op-program: Handle pre-images that already exist

The exact same receipt RLP may result from different transactions in different blocks so ErrAlreadyExists must be handled when storing trie nodes.

op-program/host/prefetcher/prefetcher.go

@@ -6,18 +6,17 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/common/hexutil"
-	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/crypto"
-	"github.com/ethereum/go-ethereum/log"
-
 	"github.com/ethereum-optimism/optimism/op-node/eth"
 	"github.com/ethereum-optimism/optimism/op-program/client/l1"
 	"github.com/ethereum-optimism/optimism/op-program/client/l2"
 	"github.com/ethereum-optimism/optimism/op-program/client/mpt"
 	"github.com/ethereum-optimism/optimism/op-program/host/kvstore"
 	"github.com/ethereum-optimism/optimism/op-program/preimage"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/log"
 )
 
 type L1Source interface {
@@ -33,6 +32,7 @@ type L2Source interface {
 }
 
 type Prefetcher struct {
+	logger    log.Logger
 	l1Fetcher L1Source
 	l2Fetcher L2Source
 	lastHint  string
@@ -41,6 +41,7 @@ type Prefetcher struct {
 
 func NewPrefetcher(logger log.Logger, l1Fetcher L1Source, l2Fetcher L2Source, kvStore kvstore.KV) *Prefetcher {
 	return &Prefetcher{
+		logger:    logger,
 		l1Fetcher: NewRetryingL1Source(logger, l1Fetcher),
 		l2Fetcher: NewRetryingL2Source(logger, l2Fetcher),
 		kvStore:   kvStore,
@@ -71,6 +72,7 @@ func (p *Prefetcher) prefetch(ctx context.Context, hint string) error {
 	if err != nil {
 		return err
 	}
+	p.logger.Debug("Prefetching", "type", hintType, "hash", hash)
 	switch hintType {
 	case l1.HintL1BlockHeader:
 		header, err := p.l1Fetcher.InfoByHash(ctx, hash)
@@ -143,8 +145,11 @@ func (p *Prefetcher) storeTransactions(txs types.Transactions) error {
 func (p *Prefetcher) storeTrieNodes(values []hexutil.Bytes) error {
 	_, nodes := mpt.WriteTrie(values)
 	for _, node := range nodes {
-		err := p.kvStore.Put(preimage.Keccak256Key(crypto.Keccak256Hash(node)).PreimageKey(), node)
-		if err != nil {
+		key := preimage.Keccak256Key(crypto.Keccak256Hash(node)).PreimageKey()
+		if err := p.kvStore.Put(key, node); errors.Is(err, kvstore.ErrAlreadyExists) {
+			// It's not uncommon for different tries to contain common nodes (esp for receipts)
+			continue
+		} else if err != nil {
 			return fmt.Errorf("failed to store node: %w", err)
 		}
 	}

op-program/host/prefetcher/prefetcher_test.go

@@ -129,6 +129,28 @@ func TestFetchL1Receipts(t *testing.T) {
 		require.EqualValues(t, hash, header.Hash())
 		assertReceiptsEqual(t, receipts, actualReceipts)
 	})
+
+	// Blocks may have identical RLP receipts for different transactions.
+	// Check that the node already existing is handled
+	t.Run("CommonTrieNodes", func(t *testing.T) {
+		prefetcher, l1Cl, _, kv := createPrefetcher(t)
+		l1Cl.ExpectInfoByHash(hash, eth.BlockToInfo(block), nil)
+		l1Cl.ExpectInfoAndTxsByHash(hash, eth.BlockToInfo(block), block.Transactions(), nil)
+		l1Cl.ExpectFetchReceipts(hash, eth.BlockToInfo(block), receipts, nil)
+		defer l1Cl.AssertExpectations(t)
+
+		// Pre-store one receipt node (but not the whole trie leading to it)
+		// This would happen if an identical receipt was in an earlier block
+		opaqueRcpts, err := eth.EncodeReceipts(receipts)
+		require.NoError(t, err)
+		_, nodes := mpt.WriteTrie(opaqueRcpts)
+		require.NoError(t, kv.Put(preimage.Keccak256Key(crypto.Keccak256Hash(nodes[0])).PreimageKey(), nodes[0]))
+
+		oracle := l1.NewPreimageOracle(asOracleFn(t, prefetcher), asHinter(t, prefetcher))
+		header, actualReceipts := oracle.ReceiptsByBlockHash(hash)
+		require.EqualValues(t, hash, header.Hash())
+		assertReceiptsEqual(t, receipts, actualReceipts)
+	})
 }
 
 func TestFetchL2Block(t *testing.T) {

op-program/preimage/iface.go

@@ -55,6 +55,14 @@ func (k Keccak256Key) PreimageKey() (out common.Hash) {
 	return
 }
 
+func (k Keccak256Key) String() string {
+	return common.Hash(k).String()
+}
+
+func (k Keccak256Key) TerminalString() string {
+	return common.Hash(k).String()
+}
+
 // Hint is an interface to enable any program type to function as a hint,
 // when passed to the Hinter interface, returning a string representation
 // of what data the host should prepare pre-images for.