Python - unrecognized arguments error with a warning message

Question

I have the following in my run.py script.

    import time

NUM_PACKETS = 500

import random
import argparse

import threading
from scapy.all import sniff
from scapy.all import Ether, IP, IPv6, TCP

parser = argparse.ArgumentParser(description='run_test.py')
parser.add_argument('--random-dport',
                    help='Use a random TCP dest port for each packet',
                    action="store_true", default=False)
args = parser.parse_args()

class PacketQueue:
    def __init__(self):
        self.pkts = []
        self.lock = threading.Lock()
        self.ifaces = set()

    def add_iface(self, iface):
        self.ifaces.add(iface)

    def get(self):
        self.lock.acquire()
        if not self.pkts:
            self.lock.release()
            return None, None
        pkt = self.pkts.pop(0)
        self.lock.release()
        return pkt

    def add(self, iface, pkt):
        if iface not in self.ifaces:
            return
        self.lock.acquire()
        self.pkts.append( (iface, pkt) )
        self.lock.release()

queue = PacketQueue()

def pkt_handler(pkt, iface):
    if IPv6 in pkt:
        return
    queue.add(iface, pkt)

class SnifferThread(threading.Thread):
    def __init__(self, iface, handler = pkt_handler):
        threading.Thread.__init__(self)
        self.iface = iface
        self.handler = handler

    def run(self):
        sniff(
            iface = self.iface,
            prn = lambda x: self.handler(x, self.iface)
        )

class PacketDelay:
    def __init__(self, bsize, bdelay, imin, imax, num_pkts = 100):
        self.bsize = bsize
        self.bdelay = bdelay
        self.imin = imin
        self.imax = imax
        self.num_pkts = num_pkts
        self.current = 1

    def __iter__(self):
        return self

    def next(self):
        if self.num_pkts <= 0:
            raise StopIteration
        self.num_pkts -= 1
        if self.current == self.bsize:
            self.current = 1
            return random.randint(self.imin, self.imax)
        else:
            self.current += 1
            return self.bdelay


pkt = Ether()/IP(dst='10.0.0.1', ttl=64)/TCP()

port_map = {
    1: "veth3",
    2: "veth5",
    3: "veth7"
}

iface_map = {}
for p, i in port_map.items():
    iface_map[i] = p

queue.add_iface("veth3")
queue.add_iface("veth5")

for p, iface in port_map.items():
    t = SnifferThread(iface)
    t.daemon = True
    t.start()

import socket

send_socket = socket.socket(socket.AF_PACKET, socket.SOCK_RAW,
                            socket.htons(0x03))
send_socket.bind((port_map[3], 0))

delays = PacketDelay(10, 5, 25, 100, NUM_PACKETS)
ports = []
print "Sending", NUM_PACKETS, "packets ..."
for d in delays:
    # sendp is too slow...
    # sendp(pkt, iface=port_map[3], verbose=0)
    if args.random_dport:
        pkt["TCP"].dport = random.randint(1025, 65535)
    send_socket.send(str(pkt))
    time.sleep(d / 1000.)
time.sleep(1)
iface, pkt = queue.get()
while pkt:
    ports.append(iface_map[iface])
    iface, pkt = queue.get()
print ports
print "DISTRIBUTION..."
for p in port_map:
    c = ports.count(p)
    print "port {}: {:>3} [ {:>5}% ]".format(p, c, 100. * c / NUM_PACKETS)

I tried running the script using the below command

./run_test.py '--random-dport' 2

It is throwing an unrecognized arguments error with the following message.

ubuntu@workshop:~/p4lang/tutorials/workshop_/mp$ sudo ./run.py 2 
WARNING: No route found for IPv6 destination :: (no default route?)
usage: run.py [-h] [--random-dport]
run_test.py: error: unrecognized arguments: 2
ubuntu@workshop:~/p4lang/tutorials/workshop/mp$

What could be the problem here. I assume the rest of the run.py code is fine and the problem is in the above lines. I can add the rest of the code if asked for. I am stuck with this for a long time. Any inputs will help me!

Answer 1

If you want to specify a specific port (e.g. 2)

I'm not sure why you're using action="store_true".

Just do (instead of your add_argument, the rest of the code is the same):

parser.add_argument("--random-dport", type=int,
                help='Use a random TCP dest port for each packet',
                default=1) #default to port 1

Then you can access the port by doing:

./run_test.py '--random-dport' 2
args.random-dport
>> 2

---

If you want to choose a random port

If you really want a true/false flag for a random port, as it seems your code is trying to achieve, you can use your original code, but then passing the 2 is pointless, as the presence of the random-dport flag will store true into the variable:

./run_test.py
args.random-dport
>>False

It was not present->false

./run_test.py '--random-dport' 
args.random-dport
>>True

It was present->true

./run_test.py '--random-dport' 2
>>error 

It had an extra value->error.

The 2 is meaningless here, you are specifying you want a RANDOM dport, which means you can't pick a specific one. The previous section let's you pick a specific port.)

---

Either way check out the argparse tutorial. It is very helpful for giving you info on what you want to do.