enum opcode {
        CREATE = 1;
        DELETE = 2;
        READ   = 3;
        WRITE  = 4;
        START  = 5;
        STOP   = 6;
        REPLY  = 7;
}

message cdap {
        required opcode opcode    = 1;
        required uint32 invoke_id = 2;
        optional uint32 flags     = 3;
        optional string name      = 4;
        optional bytes value      = 5;
        optional int32 result     = 6;
}
