Deterministic L1 starting block selection (Config in advance)

op-chain-ops/cmd/celo-migrate/beacon.go

@@ -0,0 +1,254 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/ethereum-optimism/optimism/op-service/eth"
+	"github.com/ethereum/go-ethereum"
+	"github.com/ethereum/go-ethereum/common"
+)
+
+const (
+	// See - https://eth2book.info/capella/part3/containers/state/
+	beaconChainGenesisTimeSeconds  = 1606824000
+	beaconChainSlotDurationSeconds = 12
+	beaconSlotsPerEpoch            = 32
+)
+
+type beaconClient struct {
+	cl *http.Client
+	// A beaconchain RPC API endpoint.
+	beaconRPC string
+	// A becaoncha.in api endpoint.
+	beaconchainURL string
+}
+
+func NewBeaconClient(beaconRPC string, beaconchainURL string) *beaconClient {
+	return &beaconClient{
+		beaconRPC:      beaconRPC,
+		beaconchainURL: beaconchainURL,
+		cl:             &http.Client{},
+	}
+}
+
+// MostRecentFinalizedL1BlockAtTime returns the hash of the most recent
+// finalized L1 block at the L2 start time. It finds the epoch which started
+// most recently before the L2 start time (or on the L2 start time) and then
+// looks back from there to find the first finalized block.
+func (c *beaconClient) MostRecentFinalizedL1BlockAtTime(l2StartTimeSeconds uint64) (common.Hash, error) {
+	// Find the epoch starting at or before the L2 start time.
+	epochNumber := SlotAtOrBefore(l2StartTimeSeconds) / beaconSlotsPerEpoch
+
+	// This epoch is guaranteed to not be complete at L2 start time (if the L2 start time falls in the last
+	// second of the epoch the epoch is still not complete, and if it was we'd be selecting the next epoch)
+	// The previous epoch is the most recent completed epoch.
+	// The one prior to that is the most recent justified epoch.
+	// And the first block of the justified epoch (the epoch boundary block) will be finalized.
+	// This is assuming that there was at least 2/3 participation in the completed and justified epochs.
+	var epoch *Epoch
+	var err error
+	names := [2]string{"completed", "justified"}
+
+	// Check the most recent completed and justified epochs had a participation rate of at least 0.67.
+	for i := uint64(1); i <= 2; i++ {
+		epoch, err = c.Epoch(context.Background(), epochNumber-i)
+		if err != nil {
+			return common.Hash{}, fmt.Errorf("error fetching epoch %d: %w", epochNumber-i, err)
+		}
+		if epoch.Data.Globalparticipationrate < 0.67 {
+			return common.Hash{}, fmt.Errorf("most recent %s epoch before the L2 start time (%d) has less than 0.67 participation rate (%.2f)", names[i-1], l2StartTimeSeconds, epoch.Data.Globalparticipationrate)
+		}
+	}
+	// Calculate the first slot of the most recent justified epoch.
+	mostRecentFinalizedSlot := (epochNumber - 2) * beaconSlotsPerEpoch
+
+	// Find the most recent actual finalized block, slots can be empty so we
+	// search back if we encounter empty slots. We check up to 10 slots, if they
+	// are all empty something serious is wrong with the L1 so we abort.
+	var beaconBlock *BeaconBlock
+	for i := uint64(0); i < 10; i++ {
+		beaconBlock, err = c.BeaconBlock(context.Background(), mostRecentFinalizedSlot-i)
+		if errors.Is(err, ethereum.NotFound) {
+			// If there is not block for this slot then skip to the next.
+			continue
+		}
+		if err != nil {
+			return common.Hash{}, fmt.Errorf("error fetching beacon block at slot %d: %w", mostRecentFinalizedSlot, err)
+		}
+		if !beaconBlock.Finalized {
+			return common.Hash{}, fmt.Errorf("expecting beacon block at slot %d to be finalized", mostRecentFinalizedSlot)
+		}
+		break // We found a good block.
