internal/era: New EraE implementation (#32157)

Here is a draft for the New EraE implementation. The code follows along
with the spec listed at https://hackmd.io/pIZlxnitSciV5wUgW6W20w.

---------

Co-authored-by: shantichanal <158101918+shantichanal@users.noreply.github.com>
Co-authored-by: lightclient <lightclient@protonmail.com>
Co-authored-by: MariusVanDerWijden <m.vanderwijden@live.de>
Co-authored-by: Sina Mahmoodi <itz.s1na@gmail.com>

cmd/era/main.go

@@ -30,6 +30,8 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/execdb"
+	"github.com/ethereum/go-ethereum/internal/era/onedb"
 	"github.com/ethereum/go-ethereum/internal/ethapi"
 	"github.com/ethereum/go-ethereum/internal/flags"
 	"github.com/ethereum/go-ethereum/params"
@@ -53,7 +55,7 @@ var (
 	eraSizeFlag = &cli.IntFlag{
 		Name:  "size",
 		Usage: "number of blocks per era",
-		Value: era.MaxEra1Size,
+		Value: era.MaxSize,
 	}
 	txsFlag = &cli.BoolFlag{
 		Name:  "txs",
@@ -131,7 +133,7 @@ func block(ctx *cli.Context) error {
 	return nil
 }
 
-// info prints some high-level information about the era1 file.
+// info prints some high-level information about the era file.
 func info(ctx *cli.Context) error {
 	epoch, err := strconv.ParseUint(ctx.Args().First(), 10, 64)
 	if err != nil {
@@ -142,33 +144,34 @@ func info(ctx *cli.Context) error {
 		return err
 	}
 	defer e.Close()
-	acc, err := e.Accumulator()
-	if err != nil {
-		return fmt.Errorf("error reading accumulator: %w", err)
+	var (
+		accHex string
+		tdStr  string
+	)
+	if acc, err := e.Accumulator(); err == nil {
+		accHex = acc.Hex()
 	}
-	td, err := e.InitialTD()
-	if err != nil {
-		return fmt.Errorf("error reading total difficulty: %w", err)
+	if td, err := e.InitialTD(); err == nil {
+		tdStr = td.String()
 	}
 	info := struct {
-		Accumulator     common.Hash `json:"accumulator"`
-		TotalDifficulty *big.Int    `json:"totalDifficulty"`
+		Accumulator     string `json:"accumulator,omitempty"`
+		TotalDifficulty string `json:"totalDifficulty,omitempty"`
 		StartBlock      uint64 `json:"startBlock"`
 		Count           uint64 `json:"count"`
 	}{
-		acc, td, e.Start(), e.Count(),
+		accHex, tdStr, e.Start(), e.Count(),
 	}
 	b, _ := json.MarshalIndent(info, "", "  ")
 	fmt.Println(string(b))
 	return nil
 }
 
-// open opens an era1 file at a certain epoch.
-func open(ctx *cli.Context, epoch uint64) (*era.Era, error) {
-	var (
-		dir     = ctx.String(dirFlag.Name)
-		network = ctx.String(networkFlag.Name)
-	)
+// open opens an era file at a certain epoch.
+func open(ctx *cli.Context, epoch uint64) (era.Era, error) {
+	dir := ctx.String(dirFlag.Name)
+	network := ctx.String(networkFlag.Name)
+
 	entries, err := era.ReadDir(dir, network)
 	if err != nil {
 		return nil, fmt.Errorf("error reading era dir: %w", err)
@@ -176,7 +179,28 @@ func open(ctx *cli.Context, epoch uint64) (*era.Era, error) {
 	if epoch >= uint64(len(entries)) {
 		return nil, fmt.Errorf("epoch out-of-bounds: last %d, want %d", len(entries)-1, epoch)
 	}
-	return era.Open(filepath.Join(dir, entries[epoch]))
+	path := filepath.Join(dir, entries[epoch])
+	return openByPath(path)
+}
+
+// openByPath tries to open a single file as either eraE or era1 based on extension,
+// falling back to the other reader if needed.
+func openByPath(path string) (era.Era, error) {
+	switch strings.ToLower(filepath.Ext(path)) {
+	case ".erae":
+		if e, err := execdb.Open(path); err != nil {
+			return nil, err
+		} else {
+			return e, nil
+		}
+	case ".era1":
+		if e, err := onedb.Open(path); err != nil {
+			return nil, err
+		} else {
+			return e, nil
+		}
+	}
+	return nil, fmt.Errorf("unsupported or unreadable era file: %s", path)
 }
 
 // verify checks each era1 file in a directory to ensure it is well-formed and
@@ -203,18 +227,58 @@ func verify(ctx *cli.Context) error {
 		return fmt.Errorf("error reading %s: %w", dir, err)
 	}
 
-	if len(entries) != len(roots) {
-		return errors.New("number of era1 files should match the number of accumulator hashes")
+	// Build the verification list respecting the rule:
+	// era1: must have accumulator, always verify
+	// erae: verify only if accumulator exists (pre-merge)
+
+	// Build list of files to verify.
+	verify := make([]string, 0, len(entries))
+
+	for _, name := range entries {
+		path := filepath.Join(dir, name)
+		ext := strings.ToLower(filepath.Ext(name))
+
+		switch ext {
+		case ".era1":
+			e, err := onedb.Open(path)
+			if err != nil {
+				return fmt.Errorf("error opening era1 file %s: %w", name, err)
+			}
+			_, accErr := e.Accumulator()
+			e.Close()
+			if accErr != nil {
+				return fmt.Errorf("era1 file %s missing accumulator: %w", name, accErr)
+			}
+			verify = append(verify, path)
+
+		case ".erae":
+			e, err := execdb.Open(path)
+			if err != nil {
+				return fmt.Errorf("error opening erae file %s: %w", name, err)
+			}
+			_, accErr := e.Accumulator()
+			e.Close()
+			if accErr == nil {
+				verify = append(verify, path) // pre-merge only
+			}
+		default:
+			return fmt.Errorf("unsupported era file: %s", name)
+		}
+	}
+
+	if len(verify) != len(roots) {
+		return fmt.Errorf("mismatch between eras to verify (%d) and provided roots (%d)", len(verify), len(roots))
 	}
 
 	// Verify each epoch matches the expected root.
 	for i, want := range roots {
 		// Wrap in function so defers don't stack.
 		err := func() error {
-			name := entries[i]
-			e, err := era.Open(filepath.Join(dir, name))
+			path := verify[i]
+			name := filepath.Base(path)
+			e, err := openByPath(path)
 			if err != nil {
-				return fmt.Errorf("error opening era1 file %s: %w", name, err)
+				return fmt.Errorf("error opening era file %s: %w", name, err)
 			}
 			defer e.Close()
 			// Read accumulator and check against expected.
@@ -243,7 +307,7 @@ func verify(ctx *cli.Context) error {
 }
 
 // checkAccumulator verifies the accumulator matches the data in the Era.
-func checkAccumulator(e *era.Era) error {
+func checkAccumulator(e era.Era) error {
 	var (
 		err    error
 		want   common.Hash
@@ -257,7 +321,7 @@ func checkAccumulator(e *era.Era) error {
 	if td, err = e.InitialTD(); err != nil {
 		return fmt.Errorf("error reading total difficulty: %w", err)
 	}
-	it, err := era.NewIterator(e)
+	it, err := e.Iterator()
 	if err != nil {
 		return fmt.Errorf("error making era iterator: %w", err)
 	}
@@ -290,10 +354,14 @@ func checkAccumulator(e *era.Era) error {
 		if rr != block.ReceiptHash() {
 			return fmt.Errorf("receipt root in block %d mismatch: want %s, got %s", block.NumberU64(), block.ReceiptHash(), rr)
 		}
+		// Only include pre-merge blocks in accumulator calculation.
+		// Post-merge blocks have difficulty == 0.
+		if block.Difficulty().Sign() > 0 {
 			hashes = append(hashes, block.Hash())
 			td.Add(td, block.Difficulty())
 			tds = append(tds, new(big.Int).Set(td))
 		}
+	}
 	if it.Error() != nil {
 		return fmt.Errorf("error reading block %d: %w", it.Number(), it.Error())
 	}

cmd/geth/chaincmd.go

@@ -20,6 +20,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -43,6 +44,8 @@ import (
 	"github.com/ethereum/go-ethereum/internal/debug"
 	"github.com/ethereum/go-ethereum/internal/era"
 	"github.com/ethereum/go-ethereum/internal/era/eradl"
+	"github.com/ethereum/go-ethereum/internal/era/execdb"
+	"github.com/ethereum/go-ethereum/internal/era/onedb"
 	"github.com/ethereum/go-ethereum/internal/flags"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/node"
@@ -153,7 +156,7 @@ be gzipped.`,
 		Name:      "import-history",
 		Usage:     "Import an Era archive",
 		ArgsUsage: "<dir>",
-		Flags:     slices.Concat([]cli.Flag{utils.TxLookupLimitFlag, utils.TransactionHistoryFlag}, utils.DatabaseFlags, utils.NetworkFlags),
+		Flags:     slices.Concat([]cli.Flag{utils.TxLookupLimitFlag, utils.TransactionHistoryFlag, utils.EraFormatFlag}, utils.DatabaseFlags, utils.NetworkFlags),
 		Description: `
 The import-history command will import blocks and their corresponding receipts
 from Era archives.
@@ -164,7 +167,7 @@ from Era archives.
 		Name:      "export-history",
 		Usage:     "Export blockchain history to Era archives",
 		ArgsUsage: "<dir> <first> <last>",
-		Flags:     utils.DatabaseFlags,
+		Flags:     slices.Concat([]cli.Flag{utils.EraFormatFlag}, utils.DatabaseFlags),
 		Description: `
 The export-history command will export blocks and their corresponding receipts
 into Era archives. Eras are typically packaged in steps of 8192 blocks.
@@ -516,15 +519,27 @@ func importHistory(ctx *cli.Context) error {
 		network = networks[0]
 	}
 
-	if err := utils.ImportHistory(chain, dir, network); err != nil {
+	var (
+		format = ctx.String(utils.EraFormatFlag.Name)
+		from   func(era.ReadAtSeekCloser) (era.Era, error)
+	)
+	switch format {
+	case "era1", "era":
+		from = onedb.From
+	case "erae":
+		from = execdb.From
+	default:
+		return fmt.Errorf("unknown --era.format %q (expected 'era1' or 'erae')", format)
+	}
+	if err := utils.ImportHistory(chain, dir, network, from); err != nil {
 		return err
 	}
+
 	fmt.Printf("Import done in %v\n", time.Since(start))
 	return nil
 }
 
-// exportHistory exports chain history in Era archives at a specified
-// directory.
+// exportHistory exports chain history in Era archives at a specified directory.
 func exportHistory(ctx *cli.Context) error {
 	if ctx.Args().Len() != 3 {
 		utils.Fatalf("usage: %s", ctx.Command.ArgsUsage)
@@ -550,10 +565,26 @@ func exportHistory(ctx *cli.Context) error {
 	if head := chain.CurrentSnapBlock(); uint64(last) > head.Number.Uint64() {
 		utils.Fatalf("Export error: block number %d larger than head block %d\n", uint64(last), head.Number.Uint64())
 	}
-	err := utils.ExportHistory(chain, dir, uint64(first), uint64(last), uint64(era.MaxEra1Size))
-	if err != nil {
+
+	var (
+		format     = ctx.String(utils.EraFormatFlag.Name)
+		filename   func(network string, epoch int, root common.Hash) string
+		newBuilder func(w io.Writer) era.Builder
+	)
+	switch format {
+	case "era1", "era":
+		newBuilder = func(w io.Writer) era.Builder { return onedb.NewBuilder(w) }
+		filename = func(network string, epoch int, root common.Hash) string { return onedb.Filename(network, epoch, root) }
+	case "erae":
+		newBuilder = func(w io.Writer) era.Builder { return execdb.NewBuilder(w) }
+		filename = func(network string, epoch int, root common.Hash) string { return execdb.Filename(network, epoch, root) }
+	default:
+		return fmt.Errorf("unknown archive format %q (use 'era1' or 'erae')", format)
+	}
+	if err := utils.ExportHistory(chain, dir, uint64(first), uint64(last), newBuilder, filename); err != nil {
 		utils.Fatalf("Export error: %v\n", err)
 	}
+
 	fmt.Printf("Export done in %v\n", time.Since(start))
 	return nil
 }

cmd/utils/cmd.go

@@ -57,6 +57,8 @@ const (
 	importBatchSize = 2500
 )
 
+type EraFileFormat int
+
 // ErrImportInterrupted is returned when the user interrupts the import process.
 var ErrImportInterrupted = errors.New("interrupted")
 
