Scapy Exception: Bad condition in format string?

Question

I have this packet sniffer I made:

from scapy.all import *
def decode(rawload):
    #still trying to figure out how to decode the payload
    return str(rawload) #temporary
try:
    sniff(iface = "wlan0", filter="host 192.168.1.13", prn=lambda x:x.sprintf("src: %IP.src% (%Ether.src%) receiver: %IP.dst% load: {}".format(decode(x.payload)))) #Error right here
except KeyboardInterrupt:
    sys.exit(1)

And the error I get is "Scapy Exception: Bad condition in format string: []". Could anyone explain what I'm doing wrong here?

Pierre · Accepted Answer · 2018-03-24 21:37:41Z

1

The result of your .format() call is not a valid string for Scapy Packet.sprintf() (probably because of the content of rawload.

I guess it contains { and }, which are used in .sprintf() for conditions (see help(Packet.sprintf)).

I'd suggest that you replace your code with something like:

prn=lambda pkt: pkt.sprintf("src: %IP.src% (%Ether.src%) receiver: %IP.dst% load: ") + decode(x.payload)

answered Mar 24, 2018 at 21:37

Pierre

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