+	}
+	if beaconBlock == nil {
+		return common.Hash{}, fmt.Errorf("failed to find finalized block searching up to 10 slots back from the most recent finalized slot (%d) at the L2 fork time (%d)", mostRecentFinalizedSlot, l2StartTimeSeconds)
+	}
+	return common.HexToHash(beaconBlock.Data.Message.Body.ExecutionPayload.BlockHash), nil
+}
+
+// Gets the epoch from the beaconcha.in api
+func (c *beaconClient) Epoch(ctx context.Context, num uint64) (epoch *Epoch, err error) {
+	headers := http.Header{}
+	headers.Add("Accept", "application/json")
+	resp, err := c.cl.Get(fmt.Sprintf("%s/v1/epoch/%d", c.beaconchainURL, num))
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch epoch: %w", err)
+	}
+	defer func() {
+		err = errors.Join(err, resp.Body.Close())
+	}()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to fetch epoch, http status %d", resp.StatusCode)
+	}
+	epoch = &Epoch{}
+	if err := json.NewDecoder(resp.Body).Decode(epoch); err != nil {
+		return nil, fmt.Errorf("failed to decode epoch: %w", err)
+	}
+	return epoch, nil
+}
+
+// Gets the beacon block from the beacon rpc api
+func (c *beaconClient) BeaconBlock(ctx context.Context, slot uint64) (block *BeaconBlock, err error) {
+	headers := http.Header{}
+	headers.Add("Accept", "application/json")
+	resp, err := c.cl.Get(fmt.Sprintf("%s/eth/v2/beacon/blocks/%d", c.beaconRPC, slot))
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch becon block: %w", err)
+	}
+	defer func() {
+		err = errors.Join(err, resp.Body.Close())
+	}()
+	if resp.StatusCode != http.StatusOK {
+		if resp.StatusCode == http.StatusNotFound {
+			return nil, fmt.Errorf("failed to fetch beacon block at slot %d: %w", slot, ethereum.NotFound)
+		}
+		return nil, fmt.Errorf("failed to fetch beacon block at slot %d, http status %d", slot, resp.StatusCode)
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&block); err != nil {
+		return nil, fmt.Errorf("failed to decode beacon block: %w", err)
+	}
+	return block, nil
+}
+
+// Returns the start time of an epoch
+func EpochStartTime(epoch uint64) uint64 {
+	return beaconChainGenesisTimeSeconds + epoch*beaconSlotsPerEpoch*beaconChainSlotDurationSeconds
+}
+
+// Returns the number of the epoch starting at or before the given time.
+func EpochAtOrBefore(unixTime uint64) uint64 {
+	return SlotAtOrBefore(unixTime) / beaconSlotsPerEpoch
+}
+
+func SlotAtOrBefore(unixTime uint64) uint64 {
+	// Get the slot at or before the given time.
