op-program: Implement wrapper methods required by derive.Engine

Adds flags to specify the l2 execution genesis and agreed l2 starting head.

op-program/cmd/main.go

@@ -95,7 +95,7 @@ func FaultProofProgram(logger log.Logger, cfg *config.Config) error {
 
 	ctx := context.Background()
 	logger.Info("Connecting to L2 node", "l2", cfg.L2URL)
-	_, err := l2.NewFetchingL2Oracle(ctx, logger, cfg.L2URL)
+	_, err := l2.NewFetchingEngine(ctx, logger, cfg)
 	if err != nil {
 		return fmt.Errorf("connect l2 oracle: %w", err)
 	}

op-program/cmd/main_test.go

@@ -7,10 +7,13 @@ import (
 
 	"github.com/ethereum-optimism/optimism/op-node/chaincfg"
 	"github.com/ethereum-optimism/optimism/op-program/config"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/stretchr/testify/require"
 )
 
+var l2HeadValue = "0x6303578b1fa9480389c51bbcef6fe045bb877da39740819e9eb5f36f94949bd0"
+
 func TestLogLevel(t *testing.T) {
 	t.Run("RejectInvalid", func(t *testing.T) {
 		verifyArgsInvalid(t, "unknown level: foo", addRequiredArgs("--log.level=foo"))
@@ -28,7 +31,7 @@ func TestLogLevel(t *testing.T) {
 
 func TestDefaultCLIOptionsMatchDefaultConfig(t *testing.T) {
 	cfg := configForArgs(t, addRequiredArgs())
-	require.Equal(t, config.NewConfig(&chaincfg.Goerli), cfg)
+	require.Equal(t, config.NewConfig(&chaincfg.Goerli, "genesis.json", common.HexToHash(l2HeadValue)), cfg)
 }
 
 func TestNetwork(t *testing.T) {
@@ -72,10 +75,36 @@ func TestL2(t *testing.T) {
 	require.Equal(t, expected, cfg.L2URL)
 }
 
+func TestL2Genesis(t *testing.T) {
+	t.Run("Required", func(t *testing.T) {
+		verifyArgsInvalid(t, "flag l2.genesis is required", addRequiredArgsExcept("--l2.genesis"))
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		cfg := configForArgs(t, replaceRequiredArg("--l2.genesis", "/tmp/genesis.json"))
+		require.Equal(t, "/tmp/genesis.json", cfg.L2GenesisPath)
+	})
+}
+
+func TestL2Head(t *testing.T) {
+	t.Run("Required", func(t *testing.T) {
+		verifyArgsInvalid(t, "flag l2.head is required", addRequiredArgsExcept("--l2.head"))
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		cfg := configForArgs(t, replaceRequiredArg("--l2.head", l2HeadValue))
+		require.Equal(t, common.HexToHash(l2HeadValue), cfg.L2Head)
+	})
+
+	t.Run("Invalid", func(t *testing.T) {
+		verifyArgsInvalid(t, config.ErrInvalidL2Head.Error(), replaceRequiredArg("--l2.head", "something"))
+	})
+}
+
 // Offline support will be added later, but for now it just bails out with an error
 func TestOfflineModeNotSupported(t *testing.T) {
 	logger := log.New()
-	err := FaultProofProgram(logger, config.NewConfig(&chaincfg.Goerli))
+	err := FaultProofProgram(logger, config.NewConfig(&chaincfg.Goerli, "genesis.json", common.HexToHash(l2HeadValue)))
 	require.ErrorContains(t, err, "offline mode not supported")
 }
 
@@ -124,7 +153,9 @@ func replaceRequiredArg(name string, value string) []string {
 // to create a valid Config
 func requiredArgs() map[string]string {
 	return map[string]string{
-		"--network": "goerli",
+		"--network":    "goerli",
+		"--l2.genesis": "genesis.json",
+		"--l2.head":    l2HeadValue,
 	}
 }
 

op-program/config/config.go

@@ -6,16 +6,21 @@ import (
 	opnode "github.com/ethereum-optimism/optimism/op-node"
 	"github.com/ethereum-optimism/optimism/op-node/rollup"
 	"github.com/ethereum-optimism/optimism/op-program/flags"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/urfave/cli"
 )
 
