Mini Shell

import json
import select
import sys

from pyroute2.dhcp import (
    BOOTREQUEST,
    DHCPACK,
    DHCPDISCOVER,
    DHCPOFFER,
    DHCPREQUEST,
)
from pyroute2.dhcp.dhcp4msg import dhcp4msg
from pyroute2.dhcp.dhcp4socket import DHCP4Socket


def req(s, poll, msg, expect):
    do_req = True
    xid = None

    while True:
        # get transaction id
        if do_req:
            xid = s.put(msg)['xid']
        # wait for response
        events = poll.poll(2)
        for fd, event in events:
            response = s.get()
            if response['xid'] != xid:
                do_req = False
                continue
            if response['options']['message_type'] != expect:
                raise Exception("DHCP protocol error")
            return response
        do_req = True


def action(ifname):
    s = DHCP4Socket(ifname)
    poll = select.poll()
    poll.register(s, select.POLLIN | select.POLLPRI)

    # DISCOVER
    discover = dhcp4msg(
        {
            'op': BOOTREQUEST,
            'chaddr': s.l2addr,
            'options': {
                'message_type': DHCPDISCOVER,
                'parameter_list': [1, 3, 6, 12, 15, 28],
            },
        }
    )
    reply = req(s, poll, discover, expect=DHCPOFFER)

    # REQUEST
    request = dhcp4msg(
        {
            'op': BOOTREQUEST,
            'chaddr': s.l2addr,
            'options': {
                'message_type': DHCPREQUEST,
                'requested_ip': reply['yiaddr'],
                'server_id': reply['options']['server_id'],
                'parameter_list': [1, 3, 6, 12, 15, 28],
            },
        }
    )
    reply = req(s, poll, request, expect=DHCPACK)
    s.close()
    return reply


def run():
    if len(sys.argv) > 1:
        ifname = sys.argv[1]
    else:
        ifname = 'eth0'
    print(json.dumps(action(ifname), indent=4))


if __name__ == '__main__':
    run()