+	// Slot = (start - genesis) / slotDuration
+	return (unixTime - beaconChainGenesisTimeSeconds) / beaconChainSlotDurationSeconds
+}
+
+type BeaconBlock struct {
+	Version             string `json:"version"`
+	ExecutionOptimistic bool   `json:"execution_optimistic"`
+	Finalized           bool   `json:"finalized"`
+	Data                struct {
+		Message struct {
+			Slot          eth.Uint64String `json:"slot"`
+			ProposerIndex string           `json:"proposer_index"`
+			ParentRoot    string           `json:"parent_root"`
+			StateRoot     string           `json:"state_root"`
+			Body          struct {
+				RandaoReveal string `json:"randao_reveal"`
+				Eth1Data     struct {
+					DepositRoot  string `json:"deposit_root"`
+					DepositCount string `json:"deposit_count"`
+					BlockHash    string `json:"block_hash"`
+				} `json:"eth1_data"`
+				Graffiti          string        `json:"graffiti"`
+				ProposerSlashings []interface{} `json:"proposer_slashings"`
+				AttesterSlashings []interface{} `json:"attester_slashings"`
+				Attestations      []struct {
+					AggregationBits string `json:"aggregation_bits"`
+					Data            struct {
+						Slot            string `json:"slot"`
+						Index           string `json:"index"`
+						BeaconBlockRoot string `json:"beacon_block_root"`
+						Source          struct {
+							Epoch string `json:"epoch"`
+							Root  string `json:"root"`
+						} `json:"source"`
+						Target struct {
+							Epoch string `json:"epoch"`
+							Root  string `json:"root"`
+						} `json:"target"`
+					} `json:"data"`
+					Signature string `json:"signature"`
+				} `json:"attestations"`
+				Deposits       []interface{} `json:"deposits"`
+				VoluntaryExits []interface{} `json:"voluntary_exits"`
+				SyncAggregate  struct {
+					SyncCommitteeBits      string `json:"sync_committee_bits"`
+					SyncCommitteeSignature string `json:"sync_committee_signature"`
+				} `json:"sync_aggregate"`
+				ExecutionPayload struct {
+					ParentHash    string           `json:"parent_hash"`
+					FeeRecipient  string           `json:"fee_recipient"`
+					StateRoot     string           `json:"state_root"`
+					ReceiptsRoot  string           `json:"receipts_root"`
+					LogsBloom     string           `json:"logs_bloom"`
+					PrevRandao    string           `json:"prev_randao"`
+					BlockNumber   eth.Uint64String `json:"block_number"`
+					GasLimit      string           `json:"gas_limit"`
+					GasUsed       string           `json:"gas_used"`
+					Timestamp     eth.Uint64String `json:"timestamp"`
+					ExtraData     string           `json:"extra_data"`
+					BaseFeePerGas string           `json:"base_fee_per_gas"`
+					BlockHash     string           `json:"block_hash"`
+					Transactions  []string         `json:"transactions"`
+					Withdrawals   []struct {
+						Index          string `json:"index"`
+						ValidatorIndex string `json:"validator_index"`
+						Address        string `json:"address"`
+						Amount         string `json:"amount"`
+					} `json:"withdrawals"`
+					BlobGasUsed   string `json:"blob_gas_used"`
+					ExcessBlobGas string `json:"excess_blob_gas"`
+				} `json:"execution_payload"`
+				BlsToExecutionChanges []interface{} `json:"bls_to_execution_changes"`
+				BlobKzgCommitments    []string      `json:"blob_kzg_commitments"`
+			} `json:"body"`
+		} `json:"message"`
+		Signature string `json:"signature"`
+	} `json:"data"`
+}
+
+type Epoch struct {
+	Status string `json:"status"`
+	Data   struct {
+		Attestationscount       int       `json:"attestationscount"`
+		Attesterslashingscount  int       `json:"attesterslashingscount"`
+		Averagevalidatorbalance int64     `json:"averagevalidatorbalance"`
+		Blockscount             int       `json:"blockscount"`
+		Depositscount           int       `json:"depositscount"`
+		Eligibleether           int64     `json:"eligibleether"`
+		Epoch                   int       `json:"epoch"`
+		Finalized               bool      `json:"finalized"`
+		Globalparticipationrate float64   `json:"globalparticipationrate"`
+		Missedblocks            int       `json:"missedblocks"`
+		Orphanedblocks          int       `json:"orphanedblocks"`
+		Proposedblocks          int       `json:"proposedblocks"`
+		Proposerslashingscount  int       `json:"proposerslashingscount"`
+		RewardsExported         bool      `json:"rewards_exported"`
+		Scheduledblocks         int       `json:"scheduledblocks"`
+		Totalvalidatorbalance   int64     `json:"totalvalidatorbalance"`
+		Ts                      time.Time `json:"ts"`
+		Validatorscount         int       `json:"validatorscount"`
+		Voluntaryexitscount     int       `json:"voluntaryexitscount"`
+		Votedether              int64     `json:"votedether"`
+		Withdrawalcount         int       `json:"withdrawalcount"`
+	} `json:"data"`
+}

op-chain-ops/cmd/celo-migrate/beacon_test.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFinalizedL1BlockSelection(t *testing.T) {
+	bc := NewBeaconClient("https://eth-beacon-chain.drpc.org/rest", "https://beaconcha.in/api")
+	var targetTime uint64 = 1740759647 // this is the timestamp of slot 11161302 https://beaconcha.in/slot/11161302
+	var expectedSlot uint64 = 11161216 // this is the beginning slot of the epoch 2 before https://beaconcha.in/slot/11161216
+	expectedL1BlockHash := common.HexToHash("0x6c71e110fc83faa393017681ab97b26621cda68d12e31d24917e210d169d7be5")
+
+	// We expect the same block to be chosen regardless of which slot in an
+	// epoch the target time falls in. The only thing that would change the
+	// chosen block would be if the target time fell in a different epoch.