 var (
 	ErrMissingRollupConfig = errors.New("missing rollup config")
+	ErrMissingL2Genesis    = errors.New("missing l2 genesis")
+	ErrInvalidL2Head       = errors.New("invalid l2 head")
 )
 
 type Config struct {
-	Rollup *rollup.Config
-	L2URL  string
+	Rollup        *rollup.Config
+	L2URL         string
+	L2GenesisPath string
+	L2Head        common.Hash
 }
 
 func (c *Config) Check() error {
@@ -25,6 +30,12 @@ func (c *Config) Check() error {
 	if err := c.Rollup.Check(); err != nil {
 		return err
 	}
+	if c.L2GenesisPath == "" {
+		return ErrMissingL2Genesis
+	}
+	if c.L2Head == (common.Hash{}) {
+		return ErrInvalidL2Head
+	}
 	return nil
 }
 
@@ -33,9 +44,11 @@ func (c *Config) FetchingEnabled() bool {
 }
 
 // NewConfig creates a Config with all optional values set to the CLI default value
-func NewConfig(rollupCfg *rollup.Config) *Config {
+func NewConfig(rollupCfg *rollup.Config, l2GenesisPath string, l2Head common.Hash) *Config {
 	return &Config{
-		Rollup: rollupCfg,
+		Rollup:        rollupCfg,
+		L2GenesisPath: l2GenesisPath,
+		L2Head:        l2Head,
 	}
 }
 
@@ -47,8 +60,14 @@ func NewConfigFromCLI(ctx *cli.Context) (*Config, error) {
 	if err != nil {
 		return nil, err
 	}
+	l2Head := common.HexToHash(ctx.GlobalString(flags.L2Head.Name))
+	if l2Head == (common.Hash{}) {
+		return nil, ErrInvalidL2Head
+	}
 	return &Config{
-		Rollup: rollupCfg,
-		L2URL:  ctx.GlobalString(flags.L2NodeAddr.Name),
+		Rollup:        rollupCfg,
+		L2URL:         ctx.GlobalString(flags.L2NodeAddr.Name),
+		L2GenesisPath: ctx.GlobalString(flags.L2GenesisPath.Name),
+		L2Head:        l2Head,
 	}, nil
 }

op-program/config/config_test.go

@@ -5,34 +5,63 @@ import (
 
 	"github.com/ethereum-optimism/optimism/op-node/chaincfg"
 	"github.com/ethereum-optimism/optimism/op-node/rollup"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/stretchr/testify/require"
 )
 
+var validRollupConfig = &chaincfg.Goerli
+var validL2GenesisPath = "genesis.json"
+var validL2Head = common.HexToHash("0x6303578b1fa9480389c51bbcef6fe045bb877da39740819e9eb5f36f94949bd0")
+
 func TestDefaultConfigIsValid(t *testing.T) {
-	err := NewConfig(&chaincfg.Goerli).Check()
+	err := NewConfig(validRollupConfig, validL2GenesisPath, validL2Head).Check()
 	require.NoError(t, err)
 }
 
 func TestRollupConfig(t *testing.T) {
 	t.Run("Required", func(t *testing.T) {
-		err := NewConfig(nil).Check()
+		err := NewConfig(nil, validL2GenesisPath, validL2Head).Check()
 		require.ErrorIs(t, err, ErrMissingRollupConfig)
 	})
 
-	t.Run("Valid", func(t *testing.T) {
-		err := NewConfig(&rollup.Config{}).Check()
+	t.Run("Invalid", func(t *testing.T) {
+		err := NewConfig(&rollup.Config{}, validL2GenesisPath, validL2Head).Check()
 		require.ErrorIs(t, err, rollup.ErrBlockTimeZero)
 	})
 }
 
