#! /usr/bin/python
#
# update_dns.py - Update DNS static entries on your Mikrotik Router(s) using this python script.
# Copyright (C) 2021 WILDERNETS LLC, Distributed under GPL-3.0, GNU General Public License v3.0 only
#
# How it works:
# - Grab a copy of the master host table off the host table server.
# - Get existing DNS static entries from a list of Mikrotik routers.
# - Compare entries to the master host table
# - Issue add/set/remove commands as needed to update the Mikrotik DNS entries.
#
# Setup Notes:
# - Setup DNS server on your mikrotik router(s)
# - Run this on a trusted secure system so you don't have to trust the host master with access to your router(s).
# - OR just Comment out Step0 and run from the machine that has the host master file.
# - Setup password-less ssh to the host master machine.
# - Setup password-less ssh to your router(s).
# - Adv Topic: consider setting up a portable subnet/IP for your router so you can implement DNS server redundancy.
# (I use 10.10.10.10 on two routers and 10.10.10.1 on two routers and inject these as /32 into OSPF)
#
# Requirements:
# - Setup password-less SSH using keys to the machine that hosts the master copy of the host table
# - Setup password-less SSH using keys to the router that act as DNS servers
# - Change the Script vars listed below
# - Test on a non-production router
#
# Coding Notes:
# - Hosts file parsed into two master dictionaries.
# - For each router updated a working copy is made of these two masters.
# - As hosts are processed they are deleted from the dictionary copy.
# - Next router updated gets a brand new copy from the master.
#
import re               # strip comments
import sys              # system stuff
import subprocess       # Popen command
import os               # Execute scp command

# Script vars
#HOSTMASTER = "nismaster:etc/hosts"
#HOSTMASTER = "/etc/hosts"
HOSTSFILE  = "/root/hosts.txt"
SSHCMD     = "/ip dns static export"
routerlist = ['10.87.2.1']
routeruser = "dnsupdate"
debug      = 1

# Step0 Go Grab latest hosts file
#print "# Getting hosts file: scp "+HOSTMASTER+" "+HOSTSFILE
#os.system("scp "+HOSTMASTER+" "+HOSTSFILE)

#os.system("cp "+HOSTMASTER+" "+HOSTSFILE)

# Step1 Open hosts file, parse and check for duplicates
if debug: print("# Verifying hostsfile: "+HOSTSFILE)
error = 0
masteriphosts = {}
masterhostip  = {}
hosts = open(HOSTSFILE,'r',encoding='utf-8')

for line in hosts:
    if not line.startswith('#') and line.strip():
        line=re.sub(r'#.*$', '', line).rstrip()
        data = line.split()
        i = data.pop(0)
        if debug > 1: print("checking ip "+i)
        if (i in masteriphosts):
            print("ERROR: Duplicate ipaddress "+i+" for "+str(data)+" and "+str(masteriphosts[i]))
            error += 1
        else:
            masteriphosts[i] = data

        for h in data:
            if debug > 1: print("checking host "+h)
            if (h in masterhostip):
                print("ERROR: Duplicate hostname "+h+" in hosts file for "+i+" and "+masterhostip[h])
                error += 1
            else:
                masterhostip[h] = i
if error:
    exit(1)

for router in routerlist:
    USERHOST = routeruser+"@"+router
    iphosts  = masteriphosts.copy()
    hostip   = masterhostip.copy()
    addrname = {}
    nameaddr = {}

    # Step2 SSH to EACH DNS Router and Export the DNS static table and Parse
    print("# Getting router DNS entries: ssh",USERHOST, SSHCMD)
    ssh = subprocess.Popen(["ssh", "%s" % USERHOST, SSHCMD],
                           shell=False,
                           stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE)
    result = ssh.stdout.readlines()
    if result == []:
        error = ssh.stderr.readlines()
       # print >>sys.stderr, "ERROR: %s" % error
    else:
        if debug: print("# Parsing DNS Static Export")
        for line in result:
            if line.startswith(b'\n') :
                line=re.sub(r'add address=', '', line).rstrip()
                line=re.sub(r'name=', '', line)
                a,n = line.split()
                # Check name is a Host
                if (n in hostip):
                    i = hostip[n]
                    # Check for duplicate DNS names
                    if (n in nameaddr):
                        command = "ssh "+USERHOST+" /ip dns static remove [find name="+n+" address="+a+"]; # Delete Duplicate"
                        print(command)
                        os.system(command)
                    # Changed address for name
                    elif (a != i):
                        command = "ssh "+USERHOST+" /ip dns static set address="+i+" [find name="+n+" address="+a+"]; # Changed Address"
                        print(command)
                        os.system(command)
                    addrname[i] = n
                    nameaddr[n] = i
                    # Delete key from hostip after used so they are gone before step3
                    del hostip[n]
                else:
                    # Delete it if not Host
                    command = "ssh "+USERHOST+" /ip dns static remove [find name="+n+" address="+a+"]; # Delete Entry"
                    print(command)
                    os.system(command)

    # Step3 Remaining keys in hostip need to be added.
    if debug: print("# Generate Add Commands")
    for h in hostip:
        i = hostip[h]
        command = "ssh "+USERHOST+" /ip dns static add address="+i+" name="+h+"; # Add Entry"
        print(command)
        os.system(command)

if debug: print("# Finished")
exit(0)