+
+	t.Run("MidEpochSlot", func(t *testing.T) {
+		checkFinalizedL1BlockSelection(t, bc, targetTime, expectedSlot, expectedL1BlockHash)
+	})
+
+	t.Run("MidEpochMidSlot", func(t *testing.T) {
+		checkFinalizedL1BlockSelection(t, bc, targetTime+beaconChainSlotDurationSeconds/2, expectedSlot, expectedL1BlockHash)
+	})
+
+	epochFirstSlotTime := EpochStartTime(EpochAtOrBefore(targetTime))
+	t.Run("StartEpochSlot", func(t *testing.T) {
+		checkFinalizedL1BlockSelection(t, bc, epochFirstSlotTime, expectedSlot, expectedL1BlockHash)
+	})
+
+	epochLastSlotTime := epochFirstSlotTime + beaconChainSlotDurationSeconds*(beaconSlotsPerEpoch-1)
+	t.Run("EndEpochSlot", func(t *testing.T) {
+		checkFinalizedL1BlockSelection(t, bc, epochLastSlotTime, expectedSlot, expectedL1BlockHash)
+	})
+
+	// Execution payload block hash retrieved here - https://beaconcha.in/slot/11161184
+	expectedL1BlockHashPrevEpoch := common.HexToHash("0xca6237f41190e1adfa52ba20fadb03ef14a7f57c516806edf7660f301b08de36")
+	t.Run("PriorEpochEndSlot", func(t *testing.T) {
+		checkFinalizedL1BlockSelection(t, bc, epochFirstSlotTime-1, expectedSlot-beaconSlotsPerEpoch, expectedL1BlockHashPrevEpoch)
+	})
+
+	// Execution payload block hash retrieved here - https://beaconcha.in/slot/11161248
+	expectedL1BlockHashNextEpoch := common.HexToHash("0x7892cbc14d57ab7036a722306bcae1fc07a202fc5907a227cce539b5f1ca41b3")
+	t.Run("NextEpochStartSlot", func(t *testing.T) {
+		checkFinalizedL1BlockSelection(t, bc, epochLastSlotTime+beaconChainSlotDurationSeconds, expectedSlot+beaconSlotsPerEpoch, expectedL1BlockHashNextEpoch)
+	})
+}
+
+func checkFinalizedL1BlockSelection(t *testing.T, bc *beaconClient, targetTime, expectedSlot uint64, expectedBlockHash common.Hash) {
+	ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
+	t.Cleanup(cancel)
+	calculatedHash, err := bc.MostRecentFinalizedL1BlockAtTime(targetTime)
+	require.NoError(t, err)
+	assert.Equal(t, expectedBlockHash, calculatedHash)
+	// Double check that we are targeting the correct slot
+	block, err := bc.BeaconBlock(ctx, expectedSlot)
+	require.NoError(t, err)
+	assert.Equal(t, expectedBlockHash.String(), block.Data.Message.Body.ExecutionPayload.BlockHash)
+}