********************
Build your own tools
********************

.. note::

   This section has not been updated for scapy3k yet. Code examples may not work directly. Try bytes() instead of str() and b'string' instead of b'somestring'.

You can use Scapy to make your own automated tools. You can also extend Scapy without having to edit its source file.

If you have built some interesting tools, please contribute back to the mailing-list!

    
Using Scapy in your tools
=========================
You can easily use Scapy in your own tools. Just import what you need and do it.

This first example takes an IP or a name as the first parameter, sends an ICMP echo request packet and displays the completely dissected return packet::

    #! /usr/bin/env python3
    
    import sys
    from scapy.all import sr1,IP,ICMP
    
    p=sr1(IP(dst=sys.argv[1])/ICMP())
    if p:
        p.show()

This is a more complex example which does an ARP ping and reports what it found with LaTeX formating::

    #! /usr/bin/env python3
    # arping2tex : arpings a network and outputs a LaTeX table as a result
    
    import sys
    if len(sys.argv) != 2:
        print("Usage: arping2tex <net>\n  eg: arping2tex 192.168.1.0/24")
        sys.exit(1)
    
    from scapy.all import srp,Ether,ARP,conf
    conf.verb=0
    ans,unans=srp(Ether(dst="ff:ff:ff:ff:ff:ff")/ARP(pdst=sys.argv[1]),
                  timeout=2)
    
    print(r"\begin{tabular}{|l|l|}")
    print(r"\hline")
    print(r"MAC & IP\\")
    print(r"\hline")
    for snd,rcv in ans:
        print(rcv.sprintf(r"%Ether.src% & %ARP.psrc%\\"))
    print(r"\hline")
    print(r"\end{tabular}")

Here is another tool that will constantly monitor all interfaces on a machine and print all ARP request it sees, even on 802.11 frames from a Wi-Fi card in monitor mode. Note the store=0 parameter to sniff() to avoid storing all packets in memory for nothing::

    #! /usr/bin/env python3
    from scapy.all import *
    
    def arp_monitor_callback(pkt):
        if ARP in pkt and pkt[ARP].op in (1,2): #who-has or is-at
            return pkt.sprintf("%ARP.hwsrc% %ARP.psrc%")
    
    sniff(prn=arp_monitor_callback, filter="arp", store=0)

For a real life example, you can check `Wifitap <http://sid.rstack.org/static/articles/w/i/f/Wifitap_EN_9613.html>`_.


Extending Scapy with add-ons
============================

If you need to add some new protocols, new functions, anything, you can write it directly into Scapy source file. But this is not very convenient. Even if those modifications are to be integrated into Scapy, it can be more convenient to write them in a separate file.

Once you've done that, you can launch Scapy and import your file, but this is still not very convenient. Another way to do that is to make your file executable and have it call the Scapy function named interact()::

    #! /usr/bin/env python3
    
    # Set log level to benefit from Scapy warnings
    import logging
    logging.getLogger("scapy").setLevel(1)
    
    from scapy.all import *
    
    class Test(Packet):
        name = "Test packet"
        fields_desc = [ ShortField("test1", 1),
                        ShortField("test2", 2) ]
    
    def make_test(x,y):
        return Ether()/IP()/Test(test1=x,test2=y)
    
    if __name__ == "__main__":
        interact(mydict=globals(), mybanner="Test add-on v3.14")


If you put the above listing in the test_interact.py file and make it executable, you'll get::

    # ./test_interact.py 
    Welcome to Scapy (0.9.17.109beta)
    Test add-on v3.14
    >>> make_test(42,666)
    <Ether type=0x800 |<IP |<Test test1=42 test2=666 |>>>
    

