interop: draft interop messages RPC

eth/backend.go

@@ -357,6 +357,13 @@ func (s *Ethereum) APIs() []rpc.API {
 	// Append any APIs exposed explicitly by the consensus engine
 	apis = append(apis, s.engine.APIs(s.BlockChain())...)
 
+	if s.BlockChain().Config().IsOptimism() {
+		apis = append(apis, rpc.API{
+			Namespace: "opstack",
+			Service:   ethapi.NewOPStackAPI(s.APIBackend),
+		})
+	}
+
 	// Append all the local APIs and return
 	return append(apis, []rpc.API{
 		{

internal/ethapi/api_opstack.go

@@ -0,0 +1,112 @@
+package ethapi
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/holiman/uint256"
+
+	"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/rpc"
+)
+
+type OPStackBackend interface {
+	Backend // TODO we can narrow down the backend interface, instead of relying on the full backend
+}
+
+// OPStackAPI provides an API to access OP-Stack specific data
+type OPStackAPI struct {
+	backend OPStackBackend
+}
+
+// NewOPStackAPI creates a new Ethereum protocol API for full nodes.
+func NewOPStackAPI(backend OPStackBackend) *OPStackAPI {
+	return &OPStackAPI{backend: backend}
+}
+
+type InteropMessage struct {
+	Nonce uint256.Int
+
+	SourceChain common.Hash
+	TargetChain common.Hash
+
+	From common.Address
+	To   common.Address
+
+	Value uint256.Int
+
+	// TODO limit this to u64 in contract
+	GasLimit hexutil.Uint64
+
+	Data hexutil.Bytes
+}
+
+func (msg *InteropMessage) Root() common.Hash {
+	return common.Hash{}
+}
+
+type InteropSourceInfo struct {
+	BlockHash              common.Hash
+	StateHash              common.Hash
+	BlockNumber            hexutil.Uint64
+	Timestamp              hexutil.Uint64
+	WithdrawalsStorageHash common.Hash
+}
+
+// The L2 output root (of different versions) can be computed from the above data.
+
+type InteropMessages struct {
+	Info     *InteropSourceInfo
+	Messages []*InteropMessage
+}
+
+var crossL2OutboxAddr = common.HexToAddress("")
+
+func (api *OPStackAPI) InteropMessages(ctx context.Context, blockNrOrHash rpc.BlockNumberOrHash) (*InteropMessages, error) {
+	header, err := api.backend.HeaderByNumberOrHash(ctx, blockNrOrHash)
+	if err != nil {
+		return nil, fmt.Errorf("failed to retrieve header of %s: %v", blockNrOrHash.String(), err)
+	}
+	info := &InteropSourceInfo{
+		BlockHash:              header.Hash(),
+		StateHash:              header.Root,
+		BlockNumber:            hexutil.Uint64(header.Number.Uint64()),
+		Timestamp:              hexutil.Uint64(header.Time),
+		WithdrawalsStorageHash: common.Hash{}, // TODO need a backend method for state storage read
+	}
+	// warning: the retrieved logs raw, not hydrated, i.e. we do not spend time on adding metadata like hashes etc. to them.
+	blockLogs, err := api.backend.GetLogs(ctx, header.Hash(), header.Number.Uint64())
+	if err != nil {
+		return nil, fmt.Errorf("failed to retrieve logs of %s (%d): %v", header.Hash(), header.Number.Uint64(), err)
+	}
+	var messages []*InteropMessage
+	for i, txLogs := range blockLogs {
+		for j, log := range txLogs {
+			msg, err := logToInteropMessageMaybe(log)
+			if err != nil {
+				return nil, fmt.Errorf("failed to parse interop log of block %s, tx %d, relative index %d: %w", header.Hash(), i, j, err)
+			}
+			if msg != nil {
+				messages = append(messages, msg)
+			}
+		}
+	}
+	return &InteropMessages{
+		Info:     info,
+		Messages: messages,
+	}, nil
+}
+
+// logToInteropMessageMaybe parses log data into an interop message.
+// Nil, nil is returned if it's not an interop log.
+// An error is returned if it's an invalid interop log
+func logToInteropMessageMaybe(log *types.Log) (*InteropMessage, error) {
+	if log.Address != crossL2OutboxAddr {
+		return nil, nil
+	}
+	// TODO check log topic
+	// TODO parse log contents into message
+	return nil, nil
+}