remove duplicates from fanout leaders (#5109)

Currently, when sending transactions to future leaders, duplicate leaders may appear in consecutive slots, resulting in unnecessary spam.
This PRs removes duplicates from the fanout leaders set.

Author: KirillLykov

tpu-client-next/src/connection_workers_scheduler.rs

@@ -217,29 +217,28 @@ impl ConnectionWorkersScheduler {
                 }
             };
 
-            let updated_leaders = leader_updater.next_leaders(leaders_fanout.connect);
+            let connect_leaders = leader_updater.next_leaders(leaders_fanout.connect);
+            let send_leaders = extract_send_leaders(&connect_leaders, leaders_fanout.send);
 
-            let (fanout_leaders, connect_leaders) =
-                split_leaders(&updated_leaders, &leaders_fanout);
             // add future leaders to the cache to hide the latency of opening
             // the connection.
             for peer in connect_leaders {
-                if !workers.contains(peer) {
+                if !workers.contains(&peer) {
                     let stats = send_stats_per_addr.entry(peer.ip()).or_default();
                     let worker = Self::spawn_worker(
                         &endpoint,
-                        peer,
+                        &peer,
                         worker_channel_size,
                         skip_check_transaction_age,
                         max_reconnect_attempts,
                         stats.clone(),
                     );
-                    maybe_shutdown_worker(workers.push(*peer, worker));
+                    maybe_shutdown_worker(workers.push(peer, worker));
                 }
             }
 
             if let Err(error) =
-                Broadcaster::send_to_workers(&mut workers, fanout_leaders, transaction_batch).await
+                Broadcaster::send_to_workers(&mut workers, &send_leaders, transaction_batch).await
             {
                 last_error = Some(error);
                 break;
@@ -338,21 +337,23 @@ impl WorkersBroadcaster for NonblockingBroadcaster {
     }
 }
 
-/// Splits `leaders` into two slices based on the `fanout` configuration:
-/// * the first slice contains the leaders to which transactions will be sent,
-/// * the second vector contains the leaders, used to warm up connections. This
-///   slice includes the first set.
-fn split_leaders<'leaders>(
-    leaders: &'leaders [SocketAddr],
-    fanout: &Fanout,
-) -> (&'leaders [SocketAddr], &'leaders [SocketAddr]) {
-    let Fanout { send, connect } = fanout;
-    assert!(send <= connect);
-    let send_count = (*send).min(leaders.len());
-    let connect_count = (*connect).min(leaders.len());
-
-    let send_slice = &leaders[..send_count];
-    let connect_slice = &leaders[..connect_count];
-
-    (send_slice, connect_slice)
+/// Extracts a list of unique leader addresses to which transactions will be sent.
+///
+/// This function selects up to `send_fanout` addresses from the `leaders` list, ensuring that
+/// only unique addresses are included while maintaining their original order.
+fn extract_send_leaders(leaders: &[SocketAddr], send_fanout: usize) -> Vec<SocketAddr> {
+    let send_count = send_fanout.min(leaders.len());
+    remove_duplicates(&leaders[..send_count])
+}
+
+/// Removes duplicate `SocketAddr` elements from the given slice while
+/// preserving their original order.
+fn remove_duplicates(input: &[SocketAddr]) -> Vec<SocketAddr> {
+    let mut res = Vec::with_capacity(input.len());
+    for address in input {
+        if !res.contains(address) {
+            res.push(*address);
+        }
+    }
+    res
 }