如何使用Scapy计算捕获的数据包大小

Question

Recently I started to code using Scapy. Basing on the example from:

Scapy Sniffing with Custom Actions

I capture multicast UDP datagrams, but besides the amount of captured packets per second, I would like to store the size(in bytes) of packets captured each second(by that I'd multiply the result by 8 and I'd have bitrate). The problem is that capturedPacketsSize seems to be undefined nevertheless I defined it before def custom_action() .

I tried to define capturedPacketsSize in different places for eg before sniffing in while 1 loop. The same result.

from collections import Counter
from scapy.all import sniff

packet_counts = Counter()

capturedPacketsSize = 0

## Define our Custom Action function
def custom_action(packet):
    # Create tuple of Src/Dst in sorted order
    capturedPacketsSize += len(packet)     #here occurs error
    key = tuple(sorted([packet[0][1].src, packet[0][1].dst]))
    packet_counts.update([key])
    #return "Packet #{0}: {1} ==> {2}".format(sum(packet_counts.values()), packet[0][1].src, packet[0][1].dst)



print("_____.:|Entering infinite while loop|:._____")

while 1:
    print("Analysing Multicast packets")
    pkt = sniff(iface="eno4", filter="udp", prn=custom_action, timeout=1)
    print("\n".join("{0} <--> {1} :{2}".format(key[0], key[1], count) for key, count in packet_counts.items()))
    packet_counts.clear()
    print("Byterate for this moment is equal to: {0} Bytes per second".format(capturedPacketsSize))

Answer 1

Use the global keyword for the variable names inside the function-

def custom_action(packet):
    global capturedPacketsSize
    global packet_counts
    # Create tuple of Src/Dst in sorted order
    capturedPacketsSize += len(packet)     #here occurs error
    key = tuple(sorted([packet[0][1].src, packet[0][1].dst]))
    packet_counts.update([key])

You can read more about this keyword here