8; 32]>, msg: Vec<u8>) {
+    self.broadcast_raw(genesis, msg).await;
+  }
+
+  async fn broadcast_raw(&self, genesis: Option<[u8; 32]>, msg: Vec<u8>) {
+    self
+      .broadcast
+      .lock()
+      .await
+      .send((genesis, msg))
+      .expect("broadcast_send closed. are we shutting down?");
   }
 
   // TODO: We only have a single handle call this. Differentiate Send/Recv to remove this constant
   // lock acquisition?
   async fn receive_raw(&self) -> (Self::Id, Vec<u8>) {
-    self.1.lock().await.recv().await.expect("receive_recv closed. are we shutting down?")
+    self.receive.lock().await.recv().await.expect("receive_recv closed. are we shutting down?")
   }
 }
 
@@ -473,6 +546,9 @@ pub async fn handle_p2p_task<D: Db, P: P2p>(
             let (send, mut recv) = mpsc::unbounded_channel();
             channels.write().await.insert(genesis, send);
 
+            // Subscribe to the topic for this tributary
+            p2p.subscribe(genesis).await;
+
             // Per-Tributary P2P message handler
             tokio::spawn({
               let p2p = p2p.clone();
@@ -595,6 +671,7 @@ pub async fn handle_p2p_task<D: Db, P: P2p>(
           TributaryEvent::TributaryRetired(set) => {
             if let Some(genesis) = set_to_genesis.remove(&set) {
               channels.write().await.remove(&genesis);
+              p2p.unsubscribe(genesis).await;
             }
           }
         }

coordinator/src/tests/mod.rs

@@ -62,11 +62,14 @@ impl LocalP2p {
 impl P2p for LocalP2p {
   type Id = usize;
 
-  async fn send_raw(&self, to: Self::Id, msg: Vec<u8>) {
+  async fn subscribe(&self, _genesis: [u8; 32]) {}
+  async fn unsubscribe(&self, _genesis: [u8; 32]) {}
+
+  async fn send_raw(&self, to: Self::Id, _genesis: Option<[u8; 32]>, msg: Vec<u8>) {
     self.1.write().await.1[to].push_back((self.0, msg));
   }
 
-  async fn broadcast_raw(&self, msg: Vec<u8>) {
+  async fn broadcast_raw(&self, _genesis: Option<[u8; 32]>, msg: Vec<u8>) {
     // Content-based deduplication
     let mut lock = self.1.write().await;
     {