diff --git a/pkg/packet/packet.go b/pkg/packet/packet.go
index 074b7175..17a5638e 100644
--- a/pkg/packet/packet.go
+++ b/pkg/packet/packet.go
@@ -477,10 +477,18 @@ type ErrorPacketType struct {
 	Error string          `json:"error"`
 }
 
-func (et *ErrorPacketType) GetType() string {
+func (*ErrorPacketType) GetType() string {
 	return ErrorPacketStr
 }
 
+func (p *ErrorPacketType) String() string {
+	ckStr := ""
+	if p.CK != "" {
+		ckStr = fmt.Sprintf(", ck=%s", p.CK)
+	}
+	return fmt.Sprintf("error[%s%s]", p.Error, ckStr)
+}
+
 func MakeErrorPacket(errorStr string) *ErrorPacketType {
 	return &ErrorPacketType{Type: ErrorPacketStr, Error: errorStr}
 }
diff --git a/pkg/server/server.go b/pkg/server/server.go
index b7996b05..cc0c84f3 100644
--- a/pkg/server/server.go
+++ b/pkg/server/server.go
@@ -147,20 +147,24 @@ func RunServer() (int, error) {
 	initPacket := packet.MakeInitPacket()
 	initPacket.Version = base.MShellVersion
 	server.Sender.SendPacket(initPacket)
+	builder := packet.MakeRunPacketBuilder()
 	for pk := range server.MainInput.MainCh {
 		if server.Debug {
 			fmt.Printf("PK> %s\n", packet.AsString(pk))
 		}
-		if pk.GetType() == packet.RunPacketStr {
-			runPacket := pk.(*packet.RunPacketType)
-			server.runCommand(runPacket)
+		ok, runPacket := builder.ProcessPacket(pk)
+		if ok {
+			if runPacket != nil {
+				server.runCommand(runPacket)
+				continue
+			}
 			continue
 		}
 		if cmdPk, ok := pk.(packet.CommandPacketType); ok {
 			server.ProcessCommandPacket(cmdPk)
 			continue
 		}
-		server.Sender.SendErrorPacket(fmt.Sprintf("invalid packet '%s' sent to mshell", packet.AsExtType(pk)))
+		server.Sender.SendErrorPacket(fmt.Sprintf("invalid packet '%s' sent to mshell", packet.AsString(pk)))
 		continue
 	}
 	return 0, nil