@@ -250,7 +252,7 @@ func readList(filename string) ([]string, error) {
 // ImportHistory imports Era1 files containing historical block information,
 // starting from genesis. The assumption is held that the provided chain
 // segment in Era1 file should all be canonical and verified.
-func ImportHistory(chain *core.BlockChain, dir string, network string) error {
+func ImportHistory(chain *core.BlockChain, dir string, network string, from func(f era.ReadAtSeekCloser) (era.Era, error)) error {
 	if chain.CurrentSnapBlock().Number.BitLen() != 0 {
 		return errors.New("history import only supported when starting from genesis")
 	}
@@ -263,42 +265,49 @@ func ImportHistory(chain *core.BlockChain, dir string, network string) error {
 		return fmt.Errorf("unable to read checksums.txt: %w", err)
 	}
 	if len(checksums) != len(entries) {
-		return fmt.Errorf("expected equal number of checksums and entries, have: %d checksums, %d entries", len(checksums), len(entries))
+		return fmt.Errorf("expected equal number of checksums and entries, have: %d checksums, %d entries",
+			len(checksums), len(entries))
 	}
+
 	var (
 		start    = time.Now()
 		reported = time.Now()
 		imported = 0
 		h        = sha256.New()
-		buf      = bytes.NewBuffer(nil)
+		scratch  = bytes.NewBuffer(nil)
 	)
-	for i, filename := range entries {
+
+	for i, file := range entries {
 		err := func() error {
-			f, err := os.Open(filepath.Join(dir, filename))
+			path := filepath.Join(dir, file)
+
+			// validate against checksum file in directory
+			f, err := os.Open(path)
 			if err != nil {
-				return fmt.Errorf("unable to open era: %w", err)
+				return fmt.Errorf("open %s: %w", path, err)
 			}
 			defer f.Close()
-
-			// Validate checksum.
 			if _, err := io.Copy(h, f); err != nil {
-				return fmt.Errorf("unable to recalculate checksum: %w", err)
-			}
-			if have, want := common.BytesToHash(h.Sum(buf.Bytes()[:])).Hex(), checksums[i]; have != want {
-				return fmt.Errorf("checksum mismatch: have %s, want %s", have, want)
+				return fmt.Errorf("checksum %s: %w", path, err)
 			}
+			got := common.BytesToHash(h.Sum(scratch.Bytes()[:])).Hex()
+			want := checksums[i]
 			h.Reset()
-			buf.Reset()
+			scratch.Reset()
 
+			if got != want {
+				return fmt.Errorf("%s checksum mismatch: have %s want %s", file, got, want)
+			}
 			// Import all block data from Era1.
-			e, err := era.From(f)
+			e, err := from(f)
 			if err != nil {
 				return fmt.Errorf("error opening era: %w", err)
 			}
-			it, err := era.NewIterator(e)
+			it, err := e.Iterator()
 			if err != nil {
-				return fmt.Errorf("error making era reader: %w", err)
+				return fmt.Errorf("error creating iterator: %w", err)
 			}
+
 			for it.Next() {
 				block, err := it.Block()
 				if err != nil {
@@ -311,26 +320,28 @@ func ImportHistory(chain *core.BlockChain, dir string, network string) error {
 				if err != nil {
 					return fmt.Errorf("error reading receipts %d: %w", it.Number(), err)
 				}
-				encReceipts := types.EncodeBlockReceiptLists([]types.Receipts{receipts})
-				if _, err := chain.InsertReceiptChain([]*types.Block{block}, encReceipts, math.MaxUint64); err != nil {
+				enc := types.EncodeBlockReceiptLists([]types.Receipts{receipts})
+				if _, err := chain.InsertReceiptChain([]*types.Block{block}, enc, math.MaxUint64); err != nil {
 					return fmt.Errorf("error inserting body %d: %w", it.Number(), err)
 				}
-				imported += 1
+				imported++
 
-				// Give the user some feedback that something is happening.
 				if time.Since(reported) >= 8*time.Second {
-					log.Info("Importing Era files", "head", it.Number(), "imported", imported, "elapsed", common.PrettyDuration(time.Since(start)))
+					log.Info("Importing Era files", "head", it.Number(), "imported", imported,
+						"elapsed", common.PrettyDuration(time.Since(start)))
 					imported = 0
 					reported = time.Now()
 				}
 			}
+			if err := it.Error(); err != nil {
+				return err
+			}
 			return nil
 		}()
 		if err != nil {
 			return err
 		}
 	}
-
 	return nil
 }
 
@@ -389,7 +400,6 @@ func ExportAppendChain(blockchain *core.BlockChain, fn string, first uint64, las
 		return err
 	}
 	defer fh.Close()
-
 	var writer io.Writer = fh
 	if strings.HasSuffix(fn, ".gz") {
 		writer = gzip.NewWriter(writer)
@@ -405,7 +415,7 @@ func ExportAppendChain(blockchain *core.BlockChain, fn string, first uint64, las
 
 // ExportHistory exports blockchain history into the specified directory,
 // following the Era format.
-func ExportHistory(bc *core.BlockChain, dir string, first, last, step uint64) error {
+func ExportHistory(bc *core.BlockChain, dir string, first, last uint64, newBuilder func(io.Writer) era.Builder, filename func(network string, epoch int, lastBlockHash common.Hash) string) error {
 	log.Info("Exporting blockchain history", "dir", dir)
 	if head := bc.CurrentBlock().Number.Uint64(); head < last {
 		log.Warn("Last block beyond head, setting last = head", "head", head, "last", last)
@@ -418,76 +428,100 @@ func ExportHistory(bc *core.BlockChain, dir string, first, last, step uint64) er
 	if err := os.MkdirAll(dir, os.ModePerm); err != nil {
 		return fmt.Errorf("error creating output directory: %w", err)
 	}
+
 	var (
 		start     = time.Now()
 		reported  = time.Now()
 		h         = sha256.New()
 		buf       = bytes.NewBuffer(nil)
+		td        = new(big.Int)
 		checksums []string
 	)
-	td := new(big.Int)
-	for i := uint64(0); i < first; i++ {
-		td.Add(td, bc.GetHeaderByNumber(i).Difficulty)
+
+	// Compute initial TD by accumulating difficulty from genesis to first-1.
+	// This is necessary because TD is no longer stored in the database. Only
+	// compute if a segment of the export is pre-merge.
+	b := bc.GetBlockByNumber(first)
+	if b == nil {
+		return fmt.Errorf("block #%d not found", first)
 	}
-	for i := first; i <= last; i += step {
-		err := func() error {
-			filename := filepath.Join(dir, era.Filename(network, int(i/step), common.Hash{}))
-			f, err := os.Create(filename)
+	if first > 0 && b.Difficulty().Sign() != 0 {
+		log.Info("Computing initial total difficulty", "from", 0, "to", first-1)
+		for i := uint64(0); i < first; i++ {
+			b := bc.GetBlockByNumber(i)
+			if b == nil {
+				return fmt.Errorf("block #%d not found while computing initial TD", i)
+			}
+			td.Add(td, b.Difficulty())
+		}
+		log.Info("Initial total difficulty computed", "td", td)
+	}
+
+	for batch := first; batch <= last; batch += uint64(era.MaxSize) {
+		idx := int(batch / uint64(era.MaxSize))
+		tmpPath := filepath.Join(dir, filename(network, idx, common.Hash{}))
+
+		if err := func() error {
+			f, err := os.Create(tmpPath)
 			if err != nil {
-				return fmt.Errorf("could not create era file: %w", err)
+				return err
 			}
 			defer f.Close()
 
-			w := era.NewBuilder(f)
-			for j := uint64(0); j < step && j <= last-i; j++ {
-				var (
-					n     = i + j
-					block = bc.GetBlockByNumber(n)
-				)
+			builder := newBuilder(f)
+
+			for j := uint64(0); j < uint64(era.MaxSize) && batch+j <= last; j++ {
+				n := batch + j
+				block := bc.GetBlockByNumber(n)
 				if block == nil {
-					return fmt.Errorf("export failed on #%d: not found", n)
+					return fmt.Errorf("block #%d not found", n)
 				}
-				receipts := bc.GetReceiptsByHash(block.Hash())
-				if receipts == nil {
-					return fmt.Errorf("export failed on #%d: receipts not found", n)
+				receipt := bc.GetReceiptsByHash(block.Hash())
+				if receipt == nil {
+					return fmt.Errorf("receipts for #%d missing", n)
 				}
+
+				// For pre-merge blocks, pass accumulated TD.
+				// For post-merge blocks (difficulty == 0), pass nil TD.
+				var blockTD *big.Int
+				if block.Difficulty().Sign() != 0 {
 					td.Add(td, block.Difficulty())
-				if err := w.Add(block, receipts, new(big.Int).Set(td)); err != nil {
+					blockTD = new(big.Int).Set(td)
+				}
+
+				if err := builder.Add(block, receipt, blockTD); err != nil {
 					return err
 				}
 			}
-			root, err := w.Finalize()
+			id, err := builder.Finalize()
 			if err != nil {
-				return fmt.Errorf("export failed to finalize %d: %w", step/i, err)
+				return err
 			}
-			// Set correct filename with root.
-			os.Rename(filename, filepath.Join(dir, era.Filename(network, int(i/step), root)))
-
-			// Compute checksum of entire Era1.
 			if _, err := f.Seek(0, io.SeekStart); err != nil {
 				return err
 			}
-			if _, err := io.Copy(h, f); err != nil {
-				return fmt.Errorf("unable to calculate checksum: %w", err)
-			}
-			checksums = append(checksums, common.BytesToHash(h.Sum(buf.Bytes()[:])).Hex())
 			h.Reset()
 			buf.Reset()
-			return nil
-		}()
-		if err != nil {
+			if _, err := io.Copy(h, f); err != nil {
 				return err
 			}
+			checksums = append(checksums, common.BytesToHash(h.Sum(buf.Bytes()[:])).Hex())
+
+			// Close before rename. It's required on Windows.
+			f.Close()
+			final := filepath.Join(dir, filename(network, idx, id))
+			return os.Rename(tmpPath, final)
+		}(); err != nil {
+			return err
+		}
+
 		if time.Since(reported) >= 8*time.Second {
-			log.Info("Exporting blocks", "exported", i, "elapsed", common.PrettyDuration(time.Since(start)))
+			log.Info("export progress", "exported", batch, "elapsed", common.PrettyDuration(time.Since(start)))
 			reported = time.Now()
 		}
 	}
 
-	os.WriteFile(filepath.Join(dir, "checksums.txt"), []byte(strings.Join(checksums, "\n")), os.ModePerm)
-
-	log.Info("Exported blockchain to", "dir", dir)
-
+	_ = os.WriteFile(filepath.Join(dir, "checksums.txt"), []byte(strings.Join(checksums, "\n")), os.ModePerm)
 	return nil
 }
 

cmd/utils/flags.go

@@ -1042,6 +1042,12 @@ Please note that --` + MetricsHTTPFlag.Name + ` must be set to start the server.
 		Value:    metrics.DefaultConfig.InfluxDBOrganization,
 		Category: flags.MetricsCategory,
 	}
+
+	// Era flags are a group of flags related to the era archive format.
+	EraFormatFlag = &cli.StringFlag{
+		Name:  "era.format",
+		Usage: "Archive format: 'era1' or 'erae'",
+	}
 )
 
 var (

cmd/utils/history_test.go

@@ -33,6 +33,8 @@ import (
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/execdb"
+	"github.com/ethereum/go-ethereum/internal/era/onedb"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/trie"
 	"github.com/ethereum/go-ethereum/triedb"
@@ -44,6 +46,16 @@ var (
 )
 
 func TestHistoryImportAndExport(t *testing.T) {
+	for _, tt := range []struct {
+		name     string
+		builder  func(io.Writer) era.Builder
+		filename func(network string, epoch int, root common.Hash) string
+		from     func(f era.ReadAtSeekCloser) (era.Era, error)
+	}{
+		{"era1", onedb.NewBuilder, onedb.Filename, onedb.From},
+		{"erae", execdb.NewBuilder, execdb.Filename, execdb.From},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
 			var (
 				key, _  = crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
 				address = crypto.PubkeyToAddress(key.PublicKey)
@@ -89,7 +101,7 @@ func TestHistoryImportAndExport(t *testing.T) {
 			dir := t.TempDir()
 
 			// Export history to temp directory.
-	if err := ExportHistory(chain, dir, 0, count, step); err != nil {
+			if err := ExportHistory(chain, dir, 0, count, tt.builder, tt.filename); err != nil {
 				t.Fatalf("error exporting history: %v", err)
 			}
 
@@ -118,12 +130,12 @@ func TestHistoryImportAndExport(t *testing.T) {
 					if got, want := common.BytesToHash(h.Sum(buf.Bytes()[:])).Hex(), checksums[i]; got != want {
 						t.Fatalf("checksum %d does not match: got %s, want %s", i, got, want)
 					}
-			e, err := era.From(f)
+					e, err := tt.from(f)
 					if err != nil {
 						t.Fatalf("error opening era: %v", err)
 					}
 					defer e.Close()
-			it, err := era.NewIterator(e)
+					it, err := e.Iterator()
 					if err != nil {
 						t.Fatalf("error making era reader: %v", err)
 					}
@@ -170,10 +182,12 @@ func TestHistoryImportAndExport(t *testing.T) {
 			if err != nil {
 				t.Fatalf("unable to initialize chain: %v", err)
 			}
-	if err := ImportHistory(imported, dir, "mainnet"); err != nil {
+			if err := ImportHistory(imported, dir, "mainnet", tt.from); err != nil {
 				t.Fatalf("failed to import chain: %v", err)
 			}
 			if have, want := imported.CurrentHeader(), chain.CurrentHeader(); have.Hash() != want.Hash() {
 				t.Fatalf("imported chain does not match expected, have (%d, %s) want (%d, %s)", have.Number, have.Hash(), want.Number, want.Hash())
 			}
+		})
+	}
 }

core/rawdb/eradb/eradb.go

@@ -27,6 +27,7 @@ import (
 
 	"github.com/ethereum/go-ethereum/common/lru"
 	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/onedb"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/rlp"
 )
@@ -51,7 +52,7 @@ type Store struct {
 type fileCacheEntry struct {
 	refcount int           // reference count. This is protected by Store.mu!
 	opened   chan struct{} // signals opening of file has completed
-	file     *era.Era      // the file
+	file     *onedb.Era    // the file
 	err      error         // error from opening the file
 }
 
