From 4f18fc836fa47f0a456724532aa57ebed3583204 Mon Sep 17 00:00:00 2001
From: Pankaj Garg <pankaj@solana.com>
Date: Wed, 1 May 2019 11:37:29 -0700
Subject: [PATCH] Forward transactions to the next slot leader (#4092)

- this ensures that transactions will reach in time for the next node to process them
---
 core/src/banking_stage.rs | 37 ++++++++++++++++++++++++++-----------
 core/src/poh_recorder.rs  |  6 ++++++
 2 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/core/src/banking_stage.rs b/core/src/banking_stage.rs
index 2ab237c72..60603b667 100644
--- a/core/src/banking_stage.rs
+++ b/core/src/banking_stage.rs
@@ -241,11 +241,19 @@ impl BankingStage {
             }
             BufferedPacketsDecision::Forward => {
                 if enable_forwarding {
-                    let _ = Self::forward_unprocessed_packets(
-                        &socket,
-                        &rcluster_info.leader_data().unwrap().tpu_via_blobs,
-                        &buffered_packets,
-                    );
+                    if let Some(leader_id) = poh_recorder
+                        .lock()
+                        .unwrap()
+                        .next_slot_leader(DEFAULT_TICKS_PER_SLOT, None)
+                    {
+                        if let Some(leader) = rcluster_info.lookup(&leader_id) {
+                            let _ = Self::forward_unprocessed_packets(
+                                &socket,
+                                &leader.tpu_via_blobs,
+                                &buffered_packets,
+                            );
+                        }
+                    }
                 }
                 Ok(vec![])
             }
@@ -337,12 +345,19 @@ impl BankingStage {
                     }
 
                     if enable_forwarding {
-                        if let Some(leader) = cluster_info.read().unwrap().leader_data() {
-                            let _ = Self::forward_unprocessed_packets(
-                                &socket,
-                                &leader.tpu_via_blobs,
-                                &unprocessed_packets,
-                            );
+                        let rcluster_info = cluster_info.read().unwrap();
+                        if let Some(leader_id) = poh_recorder
+                            .lock()
+                            .unwrap()
+                            .next_slot_leader(DEFAULT_TICKS_PER_SLOT, None)
+                        {
+                            if let Some(leader) = rcluster_info.lookup(&leader_id) {
+                                let _ = Self::forward_unprocessed_packets(
+                                    &socket,
+                                    &leader.tpu_via_blobs,
+                                    &unprocessed_packets,
+                                );
+                            }
                         }
                     }
                 }
diff --git a/core/src/poh_recorder.rs b/core/src/poh_recorder.rs
index 2b8155d3d..72bb2debb 100644
--- a/core/src/poh_recorder.rs
+++ b/core/src/poh_recorder.rs
@@ -13,6 +13,7 @@
 use crate::blocktree::Blocktree;
 use crate::entry::Entry;
 use crate::leader_schedule_cache::LeaderScheduleCache;
+use crate::leader_schedule_utils;
 use crate::poh::Poh;
 use crate::result::{Error, Result};
 use solana_runtime::bank::Bank;
@@ -91,6 +92,11 @@ impl PohRecorder {
         self.working_bank.is_some() || close_to_leader_tick
     }
 
+    pub fn next_slot_leader(&self, ticks_per_slot: u64, bank: Option<&Bank>) -> Option<Pubkey> {
+        let slot = leader_schedule_utils::tick_height_to_slot(ticks_per_slot, self.tick_height());
+        self.leader_schedule_cache.slot_leader_at(slot + 1, bank)
+    }
+
     pub fn hash(&mut self) {
         // TODO: amortize the cost of this lock by doing the loop in here for
         // some min amount of hashes