Implement CheckMessages API

op-supervisor/supervisor/backend/backend.go

@@ -159,6 +159,24 @@ func (su *SupervisorBackend) CheckMessage(identifier types.Identifier, payloadHa
 	return safest, nil
 }
 
+func (su *SupervisorBackend) CheckMessages(
+	messages []types.Message,
+	minSafety types.SafetyLevel) error {
+	for _, msg := range messages {
+		safety, err := su.CheckMessage(msg.Identifier, msg.PayloadHash)
+		if err != nil {
+			return fmt.Errorf("failed to check message: %w", err)
+		}
+		if !safety.AtLeastAsSafe(minSafety) {
+			return fmt.Errorf("message %v (safety level: %v) does not meet the minimum safety %v",
+				msg.Identifier,
+				safety,
+				minSafety)
+		}
+	}
+	return nil
+}
+
 // CheckBlock checks if the block is safe according to the safety level
 // The block is considered safe if all logs in the block are safe
 // this is decided by finding the last log in the block and

op-supervisor/supervisor/backend/mock.go

@@ -43,6 +43,10 @@ func (m *MockBackend) CheckMessage(identifier types.Identifier, payloadHash comm
 	return types.CrossUnsafe, nil
 }
 
+func (m *MockBackend) CheckMessages(messages []types.Message, minSafety types.SafetyLevel) error {
+	return nil
+}
+
 func (m *MockBackend) CheckBlock(chainID *hexutil.U256, blockHash common.Hash, blockNumber hexutil.Uint64) (types.SafetyLevel, error) {
 	return types.CrossUnsafe, nil
 }

op-supervisor/supervisor/frontend/frontend.go

@@ -16,6 +16,7 @@ type AdminBackend interface {
 
 type QueryBackend interface {
 	CheckMessage(identifier types.Identifier, payloadHash common.Hash) (types.SafetyLevel, error)
+	CheckMessages(messages []types.Message, minSafety types.SafetyLevel) error
 	CheckBlock(chainID *hexutil.U256, blockHash common.Hash, blockNumber hexutil.Uint64) (types.SafetyLevel, error)
 }
 
@@ -34,6 +35,14 @@ func (q *QueryFrontend) CheckMessage(identifier types.Identifier, payloadHash co
 	return q.Supervisor.CheckMessage(identifier, payloadHash)
 }
 
+// CheckMessage checks the safety-level of a collection of messages,
+// and returns if the minimum safety-level is met for all messages.
+func (q *QueryFrontend) CheckMessages(
+	messages []types.Message,
+	minSafety types.SafetyLevel) error {
+	return q.Supervisor.CheckMessages(messages, minSafety)
+}
+
 // CheckBlock checks the safety-level of an L2 block as a whole.
 func (q *QueryFrontend) CheckBlock(chainID *hexutil.U256, blockHash common.Hash, blockNumber hexutil.Uint64) (types.SafetyLevel, error) {
 	return q.Supervisor.CheckBlock(chainID, blockHash, blockNumber)

op-supervisor/supervisor/types/types.go

@@ -13,6 +13,11 @@ import (
 	"github.com/ethereum/go-ethereum/common/hexutil"
 )
 
+type Message struct {
+	Identifier  Identifier  `json:"identifier"`
+	PayloadHash common.Hash `json:"payloadHash"`
+}
+
 type Identifier struct {
 	Origin      common.Address
 	BlockNumber uint64
@@ -83,6 +88,22 @@ func (lvl *SafetyLevel) UnmarshalText(text []byte) error {
 	return nil
 }
 
+// AtLeastAsSafe returns true if the receiver is at least as safe as the other SafetyLevel.
+func (lvl *SafetyLevel) AtLeastAsSafe(min SafetyLevel) bool {
+	switch min {
+	case Invalid:
+		return true
+	case Unsafe:
+		return *lvl != Invalid
+	case Safe:
+		return *lvl == Safe || *lvl == Finalized
+	case Finalized:
+		return *lvl == Finalized
+	default:
+		return false
+	}
+}
+
 const (
 	CrossFinalized SafetyLevel = "cross-finalized"
 	Finalized      SafetyLevel = "finalized"