From 6714d85903e663e6d85ca64a300cbd1650f269a1 Mon Sep 17 00:00:00 2001
From: Matus Kysel <matus.kysel@bnbchain.org>
Date: Wed, 17 Jul 2024 18:17:16 +0200
Subject: [PATCH] consensus/parlia: support recovery when snapshot of parlia
 gone in disk

---
 consensus/parlia/parlia.go | 33 +++++++++++++++++++++++++--------
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/consensus/parlia/parlia.go b/consensus/parlia/parlia.go
index e9adc8e27e7..7fb7250f424 100644
--- a/consensus/parlia/parlia.go
+++ b/consensus/parlia/parlia.go
@@ -54,7 +54,7 @@ const (
 	inMemorySignatures = 4096 // Number of recent block signatures to keep in memory
 
 	CheckpointInterval = 1024        // Number of blocks after which to save the snapshot to the database
-	defaultEpochLength = uint64(100) // Default number of blocks of checkpoint to update validatorSet from contract
+	defaultEpochLength = uint64(200) // Default number of blocks of checkpoint to update validatorSet from contract
 
 	extraVanity      = 32 // Fixed number of extra-data prefix bytes reserved for signer vanity
 	extraSeal        = 65 // Fixed number of extra-data suffix bytes reserved for signer seal
@@ -750,22 +750,39 @@ func (p *Parlia) snapshot(chain consensus.ChainHeaderReader, number uint64, hash
 				}
 			}
 		}
-		// If we're at the genesis, snapshot the initial state.
-		if number == 0 {
-			// Headers included into the snapshots have to be trusted as checkpoints
-			checkpoint := chain.GetHeader(hash, number)
-			if checkpoint != nil {
+		// If we're at the genesis, snapshot the initial state. Alternatively if we have
+		// piled up more headers than allowed to be reorged (chain reinit from a freezer),
+		// consider the checkpoint trusted and snapshot it.
+		// even BEP-341 enabled, an offset `defaultEpochLength/2` can ensure getting the right validators.
+		if number == 0 || (number%p.config.Epoch == defaultEpochLength/2 && (len(headers) > int(params.FullImmutabilityThreshold))) {
+			var (
+				checkpoint *types.Header
+				blockHash  libcommon.Hash
+			)
+			if number == 0 {
+				checkpoint = chain.GetHeaderByNumber(0)
+				if checkpoint != nil {
+					blockHash = checkpoint.Hash()
+				}
+			} else {
+				checkpoint = chain.GetHeaderByNumber(number - defaultEpochLength/2)
+				blockHeader := chain.GetHeaderByNumber(number)
+				if blockHeader != nil {
+					blockHash = blockHeader.Hash()
+				}
+			}
+			if checkpoint != nil && blockHash != (libcommon.Hash{}) {
 				// get validators from headers
 				validators, voteAddrs, err := parseValidators(checkpoint, p.chainConfig, p.config)
 				if err != nil {
 					return nil, err
 				}
 				// new snapshot
-				snap = newSnapshot(p.config, p.signatures, number, hash, validators, voteAddrs)
+				snap = newSnapshot(p.config, p.signatures, number, blockHash, validators, voteAddrs)
 				if err := snap.store(p.db); err != nil {
 					return nil, err
 				}
-				p.logger.Info("Stored checkpoint snapshot to disk", "number", number, "hash", hash)
+				p.logger.Info("Stored checkpoint snapshot to disk", "number", number, "hash", blockHash)
 				break
 			}
 		}