Hackish dhcpd.leases to hosts converter (for mdns emulation with dnsmasq)

leases_to_hosts.py

#!/usr/bin/env python3

import sys

if len(sys.argv) != 3:
    print("Usage ./leases_to_hosts.py <DHCPD LEASES FILE> <OUTFILE>")
    sys.exit(1)

def parse_string(f):
    res = b''
    escaped = False
    while True:
        c = f.read(1)
        if c == b'' or (c == b'"' and (not escaped)):
            return res
        if c == b'\\':
            escaped = True
        else:
            escaped = False
        res = res + c

def parse_dict(f):
    res = []
    while True:
        c = f.read(1)
        if c == b'}' or c == b'':
            return res
        else:
            f.seek(-1, 1)
        t = parse_tuple(f)
        if len(t) > 0:
            res += [t]

def parse_tuple(f):
    res = []
    s = b''
    in_comment = False
    while True:
        c = f.read(1)

        if c == b'#':
            in_comment = True
        elif c == b'\n':
            in_comment = False

        if (c == b'' or c == b' ' or c == b'\n' or c == b'{' or c == b'"' 
                     or c == b';' or c == b'}'):
            if len(s) > 0:
                res = res + [s]
                s = b''
            if c == b'{':
                res = res + [parse_dict(f)]
                return res
            elif c == b'"':
                res = res + [parse_string(f)]
            elif c == b';' or c == b'' or c == b'}':
                if c == b'}':
                    f.seek(-1, 1)
                return res
        elif not in_comment:
            s = s + c

def to_dict(arr):
    res = {}
    for v in arr:
        if isinstance(v, (list, tuple)) and len(v) >= 2:
            if len(v) == 2:
                res[v[0]] = v[1]
            else:
                res[v[0]] = v[1:]
    return res

with open(sys.argv[1], 'rb') as f:
    leases = {}
    while True:
        t = parse_tuple(f)
        if len(t) == 0:
            break
        if len(t) == 3 and t[0] == b'lease':
            leases[t[1]] = to_dict(t[2])

    hosts = {}
    for ip, info in leases.items():
        if b'client-hostname' in info:
            host = info[b'client-hostname']
            if not host in hosts:
                hosts[host] = ip

with open(sys.argv[2], 'wb') as f:
    f.write(b'192.168.180.1 andreas-router.local\n')
    f.write(b'192.168.180.1 andreas-router.lan\n')
    for host, ip in hosts.items():
        f.write(ip)
        f.write(b' ')
        f.write(host)
        f.write(b'.local\n')

        f.write(ip)
        f.write(b' ')
        f.write(host)
        f.write(b'.lan\n')