【Python Network】权威域名服务器级联查询

如果PyDNS库，跳过本地名称服务器，直接向权威名称服务器查询。如baidu.com查询.com域名服务器，并从各个域名服务器中查询下一即域名，并输出相关信息。

#! /usr/bin/env python
# Expanded DNS library example - Chapter 4 - DNSany.py

import sys, DNS

def hierquery(qstring, qtype):
    """Given a query type qtype, returns answers of that type for lookup
        qstring. If no answers are found, removes the most specific component
        (the part before the leftmost period) and retries the query with the result.
        If the topmost query fails, returns None. """
    reqobj = DNS.Request()
    try:
        answerobj = reqobj.req(name=qstring, qtype=qtype)
        answers = [x['data'] for x in answerobj.answers if x['type']==qtype]
    except DNS.Base.DNSError:
        answers = []
    if len(answers):
        return answers
    else:
        remainder = qstring.split(".", 1);
        if len(remainder) == 1:
            return None
        else:
            return hierquery(remainder[1], qtype)

def findnameservers(hostname):
    """Attempts to determine the authoritative nameservers for a given
        hostname, Returns None on failure. """
    return hierquery(hostname, DNS.Type.NS)

def getrecordsfromnameserver(qstring, qtype, nslist):
    """Given a list of nameservers in nslist, executes the query requested
        by qstring and qtype on each in order, returning the data from the
        first server that returned 1 or more answers. If no server returned
        any answers, return []. """
    for ns in nslist:
        reqobj = DNS.Request(server = ns)
        try:
            answers = reqobj.req(name=qstring, qtype=qtype).answers
            if len(answers):
                return answers
        except DNS.Base.DNSError:
            pass
        return []

def nslookup(qstring, qtype, verbose = -1):
    nslist = findnameservers(qstring)
    if nslist is None:
        raise RuntimeError, "Could not find nameserver to use."
    if verbose:
        print "Using nameservers:", ", ".join(nslist)
    return getrecordsfromnameserver(qstring, qtype, nslist)

if __name__ == "__main__":
    query = sys.argv[1]
    DNS.DiscoverNameServers()

    answers = nslookup(query, DNS.Type.ANY)
    if not len(answers):
        print "Not found."
    for item in answers:
        print "%-5s %s" % (item['typename'], item['data'])

运行结果如图所示：