Initial pruning of backlogged consensus messages

coordinator/tributary/src/lib.rs

@@ -1,5 +1,5 @@
 use core::{marker::PhantomData, fmt::Debug};
-use std::{sync::Arc, io};
+use std::{sync::Arc, io, collections::VecDeque};
 
 use async_trait::async_trait;
 
@@ -194,7 +194,7 @@ impl<D: Db, T: TransactionTrait, P: P2p> Tributary<D, T, P> {
     );
     let blockchain = Arc::new(RwLock::new(blockchain));
 
-    let to_rebroadcast = Arc::new(RwLock::new(vec![]));
+    let to_rebroadcast = Arc::new(RwLock::new(VecDeque::new()));
     // Actively rebroadcast consensus messages to ensure they aren't prematurely dropped from the
     // P2P layer
     let p2p_meta_task_handle = Arc::new(

coordinator/tributary/src/tendermint/mod.rs

@@ -1,5 +1,8 @@
 use core::ops::Deref;
-use std::{sync::Arc, collections::HashMap};
+use std::{
+  sync::Arc,
+  collections::{VecDeque, HashMap},
+};
 
 use async_trait::async_trait;
 
@@ -268,7 +271,7 @@ pub struct TendermintNetwork<D: Db, T: TransactionTrait, P: P2p> {
   pub(crate) validators: Arc<Validators>,
   pub(crate) blockchain: Arc<RwLock<Blockchain<D, T>>>,
 
-  pub(crate) to_rebroadcast: Arc<RwLock<Vec<Vec<u8>>>>,
+  pub(crate) to_rebroadcast: Arc<RwLock<VecDeque<Vec<u8>>>>,
 
   pub(crate) p2p: P,
 }
@@ -277,29 +280,6 @@ pub const BLOCK_PROCESSING_TIME: u32 = 999;
 pub const LATENCY_TIME: u32 = 1667;
 pub const TARGET_BLOCK_TIME: u32 = BLOCK_PROCESSING_TIME + (3 * LATENCY_TIME);
 
-#[test]
-fn assert_target_block_time() {
-  use serai_db::MemDb;
-
-  #[derive(Clone, Debug)]
-  pub struct DummyP2p;
-
-  #[async_trait::async_trait]
-  impl P2p for DummyP2p {
-    async fn broadcast(&self, _: [u8; 32], _: Vec<u8>) {
-      unimplemented!()
-    }
-  }
-
-  // Type paremeters don't matter here since we only need to call the block_time()
-  // and it only relies on the constants of the trait implementation. block_time() is in seconds,
-  // TARGET_BLOCK_TIME is in milliseconds.
-  assert_eq!(
-    <TendermintNetwork<MemDb, TendermintTx, DummyP2p> as Network>::block_time(),
-    TARGET_BLOCK_TIME / 1000
-  )
-}
-
 #[async_trait]
 impl<D: Db, T: TransactionTrait, P: P2p> Network for TendermintNetwork<D, T, P> {
   type Db = D;
@@ -327,6 +307,9 @@ impl<D: Db, T: TransactionTrait, P: P2p> Network for TendermintNetwork<D, T, P>
   }
 
   async fn broadcast(&mut self, msg: SignedMessageFor<Self>) {
+    let mut to_broadcast = vec![TENDERMINT_MESSAGE];
+    to_broadcast.extend(msg.encode());
+
     // Since we're broadcasting a Tendermint message, set it to be re-broadcasted every second
     // until the block it's trying to build is complete
     // If the P2P layer drops a message before all nodes obtained access, or a node had an
@@ -334,10 +317,18 @@ impl<D: Db, T: TransactionTrait, P: P2p> Network for TendermintNetwork<D, T, P>
     // This is atrocious if there's no content-based deduplication protocol for messages actively
     // being gossiped
     // LibP2p, as used by Serai, is configured to content-based deduplicate
-    let mut to_broadcast = vec![TENDERMINT_MESSAGE];
-    to_broadcast.extend(msg.encode());
-    // TODO: Prune messages from old rounds which are no longer necessary
-    self.to_rebroadcast.write().await.push(to_broadcast.clone());
+    {
+      let mut to_rebroadcast_lock = self.to_rebroadcast.write().await;
+      to_rebroadcast_lock.push_back(to_broadcast.clone());
+      // We should have, ideally, 3 * validators messages within a round
+      // Therefore, this should keep the most recent 2-rounds
+      // TODO: This isn't perfect. Each participant should just rebroadcast their latest round of
+      // messages
+      while to_rebroadcast_lock.len() > (6 * self.validators.weights.len()) {
+        to_rebroadcast_lock.pop_front();
+      }
+    }
+
     self.p2p.broadcast(self.genesis, to_broadcast).await
   }
 
@@ -443,7 +434,7 @@ impl<D: Db, T: TransactionTrait, P: P2p> Network for TendermintNetwork<D, T, P>
     }
 
     // Since we've added a valid block, clear to_rebroadcast
-    *self.to_rebroadcast.write().await = vec![];
+    *self.to_rebroadcast.write().await = VecDeque::new();
 
     Some(TendermintBlock(
       self.blockchain.write().await.build_block::<Self>(&self.signature_scheme()).serialize(),

coordinator/tributary/src/tests/mod.rs

@@ -1,3 +1,6 @@
+#[cfg(test)]
+mod tendermint;
+
 mod transaction;
 pub use transaction::*;
 

coordinator/tributary/src/tests/tendermint.rs

@@ -0,0 +1,28 @@
+use tendermint::ext::Network;
+use crate::{
+  P2p, TendermintTx,
+  tendermint::{TARGET_BLOCK_TIME, TendermintNetwork},
+};
+
+#[test]
+fn assert_target_block_time() {
+  use serai_db::MemDb;
+
+  #[derive(Clone, Debug)]
+  pub struct DummyP2p;
+
+  #[async_trait::async_trait]
+  impl P2p for DummyP2p {
+    async fn broadcast(&self, _: [u8; 32], _: Vec<u8>) {
+      unimplemented!()
+    }
+  }
+
+  // Type paremeters don't matter here since we only need to call the block_time()
+  // and it only relies on the constants of the trait implementation. block_time() is in seconds,
+  // TARGET_BLOCK_TIME is in milliseconds.
+  assert_eq!(
+    <TendermintNetwork<MemDb, TendermintTx, DummyP2p> as Network>::block_time(),
+    TARGET_BLOCK_TIME / 1000
+  )
+}