套接字名與DNS 操作小記

代碼位置

https://github.com/duganlx/fopnp/tree/m/py3

使用getaddrinfo()創建並連接套接字

文件位置：fopnp/py3/chapter04/www_ping.py

import argparse, socket, sys


def connect_to(hostname_or_ip):
    try:
        infolist = socket.getaddrinfo(
            hostname_or_ip, 'www', 0, socket.SOCK_STREAM, 0,
            socket.AI_ADDRCONFIG | socket.AI_V4MAPPED | socket.AI_CANONNAME,
        )
    except socket.gaierror as e:
        print('Name service failure:', e.args[1])
        sys.exit(1)

    info = infolist[0]  # per standard recommendation, try the first one
    socket_args = info[0:3]
    address = info[4]
    s = socket.socket(*socket_args)
    try:
        s.connect(address)
    except socket.error as e:
        print('Network failure:', e.args[1])
    else:
        print('Success: host', info[3], 'is listening on port 80')


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Try connecting to port 80')
    parser.add_argument('hostname', help='hostname that you want to contact')
    connect_to(parser.parse_args().hostname)

運行效果

python www_ping.py www.baidu.com
Success: host www.a.shifen.com is listening on port 80

一個包含遞歸的簡單DNS查詢

文件位置：fopnp/py3/chapter04/dns_basic.py
需要先下載Python 3：pip install dnspython3

import argparse, dns.resolver


def lookup(name):
    for qtype in 'A', 'AAAA', 'CNAME', 'MX', 'NS':
        answer = dns.resolver.query(name, qtype, raise_on_no_answer=False)
        if answer.rrset is not None:
            print(answer.rrset)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Resolve a name using DNS')
    parser.add_argument('name', help='name that you want to look up in DNS')
    lookup(parser.parse_args().name)

運行效果

python dns_basic.py python.org
python.org. 603333 IN A 45.55.99.72
python.org. 580755 IN MX 50 mail.python.org.
python.org. 23296 IN NS ns2.p11.dynect.net.
python.org. 23296 IN NS ns3.p11.dynect.net.
python.org. 23296 IN NS ns1.p11.dynect.net.
python.org. 23296 IN NS ns4.p11.dynect.net.

解析電子郵件域名

文件位置：fopnp/py3/chapter04/dns_mx.py

import argparse, dns.resolver


def resolve_hostname(hostname, indent=''):
    "Print an A or AAAA record for `hostname`; follow CNAMEs if necessary."
    indent = indent + '    '
    answer = dns.resolver.query(hostname, 'A')
    if answer.rrset is not None:
        for record in answer:
            print(indent, hostname, 'has A address', record.address)
        return
    answer = dns.resolver.query(hostname, 'AAAA')
    if answer.rrset is not None:
        for record in answer:
            print(indent, hostname, 'has AAAA address', record.address)
        return
    answer = dns.resolver.query(hostname, 'CNAME')
    if answer.rrset is not None:
        record = answer[0]
        cname = record.address
        print(indent, hostname, 'is a CNAME alias for', cname)  # ?
        resolve_hostname(cname, indent)
        return
    print(indent, 'ERROR: no A, AAAA, or CNAME records for', hostname)


def resolve_email_domain(domain):
    "For an email address `name@domain` find its mail server IP addresses."
    try:
        answer = dns.resolver.query(domain, 'MX', raise_on_no_answer=False)
    except dns.resolver.NXDOMAIN:
        print('Error: No such domain', domain)
        return
    if answer.rrset is not None:
        records = sorted(answer, key=lambda record: record.preference)
        print('This domain has', len(records), 'MX records')
        for record in records:
            name = record.exchange.to_text(omit_final_dot=True)
            print('Priority', record.preference)
            resolve_hostname(name)
    else:
        print('This domain has no explicit MX records')
        print('Attempting to resolve it as an A, AAAA, or CNAME')
        resolve_hostname(domain)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='Find mailserver IP address')
    parser.add_argument('domain', help='domain that you want to send mail to')
    resolve_email_domain(parser.parse_args().domain)

運行效果

python dns_mx.py python.org
This domain has 1 MX records
Priority 50
     mail.python.org has A address 188.166.95.178