from trex_stl_lib.api import *

class STLS1(object):
    """ attack 48.0.0.1 at port 80
    """

    def __init__ (self):
        self.max_pkt_size_l3  =9*1024;

    def create_stream (self):

        # TCP SYN
        base_pkt  = Ether()/IP(dst="48.0.0.1")/TCP(dport=80,flags="S")


        # vm
        vm = STLScVmRaw( [ STLVmFlowVar(name="ip_src", 
                                              min_value="16.0.0.0", 
                                              max_value="18.0.0.254", 
                                              size=4, op="random"),

                           STLVmFlowVar(name="src_port", 
                                              min_value=1025, 
                                              max_value=65000, 
                                              size=2, op="random"),

                           STLVmWrFlowVar(fv_name="ip_src", pkt_offset= "IP.src" ),


                           STLVmWrFlowVar(fv_name="src_port", 
                                          pkt_offset= "TCP.sport"), # fix udp len  

                           # must be last 
                           STLVmFixChecksumHw(l3_offset = "IP",
                                              l4_offset = "TCP",
                                              l4_type  = CTRexVmInsFixHwCs.L4_TYPE_TCP )# hint, TRex can know that 

                          ]
                       )

        pkt = STLPktBuilder(pkt = base_pkt,
                            vm = vm)

        return STLStream(packet = pkt,
                         random_seed = 0x1234,# can be remove. will give the same random value any run
                         mode = STLTXCont())



    def get_streams (self, direction = 0, **kwargs):
        # create 1 stream 
        return [ self.create_stream() ]


# dynamic load - used for trex console or simulator
def register():
    return STLS1()




add simple example for FixHwChecksum instruction