@@ -102,7 +103,7 @@ func (db *Store) Close() {
 
 // GetRawBody returns the raw body for a given block number.
 func (db *Store) GetRawBody(number uint64) ([]byte, error) {
-	epoch := number / uint64(era.MaxEra1Size)
+	epoch := number / uint64(era.MaxSize)
 	entry := db.getEraByEpoch(epoch)
 	if entry.err != nil {
 		if errors.Is(entry.err, fs.ErrNotExist) {
@@ -117,7 +118,7 @@ func (db *Store) GetRawBody(number uint64) ([]byte, error) {
 
 // GetRawReceipts returns the raw receipts for a given block number.
 func (db *Store) GetRawReceipts(number uint64) ([]byte, error) {
-	epoch := number / uint64(era.MaxEra1Size)
+	epoch := number / uint64(era.MaxSize)
 	entry := db.getEraByEpoch(epoch)
 	if entry.err != nil {
 		if errors.Is(entry.err, fs.ErrNotExist) {
@@ -249,7 +250,7 @@ func (db *Store) getCacheEntry(epoch uint64) (stat fileCacheStatus, entry *fileC
 }
 
 // fileOpened is called after an era file has been successfully opened.
-func (db *Store) fileOpened(epoch uint64, entry *fileCacheEntry, file *era.Era) {
+func (db *Store) fileOpened(epoch uint64, entry *fileCacheEntry, file *onedb.Era) {
 	db.mu.Lock()
 	defer db.mu.Unlock()
 
@@ -282,7 +283,7 @@ func (db *Store) fileFailedToOpen(epoch uint64, entry *fileCacheEntry, err error
 	entry.err = err
 }
 
-func (db *Store) openEraFile(epoch uint64) (*era.Era, error) {
+func (db *Store) openEraFile(epoch uint64) (*onedb.Era, error) {
 	// File name scheme is <network>-<epoch>-<root>.
 	glob := fmt.Sprintf("*-%05d-*.era1", epoch)
 	matches, err := filepath.Glob(filepath.Join(db.datadir, glob))
@@ -297,17 +298,17 @@ func (db *Store) openEraFile(epoch uint64) (*era.Era, error) {
 	}
 	filename := matches[0]
 
-	e, err := era.Open(filename)
+	e, err := onedb.Open(filename)
 	if err != nil {
 		return nil, err
 	}
 	// Sanity-check start block.
-	if e.Start()%uint64(era.MaxEra1Size) != 0 {
+	if e.Start()%uint64(era.MaxSize) != 0 {
 		e.Close()
-		return nil, fmt.Errorf("pre-merge era1 file has invalid boundary. %d %% %d != 0", e.Start(), era.MaxEra1Size)
+		return nil, fmt.Errorf("pre-merge era1 file has invalid boundary. %d %% %d != 0", e.Start(), era.MaxSize)
 	}
 	log.Debug("Opened era1 file", "epoch", epoch)
-	return e, nil
+	return e.(*onedb.Era), nil
 }
 
 // doneWithFile signals that the caller has finished using a file.

core/types/receipt.go

@@ -424,3 +424,33 @@ func EncodeBlockReceiptLists(receipts []Receipts) []rlp.RawValue {
 	}
 	return result
 }
+
+// SlimReceipt is a wrapper around a Receipt with RLP serialization that omits
+// the Bloom field and includes the tx type. Used for era files.
+type SlimReceipt Receipt
+
+type slimReceiptRLP struct {
+	Type              uint8
+	StatusEncoding    []byte
+	CumulativeGasUsed uint64
+	Logs              []*Log
+}
+
+// EncodeRLP implements rlp.Encoder, encoding the receipt as
+// [tx-type, post-state-or-status, cumulative-gas, logs].
+func (r *SlimReceipt) EncodeRLP(w io.Writer) error {
+	data := &slimReceiptRLP{r.Type, (*Receipt)(r).statusEncoding(), r.CumulativeGasUsed, r.Logs}
+	return rlp.Encode(w, data)
+}
+
+// DecodeRLP implements rlp.Decoder.
+func (r *SlimReceipt) DecodeRLP(s *rlp.Stream) error {
+	var data slimReceiptRLP
+	if err := s.Decode(&data); err != nil {
+		return err
+	}
+	r.Type = data.Type
+	r.CumulativeGasUsed = data.CumulativeGasUsed
+	r.Logs = data.Logs
+	return (*Receipt)(r).setStatus(data.StatusEncoding)
+}

core/types/receipt_test.go

@@ -512,6 +512,45 @@ func TestReceiptUnmarshalBinary(t *testing.T) {
 	}
 }
 
+func TestSlimReceiptEncodingDecoding(t *testing.T) {
+	tests := []*Receipt{
+		legacyReceipt,
+		accessListReceipt,
+		eip1559Receipt,
+		{
+			Type:              BlobTxType,
+			Status:            ReceiptStatusSuccessful,
+			CumulativeGasUsed: 100,
+			Logs:              []*Log{},
+		},
+	}
+	for i, want := range tests {
+		enc, err := rlp.EncodeToBytes((*SlimReceipt)(want))
+		if err != nil {
+			t.Fatalf("test %d: encode error: %v", i, err)
+		}
+		got := new(SlimReceipt)
+		if err := rlp.DecodeBytes(enc, got); err != nil {
+			t.Fatalf("test %d: decode error: %v", i, err)
+		}
+		if got.Type != want.Type {
+			t.Errorf("test %d: Type mismatch: got %d, want %d", i, got.Type, want.Type)
+		}
+		if got.Status != want.Status {
+			t.Errorf("test %d: Status mismatch: got %d, want %d", i, got.Status, want.Status)
+		}
+		if !bytes.Equal(got.PostState, want.PostState) {
+			t.Errorf("test %d: PostState mismatch: got %x, want %x", i, got.PostState, want.PostState)
+		}
+		if got.CumulativeGasUsed != want.CumulativeGasUsed {
+			t.Errorf("test %d: CumulativeGasUsed mismatch: got %d, want %d", i, got.CumulativeGasUsed, want.CumulativeGasUsed)
+		}
+		if len(got.Logs) != len(want.Logs) {
+			t.Errorf("test %d: Logs length mismatch: got %d, want %d", i, len(got.Logs), len(want.Logs))
+		}
+	}
+}
+
 func clearComputedFieldsOnReceipts(receipts []*Receipt) []*Receipt {
 	r := make([]*Receipt, len(receipts))
 	for i, receipt := range receipts {

go.mod

@@ -44,6 +44,7 @@ require (
 	github.com/jackpal/go-nat-pmp v1.0.2
 	github.com/jedisct1/go-minisign v0.0.0-20230811132847-661be99b8267
 	github.com/karalabe/hid v1.0.1-0.20240306101548-573246063e52
+	github.com/klauspost/compress v1.17.8
 	github.com/kylelemons/godebug v1.1.0
 	github.com/mattn/go-colorable v0.1.13
 	github.com/mattn/go-isatty v0.0.20
@@ -126,7 +127,6 @@ require (
 	github.com/influxdata/line-protocol v0.0.0-20200327222509-2487e7298839 // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect
 	github.com/kilic/bls12-381 v0.1.0 // indirect
-	github.com/klauspost/compress v1.17.8 // indirect
 	github.com/klauspost/cpuid/v2 v2.0.9 // indirect
 	github.com/kr/pretty v0.3.1 // indirect
 	github.com/kr/text v0.2.0 // indirect

internal/era/accumulator.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"math/big"
+	"slices"
 
 	"github.com/ethereum/go-ethereum/common"
 	ssz "github.com/ferranbt/fastssz"
@@ -31,8 +32,8 @@ func ComputeAccumulator(hashes []common.Hash, tds []*big.Int) (common.Hash, erro
 	if len(hashes) != len(tds) {
 		return common.Hash{}, errors.New("must have equal number hashes as td values")
 	}
-	if len(hashes) > MaxEra1Size {
-		return common.Hash{}, fmt.Errorf("too many records: have %d, max %d", len(hashes), MaxEra1Size)
+	if len(hashes) > MaxSize {
+		return common.Hash{}, fmt.Errorf("too many records: have %d, max %d", len(hashes), MaxSize)
 	}
 	hh := ssz.NewHasher()
 	for i := range hashes {
@@ -43,7 +44,7 @@ func ComputeAccumulator(hashes []common.Hash, tds []*big.Int) (common.Hash, erro
 		}
 		hh.Append(root[:])
 	}
-	hh.MerkleizeWithMixin(0, uint64(len(hashes)), uint64(MaxEra1Size))
+	hh.MerkleizeWithMixin(0, uint64(len(hashes)), uint64(MaxSize))
 	return hh.HashRoot()
 }
 
@@ -69,23 +70,15 @@ func (h *headerRecord) HashTreeRoot() ([32]byte, error) {
 // HashTreeRootWith ssz hashes the headerRecord object with a hasher.
 func (h *headerRecord) HashTreeRootWith(hh ssz.HashWalker) (err error) {
 	hh.PutBytes(h.Hash[:])
-	td := bigToBytes32(h.TotalDifficulty)
+	td := BigToBytes32(h.TotalDifficulty)
 	hh.PutBytes(td[:])
 	hh.Merkleize(0)
 	return
 }
 
 // bigToBytes32 converts a big.Int into a little-endian 32-byte array.
-func bigToBytes32(n *big.Int) (b [32]byte) {
+func BigToBytes32(n *big.Int) (b [32]byte) {
 	n.FillBytes(b[:])
-	reverseOrder(b[:])
+	slices.Reverse(b[:])
 	return
 }
-
-// reverseOrder reverses the byte order of a slice.
-func reverseOrder(b []byte) []byte {
-	for i := 0; i < 16; i++ {
-		b[i], b[32-i-1] = b[32-i-1], b[i]
-	}
-	return b
-}

internal/era/era.go

@@ -1,4 +1,4 @@
-// Copyright 2024 The go-ethereum Authors
+// Copyright 2025 The go-ethereum Authors
 // This file is part of the go-ethereum library.
 //
 // The go-ethereum library is free software: you can redistribute it and/or modify
@@ -17,7 +17,6 @@
 package era
 
 import (
-	"encoding/binary"
 	"fmt"
 	"io"
 	"math/big"
@@ -25,15 +24,12 @@ import (
 	"path"
 	"strconv"
 	"strings"
-	"sync"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/internal/era/e2store"
-	"github.com/ethereum/go-ethereum/rlp"
-	"github.com/golang/snappy"
 )
 
+// Type constants for the e2store entries in the Era1 and EraE formats.
 var (
 	TypeVersion                uint16 = 0x3265
 	TypeCompressedHeader       uint16 = 0x03
@@ -41,277 +37,119 @@ var (
 	TypeCompressedReceipts     uint16 = 0x05
 	TypeTotalDifficulty        uint16 = 0x06
 	TypeAccumulator            uint16 = 0x07
+	TypeCompressedSlimReceipts uint16 = 0x08 // uses eth/69 encoding
+	TypeProof                  uint16 = 0x09
 	TypeBlockIndex             uint16 = 0x3266
+	TypeComponentIndex         uint16 = 0x3267
 
-	MaxEra1Size = 8192
+	MaxSize = 8192
+	// headerSize uint64 = 8
 )
 
-// Filename returns a recognizable Era1-formatted file name for the specified
-// epoch and network.
-func Filename(network string, epoch int, root common.Hash) string {
-	return fmt.Sprintf("%s-%05d-%s.era1", network, epoch, root.Hex()[2:10])
-}
-
-// ReadDir reads all the era1 files in a directory for a given network.
-// Format: <network>-<epoch>-<hexroot>.era1
-func ReadDir(dir, network string) ([]string, error) {
-	entries, err := os.ReadDir(dir)
-	if err != nil {
-		return nil, fmt.Errorf("error reading directory %s: %w", dir, err)
-	}
-	var (
-		next = uint64(0)
-		eras []string
-	)
-	for _, entry := range entries {
-		if path.Ext(entry.Name()) != ".era1" {
-			continue
-		}
-		parts := strings.Split(entry.Name(), "-")
-		if len(parts) != 3 || parts[0] != network {
-			// Invalid era1 filename, skip.
-			continue
-		}
-		if epoch, err := strconv.ParseUint(parts[1], 10, 64); err != nil {
-			return nil, fmt.Errorf("malformed era1 filename: %s", entry.Name())
-		} else if epoch != next {
-			return nil, fmt.Errorf("missing epoch %d", next)
-		}
-		next += 1
-		eras = append(eras, entry.Name())
-	}
-	return eras, nil
-}
-
 type ReadAtSeekCloser interface {
 	io.ReaderAt
 	io.Seeker
 	io.Closer
 }
 
-// Era reads and Era1 file.
-type Era struct {
-	f   ReadAtSeekCloser // backing era1 file
-	s   *e2store.Reader  // e2store reader over f
-	m   metadata         // start, count, length info
-	mu  *sync.Mutex      // lock for buf
-	buf [8]byte          // buffer reading entry offsets
+// Iterator provides sequential access to blocks in an era file.
+type Iterator interface {
+	// Next advances to the next block. Returns true if a block is available,
+	// false when iteration is complete or an error occurred.
+	Next() bool
+
+	// Number returns the block number of the current block.
+	Number() uint64
+
+	// Block returns the current block.
+	Block() (*types.Block, error)
+
+	// BlockAndReceipts returns the current block and its receipts.
+	BlockAndReceipts() (*types.Block, types.Receipts, error)
+
+	// Receipts returns the receipts for the current block.
+	Receipts() (types.Receipts, error)
+
+	// Error returns any error encountered during iteration.
+	Error() error
 }
 