+func TestL2Genesis(t *testing.T) {
+	t.Run("Required", func(t *testing.T) {
+		err := NewConfig(validRollupConfig, "", validL2Head).Check()
+		require.ErrorIs(t, err, ErrMissingL2Genesis)
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		err := NewConfig(validRollupConfig, validL2GenesisPath, validL2Head).Check()
+		require.NoError(t, err)
+	})
+}
+
+func TestL2Head(t *testing.T) {
+	t.Run("Required", func(t *testing.T) {
+		err := NewConfig(validRollupConfig, validL2GenesisPath, common.Hash{}).Check()
+		require.ErrorIs(t, err, ErrInvalidL2Head)
+	})
+
+	t.Run("Valid", func(t *testing.T) {
+		err := NewConfig(validRollupConfig, validL2GenesisPath, validL2Head).Check()
+		require.NoError(t, err)
+	})
+}
+
 func TestFetchingEnabled(t *testing.T) {
 	t.Run("FetchingNotEnabledWhenNoFetcherUrlsSpecified", func(t *testing.T) {
-		cfg := NewConfig(&chaincfg.Beta1)
+		cfg := NewConfig(&chaincfg.Beta1, validL2GenesisPath, validL2Head)
 		require.False(t, cfg.FetchingEnabled(), "Should not enable fetching when node URL not supplied")
 	})
 
 	t.Run("FetchingEnabledWhenFetcherUrlsSpecified", func(t *testing.T) {
-		cfg := NewConfig(&chaincfg.Beta1)
+		cfg := NewConfig(&chaincfg.Beta1, validL2GenesisPath, validL2Head)
 		cfg.L2URL = "https://example.com:1234"
 		require.True(t, cfg.FetchingEnabled(), "Should enable fetching when node URL supplied")
 	})

op-program/flags/flags.go

@@ -28,6 +28,16 @@ var (
 		Usage:  "Address of L2 JSON-RPC endpoint to use (eth and debug namespace required)",
 		EnvVar: service.PrefixEnvVar(envVarPrefix, "L2_RPC"),
 	}
+	L2GenesisPath = cli.StringFlag{
+		Name:   "l2.genesis",
+		Usage:  "Path to the op-geth genesis file",
+		EnvVar: service.PrefixEnvVar(envVarPrefix, "L2_GENESIS"),
+	}
+	L2Head = cli.StringFlag{
+		Name:   "l2.head",
+		Usage:  "Hash of the agreed L2 block to start derivation from",
+		EnvVar: service.PrefixEnvVar(envVarPrefix, "L2_HEAD"),
+	}
 )
 
 // Flags contains the list of configuration options available to the binary.
@@ -37,6 +47,8 @@ var programFlags = []cli.Flag{
 	RollupConfig,
 	Network,
 	L2NodeAddr,
+	L2GenesisPath,
+	L2Head,
 }
 
 func init() {
@@ -53,5 +65,11 @@ func CheckRequired(ctx *cli.Context) error {
 	if rollupConfig != "" && network != "" {
 		return fmt.Errorf("cannot specify both %s and %s", RollupConfig.Name, Network.Name)
 	}
+	if ctx.GlobalString(L2GenesisPath.Name) == "" {
+		return fmt.Errorf("flag %s is required", L2GenesisPath.Name)
+	}
+	if ctx.GlobalString(L2Head.Name) == "" {
+		return fmt.Errorf("flag %s is required", L2Head.Name)
+	}
 	return nil
 }

