Python supress warnings while creating a empty pcap file with Scapy

Question

I want to create an empty pcap file. I’m using wrpcap module of ‘Scapy’. But wrpcap takes exactly 2 arguments: one is the file name and other is the packet list like:

wrpcap("my.pcap",my_pkt_list)

Since I want to make it, empty and I don’t have a packet list, I’m writing an empty string to the pcap file. Which is creating the file but also giving a warning as well as errors since a string doesn’t match to a packet type.

WARNING: PcapWriter: unknown LL type for str. Using type 1 (Ethernet)
Traceback (most recent call last):
  File "test.py", line 35, in <module>
    wrpcap("pcap/FU.pcap","")
  File "/usr/lib/python2.7/site-packages/scapy/utils.py", line 466, in wrpcap
    PcapWriter(filename, *args, **kargs).write(pkt)
  File "/usr/lib/python2.7/site-packages/scapy/utils.py", line 646, in write
    self._write_packet(pkt)
  File "/usr/lib/python2.7/site-packages/scapy/utils.py", line 688, in _write_packet
    sec = int(packet.time)
AttributeError: 'str' object has no attribute 'time'

For now, I’m able to suppress the errors with try and except but unable to suppress the warning.

Code

from scapy.all import *
try:
    wrpcap("my.pcap","")
except:
    pass

and the warning is still there:

WARNING: PcapWriter: unknown LL type for str. Using type 1 (Ethernet)

How to suppress it from inside the python code?

Asked By: RatDon

||

Source

Answer 1

The text “WARNING: …” is not part of the exception and will thus not be surpressed by your try clause.

An idea I got was to redirect stdout during the call

from scapy.all import *
try:
    old_stdout = sys.stdout
    sys.stdout = None
    wrpcap("my.pcap","")
    sys.stdout = old_stdout
except:
    pass

that should surpress any and all output during the call

Answered By: Johan

Answer 2

Python has a built in method in the standard library for supressing warnings:

import warnings
warnings.simplefilter("ignore", Warning)

You can read more about the warnings library in the docs.

EDIT

It doesn’t look like scapy uses the warnings library to generate this. Instead it logs them to a logger called scapy.runtime with a level of warning. There’s obviously some default logging config to echo that to stdout. You could add your own logging handler for scapy.runtime to supress them.

Answered By: Ben

Answer 3

You can avoid that warning by using PcapWriter method of scapy.

from scapy.all import *
try:
    writer=PcapWriter("my.pcap")
except:
    pass

This creates your empty pcap file. When you want to write some packets to it, just use the following code:

writer.write(<Your_packets>)
writer.flush()

Answered By: wonder

Answer 4

You can suppress this warning by disabling warning logging before the call wrpcap:

import logging
logging.getLogger("scapy.runtime").setLevel(logging.ERROR)

Answered By: ecdhe

Python supress warnings while creating a empty pcap file with Scapy

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