-// From returns an Era backed by f.
-func From(f ReadAtSeekCloser) (*Era, error) {
-	m, err := readMetadata(f)
-	if err != nil {
-		return nil, err
-	}
-	return &Era{
-		f:  f,
-		s:  e2store.NewReader(f),
-		m:  m,
-		mu: new(sync.Mutex),
-	}, nil
+// Builder constructs era files from blocks and receipts.
+//
+// Builders handle three epoch types automatically:
+//   - Pre-merge: all blocks have difficulty > 0, TD is stored for each block
+//   - Transition: starts pre-merge, ends post-merge; TD stored for all blocks
+//   - Post-merge: all blocks have difficulty == 0, no TD stored
+type Builder interface {
+	// Add appends a block and its receipts to the era file.
+	// For pre-merge blocks, td must be provided.
+	// For post-merge blocks, td should be nil.
+	Add(block *types.Block, receipts types.Receipts, td *big.Int) error
+
+	// AddRLP appends RLP-encoded block components to the era file.
+	// For pre-merge blocks, td and difficulty must be provided.
+	// For post-merge blocks, td and difficulty should be nil.
+	AddRLP(header, body, receipts []byte, number uint64, hash common.Hash, td, difficulty *big.Int) error
+
+	// Finalize writes all collected entries and returns the epoch identifier.
+	// For Era1 (onedb): returns the accumulator root.
+	// For EraE (execdb): returns the last block hash.
+	Finalize() (common.Hash, error)
+
+	// Accumulator returns the accumulator root after Finalize has been called.
+	// Returns nil for post-merge epochs where no accumulator exists.
+	Accumulator() *common.Hash
 }
 
-// Open returns an Era backed by the given filename.
-func Open(filename string) (*Era, error) {
-	f, err := os.Open(filename)
-	if err != nil {
-		return nil, err
-	}
-	return From(f)
+// Era represents the interface for reading era data.
+type Era interface {
+	Close() error
+	Start() uint64
+	Count() uint64
+	Iterator() (Iterator, error)
+	GetBlockByNumber(num uint64) (*types.Block, error)
+	GetRawBodyByNumber(num uint64) ([]byte, error)
+	GetRawReceiptsByNumber(num uint64) ([]byte, error)
+	InitialTD() (*big.Int, error)
+	Accumulator() (common.Hash, error)
 }
 
-func (e *Era) Close() error {
-	return e.f.Close()
-}
+// ReadDir reads all the era files in a directory for a given network.
+// Format: <network>-<epoch>-<hexroot>.erae or <network>-<epoch>-<hexroot>.era1
+func ReadDir(dir, network string) ([]string, error) {
+	entries, err := os.ReadDir(dir)
 
-// GetBlockByNumber returns the block for the given block number.
-func (e *Era) GetBlockByNumber(num uint64) (*types.Block, error) {
-	if e.m.start > num || e.m.start+e.m.count <= num {
-		return nil, fmt.Errorf("out-of-bounds: %d not in [%d, %d)", num, e.m.start, e.m.start+e.m.count)
-	}
-	off, err := e.readOffset(num)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("error reading directory %s: %w", dir, err)
 	}
-	r, n, err := newSnappyReader(e.s, TypeCompressedHeader, off)
-	if err != nil {
-		return nil, err
-	}
-	var header types.Header
-	if err := rlp.Decode(r, &header); err != nil {
-		return nil, err
-	}
-	off += n
-	r, _, err = newSnappyReader(e.s, TypeCompressedBody, off)
-	if err != nil {
-		return nil, err
-	}
-	var body types.Body
-	if err := rlp.Decode(r, &body); err != nil {
-		return nil, err
-	}
-	return types.NewBlockWithHeader(&header).WithBody(body), nil
-}
-
-// GetRawBodyByNumber returns the RLP-encoded body for the given block number.
-func (e *Era) GetRawBodyByNumber(num uint64) ([]byte, error) {
-	if e.m.start > num || e.m.start+e.m.count <= num {
-		return nil, fmt.Errorf("out-of-bounds: %d not in [%d, %d)", num, e.m.start, e.m.start+e.m.count)
-	}
-	off, err := e.readOffset(num)
-	if err != nil {
-		return nil, err
-	}
-	off, err = e.s.SkipN(off, 1)
-	if err != nil {
-		return nil, err
-	}
-	r, _, err := newSnappyReader(e.s, TypeCompressedBody, off)
-	if err != nil {
-		return nil, err
-	}
-	return io.ReadAll(r)
-}
-
-// GetRawReceiptsByNumber returns the RLP-encoded receipts for the given block number.
-func (e *Era) GetRawReceiptsByNumber(num uint64) ([]byte, error) {
-	if e.m.start > num || e.m.start+e.m.count <= num {
-		return nil, fmt.Errorf("out-of-bounds: %d not in [%d, %d)", num, e.m.start, e.m.start+e.m.count)
-	}
-	off, err := e.readOffset(num)
-	if err != nil {
-		return nil, err
-	}
-
-	// Skip over header and body.
-	off, err = e.s.SkipN(off, 2)
-	if err != nil {
-		return nil, err
-	}
-
-	r, _, err := newSnappyReader(e.s, TypeCompressedReceipts, off)
-	if err != nil {
-		return nil, err
-	}
-	return io.ReadAll(r)
-}
-
-// Accumulator reads the accumulator entry in the Era1 file.
-func (e *Era) Accumulator() (common.Hash, error) {
-	entry, err := e.s.Find(TypeAccumulator)
-	if err != nil {
-		return common.Hash{}, err
-	}
-	return common.BytesToHash(entry.Value), nil
-}
-
-// InitialTD returns initial total difficulty before the difficulty of the
-// first block of the Era1 is applied.
-func (e *Era) InitialTD() (*big.Int, error) {
 	var (
-		r      io.Reader
-		header types.Header
-		rawTd  []byte
-		n      int64
-		off    int64
-		err    error
+		next    = uint64(0)
+		eras    []string
+		dirType string
 	)
-
-	// Read first header.
-	if off, err = e.readOffset(e.m.start); err != nil {
-		return nil, err
+	for _, entry := range entries {
+		ext := path.Ext(entry.Name())
+		if ext != ".erae" && ext != ".era1" {
+			continue
 		}
-	if r, n, err = newSnappyReader(e.s, TypeCompressedHeader, off); err != nil {
-		return nil, err
+		if dirType == "" {
+			dirType = ext
 		}
-	if err := rlp.Decode(r, &header); err != nil {
-		return nil, err
+		parts := strings.Split(entry.Name(), "-")
+		if len(parts) != 3 || parts[0] != network {
+			// Invalid era filename, skip.
+			continue
 		}
-	off += n
-
-	// Skip over header and body.
-	off, err = e.s.SkipN(off, 2)
-	if err != nil {
-		return nil, err
+		if epoch, err := strconv.ParseUint(parts[1], 10, 64); err != nil {
+			return nil, fmt.Errorf("malformed era filenames: %s", entry.Name())
+		} else if epoch != next {
+			return nil, fmt.Errorf("missing epoch %d", next)
 		}
-
-	// Read total difficulty after first block.
-	if r, _, err = e.s.ReaderAt(TypeTotalDifficulty, off); err != nil {
-		return nil, err
+		if dirType != ext {
+			return nil, fmt.Errorf("directory %s contains mixed era file formats: want %s, have %s", dir, dirType, ext)
 		}
-	rawTd, err = io.ReadAll(r)
-	if err != nil {
-		return nil, err
+		next += 1
+		eras = append(eras, entry.Name())
 	}
-	td := new(big.Int).SetBytes(reverseOrder(rawTd))
-	return td.Sub(td, header.Difficulty), nil
-}
-
-// Start returns the listed start block.
-func (e *Era) Start() uint64 {
-	return e.m.start
-}
-
-// Count returns the total number of blocks in the Era1.
-func (e *Era) Count() uint64 {
-	return e.m.count
-}
-
-// readOffset reads a specific block's offset from the block index. The value n
-// is the absolute block number desired.
-func (e *Era) readOffset(n uint64) (int64, error) {
-	var (
-		blockIndexRecordOffset = e.m.length - 24 - int64(e.m.count)*8 // skips start, count, and header
-		firstIndex             = blockIndexRecordOffset + 16          // first index after header / start-num
-		indexOffset            = int64(n-e.m.start) * 8               // desired index * size of indexes
-		offOffset              = firstIndex + indexOffset             // offset of block offset
-	)
-	e.mu.Lock()
-	defer e.mu.Unlock()
-	clear(e.buf[:])
-	if _, err := e.f.ReadAt(e.buf[:], offOffset); err != nil {
-		return 0, err
-	}
-	// Since the block offset is relative from the start of the block index record
-	// we need to add the record offset to it's offset to get the block's absolute
-	// offset.
-	return blockIndexRecordOffset + int64(binary.LittleEndian.Uint64(e.buf[:])), nil
-}
-
-// newSnappyReader returns a snappy.Reader for the e2store entry value at off.
-func newSnappyReader(e *e2store.Reader, expectedType uint16, off int64) (io.Reader, int64, error) {
-	r, n, err := e.ReaderAt(expectedType, off)
-	if err != nil {
-		return nil, 0, err
-	}
-	return snappy.NewReader(r), int64(n), err
-}
-
-// metadata wraps the metadata in the block index.
-type metadata struct {
-	start  uint64
-	count  uint64
-	length int64
-}
-
-// readMetadata reads the metadata stored in an Era1 file's block index.
-func readMetadata(f ReadAtSeekCloser) (m metadata, err error) {
-	// Determine length of reader.
-	if m.length, err = f.Seek(0, io.SeekEnd); err != nil {
-		return
-	}
-	b := make([]byte, 16)
-	// Read count. It's the last 8 bytes of the file.
-	if _, err = f.ReadAt(b[:8], m.length-8); err != nil {
-		return
-	}
-	m.count = binary.LittleEndian.Uint64(b)
-	// Read start. It's at the offset -sizeof(m.count) -
-	// count*sizeof(indexEntry) - sizeof(m.start)
-	if _, err = f.ReadAt(b[8:], m.length-16-int64(m.count*8)); err != nil {
-		return
-	}
-	m.start = binary.LittleEndian.Uint64(b[8:])
-	return
+	return eras, nil
 }

internal/era/eradl/eradl.go

@@ -86,8 +86,8 @@ func (l *Loader) DownloadAll(destDir string) error {
 
 // DownloadBlockRange fetches the era1 files for the given block range.
 func (l *Loader) DownloadBlockRange(start, end uint64, destDir string) error {
-	startEpoch := start / uint64(era.MaxEra1Size)
-	endEpoch := end / uint64(era.MaxEra1Size)
+	startEpoch := start / uint64(era.MaxSize)
+	endEpoch := end / uint64(era.MaxSize)
 	return l.DownloadEpochRange(startEpoch, endEpoch, destDir)
 }
 

