supervisor: add Identifier JSON marshaling (#10718)

* supervisor: add Identifier JSON marshaling

Adds json marshaling so that the type used within
is easier to deal with.

* op-supervisor: fix identifier struct

---------
Co-authored-by: protolambda <proto@protolambda.com>

op-supervisor/supervisor/types/types.go

 package types
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 
+	"github.com/holiman/uint256"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
 )
 
 type Identifier struct {
+	Origin      common.Address
+	BlockNumber uint64
+	LogIndex    uint64
+	Timestamp   uint64
+	ChainID     uint256.Int // flat, not a pointer, to make Identifier safe as map key
+}
+
+type identifierMarshaling struct {
 	Origin      common.Address `json:"origin"`
 	BlockNumber hexutil.Uint64 `json:"blockNumber"`
 	LogIndex    hexutil.Uint64 `json:"logIndex"`
@@ -16,6 +27,29 @@ type Identifier struct {
 	ChainID     hexutil.U256   `json:"chainID"`
 }
 
+func (id Identifier) MarshalJSON() ([]byte, error) {
+	var enc identifierMarshaling
+	enc.Origin = id.Origin
+	enc.BlockNumber = hexutil.Uint64(id.BlockNumber)
+	enc.LogIndex = hexutil.Uint64(id.LogIndex)
+	enc.Timestamp = hexutil.Uint64(id.Timestamp)
+	enc.ChainID = (hexutil.U256)(id.ChainID)
+	return json.Marshal(&enc)
+}
+
+func (id *Identifier) UnmarshalJSON(input []byte) error {
+	var dec identifierMarshaling
+	if err := json.Unmarshal(input, &dec); err != nil {
+		return err
+	}
+	id.Origin = dec.Origin
+	id.BlockNumber = uint64(dec.BlockNumber)
+	id.LogIndex = uint64(dec.LogIndex)
+	id.Timestamp = uint64(dec.Timestamp)
+	id.ChainID = (uint256.Int)(dec.ChainID)
+	return nil
+}
+
 type SafetyLevel string
 
 func (lvl SafetyLevel) String() string {

op-supervisor/supervisor/types/types_test.go

+package types
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/holiman/uint256"
+)
+
+func FuzzRoundtripIdentifierJSONMarshal(f *testing.F) {
+	f.Fuzz(func(t *testing.T, origin []byte, blockNumber uint64, logIndex uint64, timestamp uint64, chainID []byte) {
+		if len(chainID) > 32 {
+			chainID = chainID[:32]
+		}
+
+		id := Identifier{
+			Origin:      common.BytesToAddress(origin),
+			BlockNumber: blockNumber,
+			LogIndex:    logIndex,
+			Timestamp:   timestamp,
+			ChainID:     uint256.Int{},
+		}
+		id.ChainID.SetBytes(chainID)
+
+		raw, err := json.Marshal(&id)
+		require.NoError(t, err)
+
+		var dec Identifier
+		require.NoError(t, json.Unmarshal(raw, &dec))
+
+		require.Equal(t, id.Origin, dec.Origin)
+		require.Equal(t, id.BlockNumber, dec.BlockNumber)
+		require.Equal(t, id.LogIndex, dec.LogIndex)
+		require.Equal(t, id.Timestamp, dec.Timestamp)
+		require.Equal(t, id.ChainID, dec.ChainID)
+	})
+}