op-program/l2/engine.go

+package l2
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/ethereum-optimism/optimism/op-node/eth"
+	"github.com/ethereum-optimism/optimism/op-node/rollup"
+	"github.com/ethereum-optimism/optimism/op-node/rollup/derive"
+	"github.com/ethereum-optimism/optimism/op-program/l2/engineapi"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/log"
+)
+
+var (
+	ErrNotFound = errors.New("not found")
+)
+
+type OracleEngine struct {
+	api       *engineapi.L2EngineAPI
+	backend   engineapi.EngineBackend
+	rollupCfg *rollup.Config
+}
+
+func NewOracleEngine(rollupCfg *rollup.Config, logger log.Logger, backend engineapi.EngineBackend) *OracleEngine {
+	engineAPI := engineapi.NewL2EngineAPI(logger, backend)
+	return &OracleEngine{
+		api:       engineAPI,
+		backend:   backend,
+		rollupCfg: rollupCfg,
+	}
+}
+
+func (o OracleEngine) GetPayload(ctx context.Context, payloadId eth.PayloadID) (*eth.ExecutionPayload, error) {
+	return o.api.GetPayloadV1(ctx, payloadId)
+}
+
+func (o OracleEngine) ForkchoiceUpdate(ctx context.Context, state *eth.ForkchoiceState, attr *eth.PayloadAttributes) (*eth.ForkchoiceUpdatedResult, error) {
+	return o.api.ForkchoiceUpdatedV1(ctx, state, attr)
+}
+
+func (o OracleEngine) NewPayload(ctx context.Context, payload *eth.ExecutionPayload) (*eth.PayloadStatusV1, error) {
+	return o.api.NewPayloadV1(ctx, payload)
+}
+
+func (o OracleEngine) PayloadByHash(ctx context.Context, hash common.Hash) (*eth.ExecutionPayload, error) {
+	block := o.backend.GetBlockByHash(hash)
+	if block == nil {
+		return nil, ErrNotFound
+	}
+	return eth.BlockAsPayload(block)
+}
+
+func (o OracleEngine) PayloadByNumber(ctx context.Context, n uint64) (*eth.ExecutionPayload, error) {
+	hash := o.backend.GetCanonicalHash(n)
+	if hash == (common.Hash{}) {
+		return nil, ErrNotFound
+	}
+	return o.PayloadByHash(ctx, hash)
+}
+
+func (o OracleEngine) L2BlockRefByLabel(ctx context.Context, label eth.BlockLabel) (eth.L2BlockRef, error) {
+	var header *types.Header
+	switch label {
+	case eth.Unsafe:
+		header = o.backend.CurrentHeader()
+	case eth.Safe:
+		header = o.backend.CurrentSafeBlock()
+	case eth.Finalized:
+		header = o.backend.CurrentFinalBlock()
+	default:
+		return eth.L2BlockRef{}, fmt.Errorf("unknown label: %v", label)
+	}
+	if header == nil {
+		return eth.L2BlockRef{}, ErrNotFound
+	}
+	block := o.backend.GetBlockByHash(header.Hash())
+	if block == nil {
+		return eth.L2BlockRef{}, ErrNotFound
+	}
+	return derive.L2BlockToBlockRef(block, &o.rollupCfg.Genesis)
+}
+
+func (o OracleEngine) L2BlockRefByHash(ctx context.Context, l2Hash common.Hash) (eth.L2BlockRef, error) {
+	block := o.backend.GetBlockByHash(l2Hash)
+	if block == nil {
+		return eth.L2BlockRef{}, ErrNotFound
+	}
+	return derive.L2BlockToBlockRef(block, &o.rollupCfg.Genesis)
+}
+
+func (o OracleEngine) SystemConfigByL2Hash(ctx context.Context, hash common.Hash) (eth.SystemConfig, error) {
+	payload, err := o.PayloadByHash(ctx, hash)
+	if err != nil {
+		return eth.SystemConfig{}, err
+	}
+	return derive.PayloadToSystemConfig(payload, o.rollupCfg)
+}