internal/era/execdb/builder.go

@@ -0,0 +1,332 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package execdb
+
+// EraE file format specification.
+//
+// The format can be summarized with the following expression:
+//
+//	eraE := Version | CompressedHeader* | CompressedBody* | CompressedSlimReceipts* | TotalDifficulty* | other-entries* | Accumulator? | ComponentIndex
+//
+// Each basic element is its own e2store entry:
+//
+//	Version              = { type: 0x3265, data: nil }
+//	CompressedHeader     = { type: 0x03,   data: snappyFramed(rlp(header)) }
+//	CompressedBody       = { type: 0x04,   data: snappyFramed(rlp(body)) }
+//	CompressedSlimReceipts = { type: 0x08, data: snappyFramed(rlp([tx-type, post-state-or-status, cumulative-gas, logs])) }
+//	TotalDifficulty      = { type: 0x06,   data: uint256 (header.total_difficulty) }
+//	AccumulatorRoot      = { type: 0x07,   data: hash_tree_root(List(HeaderRecord, 8192)) }
+//	ComponentIndex       = { type: 0x3267, data: component-index }
+//
+// Notes:
+//   - TotalDifficulty is present for pre-merge and merge transition epochs.
+//     For pure post-merge epochs, TotalDifficulty is omitted entirely.
+//   - In merge transition epochs, post-merge blocks store the final total
+//     difficulty (the TD at which the merge occurred).
+//   - AccumulatorRoot is only written for pre-merge epochs.
+//   - HeaderRecord is defined in the Portal Network specification.
+//   - Proofs (type 0x09) are defined in the spec but not yet supported in this implementation.
+//
+// ComponentIndex stores relative offsets to each block's components:
+//
+//	component-index := starting-number | indexes | indexes | ... | component-count | count
+//	indexes := header-offset | body-offset | receipts-offset | td-offset?
+//
+// All values are little-endian uint64.
+//
+// Due to the accumulator size limit of 8192, the maximum number of blocks in an
+// EraE file is also 8192.
+
+import (
+	"bytes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/e2store"
+	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/golang/snappy"
+)
+
+// Builder is used to build an EraE e2store file. It collects block entries and
+// writes them to the underlying e2store.Writer.
+type Builder struct {
+	w *e2store.Writer
+
+	headers  [][]byte
+	hashes   []common.Hash // only pre-merge block hashes, for accumulator
+	bodies   [][]byte
+	receipts [][]byte
+	tds      []*big.Int
+
+	startNum    *uint64
+	ttd         *big.Int     // terminal total difficulty
+	last        common.Hash  // hash of last block added
+	accumulator *common.Hash // accumulator root, set by Finalize (nil for post-merge)
+
+	written uint64
+
+	buf    *bytes.Buffer
+	snappy *snappy.Writer
+}
+
+// NewBuilder returns a new Builder instance.
+func NewBuilder(w io.Writer) era.Builder {
+	return &Builder{
+		w: e2store.NewWriter(w),
+	}
+}
+
+// Add writes a block entry and its receipts into the e2store file.
+func (b *Builder) Add(block *types.Block, receipts types.Receipts, td *big.Int) error {
+	eh, err := rlp.EncodeToBytes(block.Header())
+	if err != nil {
+		return fmt.Errorf("encode header: %w", err)
+	}
+	eb, err := rlp.EncodeToBytes(block.Body())
+	if err != nil {
+		return fmt.Errorf("encode body: %w", err)
+	}
+
+	rs := make([]*types.SlimReceipt, len(receipts))
+	for i, receipt := range receipts {
+		rs[i] = (*types.SlimReceipt)(receipt)
+	}
+	er, err := rlp.EncodeToBytes(rs)
+	if err != nil {
+		return fmt.Errorf("encode receipts: %w", err)
+	}
+
+	return b.AddRLP(eh, eb, er, block.Number().Uint64(), block.Hash(), td, block.Difficulty())
+}
+
+// AddRLP takes the RLP encoded block components and writes them to the underlying e2store file.
+// The builder automatically handles transition epochs where both pre and post-merge blocks exist.
+func (b *Builder) AddRLP(header, body, receipts []byte, number uint64, blockHash common.Hash, td, difficulty *big.Int) error {
+	if len(b.headers) >= era.MaxSize {
+		return fmt.Errorf("exceeds max size %d", era.MaxSize)
+	}
+	// Set starting block number on first add.
+	if b.startNum == nil {
+		b.startNum = new(uint64)
+		*b.startNum = number
+	}
+
+	if difficulty == nil {
+		return fmt.Errorf("invalid block: difficulty is nil")
+	}
+	hasDifficulty := difficulty.Sign() > 0
+	// Expect td to be nil for post-merge blocks
+	// and non-nil for pre-merge blocks.
+	if hasDifficulty != (td != nil) {
+		return fmt.Errorf("TD and difficulty mismatch: expected both nil or both non-nil")
+	}
+	// After the merge, difficulty must be nil.
+	post := (b.tds == nil && len(b.headers) > 0) || b.ttd != nil
+	if post && hasDifficulty {
+		return fmt.Errorf("post-merge epoch: cannot accept total difficulty for block %d", number)
+	}
+
+	// If this marks the start of the transition, record final total
+	// difficulty value.
+	if b.ttd == nil && len(b.tds) > 0 && !hasDifficulty {
+		b.ttd = new(big.Int).Set(b.tds[len(b.tds)-1])
+	}
+
+	// Record block data.
+	b.headers = append(b.headers, header)
+	b.bodies = append(b.bodies, body)
+	b.receipts = append(b.receipts, receipts)
+	b.last = blockHash
+
+	// Conditionally write the total difficulty and block hashes.
+	//   - Pre-merge: store total difficulty and block hashes.
+	//   - Transition: only store total difficulty.
+	//   - Post-merge: store neither.
+	if hasDifficulty {
+		b.hashes = append(b.hashes, blockHash)
+		b.tds = append(b.tds, new(big.Int).Set(td))
+	} else if b.ttd != nil {
+		b.tds = append(b.tds, new(big.Int).Set(b.ttd))
+	} else {
+		// Post-merge: no TD or block hashes stored.
+	}
+
+	return nil
+}
+
+// Accumulator returns the accumulator root after Finalize has been called.
+// Returns nil for post-merge epochs where no accumulator exists.
+func (b *Builder) Accumulator() *common.Hash {
+	return b.accumulator
+}
+
+type offsets struct {
+	headers  []uint64
+	bodies   []uint64
+	receipts []uint64
+	tds      []uint64
+}
+
+// Finalize writes all collected block entries to the e2store file.
+// For pre-merge or transition epochs, the accumulator root is computed over
+// pre-merge blocks and written. For pure post-merge epochs, no accumulator
+// is written. Always returns the last block hash as the epoch identifier.
+func (b *Builder) Finalize() (common.Hash, error) {
+	if b.startNum == nil {
+		return common.Hash{}, errors.New("no blocks added, cannot finalize")
+	}
+	// Write version before writing any blocks.
+	if n, err := b.w.Write(era.TypeVersion, nil); err != nil {
+		return common.Hash{}, fmt.Errorf("write version entry: %w", err)
+	} else {
+		b.written += uint64(n)
+	}
+
+	// Convert TD values to byte-level LE representation.
+	var tds [][]byte
+	for _, td := range b.tds {
+		tds = append(tds, uint256LE(td))
+	}
+
+	// Create snappy writer.
+	b.buf = bytes.NewBuffer(nil)
+	b.snappy = snappy.NewBufferedWriter(b.buf)
+
+	var o offsets
+	for _, section := range []struct {
+		typ        uint16
+		data       [][]byte
+		compressed bool
+		offsets    *[]uint64
+	}{
+		{era.TypeCompressedHeader, b.headers, true, &o.headers},
+		{era.TypeCompressedBody, b.bodies, true, &o.bodies},
+		{era.TypeCompressedSlimReceipts, b.receipts, true, &o.receipts},
+		{era.TypeTotalDifficulty, tds, false, &o.tds},
+	} {
+		for _, data := range section.data {
+			*section.offsets = append(*section.offsets, b.written)
+			if section.compressed {
+				// Write snappy compressed data.
+				if err := b.snappyWrite(section.typ, data); err != nil {
+					return common.Hash{}, err
+				}
+			} else {
+				// Directly write uncompressed data.
+				n, err := b.w.Write(section.typ, data)
+				if err != nil {
+					return common.Hash{}, err
+				}
+				b.written += uint64(n)
+			}
+		}
+	}
+
+	// Compute and write accumulator root only for epochs that started pre-merge.
+	// The accumulator is computed over only the pre-merge blocks (b.hashes).
+	// Pure post-merge epochs have no accumulator.
+	if len(b.tds) > 0 {
+		accRoot, err := era.ComputeAccumulator(b.hashes, b.tds[:len(b.hashes)])
+		if err != nil {
+			return common.Hash{}, fmt.Errorf("compute accumulator: %w", err)
+		}
+		if n, err := b.w.Write(era.TypeAccumulator, accRoot[:]); err != nil {
+			return common.Hash{}, fmt.Errorf("write accumulator: %w", err)
+		} else {
+			b.written += uint64(n)
+		}
+		b.accumulator = &accRoot
+		if err := b.writeIndex(&o); err != nil {
+			return common.Hash{}, err
+		}
+		return b.last, nil
+	}
+
+	// Pure post-merge epoch: no accumulator.
+	if err := b.writeIndex(&o); err != nil {
+		return common.Hash{}, err
+	}
+	return b.last, nil
+}
+
+// uin256LE writes 32 byte big integers to little endian.
+func uint256LE(v *big.Int) []byte {
+	b := v.FillBytes(make([]byte, 32))
+	for i := 0; i < 16; i++ {
+		b[i], b[31-i] = b[31-i], b[i]
+	}
+	return b
+}
+
+// SnappyWrite compresses the input data using snappy and writes it to the e2store file.
+func (b *Builder) snappyWrite(typ uint16, in []byte) error {
+	b.buf.Reset()
+	b.snappy.Reset(b.buf)
+	if _, err := b.snappy.Write(in); err != nil {
+		return fmt.Errorf("error snappy encoding: %w", err)
+	}
+	if err := b.snappy.Flush(); err != nil {
+		return fmt.Errorf("error flushing snappy encoding: %w", err)
+	}
+	n, err := b.w.Write(typ, b.buf.Bytes())
+	b.written += uint64(n)
+	if err != nil {
+		return fmt.Errorf("error writing e2store entry: %w", err)
+	}
+	return nil
+}
+
+// writeIndex writes the component index to the file.
+func (b *Builder) writeIndex(o *offsets) error {
+	count := len(o.headers)
+
+	// Post-merge, we only index headers, bodies, and receipts. Pre-merge, we also
+	// need to index the total difficulties.
+	componentCount := 3
+	if len(o.tds) > 0 {
+		componentCount++
+	}
+
+	// Offsets are stored relative to the index position (negative, stored as uint64).
+	base := int64(b.written)
+	rel := func(abs uint64) uint64 { return uint64(int64(abs) - base) }
+
+	var buf bytes.Buffer
+	write := func(v uint64) { binary.Write(&buf, binary.LittleEndian, v) }
+
+	write(*b.startNum)
+	for i := range o.headers {
+		write(rel(o.headers[i]))
+		write(rel(o.bodies[i]))
+		write(rel(o.receipts[i]))
+		if len(o.tds) > 0 {
+			write(rel(o.tds[i]))
+		}
+	}
+	write(uint64(componentCount))
+	write(uint64(count))
+
+	n, err := b.w.Write(era.TypeComponentIndex, buf.Bytes())
+	b.written += uint64(n)
+	return err
+}

