add system lane match handler

x/opchild/lanes/free_test.go

@@ -58,6 +58,7 @@ var _ sdk.Tx = MockTx{}
 var _ sdk.FeeTx = &MockTx{}
 
 type MockTx struct {
+	msgs     []sdk.Msg
 	feePayer []byte
 }
 
@@ -66,7 +67,7 @@ func (tx MockTx) GetMsgsV2() ([]protov2.Message, error) {
 }
 
 func (tx MockTx) GetMsgs() []sdk.Msg {
-	return nil
+	return tx.msgs
 }
 
 func (tx MockTx) GetGas() uint64 {

x/opchild/lanes/system.go

@@ -0,0 +1,28 @@
+package lanes
+
+import (
+	sdk "github.com/cosmos/cosmos-sdk/types"
+
+	blockbase "github.com/skip-mev/block-sdk/v2/block/base"
+
+	"github.com/initia-labs/OPinit/x/opchild/types"
+)
+
+// SystemLaneMatchHandler returns the default match handler for the system lane.
+func SystemLaneMatchHandler() blockbase.MatchHandler {
+	return func(ctx sdk.Context, tx sdk.Tx) bool {
+		if len(tx.GetMsgs()) != 1 {
+			return false
+		}
+
+		for _, msg := range tx.GetMsgs() {
+			switch msg.(type) {
+			case *types.MsgUpdateOracle:
+			default:
+				return false
+			}
+		}
+
+		return true
+	}
+}

x/opchild/lanes/system_test.go

@@ -0,0 +1,44 @@
+package lanes_test
+
+import (
+	"testing"
+
+	"cosmossdk.io/log"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	banktypes "github.com/cosmos/cosmos-sdk/x/bank/types"
+
+	"github.com/cometbft/cometbft/proto/tendermint/types"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/initia-labs/OPinit/x/opchild/lanes"
+	opchildtypes "github.com/initia-labs/OPinit/x/opchild/types"
+)
+
+func Test_SystemLaneMatchHandler(t *testing.T) {
+	ctx := sdk.NewContext(nil, types.Header{}, false, log.NewNopLogger())
+
+	handler := lanes.SystemLaneMatchHandler()
+
+	// 1 system message
+	require.True(t, handler(ctx, MockTx{
+		msgs: []sdk.Msg{
+			&opchildtypes.MsgUpdateOracle{},
+		},
+	}))
+
+	// 2 system messages
+	require.False(t, handler(ctx, MockTx{
+		msgs: []sdk.Msg{
+			&opchildtypes.MsgUpdateOracle{},
+			&opchildtypes.MsgUpdateOracle{},
+		},
+	}))
+
+	// 1 non-system message
+	require.False(t, handler(ctx, MockTx{
+		msgs: []sdk.Msg{
+			&banktypes.MsgSend{},
+		},
+	}))
+}