eth/downloader, cmd: add --snap.skipreceipts for state-only snap sync

Add an opt-in --snap.skipreceipts flag that makes snap sync neither
schedule, fetch nor validate historical block receipts. The state trie is
still reconstructed and verified in full; only the receipt backfill is
skipped.

Receipts are execution outputs (re-derivable by re-executing blocks) and
are not required to reconstruct or validate state. Skipping them lets a
node snap-sync the state from a peer that does not retain historical
receipts (for example a snapshot-restored, state-only source), where the
default receipt backfill otherwise fails receipt-root validation and drops
the only peer. This mirrors the state-only snap behaviour Nethermind
already supports via its static snap pivot.

The flag defaults to false, so default behaviour is unchanged.

cmd/geth/main.go

@@ -76,6 +76,7 @@ var (
 		utils.BlobPoolDataCapFlag,
 		utils.BlobPoolPriceBumpFlag,
 		utils.SyncModeFlag,
+		utils.SnapSkipReceiptsFlag,
 		utils.SyncTargetFlag,
 		utils.ExitWhenSyncedFlag,
 		utils.GCModeFlag,

cmd/utils/flags.go

@@ -280,6 +280,15 @@ var (
 		Value:    ethconfig.Defaults.SyncMode.String(),
 		Category: flags.StateCategory,
 	}
+	SnapSkipReceiptsFlag = &cli.BoolFlag{
+		Name: "snap.skipreceipts",
+		Usage: "Skip the historical receipt backfill during snap sync, reconstructing state only. " +
+			"Lets a node snap-sync from a peer that does not retain historical receipts (e.g. a state-only / " +
+			"snapshot-restored source). The resulting node has no receipts for the pre-sync range, so " +
+			"eth_getLogs / eth_getTransactionReceipt / eth_getBlockReceipts return a pruned-history error there. " +
+			"Intended for state-growth benchmarking and trusted-peer setups, not general mainnet operation.",
+		Category: flags.StateCategory,
+	}
 	GCModeFlag = &cli.StringFlag{
 		Name:     "gcmode",
 		Usage:    `Blockchain garbage collection mode ("full", "archive")`,
@@ -1764,6 +1773,15 @@ func SetEthConfig(ctx *cli.Context, stack *node.Node, cfg *ethconfig.Config) {
 		}
 	}
 
+	if ctx.IsSet(SnapSkipReceiptsFlag.Name) {
+		cfg.SnapSkipReceipts = ctx.Bool(SnapSkipReceiptsFlag.Name)
+		if cfg.SnapSkipReceipts {
+			log.Warn("Snap sync receipt backfill disabled via --snap.skipreceipts: state is reconstructed in full, " +
+				"but the node will have no receipts for the pre-sync range. eth_getLogs, eth_getTransactionReceipt and " +
+				"eth_getBlockReceipts will report pruned history there. Use only for benchmarking / trusted-peer setups.")
+		}
+	}
+
 	if ctx.IsSet(CacheFlag.Name) || ctx.IsSet(CacheDatabaseFlag.Name) {
 		cfg.DatabaseCache = ctx.Int(CacheFlag.Name) * ctx.Int(CacheDatabaseFlag.Name) / 100
 	}

eth/backend.go

@@ -346,15 +346,16 @@ func New(stack *node.Node, config *ethconfig.Config) (*Ethereum, error) {
 	// Permit the downloader to use the trie cache allowance during fast sync
 	cacheLimit := options.TrieCleanLimit + options.TrieDirtyLimit + options.SnapshotLimit
 	if eth.handler, err = newHandler(&handlerConfig{
-		NodeID:         eth.p2pServer.Self().ID(),
+		NodeID:           eth.p2pServer.Self().ID(),
-		Database:       chainDb,
+		Database:         chainDb,
-		Chain:          eth.blockchain,
+		Chain:            eth.blockchain,
-		TxPool:         eth.txPool,
+		TxPool:           eth.txPool,
-		Network:        networkID,
+		Network:          networkID,
-		Sync:           config.SyncMode,
+		Sync:             config.SyncMode,
-		BloomCache:     uint64(cacheLimit),
+		SnapSkipReceipts: config.SnapSkipReceipts,
-		RequiredBlocks: config.RequiredBlocks,
+		BloomCache:       uint64(cacheLimit),
-		SnapV2:         config.SnapV2,
+		RequiredBlocks:   config.RequiredBlocks,
+		SnapV2:           config.SnapV2,
 	}); err != nil {
 		return nil, err
 	}

eth/downloader/downloader.go

@@ -261,6 +261,12 @@ func New(stateDb ethdb.Database, mode ethconfig.SyncMode, chain BlockChain, drop
 	return dl
 }
 
+// SetSkipReceipts skips the historical receipt backfill during snap sync,
+// reconstructing state only. Must be set before synchronisation starts.
+func (d *Downloader) SetSkipReceipts(v bool) {
+	d.queue.skipReceipts = v
+}
+
 // Progress retrieves the synchronisation boundaries, specifically the origin
 // block where synchronisation started at (may have failed/suspended); the block
 // or header sync is currently at; and the latest known block which the sync targets.

