#!/usr/bin/env python3
#
# Tests the DNS configuration of a Mail-in-a-Box.
#
# tests/dns.py ipaddr hostname
#
# where ipaddr is the IP address of your Mail-in-a-Box
# and hostname is the domain name to check the DNS for.

import sys
import re
import difflib
import dns.reversename
import dns.resolver

if len(sys.argv) < 3:
    print("Usage: tests/dns.py ipaddress hostname [primary hostname]")
    sys.exit(1)

ipaddr, hostname = sys.argv[1:3]
primary_hostname = hostname
if len(sys.argv) == 4:
    primary_hostname = sys.argv[3]


def test(server, description):
    tests = [
        (hostname, "A", ipaddr),
        #(hostname, "NS", "ns1.%s.;ns2.%s." % (primary_hostname, primary_hostname)),
        ("ns1." + primary_hostname, "A", ipaddr),
        ("ns2." + primary_hostname, "A", ipaddr),
        ("www." + hostname, "A", ipaddr),
        (hostname, "MX", "10 " + primary_hostname + "."),
        (hostname, "TXT", "\"v=spf1 mx -all\""),
        ("mail._domainkey." + hostname, "TXT", "\"v=DKIM1; k=rsa; s=email; \" \"p=__KEY__\""),
        #("_adsp._domainkey." + hostname, "TXT", "\"dkim=all\""),
        ("_dmarc." + hostname, "TXT", "\"v=DMARC1; p=quarantine\""),
    ]
    return test2(tests, server, description)


def test_ptr(server, description):
    ipaddr_rev = dns.reversename.from_address(ipaddr)
    tests = [
        (ipaddr_rev, "PTR", hostname+'.'),
    ]
    return test2(tests, server, description)


def test2(tests, server, description):
    first = True
    resolver = dns.resolver.get_default_resolver()
    resolver.nameservers = [server]
    for qname, rtype, expected_answer in tests:
        # do the query and format the result as a string
        try:
            response = dns.resolver.query(qname, rtype)
        except dns.resolver.NoNameservers:
            # host did not have an answer for this query
            print("Could not connect to %s for DNS query." % server)
            sys.exit(1)
        except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
            # host did not have an answer for this query; not sure what the
            # difference is between the two exceptions
            response = ["[no value]"]
        response = ";".join(str(r) for r in response)
        # normalize DKIM key
        response = re.sub(r"(\"p=).*(\")", r"\1__KEY__\2", response)
        # normalize TXT records (DNSSEC signing inserts empty text
        # string components)
        response = response.replace("\"\" ", "")

        # is it right?
        if response == expected_answer:
            #print(server, ":", qname, rtype, "?", response)
            continue

        # show problem
        if first:
            print("Incorrect DNS Response from", description)
            print()
            print("QUERY               ", "RESPONSE    ", "CORRECT VALUE", sep='\t')
            first = False

        print((qname + "/" + rtype).ljust(20), response.ljust(12), expected_answer, sep='\t')
    # success
    return first

# Test the response from the machine itself.
if not test(ipaddr, "Mail-in-a-Box"):
    print ()
    print ("Please run the Mail-in-a-Box setup script on %s again." % hostname)
    sys.exit(1)
else:
    print ("The Mail-in-a-Box provided correct DNS answers.")
    print ()

    # If those settings are OK, also test Google's Public DNS
    # to see if the machine is hooked up to recursive DNS properly.
    if not test("8.8.8.8", "Google Public DNS"):
        print ()
        print ("Check that the nameserver settings for %s are correct at your domain registrar. It may take a few hours for Google Public DNS to update after changes on your Mail-in-a-Box." % hostname)
        sys.exit(1)
    else:
        print ("Your domain registrar or DNS host appears to be configured correctly as well. Public DNS provides the same answers.")
        print ()

        # And if that's OK, also check reverse DNS (the PTR record).
        if not test_ptr("8.8.8.8", "Google Public DNS (Reverse DNS)"):
            print ()
            print ("The reverse DNS for %s is not correct. Consult your ISP for how to set the reverse DNS (also called the PTR record) for %s to %s." % (hostname, hostname, ipaddr))
            sys.exit(1)
        else:
            print ("And the reverse DNS for the domain is correct.")
            print ()
            print ("DNS is OK.")