core/state/snapshot: handle legacy journal (#30802)

This workaround is meant to minimize the possibility for snapshot generation
once the geth node upgrades to new version (specifically #30752 )

In #30752, the journal format in state snapshot is modified by removing
the destruct set. Therefore, the existing old format (version = 0) will be
discarded and all in-memory layers will be lost. Unfortunately, the lost 
in-memory layers can't be recovered by some other approaches, and the 
entire state snapshot will be regenerated (it will last about 2.5 hours).

This pull request introduces a workaround to adopt the legacy journal if
the destruct set contained is empty. Since self-destruction has been
deprecated following the cancun fork, the destruct set is expected to be nil for
layers above the fork block. However, an exception occurs during contract 
deployment: pre-funded accounts may self-destruct, causing accounts with 
non-zero balances to be removed from the state. For example,
https://etherscan.io/tx/0xa087333d83f0cd63b96bdafb686462e1622ce25f40bd499e03efb1051f31fe49).


For nodes with a fully synced state, the legacy journal is likely compatible with
the updated definition, eliminating the need for regeneration. Unfortunately,
nodes performing a full sync of historical chain segments or encountering 
pre-funded account deletions may face incompatibilities, leading to automatic 
snapshot regeneration.

Author: rjl493456442

core/state/snapshot/journal.go

@@ -33,9 +33,11 @@ import (
 	"github.com/ethereum/go-ethereum/triedb"
 )
 
-// 0: initial version
-// 1: destruct flag in diff layer is removed
-const journalVersion uint64 = 1
+const (
+	journalV0             uint64 = 0 // initial version
+	journalV1             uint64 = 1 // current version, with destruct flag (in diff layers) removed
+	journalCurrentVersion        = journalV1
+)
 
 // journalGenerator is a disk layer entry containing the generator progress marker.
 type journalGenerator struct {
@@ -50,6 +52,11 @@ type journalGenerator struct {
 	Storage  uint64
 }
 
+// journalDestruct is an account deletion entry in a diffLayer's disk journal.
+type journalDestruct struct {
+	Hash common.Hash
+}
+
 // journalAccount is an account entry in a diffLayer's disk journal.
 type journalAccount struct {
 	Hash common.Hash
@@ -285,8 +292,8 @@ func iterateJournal(db ethdb.KeyValueReader, callback journalCallback) error {
 		log.Warn("Failed to resolve the journal version", "error", err)
 		return errors.New("failed to resolve journal version")
 	}
-	if version != journalVersion {
-		log.Warn("Discarded the snapshot journal with wrong version", "required", journalVersion, "got", version)
+	if version != journalV0 && version != journalCurrentVersion {
+		log.Warn("Discarded journal with wrong version", "required", journalCurrentVersion, "got", version)
 		return errors.New("wrong journal version")
 	}
 	// Secondly, resolve the disk layer root, ensure it's continuous
@@ -316,6 +323,36 @@ func iterateJournal(db ethdb.KeyValueReader, callback journalCallback) error {
 			}
 			return fmt.Errorf("load diff root: %v", err)
 		}
+		// If a legacy journal is detected, decode the destruct set from the stream.
+		// The destruct set has been deprecated. If the journal contains non-empty
+		// destruct set, then it is deemed incompatible.
+		//
+		// Since self-destruction has been deprecated following the cancun fork,
+		// the destruct set is expected to be nil for layers above the fork block.
+		// However, an exception occurs during contract deployment: pre-funded accounts
+		// may self-destruct, causing accounts with non-zero balances to be removed
+		// from the state. For example,
+		// https://etherscan.io/tx/0xa087333d83f0cd63b96bdafb686462e1622ce25f40bd499e03efb1051f31fe49).
+		//
+		// For nodes with a fully synced state, the legacy journal is likely compatible
+		// with the updated definition, eliminating the need for regeneration. Unfortunately,
+		// nodes performing a full sync of historical chain segments or encountering
+		// pre-funded account deletions may face incompatibilities, leading to automatic
+		// snapshot regeneration.
+		//
+		// This approach minimizes snapshot regeneration for Geth nodes upgrading from a
+		// legacy version that are already synced. The workaround can be safely removed
+		// after the next hard fork.
+		if version == journalV0 {
+			var destructs []journalDestruct
+			if err := r.Decode(&destructs); err != nil {
+				return fmt.Errorf("load diff destructs: %v", err)
+			}
+			if len(destructs) > 0 {
+				log.Warn("Incompatible legacy journal detected", "version", journalV0)
+				return fmt.Errorf("incompatible legacy journal detected")
+			}
+		}
 		if err := r.Decode(&accounts); err != nil {
 			return fmt.Errorf("load diff accounts: %v", err)
 		}

core/state/snapshot/snapshot.go

@@ -664,7 +664,7 @@ func (t *Tree) Journal(root common.Hash) (common.Hash, error) {
 
 	// Firstly write out the metadata of journal
 	journal := new(bytes.Buffer)
-	if err := rlp.Encode(journal, journalVersion); err != nil {
+	if err := rlp.Encode(journal, journalCurrentVersion); err != nil {
 		return common.Hash{}, err
 	}
 	diskroot := t.diskRoot()