op-program/l2/engine_test.go

+package l2
+
+import (
+	"context"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum-optimism/optimism/op-node/chaincfg"
+	"github.com/ethereum-optimism/optimism/op-node/eth"
+	"github.com/ethereum-optimism/optimism/op-node/rollup/derive"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/core/state"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/params"
+	"github.com/ethereum/go-ethereum/trie"
+	"github.com/stretchr/testify/require"
+)
+
+// Should implement derive.Engine
+var _ derive.Engine = (*OracleEngine)(nil)
+
+func TestPayloadByHash(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("KnownBlock", func(t *testing.T) {
+		engine, stub := createOracleEngine(t)
+		block := stub.head
+		payload, err := engine.PayloadByHash(ctx, block.Hash())
+		require.NoError(t, err)
+		expected, err := eth.BlockAsPayload(block)
+		require.NoError(t, err)
+		require.Equal(t, expected, payload)
+	})
+
+	t.Run("UnknownBlock", func(t *testing.T) {
+		engine, _ := createOracleEngine(t)
+		hash := common.HexToHash("0x878899")
+		payload, err := engine.PayloadByHash(ctx, hash)
+		require.ErrorIs(t, err, ErrNotFound)
+		require.Nil(t, payload)
+	})
+}
+
+func TestPayloadByNumber(t *testing.T) {
+	ctx := context.Background()
+
+	t.Run("KnownBlock", func(t *testing.T) {
+		engine, stub := createOracleEngine(t)
+		block := stub.head
+		payload, err := engine.PayloadByNumber(ctx, block.NumberU64())
+		require.NoError(t, err)
+		expected, err := eth.BlockAsPayload(block)
+		require.NoError(t, err)
+		require.Equal(t, expected, payload)
+	})
+
+	t.Run("NoCanonicalHash", func(t *testing.T) {
+		engine, _ := createOracleEngine(t)
+		payload, err := engine.PayloadByNumber(ctx, uint64(700))
+		require.ErrorIs(t, err, ErrNotFound)
+		require.Nil(t, payload)
+	})
+
+	t.Run("UnknownBlock", func(t *testing.T) {
+		engine, stub := createOracleEngine(t)
+		hash := common.HexToHash("0x878899")
+		number := uint64(700)
+		stub.canonical[number] = hash
+		payload, err := engine.PayloadByNumber(ctx, number)
+		require.ErrorIs(t, err, ErrNotFound)
+		require.Nil(t, payload)
+	})
+}
+
+func TestL2BlockRefByLabel(t *testing.T) {
+	ctx := context.Background()
+	engine, stub := createOracleEngine(t)
+	tests := []struct {
+		name  eth.BlockLabel
+		block *types.Block
+	}{
+		{eth.Unsafe, stub.head},
+		{eth.Safe, stub.safe},
+		{eth.Finalized, stub.finalized},
+	}
+	for _, test := range tests {
+		t.Run(string(test.name), func(t *testing.T) {
+			expected, err := derive.L2BlockToBlockRef(test.block, &engine.rollupCfg.Genesis)
+			require.NoError(t, err)
+			blockRef, err := engine.L2BlockRefByLabel(ctx, test.name)
+			require.NoError(t, err)
+			require.Equal(t, expected, blockRef)
+		})
+	}
+	t.Run("UnknownLabel", func(t *testing.T) {
+		_, err := engine.L2BlockRefByLabel(ctx, "nope")
+		require.ErrorContains(t, err, "unknown label")
+	})
+}
+
+func TestL2BlockRefByHash(t *testing.T) {
+	ctx := context.Background()
+	engine, stub := createOracleEngine(t)
+
+	t.Run("KnownBlock", func(t *testing.T) {
+		expected, err := derive.L2BlockToBlockRef(stub.safe, &engine.rollupCfg.Genesis)
+		require.NoError(t, err)
+		ref, err := engine.L2BlockRefByHash(ctx, stub.safe.Hash())
+		require.NoError(t, err)
+		require.Equal(t, expected, ref)
+	})
+
+	t.Run("UnknownBlock", func(t *testing.T) {
+		ref, err := engine.L2BlockRefByHash(ctx, common.HexToHash("0x878899"))
+		require.ErrorIs(t, err, ErrNotFound)
+		require.Equal(t, eth.L2BlockRef{}, ref)
+	})
+}
+
+func TestSystemConfigByL2Hash(t *testing.T) {
+	ctx := context.Background()
+	engine, stub := createOracleEngine(t)
+
+	t.Run("KnownBlock", func(t *testing.T) {
+		payload, err := eth.BlockAsPayload(stub.safe)
+		require.NoError(t, err)
+		expected, err := derive.PayloadToSystemConfig(payload, engine.rollupCfg)
+		require.NoError(t, err)
+		cfg, err := engine.SystemConfigByL2Hash(ctx, stub.safe.Hash())
+		require.NoError(t, err)
+		require.Equal(t, expected, cfg)
+	})
+
+	t.Run("UnknownBlock", func(t *testing.T) {
+		ref, err := engine.SystemConfigByL2Hash(ctx, common.HexToHash("0x878899"))
+		require.ErrorIs(t, err, ErrNotFound)
+		require.Equal(t, eth.SystemConfig{}, ref)
+	})
+}
+
+func createOracleEngine(t *testing.T) (*OracleEngine, *stubEngineBackend) {
+	head := createL2Block(t, 4)
+	safe := createL2Block(t, 3)
+	finalized := createL2Block(t, 2)
+	backend := &stubEngineBackend{
+		head:      head,
+		safe:      safe,
+		finalized: finalized,
+		blocks: map[common.Hash]*types.Block{
+			head.Hash():      head,
+			safe.Hash():      safe,
+			finalized.Hash(): finalized,
+		},
+		canonical: map[uint64]common.Hash{
+			head.NumberU64():      head.Hash(),
+			safe.NumberU64():      safe.Hash(),
+			finalized.NumberU64(): finalized.Hash(),
+		},
+	}
+	engine := OracleEngine{
+		backend:   backend,
+		rollupCfg: &chaincfg.Goerli,
+	}
+	return &engine, backend
+}
+
+func createL2Block(t *testing.T, number int) *types.Block {
+	tx, err := derive.L1InfoDeposit(uint64(1), eth.HeaderBlockInfo(&types.Header{
+		Number:  big.NewInt(32),
+		BaseFee: big.NewInt(7),
+	}), eth.SystemConfig{}, true)
+	require.NoError(t, err)
+	header := &types.Header{
+		Number:  big.NewInt(int64(number)),
+		BaseFee: big.NewInt(7),
+	}
+	return types.NewBlock(header, []*types.Transaction{types.NewTx(tx)}, nil, nil, trie.NewStackTrie(nil))
+}
+
+type stubEngineBackend struct {
+	head      *types.Block
+	safe      *types.Block
+	finalized *types.Block
+	blocks    map[common.Hash]*types.Block
+	canonical map[uint64]common.Hash
+}
+
+func (s stubEngineBackend) CurrentHeader() *types.Header {
+	return s.head.Header()
+}
+
+func (s stubEngineBackend) CurrentSafeBlock() *types.Header {
+	return s.safe.Header()
+}
+
+func (s stubEngineBackend) CurrentFinalBlock() *types.Header {
+	return s.finalized.Header()
+}
+
+func (s stubEngineBackend) GetBlockByHash(hash common.Hash) *types.Block {
+	return s.blocks[hash]
+}
+
+func (s stubEngineBackend) GetCanonicalHash(n uint64) common.Hash {
+	return s.canonical[n]
+}
+
+func (s stubEngineBackend) GetBlock(hash common.Hash, number uint64) *types.Block {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) HasBlockAndState(hash common.Hash, number uint64) bool {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) GetVMConfig() *vm.Config {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) Config() *params.ChainConfig {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) Engine() consensus.Engine {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) StateAt(root common.Hash) (*state.StateDB, error) {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) InsertBlockWithoutSetHead(block *types.Block) error {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) SetCanonical(head *types.Block) (common.Hash, error) {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) SetFinalized(header *types.Header) {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) SetSafe(header *types.Header) {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) GetHeader(hash common.Hash, number uint64) *types.Header {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) GetHeaderByNumber(number uint64) *types.Header {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) GetHeaderByHash(hash common.Hash) *types.Header {
+	panic("unsupported")
+}
+
+func (s stubEngineBackend) GetTd(hash common.Hash, number uint64) *big.Int {
+	panic("unsupported")
+}