internal/era/execdb/era_test.go

@@ -0,0 +1,348 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package execdb
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"math/big"
+	"os"
+	"slices"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+func TestEraE(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name        string
+		start       uint64
+		preMerge    int
+		postMerge   int
+		accumulator bool // whether accumulator should exist
+	}{
+		{
+			name:        "pre-merge",
+			start:       0,
+			preMerge:    128,
+			postMerge:   0,
+			accumulator: true,
+		},
+		{
+			name:        "post-merge",
+			start:       0,
+			preMerge:    0,
+			postMerge:   64,
+			accumulator: false,
+		},
+		{
+			name:        "transition",
+			start:       0,
+			preMerge:    32,
+			postMerge:   32,
+			accumulator: true,
+		},
+		{
+			name:        "non-zero-start",
+			start:       8192,
+			preMerge:    64,
+			postMerge:   0,
+			accumulator: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			f, err := os.CreateTemp(t.TempDir(), "erae-test")
+			if err != nil {
+				t.Fatalf("error creating temp file: %v", err)
+			}
+			defer f.Close()
+
+			// Build test data.
+			type blockData struct {
+				header, body, receipts []byte
+				hash                   common.Hash
+				td                     *big.Int
+				difficulty             *big.Int
+			}
+			var (
+				builder     = NewBuilder(f)
+				blocks      []blockData
+				totalBlocks = tt.preMerge + tt.postMerge
+				finalTD     = big.NewInt(int64(tt.preMerge))
+			)
+
+			// Add pre-merge blocks.
+			for i := 0; i < tt.preMerge; i++ {
+				num := tt.start + uint64(i)
+				blk := blockData{
+					header:     mustEncode(&types.Header{Number: big.NewInt(int64(num)), Difficulty: big.NewInt(1)}),
+					body:       mustEncode(&types.Body{Transactions: []*types.Transaction{types.NewTransaction(0, common.Address{byte(i)}, nil, 0, nil, nil)}}),
+					receipts:   mustEncode([]types.SlimReceipt{{CumulativeGasUsed: uint64(i)}}),
+					hash:       common.Hash{byte(i)},
+					td:         big.NewInt(int64(i + 1)),
+					difficulty: big.NewInt(1),
+				}
+				blocks = append(blocks, blk)
+				if err := builder.AddRLP(blk.header, blk.body, blk.receipts, num, blk.hash, blk.td, blk.difficulty); err != nil {
+					t.Fatalf("error adding pre-merge block %d: %v", i, err)
+				}
+			}
+
+			// Add post-merge blocks.
+			for i := 0; i < tt.postMerge; i++ {
+				idx := tt.preMerge + i
+				num := tt.start + uint64(idx)
+				blk := blockData{
+					header:     mustEncode(&types.Header{Number: big.NewInt(int64(num)), Difficulty: big.NewInt(0)}),
+					body:       mustEncode(&types.Body{}),
+					receipts:   mustEncode([]types.SlimReceipt{}),
+					hash:       common.Hash{byte(idx)},
+					difficulty: big.NewInt(0),
+				}
+				blocks = append(blocks, blk)
+				if err := builder.AddRLP(blk.header, blk.body, blk.receipts, num, blk.hash, nil, big.NewInt(0)); err != nil {
+					t.Fatalf("error adding post-merge block %d: %v", idx, err)
+				}
+			}
+
+			// Finalize and check return values.
+			epochID, err := builder.Finalize()
+			if err != nil {
+				t.Fatalf("error finalizing: %v", err)
+			}
+
+			// Verify epoch ID is always the last block hash.
+			expectedLastHash := blocks[len(blocks)-1].hash
+			if epochID != expectedLastHash {
+				t.Fatalf("wrong epoch ID: want %s, got %s", expectedLastHash.Hex(), epochID.Hex())
+			}
+
+			// Verify accumulator presence.
+			if tt.accumulator {
+				if builder.Accumulator() == nil {
+					t.Fatal("expected non-nil accumulator")
+				}
+			} else {
+				if builder.Accumulator() != nil {
+					t.Fatalf("expected nil accumulator, got %s", builder.Accumulator().Hex())
+				}
+			}
+
+			// Open and verify the era file.
+			e, err := Open(f.Name())
+			if err != nil {
+				t.Fatalf("failed to open era: %v", err)
+			}
+			defer e.Close()
+
+			// Verify metadata.
+			if e.Start() != tt.start {
+				t.Fatalf("wrong start block: want %d, got %d", tt.start, e.Start())
+			}
+			if e.Count() != uint64(totalBlocks) {
+				t.Fatalf("wrong block count: want %d, got %d", totalBlocks, e.Count())
+			}
+
+			// Verify accumulator in file.
+			if tt.accumulator {
+				accRoot, err := e.Accumulator()
+				if err != nil {
+					t.Fatalf("error getting accumulator: %v", err)
+				}
+				if accRoot != *builder.Accumulator() {
+					t.Fatalf("accumulator mismatch: builder has %s, file contains %s",
+						builder.Accumulator().Hex(), accRoot.Hex())
+				}
+			} else {
+				if _, err := e.Accumulator(); err == nil {
+					t.Fatal("expected error when reading accumulator from post-merge epoch")
+				}
+			}
+
+			// Verify blocks via raw iterator.
+			it, err := NewRawIterator(e)
+			if err != nil {
+				t.Fatalf("failed to make iterator: %v", err)
+			}
+			for i := 0; i < totalBlocks; i++ {
+				if !it.Next() {
+					t.Fatalf("expected more entries at %d", i)
+				}
+				if it.Error() != nil {
+					t.Fatalf("unexpected error: %v", it.Error())
+				}
+
+				// Check header.
+				rawHeader, err := io.ReadAll(it.Header)
+				if err != nil {
+					t.Fatalf("error reading header: %v", err)
+				}
+				if !bytes.Equal(rawHeader, blocks[i].header) {
+					t.Fatalf("mismatched header at %d", i)
+				}
+
+				// Check body.
+				rawBody, err := io.ReadAll(it.Body)
+				if err != nil {
+					t.Fatalf("error reading body: %v", err)
+				}
+				if !bytes.Equal(rawBody, blocks[i].body) {
+					t.Fatalf("mismatched body at %d", i)
+				}
+
+				// Check receipts.
+				rawReceipts, err := io.ReadAll(it.Receipts)
+				if err != nil {
+					t.Fatalf("error reading receipts: %v", err)
+				}
+				if !bytes.Equal(rawReceipts, blocks[i].receipts) {
+					t.Fatalf("mismatched receipts at %d", i)
+				}
+
+				// Check TD (only for epochs that have TD stored).
+				if tt.preMerge > 0 && it.TotalDifficulty != nil {
+					rawTd, err := io.ReadAll(it.TotalDifficulty)
+					if err != nil {
+						t.Fatalf("error reading TD: %v", err)
+					}
+					slices.Reverse(rawTd)
+					td := new(big.Int).SetBytes(rawTd)
+					var expectedTD *big.Int
+					if i < tt.preMerge {
+						expectedTD = blocks[i].td
+					} else {
+						// Post-merge blocks in transition epoch use final TD.
+						expectedTD = finalTD
+					}
+					if td.Cmp(expectedTD) != 0 {
+						t.Fatalf("mismatched TD at %d: want %s, got %s", i, expectedTD, td)
+					}
+				}
+			}
+
+			// Verify random access.
+			for _, blockNum := range []uint64{tt.start, tt.start + uint64(totalBlocks) - 1} {
+				blk, err := e.GetBlockByNumber(blockNum)
+				if err != nil {
+					t.Fatalf("error getting block %d: %v", blockNum, err)
+				}
+				if blk.Number().Uint64() != blockNum {
+					t.Fatalf("wrong block number: want %d, got %d", blockNum, blk.Number().Uint64())
+				}
+			}
+
+			// Verify out-of-range access fails.
+			if _, err := e.GetBlockByNumber(tt.start + uint64(totalBlocks)); err == nil {
+				t.Fatal("expected error for out-of-range block")
+			}
+			if tt.start > 0 {
+				if _, err := e.GetBlockByNumber(tt.start - 1); err == nil {
+					t.Fatal("expected error for block before start")
+				}
+			}
+
+			// Verify high-level iterator.
+			hlIt, err := e.Iterator()
+			if err != nil {
+				t.Fatalf("failed to create iterator: %v", err)
+			}
+			count := 0
+			for hlIt.Next() {
+				blk, err := hlIt.Block()
+				if err != nil {
+					t.Fatalf("error getting block: %v", err)
+				}
+				if blk.Number().Uint64() != tt.start+uint64(count) {
+					t.Fatalf("wrong block number: want %d, got %d", tt.start+uint64(count), blk.Number().Uint64())
+				}
+				count++
+			}
+			if hlIt.Error() != nil {
+				t.Fatalf("iterator error: %v", hlIt.Error())
+			}
+			if count != totalBlocks {
+				t.Fatalf("wrong iteration count: want %d, got %d", totalBlocks, count)
+			}
+		})
+	}
+}
+
+// TestInitialTD tests the InitialTD calculation separately since it requires
+// specific TD/difficulty values.
+func TestInitialTD(t *testing.T) {
+	t.Parallel()
+
+	f, err := os.CreateTemp(t.TempDir(), "erae-initial-td-test")
+	if err != nil {
+		t.Fatalf("error creating temp file: %v", err)
+	}
+	defer f.Close()
+
+	builder := NewBuilder(f)
+
+	// First block: difficulty=5, TD=10, so initial TD = 10-5 = 5.
+	header := mustEncode(&types.Header{Number: big.NewInt(0), Difficulty: big.NewInt(5)})
+	body := mustEncode(&types.Body{})
+	receipts := mustEncode([]types.SlimReceipt{})
+
+	if err := builder.AddRLP(header, body, receipts, 0, common.Hash{0}, big.NewInt(10), big.NewInt(5)); err != nil {
+		t.Fatalf("error adding block: %v", err)
+	}
+
+	// Second block: difficulty=3, TD=13.
+	header2 := mustEncode(&types.Header{Number: big.NewInt(1), Difficulty: big.NewInt(3)})
+	if err := builder.AddRLP(header2, body, receipts, 1, common.Hash{1}, big.NewInt(13), big.NewInt(3)); err != nil {
+		t.Fatalf("error adding block: %v", err)
+	}
+
+	if _, err := builder.Finalize(); err != nil {
+		t.Fatalf("error finalizing: %v", err)
+	}
+
+	e, err := Open(f.Name())
+	if err != nil {
+		t.Fatalf("failed to open era: %v", err)
+	}
+	defer e.Close()
+
+	initialTD, err := e.InitialTD()
+	if err != nil {
+		t.Fatalf("error getting initial TD: %v", err)
+	}
+
+	// Initial TD should be TD[0] - Difficulty[0] = 10 - 5 = 5.
+	if initialTD.Cmp(big.NewInt(5)) != 0 {
+		t.Fatalf("wrong initial TD: want 5, got %s", initialTD)
+	}
+}
+
+func mustEncode(obj any) []byte {
+	b, err := rlp.EncodeToBytes(obj)
+	if err != nil {
+		panic(fmt.Sprintf("failed to encode obj: %v", err))
+	}
+	return b
+}

internal/era/execdb/iterator.go

@@ -0,0 +1,240 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package execdb
+
+import (
+	"errors"
+	"io"
+	"math/big"
+	"slices"
+
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/e2store"
+	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/klauspost/compress/snappy"
+)
+
+type Iterator struct {
+	inner *RawIterator
+	block *types.Block // cache for decoded block
+}
+
+// NewIterator returns a header/body/receipt iterator over the archive.
+// Call Next immediately to position on the first block.
+func NewIterator(e era.Era) (era.Iterator, error) {
+	inner, err := NewRawIterator(e.(*Era))
+	if err != nil {
+		return nil, err
+	}
+	return &Iterator{inner: inner}, nil
+}
+
+// Next advances to the next block entry.
+func (it *Iterator) Next() bool {
+	it.block = nil
+	return it.inner.Next()
+}
+
+// Number is the number of the block currently loaded.
+func (it *Iterator) Number() uint64 { return it.inner.next - 1 }
+
+// Error returns any iteration error (EOF is reported as nil, identical
+// to the Era‑1 iterator behaviour).
+func (it *Iterator) Error() error { return it.inner.Error() }
+
+// Block decodes the current header+body into a *types.Block.
+func (it *Iterator) Block() (*types.Block, error) {
+	if it.block != nil {
+		return it.block, nil
+	}
+	if it.inner.Header == nil || it.inner.Body == nil {
+		return nil, errors.New("header and body must be non‑nil")
+	}
+	var (
+		h types.Header
+		b types.Body
+	)
+	if err := rlp.Decode(it.inner.Header, &h); err != nil {
+		return nil, err
+	}
+	if err := rlp.Decode(it.inner.Body, &b); err != nil {
+		return nil, err
+	}
+	it.block = types.NewBlockWithHeader(&h).WithBody(b)
+	return it.block, nil
+}
+
+// Receipts decodes receipts for the current block.
+func (it *Iterator) Receipts() (types.Receipts, error) {
+	block, err := it.Block()
+	if err != nil {
+		return nil, err
+	}
+	if it.inner.Receipts == nil {
+		return nil, errors.New("receipts must be non‑nil")
+	}
+	var rs []*types.SlimReceipt
+	if err := rlp.Decode(it.inner.Receipts, &rs); err != nil {
+		return nil, err
+	}
+	if len(rs) != len(block.Transactions()) {
+		return nil, errors.New("number of txs does not match receipts")
+	}
+	receipts := make([]*types.Receipt, len(rs))
+	for i, receipt := range rs {
+		receipts[i] = (*types.Receipt)(receipt)
+		receipts[i].Bloom = types.CreateBloom(receipts[i])
+	}
+	return receipts, nil
+}
+
+// BlockAndReceipts is a convenience wrapper.
+func (it *Iterator) BlockAndReceipts() (*types.Block, types.Receipts, error) {
+	b, err := it.Block()
+	if err != nil {
+		return nil, nil, err
+	}
+	r, err := it.Receipts()
+	if err != nil {
+		return nil, nil, err
+	}
+	return b, r, nil
+}
+
+// TotalDifficulty returns the TD at the current position (if present).
+func (it *Iterator) TotalDifficulty() (*big.Int, error) {
+	if it.inner.TotalDifficulty == nil {
+		return nil, errors.New("total‑difficulty stream is nil")
+	}
+	tdBytes, err := io.ReadAll(it.inner.TotalDifficulty)
+	if err != nil {
+		return nil, err
+	}
+	slices.Reverse(tdBytes)
+	return new(big.Int).SetBytes(tdBytes), nil
+}
+
+// -----------------------------------------------------------------------------
+// Low‑level iterator (raw TLV/offset handling, no decoding)
+// -----------------------------------------------------------------------------
+
+type RawIterator struct {
+	e    *Era
+	next uint64 // next block to pull
+	err  error
+
+	Header          io.Reader
+	Body            io.Reader
+	Receipts        io.Reader
+	TotalDifficulty io.Reader // nil when archive omits TD
+}
+
+// NewRawIterator creates an iterator positioned *before* the first block.
+func NewRawIterator(e *Era) (*RawIterator, error) {
+	return &RawIterator{e: e, next: e.m.start}, nil
+}
+
+// Next loads the next block’s components; returns false on EOF or error.
+func (it *RawIterator) Next() bool {
+	it.err = nil // clear previous error
+
+	if it.next >= it.e.m.start+it.e.m.count {
+		it.clear()
+		return false
+	}
+
+	headerOffset, err := it.e.headerOff(it.next)
+	if err != nil {
+		it.setErr(err)
+		return false
+	}
+	it.Header, _, err = newSnappyReader(it.e.s, era.TypeCompressedHeader, headerOffset)
+	if err != nil {
+		it.setErr(err)
+		return false
+	}
+
+	bodyOffset, err := it.e.bodyOff(it.next)
+	if err != nil {
+		it.setErr(err)
+		return false
+	}
+	it.Body, _, err = newSnappyReader(it.e.s, era.TypeCompressedBody, bodyOffset)
+	if err != nil {
+		it.setErr(err)
+		return false
+	}
+
+	receiptsOffset, err := it.e.receiptOff(it.next)
+	if err != nil {
+		it.setErr(err)
+		return false
+	}
+	it.Receipts, _, err = newSnappyReader(it.e.s, era.TypeCompressedSlimReceipts, receiptsOffset)
+	if err != nil {
+		it.setErr(err)
+		return false
+	}
+
+	// Check if TD component is present in this file (pre-merge or merge-transition epoch).
+	if int(td) < int(it.e.m.components) {
+		tdOffset, err := it.e.tdOff(it.next)
+		if err != nil {
+			it.setErr(err)
+			return false
+		}
+		it.TotalDifficulty, _, err = it.e.s.ReaderAt(era.TypeTotalDifficulty, tdOffset)
+		if err != nil {
+			it.setErr(err)
+			return false
+		}
+	} else {
+		it.TotalDifficulty = nil
+	}
+
+	it.next++
+	return true
+}
+
+func (it *RawIterator) Number() uint64 { return it.next - 1 }
+
+func (it *RawIterator) Error() error {
+	if it.err == io.EOF {
+		return nil
+	}
+	return it.err
+}
+
+func (it *RawIterator) setErr(err error) {
+	it.err = err
+	it.clear()
+}
+
+func (it *RawIterator) clear() {
+	it.Header, it.Body, it.Receipts, it.TotalDifficulty = nil, nil, nil, nil
+}
+
+// newSnappyReader behaves like era.newSnappyReader: returns a snappy.Reader
+// plus the length of the underlying TLV payload so callers can advance offsets.
+func newSnappyReader(r *e2store.Reader, typ uint16, off int64) (io.Reader, int64, error) {
+	raw, n, err := r.ReaderAt(typ, off)
+	if err != nil {
+		return nil, 0, err
+	}
+	return snappy.NewReader(raw), int64(n), nil
+}

