cmd/{geth,utils}: add cmd to export preimages in snap enumeration order (#28256)

Adds a subcommand: `geth snapshot export-preimages`, to export preimages of every hash found during a snapshot enumeration: that is, it exports _only the active state_, and not _all_ preimages that have been used but are no longer part of the state. 

This tool is needed for the verkle transition, in order to distribute the preimages needed for the conversion. Since only the 'active' preimages are exported, the output is shrunk from ~70GB to ~4GB.

The order of the output is the order used by the snapshot enumeration, which avoids database thrashing. However, it also means that storage-slot preimages are not deduplicated.

cmd/utils/cmd.go

@@ -33,6 +33,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/rawdb"
+	"github.com/ethereum/go-ethereum/core/state/snapshot"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/eth/ethconfig"
@@ -374,6 +375,101 @@ func ExportPreimages(db ethdb.Database, fn string) error {
 	return nil
 }
 
+// ExportSnapshotPreimages exports the preimages corresponding to the enumeration of
+// the snapshot for a given root.
+func ExportSnapshotPreimages(chaindb ethdb.Database, snaptree *snapshot.Tree, fn string, root common.Hash) error {
+	log.Info("Exporting preimages", "file", fn)
+
+	fh, err := os.OpenFile(fn, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.ModePerm)
+	if err != nil {
+		return err
+	}
+	defer fh.Close()
+
+	// Enable gzip compressing if file name has gz suffix.
+	var writer io.Writer = fh
+	if strings.HasSuffix(fn, ".gz") {
+		gz := gzip.NewWriter(writer)
+		defer gz.Close()
+		writer = gz
+	}
+	buf := bufio.NewWriter(writer)
+	defer buf.Flush()
+	writer = buf
+
+	type hashAndPreimageSize struct {
+		Hash common.Hash
+		Size int
+	}
+	hashCh := make(chan hashAndPreimageSize)
+
+	var (
+		start     = time.Now()
+		logged    = time.Now()
+		preimages int
+	)
+	go func() {
+		defer close(hashCh)
+		accIt, err := snaptree.AccountIterator(root, common.Hash{})
+		if err != nil {
+			log.Error("Failed to create account iterator", "error", err)
+			return
+		}
+		defer accIt.Release()
+
+		for accIt.Next() {
+			acc, err := types.FullAccount(accIt.Account())
+			if err != nil {
+				log.Error("Failed to get full account", "error", err)
+				return
+			}
+			preimages += 1
+			hashCh <- hashAndPreimageSize{Hash: accIt.Hash(), Size: common.AddressLength}
+
+			if acc.Root != (common.Hash{}) && acc.Root != types.EmptyRootHash {
+				stIt, err := snaptree.StorageIterator(root, accIt.Hash(), common.Hash{})
+				if err != nil {
+					log.Error("Failed to create storage iterator", "error", err)
+					return
+				}
+				for stIt.Next() {
+					preimages += 1
+					hashCh <- hashAndPreimageSize{Hash: stIt.Hash(), Size: common.HashLength}
+
+					if time.Since(logged) > time.Second*8 {
+						logged = time.Now()
+						log.Info("Exporting preimages", "count", preimages, "elapsed", common.PrettyDuration(time.Since(start)))
+					}
+				}
+				stIt.Release()
+			}
+			if time.Since(logged) > time.Second*8 {
+				logged = time.Now()
+				log.Info("Exporting preimages", "count", preimages, "elapsed", common.PrettyDuration(time.Since(start)))
+			}
+		}
+	}()
+
+	for item := range hashCh {
+		preimage := rawdb.ReadPreimage(chaindb, item.Hash)
+		if len(preimage) == 0 {
+			return fmt.Errorf("missing preimage for %v", item.Hash)
+		}
+		if len(preimage) != item.Size {
+			return fmt.Errorf("invalid preimage size, have %d", len(preimage))
+		}
+		rlpenc, err := rlp.EncodeToBytes(preimage)
+		if err != nil {
+			return fmt.Errorf("error encoding preimage: %w", err)
+		}
+		if _, err := writer.Write(rlpenc); err != nil {
+			return fmt.Errorf("failed to write preimage: %w", err)
+		}
+	}
+	log.Info("Exported preimages", "count", preimages, "elapsed", common.PrettyDuration(time.Since(start)), "file", fn)
+	return nil
+}
+
 // exportHeader is used in the export/import flow. When we do an export,
 // the first element we output is the exportHeader.
 // Whenever a backwards-incompatible change is made, the Version header