(fix): Impl. Lagged error in pool update channel (#4242)

crates/transaction-pool/src/pool/best.rs

@@ -7,7 +7,7 @@ use std::{
     collections::{BTreeMap, BTreeSet, HashSet},
     sync::Arc,
 };
-use tokio::sync::broadcast::Receiver;
+use tokio::sync::broadcast::{error::TryRecvError, Receiver};
 use tracing::debug;
 
 /// An iterator that returns transactions that can be executed on the current state (*best*
@@ -86,17 +86,24 @@ impl<T: TransactionOrdering> BestTransactions<T> {
 
     /// Non-blocking read on the new pending transactions subscription channel
     fn try_recv(&mut self) -> Option<PendingTransaction<T>> {
-        match self.new_transaction_reciever.try_recv() {
-            Ok(tx) => Some(tx),
-            // note TryRecvError::Lagged can be returned here, which is an error that attempts to
-            // correct itself on consecutive try_recv() attempts
+        loop {
+            match self.new_transaction_reciever.try_recv() {
+                Ok(tx) => return Some(tx),
+                // note TryRecvError::Lagged can be returned here, which is an error that attempts
+                // to correct itself on consecutive try_recv() attempts
 
-            // the cost of ignoring this error is allowing old transactions to get
-            // overwritten after the chan buffer size is met
+                // the cost of ignoring this error is allowing old transactions to get
+                // overwritten after the chan buffer size is met
+                Err(TryRecvError::Lagged(_)) => {
+                    // Handle the case where the receiver lagged too far behind.
+                    // `num_skipped` indicates the number of messages that were skipped.
+                    continue
+                }
 
-            // this case is still better than the existing iterator behavior where no new
-            // pending txs are surfaced to consumers
-            Err(_) => None,
+                // this case is still better than the existing iterator behavior where no new
+                // pending txs are surfaced to consumers
+                Err(_) => return None,
+            }
         }
     }