internal/era/execdb/reader.go

@@ -0,0 +1,296 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package execdb
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"math/big"
+	"os"
+	"slices"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/e2store"
+	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/klauspost/compress/snappy"
+)
+
+// Era object represents an era file that contains blocks and their components.
+type Era struct {
+	f era.ReadAtSeekCloser
+	s *e2store.Reader
+	m metadata // metadata for the Era file
+}
+
+// Filename returns a recognizable filename for an EraE file.
+// The filename uses the last block hash to uniquely identify the epoch's content.
+func Filename(network string, epoch int, lastBlockHash common.Hash) string {
+	return fmt.Sprintf("%s-%05d-%s.erae", network, epoch, lastBlockHash.Hex()[2:10])
+}
+
+// Open accesses the era file.
+func Open(path string) (*Era, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	e := &Era{f: f, s: e2store.NewReader(f)}
+	if err := e.loadIndex(); err != nil {
+		f.Close()
+		return nil, err
+	}
+	return e, nil
+}
+
+// Close closes the era file safely.
+func (e *Era) Close() error {
+	if e.f == nil {
+		return nil
+	}
+	err := e.f.Close()
+	e.f = nil
+	return err
+}
+
+// From returns an Era backed by f.
+func From(f era.ReadAtSeekCloser) (era.Era, error) {
+	e := &Era{f: f, s: e2store.NewReader(f)}
+	if err := e.loadIndex(); err != nil {
+		f.Close()
+		return nil, err
+	}
+	return e, nil
+}
+
+// Start retrieves the starting block number.
+func (e *Era) Start() uint64 {
+	return e.m.start
+}
+
+// Count retrieves the count of blocks present.
+func (e *Era) Count() uint64 {
+	return e.m.count
+}
+
+// Iterator returns an iterator over the era file.
+func (e *Era) Iterator() (era.Iterator, error) {
+	return NewIterator(e)
+}
+
+// GetBlockByNumber retrieves the block if present within the era file.
+func (e *Era) GetBlockByNumber(blockNum uint64) (*types.Block, error) {
+	h, err := e.GetHeader(blockNum)
+	if err != nil {
+		return nil, err
+	}
+	b, err := e.GetBody(blockNum)
+	if err != nil {
+		return nil, err
+	}
+	return types.NewBlockWithHeader(h).WithBody(*b), nil
+}
+
+// GetHeader retrieves the header from the era file through the cached offset table.
+func (e *Era) GetHeader(num uint64) (*types.Header, error) {
+	off, err := e.headerOff(num)
+	if err != nil {
+		return nil, err
+	}
+
+	r, _, err := e.s.ReaderAt(era.TypeCompressedHeader, off)
+	if err != nil {
+		return nil, err
+	}
+
+	r = snappy.NewReader(r)
+	var h types.Header
+	return &h, rlp.Decode(r, &h)
+}
+
+// GetBody retrieves the body from the era file through cached offset table.
+func (e *Era) GetBody(num uint64) (*types.Body, error) {
+	off, err := e.bodyOff(num)
+	if err != nil {
+		return nil, err
+	}
+
+	r, _, err := e.s.ReaderAt(era.TypeCompressedBody, off)
+	if err != nil {
+		return nil, err
+	}
+
+	r = snappy.NewReader(r)
+	var b types.Body
+	return &b, rlp.Decode(r, &b)
+}
+
+// GetTD retrieves the td from the era file through cached offset table.
+func (e *Era) GetTD(blockNum uint64) (*big.Int, error) {
+	off, err := e.tdOff(blockNum)
+	if err != nil {
+		return nil, err
+	}
+	r, _, err := e.s.ReaderAt(era.TypeTotalDifficulty, off)
+	if err != nil {
+		return nil, err
+	}
+	buf, _ := io.ReadAll(r)
+	slices.Reverse(buf)
+	td := new(big.Int).SetBytes(buf)
+	return td, nil
+}
+
+// GetRawBodyByNumber returns the RLP-encoded body for the given block number.
+func (e *Era) GetRawBodyByNumber(blockNum uint64) ([]byte, error) {
+	off, err := e.bodyOff(blockNum)
+	if err != nil {
+		return nil, err
+	}
+	r, _, err := e.s.ReaderAt(era.TypeCompressedBody, off)
+	if err != nil {
+		return nil, err
+	}
+	r = snappy.NewReader(r)
+	return io.ReadAll(r)
+}
+
+// GetRawReceiptsByNumber returns the RLP-encoded receipts for the given block number.
+func (e *Era) GetRawReceiptsByNumber(blockNum uint64) ([]byte, error) {
+	off, err := e.receiptOff(blockNum)
+	if err != nil {
+		return nil, err
+	}
+	r, _, err := e.s.ReaderAt(era.TypeCompressedSlimReceipts, off)
+	if err != nil {
+		return nil, err
+	}
+	r = snappy.NewReader(r)
+	return io.ReadAll(r)
+}
+
+// InitialTD returns initial total difficulty before the difficulty of the
+// first block of the Era is applied. Returns an error if TD is not available
+// (e.g., post-merge epoch).
+func (e *Era) InitialTD() (*big.Int, error) {
+	// Check if TD component exists.
+	if int(td) >= int(e.m.components) {
+		return nil, fmt.Errorf("total difficulty not available in this epoch")
+	}
+
+	// Get first header to read its difficulty.
+	header, err := e.GetHeader(e.m.start)
+	if err != nil {
+		return nil, fmt.Errorf("read first header: %w", err)
+	}
+
+	// Get TD after first block using the index.
+	firstTD, err := e.GetTD(e.m.start)
+	if err != nil {
+		return nil, fmt.Errorf("read first TD: %w", err)
+	}
+
+	// Initial TD = TD[0] - Difficulty[0]
+	return new(big.Int).Sub(firstTD, header.Difficulty), nil
+}
+
+// Accumulator reads the accumulator entry in the EraE file if it exists.
+// Note that one premerge erae files will contain an accumulator entry.
+func (e *Era) Accumulator() (common.Hash, error) {
+	entry, err := e.s.Find(era.TypeAccumulator)
+	if err != nil {
+		return common.Hash{}, err
+	}
+	return common.BytesToHash(entry.Value), nil
+}
+
+// loadIndex loads in the index table containing all offsets and caches it.
+func (e *Era) loadIndex() error {
+	var err error
+	e.m.length, err = e.f.Seek(0, io.SeekEnd)
+	if err != nil {
+		return err
+	}
+
+	b := make([]byte, 16)
+	if _, err = e.f.ReadAt(b, e.m.length-16); err != nil {
+		return err
+	}
+	e.m.components = binary.LittleEndian.Uint64(b[0:8])
+	e.m.count = binary.LittleEndian.Uint64(b[8:16])
+
+	payloadlen := 8 + 8*e.m.count*e.m.components + 16 // 8 for start block, 8 per property per block, 16 for the number of properties and the number of blocks
+	tlvstart := e.m.length - int64(payloadlen) - 8
+	_, err = e.f.ReadAt(b[:8], tlvstart+8)
+	if err != nil {
+		return err
+	}
+
+	e.m.start = binary.LittleEndian.Uint64(b[:8])
+	return nil
+}
+
+// headerOff, bodyOff, receiptOff, and tdOff return the offsets of the respective components for a given block number.
+func (e *Era) headerOff(num uint64) (int64, error)  { return e.indexOffset(num, header) }
+func (e *Era) bodyOff(num uint64) (int64, error)    { return e.indexOffset(num, body) }
+func (e *Era) receiptOff(num uint64) (int64, error) { return e.indexOffset(num, receipts) }
+func (e *Era) tdOff(num uint64) (int64, error)      { return e.indexOffset(num, td) }
+
+// indexOffset calculates offset to a certain component for a block number within a file.
+func (e *Era) indexOffset(n uint64, component componentType) (int64, error) {
+	if n < e.m.start || n >= e.m.start+e.m.count {
+		return 0, fmt.Errorf("block %d out of range [%d,%d)", n, e.m.start, e.m.start+e.m.count)
+	}
+	if int(component) >= int(e.m.components) {
+		return 0, fmt.Errorf("component %d not present", component)
+	}
+
+	payloadlen := 8 + 8*e.m.count*e.m.components + 16 // 8 for start block, 8 per property per block, 16 for the number of properties and the number of blocks
+	indstart := e.m.length - int64(payloadlen) - 8
+
+	rec := (n-e.m.start)*e.m.components + uint64(component)
+	pos := indstart + 8 + 8 + int64(rec*8)
+
+	var buf [8]byte
+	if _, err := e.f.ReadAt(buf[:], pos); err != nil {
+		return 0, err
+	}
+	rel := binary.LittleEndian.Uint64(buf[:])
+	return int64(rel) + indstart, nil
+}
+
+// metadata contains the information about the era file that is written into the file.
+type metadata struct {
+	start      uint64 // start block number
+	count      uint64 // number of blocks in the era
+	components uint64 // number of properties
+	length     int64  // length of the file in bytes
+}
+
+// componentType represents the integer form of a specific type that can be present in the era file.
+type componentType int
+
+// header, body, receipts, td, and proof are the different types of components that can be present in the era file.
+const (
+	header componentType = iota
+	body
+	receipts
+	td
+	proof
+)

internal/era/onedb/builder.go

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
-package era
+package onedb
 
 import (
 	"bytes"
@@ -26,6 +26,7 @@ import (
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/era"
 	"github.com/ethereum/go-ethereum/internal/era/e2store"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/golang/snappy"
@@ -78,6 +79,8 @@ type Builder struct {
 	indexes     []uint64
 	hashes      []common.Hash
 	tds         []*big.Int
+	accumulator *common.Hash // accumulator root, set by Finalize
+
 	written int
 
 	buf    *bytes.Buffer
@@ -85,7 +88,7 @@ type Builder struct {
 }
 
 // NewBuilder returns a new Builder instance.
-func NewBuilder(w io.Writer) *Builder {
+func NewBuilder(w io.Writer) era.Builder {
 	buf := bytes.NewBuffer(nil)
 	return &Builder{
 		w:      e2store.NewWriter(w),
@@ -117,7 +120,7 @@ func (b *Builder) Add(block *types.Block, receipts types.Receipts, td *big.Int)
 func (b *Builder) AddRLP(header, body, receipts []byte, number uint64, hash common.Hash, td, difficulty *big.Int) error {
 	// Write Era1 version entry before first block.
 	if b.startNum == nil {
-		n, err := b.w.Write(TypeVersion, nil)
+		n, err := b.w.Write(era.TypeVersion, nil)
 		if err != nil {
 			return err
 		}
@@ -126,8 +129,8 @@ func (b *Builder) AddRLP(header, body, receipts []byte, number uint64, hash comm
 		b.startTd = new(big.Int).Sub(td, difficulty)
 		b.written += n
 	}
-	if len(b.indexes) >= MaxEra1Size {
-		return fmt.Errorf("exceeds maximum batch size of %d", MaxEra1Size)
+	if len(b.indexes) >= era.MaxSize {
+		return fmt.Errorf("exceeds maximum batch size of %d", era.MaxSize)
 	}
 
 	b.indexes = append(b.indexes, uint64(b.written))
@@ -135,19 +138,19 @@ func (b *Builder) AddRLP(header, body, receipts []byte, number uint64, hash comm
 	b.tds = append(b.tds, td)
 
 	// Write block data.
-	if err := b.snappyWrite(TypeCompressedHeader, header); err != nil {
+	if err := b.snappyWrite(era.TypeCompressedHeader, header); err != nil {
 		return err
 	}
-	if err := b.snappyWrite(TypeCompressedBody, body); err != nil {
+	if err := b.snappyWrite(era.TypeCompressedBody, body); err != nil {
 		return err
 	}
-	if err := b.snappyWrite(TypeCompressedReceipts, receipts); err != nil {
+	if err := b.snappyWrite(era.TypeCompressedReceipts, receipts); err != nil {
 		return err
 	}
 
 	// Also write total difficulty, but don't snappy encode.
-	btd := bigToBytes32(td)
-	n, err := b.w.Write(TypeTotalDifficulty, btd[:])
+	btd := era.BigToBytes32(td)
+	n, err := b.w.Write(era.TypeTotalDifficulty, btd[:])
 	b.written += n
 	if err != nil {
 		return err
@@ -157,21 +160,24 @@ func (b *Builder) AddRLP(header, body, receipts []byte, number uint64, hash comm
 }
 
 // Finalize computes the accumulator and block index values, then writes the
-// corresponding e2store entries.
+// corresponding e2store entries. Era1 always has an accumulator, so this
+// always returns a valid hash.
 func (b *Builder) Finalize() (common.Hash, error) {
 	if b.startNum == nil {
 		return common.Hash{}, errors.New("finalize called on empty builder")
 	}
 	// Compute accumulator root and write entry.
-	root, err := ComputeAccumulator(b.hashes, b.tds)
+	root, err := era.ComputeAccumulator(b.hashes, b.tds)
 	if err != nil {
 		return common.Hash{}, fmt.Errorf("error calculating accumulator root: %w", err)
 	}
-	n, err := b.w.Write(TypeAccumulator, root[:])
+	n, err := b.w.Write(era.TypeAccumulator, root[:])
 	b.written += n
 	if err != nil {
 		return common.Hash{}, fmt.Errorf("error writing accumulator: %w", err)
 	}
+	b.accumulator = &root
+
 	// Get beginning of index entry to calculate block relative offset.
 	base := int64(b.written)
 
@@ -196,13 +202,19 @@ func (b *Builder) Finalize() (common.Hash, error) {
 	binary.LittleEndian.PutUint64(index[8+count*8:], uint64(count))
 