op-program/l2/l2.go

+package l2
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	"github.com/ethereum-optimism/optimism/op-node/rollup/derive"
+	"github.com/ethereum-optimism/optimism/op-program/config"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+func NewFetchingEngine(ctx context.Context, logger log.Logger, cfg *config.Config) (derive.Engine, error) {
+	genesis, err := loadL2Genesis(cfg)
+	if err != nil {
+		return nil, err
+	}
+	oracle, err := NewFetchingL2Oracle(ctx, logger, cfg.L2URL)
+	if err != nil {
+		return nil, fmt.Errorf("connect l2 oracle: %w", err)
+	}
+
+	engineBackend, err := NewOracleBackedL2Chain(logger, oracle, genesis, cfg.L2Head)
+	if err != nil {
+		return nil, fmt.Errorf("create l2 chain: %w", err)
+	}
+	return NewOracleEngine(cfg.Rollup, logger, engineBackend), nil
+}
+
+func loadL2Genesis(cfg *config.Config) (*params.ChainConfig, error) {
+	data, err := os.ReadFile(cfg.L2GenesisPath)
+	if err != nil {
+		return nil, fmt.Errorf("read l2 genesis file: %w", err)
+	}
+	var genesis core.Genesis
+	err = json.Unmarshal(data, &genesis)
+	if err != nil {
+		return nil, fmt.Errorf("parse l2 genesis file: %w", err)
+	}
+	return genesis.Config, nil
+}