【Python Network】分解DNS查询结果

针对DNS查询records，通过NS、PTR、CNAME和MX类别不同，返回数据将包含另外主机名。为了解最终的IP地址，通过将返回信息分解。继续使用PyDNS获取详细信息。

#! /usr/bin/env python
# DNS query program - Example 4 - DNSquery.py

import sys, DNS, re, DNSany

def getreverse(query):
    """ Given the query, returns an approciate reverse lookup string
        under IN-ADDR.ARPA if query is an IP address; otherwire, return
        None. This function is not IPv6-compatiable. """
    if re.search("^\d+.\d+.\d+.\d+$", query):
        octets = query.split('.')
        octets.reverse()
        return '.'.join(octets) + '.IN-ADDR.ADDR'
    return None

def formatline(index, typename, descr, data):
    retval = "%-2s %-5s" % (index, typename)
    data = data.replace("\n", "\n ")
    if descr != None and len(descr):
        retval += " %-12s" % (descr + ":")
    return retval + " " + data

DNS.DiscoverNameServers()
queries = [(sys.argv[1], DNS.Type.ANY)]
donequeries = []
descriptions = {'A': 'IP address',
                'TXT': 'Data',
                'PTR': 'Host name',
                'CNAME': 'Alias for',
                'NS': 'Name server'}

while len(queries):
    (query, qtype) = queries.pop(0)
    if query in donequeries:
        # Don't look up the same thing twice
        continue
    donequeries.append(query)
    print "-" * 77
    print "Results for %s (lookup type %s)" % (query, DNS.Type.typestr(qtype))
    print
    rev = getreverse(query)
    if rev is not None:
        print "IP address given; doing reverse lookup using", rev
        query = rev
    
    answers = DNSany.nslookup(query, qtype, verbose = 0)    
    if not len(answers):
        print "Not found"
    
    count = 0
    for answer in answers:
        count += 1
        if answer['typename'] == 'MX':
            print formatline(count, 'MX', 'Mail Server', 
                             "%s, priority %d" % (answer['data'][1], answer['data'][0]))
            queries.append((answer['data'][1], DNS.Type.A))
        elif answer['typename'] == 'SOA':
            data = "\n" + "\n".join(str(x) for x in answer['data'])
            print formatline(count, 'SOA', 'Start of authority', data)
        elif answer['typename'] in descriptions:
            print formatline(count, answer['typename'], descriptions[answer['typename']], str(answer['data']))
        else:
            print formatline(count, answer['typename'], None, str(answer['data']))

        if answer['typename'] in ['CNAME', 'PTR']:
            queries.append((answer['data'], DNS.Type.ANY))
        if answer['typename'] == 'NS':
            queries.append((answer['data'], DNS.Type.A))

以baidu.com为例，运行截图如下。