 	// Finally, write the block index entry.
-	if _, err := b.w.Write(TypeBlockIndex, index); err != nil {
+	if _, err := b.w.Write(era.TypeBlockIndex, index); err != nil {
 		return common.Hash{}, fmt.Errorf("unable to write block index: %w", err)
 	}
 
 	return root, nil
 }
 
+// Accumulator returns the accumulator root after Finalize has been called.
+// For Era1, this always returns a non-nil value since all blocks are pre-merge.
+func (b *Builder) Accumulator() *common.Hash {
+	return b.accumulator
+}
+
 // snappyWrite is a small helper to take care snappy encoding and writing an e2store entry.
 func (b *Builder) snappyWrite(typ uint16, in []byte) error {
 	var (

internal/era/onedb/builder_test.go

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
-package era
+package onedb
 
 import (
 	"bytes"
@@ -22,6 +22,7 @@ import (
 	"io"
 	"math/big"
 	"os"
+	"slices"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -82,7 +83,11 @@ func TestEra1Builder(t *testing.T) {
 		t.Fatalf("failed to open era: %v", err)
 	}
 	defer e.Close()
-	it, err := NewRawIterator(e)
+	eraPtr, ok := e.(*Era)
+	if !ok {
+		t.Fatalf("failed to assert *Era type")
+	}
+	it, err := NewRawIterator(eraPtr)
 	if err != nil {
 		t.Fatalf("failed to make iterator: %s", err)
 	}
@@ -119,7 +124,7 @@ func TestEra1Builder(t *testing.T) {
 		if !bytes.Equal(rawReceipts, chain.receipts[i]) {
 			t.Fatalf("mismatched receipts: want %s, got %s", chain.receipts[i], rawReceipts)
 		}
-		receipts, err := getReceiptsByNumber(e, i)
+		receipts, err := getReceiptsByNumber(eraPtr, i)
 		if err != nil {
 			t.Fatalf("error reading receipts: %v", err)
 		}
@@ -136,7 +141,8 @@ func TestEra1Builder(t *testing.T) {
 		if err != nil {
 			t.Fatalf("error reading td: %v", err)
 		}
-		td := new(big.Int).SetBytes(reverseOrder(rawTd))
+		slices.Reverse(rawTd)
+		td := new(big.Int).SetBytes(rawTd)
 		if td.Cmp(chain.tds[i]) != 0 {
 			t.Fatalf("mismatched tds: want %s, got %s", chain.tds[i], td)
 		}

internal/era/onedb/iterator.go

@@ -14,14 +14,16 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
-package era
+package onedb
 
 import (
 	"errors"
 	"io"
 	"math/big"
+	"slices"
 
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/era"
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
@@ -32,8 +34,8 @@ type Iterator struct {
 
 // NewIterator returns a new Iterator instance. Next must be immediately
 // called on new iterators to load the first item.
-func NewIterator(e *Era) (*Iterator, error) {
-	inner, err := NewRawIterator(e)
+func NewIterator(e era.Era) (era.Iterator, error) {
+	inner, err := NewRawIterator(e.(*Era))
 	if err != nil {
 		return nil, err
 	}
@@ -107,7 +109,8 @@ func (it *Iterator) TotalDifficulty() (*big.Int, error) {
 	if err != nil {
 		return nil, err
 	}
-	return new(big.Int).SetBytes(reverseOrder(td)), nil
+	slices.Reverse(td)
+	return new(big.Int).SetBytes(td), nil
 }
 
 // RawIterator reads an RLP-encode Era1 entries.
@@ -151,22 +154,22 @@ func (it *RawIterator) Next() bool {
 		return false
 	}
 	var n int64
-	if it.Header, n, it.err = newSnappyReader(it.e.s, TypeCompressedHeader, off); it.err != nil {
+	if it.Header, n, it.err = newSnappyReader(it.e.s, era.TypeCompressedHeader, off); it.err != nil {
 		it.clear()
 		return true
 	}
 	off += n
-	if it.Body, n, it.err = newSnappyReader(it.e.s, TypeCompressedBody, off); it.err != nil {
+	if it.Body, n, it.err = newSnappyReader(it.e.s, era.TypeCompressedBody, off); it.err != nil {
 		it.clear()
 		return true
 	}
 	off += n
-	if it.Receipts, n, it.err = newSnappyReader(it.e.s, TypeCompressedReceipts, off); it.err != nil {
+	if it.Receipts, n, it.err = newSnappyReader(it.e.s, era.TypeCompressedReceipts, off); it.err != nil {
 		it.clear()
 		return true
 	}
 	off += n
-	if it.TotalDifficulty, _, it.err = it.e.s.ReaderAt(TypeTotalDifficulty, off); it.err != nil {
+	if it.TotalDifficulty, _, it.err = it.e.s.ReaderAt(era.TypeTotalDifficulty, off); it.err != nil {
 		it.clear()
 		return true
 	}

internal/era/onedb/reader.go

@@ -0,0 +1,279 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package onedb
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+	"math/big"
+	"os"
+	"slices"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/internal/era"
+	"github.com/ethereum/go-ethereum/internal/era/e2store"
+	"github.com/ethereum/go-ethereum/rlp"
+	"github.com/golang/snappy"
+)
+
+// Filename returns a recognizable Era1-formatted file name for the specified
+// epoch and network.
+func Filename(network string, epoch int, root common.Hash) string {
+	return fmt.Sprintf("%s-%05d-%s.era1", network, epoch, root.Hex()[2:10])
+}
+
+type ReadAtSeekCloser interface {
+	io.ReaderAt
+	io.Seeker
+	io.Closer
+}
+
+// Era reads and Era1 file.
+type Era struct {
+	f   ReadAtSeekCloser // backing era1 file
+	s   *e2store.Reader  // e2store reader over f
+	m   metadata         // start, count, length info
+	mu  *sync.Mutex      // lock for buf
+	buf [8]byte          // buffer reading entry offsets
+}
+
+// From returns an Era backed by f.
+func From(f era.ReadAtSeekCloser) (era.Era, error) {
+	m, err := readMetadata(f)
+	if err != nil {
+		return nil, err
+	}
+	return &Era{
+		f:  f,
+		s:  e2store.NewReader(f),
+		m:  m,
+		mu: new(sync.Mutex),
+	}, nil
+}
+
+// Open returns an Era backed by the given filename.
+func Open(filename string) (era.Era, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+	return From(f)
+}
+
+func (e *Era) Close() error {
+	return e.f.Close()
+}
+
+// Iterator returns an iterator over the era file.
+func (e *Era) Iterator() (era.Iterator, error) {
+	return NewIterator(e)
+}
+
+// GetBlockByNumber returns the block for the given block number.
+func (e *Era) GetBlockByNumber(num uint64) (*types.Block, error) {
+	if e.m.start > num || e.m.start+e.m.count <= num {
+		return nil, fmt.Errorf("out-of-bounds: %d not in [%d, %d)", num, e.m.start, e.m.start+e.m.count)
+	}
+	off, err := e.readOffset(num)
+	if err != nil {
+		return nil, err
+	}
+	r, n, err := newSnappyReader(e.s, era.TypeCompressedHeader, off)
+	if err != nil {
+		return nil, err
+	}
+	var header types.Header
+	if err := rlp.Decode(r, &header); err != nil {
+		return nil, err
+	}
+	off += n
+	r, _, err = newSnappyReader(e.s, era.TypeCompressedBody, off)
+	if err != nil {
+		return nil, err
+	}
+	var body types.Body
+	if err := rlp.Decode(r, &body); err != nil {
+		return nil, err
+	}
+	return types.NewBlockWithHeader(&header).WithBody(body), nil
+}
+
+// GetRawBodyByNumber returns the RLP-encoded body for the given block number.
+func (e *Era) GetRawBodyByNumber(num uint64) ([]byte, error) {
+	if e.m.start > num || e.m.start+e.m.count <= num {
+		return nil, fmt.Errorf("out-of-bounds: %d not in [%d, %d)", num, e.m.start, e.m.start+e.m.count)
+	}
+	off, err := e.readOffset(num)
+	if err != nil {
+		return nil, err
+	}
+	off, err = e.s.SkipN(off, 1)
+	if err != nil {
+		return nil, err
+	}
+	r, _, err := newSnappyReader(e.s, era.TypeCompressedBody, off)
+	if err != nil {
+		return nil, err
+	}
+	return io.ReadAll(r)
+}
+
+// GetRawReceiptsByNumber returns the RLP-encoded receipts for the given block number.
+func (e *Era) GetRawReceiptsByNumber(num uint64) ([]byte, error) {
+	if e.m.start > num || e.m.start+e.m.count <= num {
+		return nil, fmt.Errorf("out-of-bounds: %d not in [%d, %d)", num, e.m.start, e.m.start+e.m.count)
+	}
+	off, err := e.readOffset(num)
+	if err != nil {
+		return nil, err
+	}
+
+	// Skip over header and body.
+	off, err = e.s.SkipN(off, 2)
+	if err != nil {
+		return nil, err
+	}
+
+	r, _, err := newSnappyReader(e.s, era.TypeCompressedReceipts, off)
+	if err != nil {
+		return nil, err
+	}
+	return io.ReadAll(r)
+}
+
+// Accumulator reads the accumulator entry in the Era1 file.
+func (e *Era) Accumulator() (common.Hash, error) {
+	entry, err := e.s.Find(era.TypeAccumulator)
+	if err != nil {
+		return common.Hash{}, err
+	}
+	return common.BytesToHash(entry.Value), nil
+}
+
+// InitialTD returns initial total difficulty before the difficulty of the
+// first block of the Era1 is applied.
+func (e *Era) InitialTD() (*big.Int, error) {
+	var (
+		r      io.Reader
+		header types.Header
+		rawTd  []byte
+		n      int64
+		off    int64
+		err    error
+	)
+
+	// Read first header.
+	if off, err = e.readOffset(e.m.start); err != nil {
+		return nil, err
+	}
+	if r, n, err = newSnappyReader(e.s, era.TypeCompressedHeader, off); err != nil {
+		return nil, err
+	}
+	if err := rlp.Decode(r, &header); err != nil {
+		return nil, err
+	}
+	off += n
+
+	// Skip over header and body.
+	off, err = e.s.SkipN(off, 2)
+	if err != nil {
+		return nil, err
+	}
+
+	// Read total difficulty after first block.
+	if r, _, err = e.s.ReaderAt(era.TypeTotalDifficulty, off); err != nil {
+		return nil, err
+	}
+	rawTd, err = io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+	slices.Reverse(rawTd)
+	td := new(big.Int).SetBytes(rawTd)
+	return td.Sub(td, header.Difficulty), nil
+}
+
+// Start returns the listed start block.
+func (e *Era) Start() uint64 {
+	return e.m.start
+}
+
+// Count returns the total number of blocks in the Era1.
+func (e *Era) Count() uint64 {
+	return e.m.count
+}
+
+// readOffset reads a specific block's offset from the block index. The value n
+// is the absolute block number desired.
+func (e *Era) readOffset(n uint64) (int64, error) {
+	var (
+		blockIndexRecordOffset = e.m.length - 24 - int64(e.m.count)*8 // skips start, count, and header
+		firstIndex             = blockIndexRecordOffset + 16          // first index after header / start-num
+		indexOffset            = int64(n-e.m.start) * 8               // desired index * size of indexes
+		offOffset              = firstIndex + indexOffset             // offset of block offset
+	)
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	clear(e.buf[:])
+	if _, err := e.f.ReadAt(e.buf[:], offOffset); err != nil {
+		return 0, err
+	}
+	// Since the block offset is relative from the start of the block index record
+	// we need to add the record offset to it's offset to get the block's absolute
+	// offset.
+	return blockIndexRecordOffset + int64(binary.LittleEndian.Uint64(e.buf[:])), nil
+}
+
+// newSnappyReader returns a snappy.Reader for the e2store entry value at off.
+func newSnappyReader(e *e2store.Reader, expectedType uint16, off int64) (io.Reader, int64, error) {
+	r, n, err := e.ReaderAt(expectedType, off)
+	if err != nil {
+		return nil, 0, err
+	}
+	return snappy.NewReader(r), int64(n), err
+}
+
+// metadata wraps the metadata in the block index.
+type metadata struct {
+	start  uint64
+	count  uint64
+	length int64
+}
+
+// readMetadata reads the metadata stored in an Era1 file's block index.
+func readMetadata(f ReadAtSeekCloser) (m metadata, err error) {
+	// Determine length of reader.
+	if m.length, err = f.Seek(0, io.SeekEnd); err != nil {
+		return
+	}
+	b := make([]byte, 16)
+	// Read count. It's the last 8 bytes of the file.
+	if _, err = f.ReadAt(b[:8], m.length-8); err != nil {
+		return
+	}
+	m.count = binary.LittleEndian.Uint64(b)
+	// Read start. It's at the offset -sizeof(m.count) -
+	// count*sizeof(indexEntry) - sizeof(m.start)
+	if _, err = f.ReadAt(b[8:], m.length-16-int64(m.count*8)); err != nil {
+		return
+	}
+	m.start = binary.LittleEndian.Uint64(b[8:])
+	return
+}

internal/era/proof.go

@@ -0,0 +1,36 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+package era
+
+import (
+	"io"
+
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+type ProofVariant uint16
+
+const (
+	ProofNone ProofVariant = iota
+)
+
+// Proof is the interface for all block proof types in the package.
+// It's a stub for later integration into Era.
+type Proof interface {
+	EncodeRLP(w io.Writer) error
+	DecodeRLP(s *rlp.Stream) error
+	Variant() ProofVariant
+}