From 6f6011cdae9f2f4cf8642412f9ed29c14851afa1 Mon Sep 17 00:00:00 2001
From: Tuyen Nguyen <vutuyen2636@gmail.com>
Date: Mon, 14 Aug 2023 14:46:22 +0700
Subject: [PATCH] fix: set vote index to null for out of date vote

---
 .../beacon-node/src/chain/archiver/index.ts    |  3 ++-
 .../fork-choice/src/forkChoice/forkChoice.ts   | 18 +++++++++++++++---
 .../src/protoArray/computeDeltas.ts            | 16 +++++++++-------
 .../fork-choice/src/protoArray/interface.ts    |  3 ++-
 4 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/packages/beacon-node/src/chain/archiver/index.ts b/packages/beacon-node/src/chain/archiver/index.ts
index 5e9dc314a351..9c0290bfd8c4 100644
--- a/packages/beacon-node/src/chain/archiver/index.ts
+++ b/packages/beacon-node/src/chain/archiver/index.ts
@@ -106,12 +106,13 @@ export class Archiver {
       this.chain.regen.pruneOnFinalized(finalizedEpoch);
 
       // tasks rely on extended fork choice
-      this.chain.forkChoice.prune(finalized.rootHex);
+      const prunedBlocks = this.chain.forkChoice.prune(finalized.rootHex);
       await this.updateBackfillRange(finalized);
 
       this.logger.verbose("Finish processing finalized checkpoint", {
         epoch: finalizedEpoch,
         rootHex: finalized.rootHex,
+        prunedBlocks: prunedBlocks.length,
       });
     } catch (e) {
       this.logger.error("Error processing finalized checkpoint", {epoch: finalized.epoch}, e as Error);
diff --git a/packages/fork-choice/src/forkChoice/forkChoice.ts b/packages/fork-choice/src/forkChoice/forkChoice.ts
index cc3f63614ca4..62a8af368b62 100644
--- a/packages/fork-choice/src/forkChoice/forkChoice.ts
+++ b/packages/fork-choice/src/forkChoice/forkChoice.ts
@@ -555,7 +555,7 @@ export class ForkChoice implements IForkChoice {
     }
     return {
       epoch: vote.nextEpoch,
-      root: this.protoArray.nodes[vote.nextIndex].blockRoot,
+      root: vote.nextIndex === null ? HEX_ZERO_HASH : this.protoArray.nodes[vote.nextIndex].blockRoot,
     };
   }
 
@@ -673,9 +673,21 @@ export class ForkChoice implements IForkChoice {
     const prunedCount = prunedNodes.length;
     for (const vote of this.votes) {
       if (vote.currentIndex !== null) {
-        vote.currentIndex -= prunedCount;
+        if (vote.currentIndex >= prunedCount) {
+          vote.currentIndex -= prunedCount;
+        } else {
+          // the vote was for a pruned proto node
+          vote.currentIndex = null;
+        }
+      }
+      if (vote.nextIndex !== null) {
+        if (vote.nextIndex >= prunedCount) {
+          vote.nextIndex -= prunedCount;
+        } else {
+          // the vote was for a pruned proto node
+          vote.nextIndex = null;
+        }
       }
-      vote.nextIndex -= prunedCount;
     }
     return prunedNodes;
   }
diff --git a/packages/fork-choice/src/protoArray/computeDeltas.ts b/packages/fork-choice/src/protoArray/computeDeltas.ts
index ac51b19c22d6..09f2cf05f1f5 100644
--- a/packages/fork-choice/src/protoArray/computeDeltas.ts
+++ b/packages/fork-choice/src/protoArray/computeDeltas.ts
@@ -22,7 +22,7 @@ export function computeDeltas(
   const deltas = Array<number>(numProtoNodes).fill(0);
   // avoid creating new variables in the loop to potentially reduce GC pressure
   let oldBalance, newBalance: number;
-  let currentIndex, nextIndex: number;
+  let currentIndex, nextIndex: number | null;
 
   for (let vIndex = 0; vIndex < votes.length; vIndex++) {
     const vote = votes[vIndex];
@@ -75,13 +75,15 @@ export function computeDeltas(
 
       // We ignore the vote if it is not known in `indices .
       // We assume that it is outside of our tree (ie: pre-finalization) and therefore not interesting
-      if (nextIndex >= numProtoNodes) {
-        throw new ProtoArrayError({
-          code: ProtoArrayErrorCode.INVALID_NODE_DELTA,
-          index: nextIndex,
-        });
+      if (nextIndex !== null) {
+        if (nextIndex >= numProtoNodes) {
+          throw new ProtoArrayError({
+            code: ProtoArrayErrorCode.INVALID_NODE_DELTA,
+            index: nextIndex,
+          });
+        }
+        deltas[nextIndex] += newBalance;
       }
-      deltas[nextIndex] += newBalance;
     }
     vote.currentIndex = nextIndex;
   }
diff --git a/packages/fork-choice/src/protoArray/interface.ts b/packages/fork-choice/src/protoArray/interface.ts
index 085714617ebc..1910ad2b4206 100644
--- a/packages/fork-choice/src/protoArray/interface.ts
+++ b/packages/fork-choice/src/protoArray/interface.ts
@@ -10,7 +10,8 @@ export const HEX_ZERO_HASH = "0x000000000000000000000000000000000000000000000000
  */
 export type VoteTracker = {
   currentIndex: number | null;
-  nextIndex: number;
+  // if a vode is out of date (the voted index was in the past while proto array is pruned), it will be set to null
+  nextIndex: number | null;
   nextEpoch: Epoch;
 };