Avoid broadcasting mempool rejected or expired transactions to peers (#2858)

* do not advertise rejected transactions

* do not broadcast transaction that are expired

* change dummy var name

* simplify code, performance

* clippy

* add some test coverage

* clippy

Co-authored-by: teor <teor@riseup.net>

zebrad/src/components/mempool.rs

@@ -245,17 +245,17 @@ impl Service<Request> for Mempool {
                     }
                 }
 
+                // Collect inserted transaction ids.
+                let mut send_to_peers_ids = HashSet::<_>::new();
+
                 // Clean up completed download tasks and add to mempool if successful.
-                // Also, send succesful transactions to peers.
-                let mut inserted_txids = HashSet::new();
                 while let Poll::Ready(Some(r)) = tx_downloads.as_mut().poll_next(cx) {
                     match r {
                         Ok(tx) => {
-                            // Storage handles conflicting transactions or a full mempool internally,
-                            // so just ignore the storage result here
-                            let _ = storage.insert(tx.clone());
-                            // Save transaction ids that we will send to peers
-                            inserted_txids.insert(tx.id);
+                            if let Ok(inserted_id) = storage.insert(tx.clone()) {
+                                // Save transaction ids that we will send to peers
+                                send_to_peers_ids.insert(inserted_id);
+                            }
                         }
                         Err((txid, e)) => {
                             reject_if_needed(storage, txid, e);
@@ -263,14 +263,18 @@ impl Service<Request> for Mempool {
                         }
                     };
                 }
-                // Send any newly inserted transactions to peers
-                if !inserted_txids.is_empty() {
-                    let _ = self.transaction_sender.send(inserted_txids)?;
-                }
 
                 // Remove expired transactions from the mempool.
                 if let Some(tip_height) = self.latest_chain_tip.best_tip_height() {
-                    remove_expired_transactions(storage, tip_height);
+                    let expired_transactions = remove_expired_transactions(storage, tip_height);
+                    // Remove transactions that are expired from the peers list
+                    send_to_peers_ids =
+                        remove_expired_from_peer_list(&send_to_peers_ids, &expired_transactions);
+                }
+
+                // Send transactions that were not rejected nor expired to peers
+                if !send_to_peers_ids.is_empty() {
+                    let _ = self.transaction_sender.send(send_to_peers_ids)?;
                 }
             }
             ActiveState::Disabled => {
@@ -347,7 +351,7 @@ impl Service<Request> for Mempool {
 fn remove_expired_transactions(
     storage: &mut storage::Storage,
     tip_height: zebra_chain::block::Height,
-) {
+) -> HashSet<UnminedTxId> {
     let mut txid_set = HashSet::new();
     // we need a separate set, since reject() takes the original unmined ID,
     // then extracts the mined ID out of it
@@ -366,9 +370,22 @@ fn remove_expired_transactions(
     storage.remove_same_effects(&txid_set);
 
     // also reject it
-    for id in unmined_id_set {
-        storage.reject(id, SameEffectsChainRejectionError::Expired.into());
+    for id in unmined_id_set.iter() {
+        storage.reject(*id, SameEffectsChainRejectionError::Expired.into());
     }
+
+    unmined_id_set
+}
+
+/// Remove expired transaction ids from a given list of inserted ones.
+fn remove_expired_from_peer_list(
+    send_to_peers_ids: &HashSet<UnminedTxId>,
+    expired_transactions: &HashSet<UnminedTxId>,
+) -> HashSet<UnminedTxId> {
+    send_to_peers_ids
+        .difference(expired_transactions)
+        .copied()
+        .collect()
 }
 
 /// Add a transaction that failed download and verification to the rejected list

zebrad/src/components/mempool/storage/tests/vectors.rs

@@ -1,8 +1,15 @@
 use std::iter;
 
+use crate::components::mempool::{remove_expired_from_peer_list, remove_expired_transactions};
+
 use super::{super::*, unmined_transactions_in_blocks};
 
-use zebra_chain::parameters::Network;
+use zebra_chain::{
+    block::{Block, Height},
+    parameters::Network,
+    serialization::ZcashDeserializeInto,
+    transaction::UnminedTxId,
+};
 
 use color_eyre::eyre::Result;
 
@@ -129,3 +136,58 @@ fn mempool_storage_basic_for_network(network: Network) -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn mempool_expired_basic() -> Result<()> {
+    zebra_test::init();
+
+    mempool_expired_basic_for_network(Network::Mainnet)?;
+    mempool_expired_basic_for_network(Network::Testnet)?;
+
+    Ok(())
+}
+
+fn mempool_expired_basic_for_network(network: Network) -> Result<()> {
+    // Create an empty storage
+    let mut storage: Storage = Default::default();
+
+    let block: Block = match network {
+        Network::Mainnet => {
+            zebra_test::vectors::BLOCK_MAINNET_982681_BYTES.zcash_deserialize_into()?
+        }
+        Network::Testnet => {
+            zebra_test::vectors::BLOCK_TESTNET_925483_BYTES.zcash_deserialize_into()?
+        }
+    };
+
+    // Get a test transaction
+    let tx = &*(block.transactions[1]).clone();
+
+    // Change the expiration height of the test transaction
+    let mut tx = tx.clone();
+    *tx.expiry_height_mut() = zebra_chain::block::Height(1);
+
+    let tx_id = tx.unmined_id();
+
+    // Insert the transaction into the mempool
+    storage.insert(UnminedTx::from(tx))?;
+
+    assert_eq!(storage.transaction_count(), 1);
+
+    // Get everything available in mempool now
+    let everything_in_mempool: HashSet<UnminedTxId> = storage.tx_ids().collect();
+    assert_eq!(everything_in_mempool.len(), 1);
+    assert!(everything_in_mempool.contains(&tx_id));
+
+    // remove_expired_transactions() will return what was removed
+    let expired = remove_expired_transactions(&mut storage, Height(1));
+    assert!(expired.contains(&tx_id));
+    let everything_in_mempool: HashSet<UnminedTxId> = storage.tx_ids().collect();
+    assert_eq!(everything_in_mempool.len(), 0);
+
+    // No transaction will be sent to peers
+    let send_to_peers = remove_expired_from_peer_list(&everything_in_mempool, &expired);
+    assert_eq!(send_to_peers.len(), 0);
+
+    Ok(())
+}