eth/downloader/queue.go

@@ -150,6 +150,10 @@ type queue struct {
 	active *sync.Cond
 	closed bool
 
+	// skipReceipts skips scheduling and fetching receipts during snap sync;
+	// state is still reconstructed in full.
+	skipReceipts bool
+
 	logTime time.Time // Time instance when status was last reported
 }
 
@@ -272,7 +276,7 @@ func (q *queue) Schedule(headers []*types.Header, hashes []common.Hash, from uin
 			q.blockTaskQueue.Push(header, -int64(header.Number.Uint64()))
 		}
 		// Queue for receipt retrieval
-		if q.mode == ethconfig.SnapSync && !header.EmptyReceipts() {
+		if q.mode == ethconfig.SnapSync && !q.skipReceipts && !header.EmptyReceipts() {
 			if _, ok := q.receiptTaskPool[hash]; ok {
 				log.Warn("Header already scheduled for receipt fetch", "number", header.Number, "hash", hash)
 			} else {
@@ -425,7 +429,7 @@ func (q *queue) reserveHeaders(p *peerConnection, count int, taskPool map[common
 		// we can ask the resultcache if this header is within the
 		// "prioritized" segment of blocks. If it is not, we need to throttle
 
-		stale, throttle, item, err := q.resultCache.AddFetch(header, q.mode == ethconfig.SnapSync)
+		stale, throttle, item, err := q.resultCache.AddFetch(header, q.mode == ethconfig.SnapSync && !q.skipReceipts)
 		if stale {
 			// Don't put back in the task queue, this item has already been
 			// delivered upstream

eth/downloader/queue_test.go

@@ -195,6 +195,28 @@ func TestBasics(t *testing.T) {
 	}
 }
 
+// TestSkipReceipts verifies that skipReceipts schedules bodies in full but no
+// receipt tasks.
+func TestSkipReceipts(t *testing.T) {
+	q := newQueue(10, 10)
+	q.skipReceipts = true
+	q.Prepare(1, SnapSync)
+
+	headers := chain.headers()
+	hashes := make([]common.Hash, len(headers))
+	for i, header := range headers {
+		hashes[i] = header.Hash()
+	}
+	q.Schedule(headers, hashes, 1)
+
+	if got, exp := q.PendingBodies(), chain.Len(); got != exp {
+		t.Errorf("wrong pending block count, got %d, exp %d", got, exp)
+	}
+	if got, exp := q.PendingReceipts(), 0; got != exp {
+		t.Errorf("wrong pending receipt count, got %d, exp %d", got, exp)
+	}
+}
+
 func TestEmptyBlocks(t *testing.T) {
 	numOfBlocks := len(emptyChain.blocks)
 

eth/ethconfig/config.go

@@ -94,6 +94,10 @@ type Config struct {
 	NetworkId uint64
 	SyncMode  SyncMode
 
+	// SnapSkipReceipts skips the historical receipt backfill during snap sync,
+	// reconstructing state only.
+	SnapSkipReceipts bool
+
 	// HistoryMode configures chain history retention.
 	HistoryMode history.HistoryMode
 

eth/handler.go

@@ -100,15 +100,16 @@ type txPool interface {
 // handlerConfig is the collection of initialization parameters to create a full
 // node network handler.
 type handlerConfig struct {
-	NodeID         enode.ID               // P2P node ID used for tx propagation topology
+	NodeID           enode.ID               // P2P node ID used for tx propagation topology
-	Database       ethdb.Database         // Database for direct sync insertions
+	Database         ethdb.Database         // Database for direct sync insertions
-	Chain          *core.BlockChain       // Blockchain to serve data from
+	Chain            *core.BlockChain       // Blockchain to serve data from
-	TxPool         txPool                 // Transaction pool to propagate from
+	TxPool           txPool                 // Transaction pool to propagate from
-	Network        uint64                 // Network identifier to advertise
+	Network          uint64                 // Network identifier to advertise
-	Sync           ethconfig.SyncMode     // Whether to snap or full sync
+	Sync             ethconfig.SyncMode     // Whether to snap or full sync
-	BloomCache     uint64                 // Megabytes to alloc for snap sync bloom
+	SnapSkipReceipts bool                   // Skip historical receipt backfill during snap sync (state-only)
-	RequiredBlocks map[uint64]common.Hash // Hard coded map of required block hashes for sync challenges
+	BloomCache       uint64                 // Megabytes to alloc for snap sync bloom
-	SnapV2         bool                   // Whether to advertise and sync via the snap/2 protocol
+	RequiredBlocks   map[uint64]common.Hash // Hard coded map of required block hashes for sync challenges
+	SnapV2           bool                   // Whether to advertise and sync via the snap/2 protocol
 }
 
 type handler struct {
@@ -158,6 +159,7 @@ func newHandler(config *handlerConfig) (*handler, error) {
 	}
 	// Construct the downloader (long sync)
 	h.downloader = downloader.New(config.Database, config.Sync, h.chain, h.removePeer, h.enableSyncedFeatures, config.SnapV2)
+	h.downloader.SetSkipReceipts(config.SnapSkipReceipts)
 
 	// If snap sync is requested but snapshots are disabled, fail loudly
 	if h.downloader.ConfigSyncMode() == ethconfig.SnapSync && (config.Chain.Snapshots() == nil && config.Chain.TrieDB().Scheme() == rawdb.HashScheme) {