refined NewBlockMsg handling in Istanbul

consensus/istanbul/backend/handler.go

@@ -18,6 +18,7 @@ package backend
 
 import (
 	"errors"
+	"github.com/ethereum/go-ethereum/consensus/istanbul/core"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/consensus"
@@ -93,8 +94,9 @@ func (sb *backend) HandleMsg(addr common.Address, msg p2p.Msg) (bool, error) {
 	}
 	if msg.Code == 0x07 && sb.core.IsProposer() { // eth.NewBlockMsg: import cycle
 		// this case is to safeguard the race of similar block which gets propagated from other node while this node is proposing
+		// need to make sure this is the Gossip message from Istanbul peers
 
-		if data, hash, err := sb.decode(msg); err == nil && len(data) > 0 {
+		if data, hash, err := sb.decode(msg); err == nil && core.IsIstanbulPayload(data) {
 			if _, ok := sb.knownMessages.Get(hash); ok {
 				return true, nil
 			}

consensus/istanbul/core/types.go

@@ -160,6 +160,15 @@ func (m *message) String() string {
 //
 // helper functions
 
+// Check if a payload is encoded from Istanbul `message` struct
+func IsIstanbulPayload(payload []byte) bool {
+	msg := new(message)
+	if err := msg.FromPayload(payload, nil); err != nil {
+		return false
+	}
+	return true
+}
+
 func Encode(val interface{}) ([]byte, error) {
 	return rlp.EncodeToBytes(val)
 }