如何在 Python 中进行 DNS 查找，包括引用 /etc/hosts？

Question

dnspython 可以很好地完成我的 DNS 查找，但它完全忽略了 /etc/hosts 的内容。

是否有一个 python 库调用可以做正确的事情？即首先检查etc/hosts，否则只回退到DNS查找？

Answer 1

我不确定您是要自己进行 DNS 查找，还是只需要主机的 ip。如果你想要后者，

/!\ socket.gethostbyname 已弃用，首选socket.getaddrinfo

来自man gethostbyname：

gethostbyname*()、gethostbyaddr*()、[...] 函数已过时。应用程序应使用 getaddrinfo(3)、getnameinfo(3)，

import socket
print(socket.gethostbyname('localhost')) # result from hosts file
print(socket.gethostbyname('google.com')) # your os sends out a dns query

Answer 2

Python 中的正常名称解析工作正常。为什么你需要 DNSpython。只需使用socket 的getaddrinfo，它遵循为您的操作系统配置的规则（在Debian 上，它遵循/etc/nsswitch.conf：

>>> print(socket.getaddrinfo('google.com', 80))
[(10, 1, 6, '', ('2a00:1450:8006::63', 80, 0, 0)), (10, 2, 17, '', ('2a00:1450:8006::63', 80, 0, 0)), (10, 3, 0, '', ('2a00:1450:8006::63', 80, 0, 0)), (10, 1, 6, '', ('2a00:1450:8006::68', 80, 0, 0)), (10, 2, 17, '', ('2a00:1450:8006::68', 80, 0, 0)), (10, 3, 0, '', ('2a00:1450:8006::68', 80, 0, 0)), (10, 1, 6, '', ('2a00:1450:8006::93', 80, 0, 0)), (10, 2, 17, '', ('2a00:1450:8006::93', 80, 0, 0)), (10, 3, 0, '', ('2a00:1450:8006::93', 80, 0, 0)), (2, 1, 6, '', ('209.85.229.104', 80)), (2, 2, 17, '', ('209.85.229.104', 80)), (2, 3, 0, '', ('209.85.229.104', 80)), (2, 1, 6, '', ('209.85.229.99', 80)), (2, 2, 17, '', ('209.85.229.99', 80)), (2, 3, 0, '', ('209.85.229.99', 80)), (2, 1, 6, '', ('209.85.229.147', 80)), (2, 2, 17, '', ('209.85.229.147', 80)), (2, 3, 0, '', ('209.85.229.147', 80))]

Answer 3

听起来您不想自己解析 dns（这可能是错误的命名法）dnspython 似乎是一个独立的 dns 客户端，可以理解的是它会忽略您的操作系统，因为它绕过了操作系统的实用程序。

我们可以查看一个名为 getent 的 shell 实用程序来了解（debian 11 类似）操作系统如何为程序解析 dns，这可能是所有使用套接字实现的类 *nix 系统的标准。

查看man getent的“主机”部分，其中提到了getaddrinfo的使用，我们可以将其视为man getaddrinfo

要在 python 中使用它，我们必须从数据结构中提取一些信息

.

import socket

def get_ipv4_by_hostname(hostname):
    # see `man getent` `/ hosts `
    # see `man getaddrinfo`

    return list(
        i        # raw socket structure
            [4]  # internet protocol info
            [0]  # address
        for i in 
        socket.getaddrinfo(
            hostname,
            0  # port, required
        )
        if i[0] is socket.AddressFamily.AF_INET  # ipv4

        # ignore duplicate addresses with other socket types
        and i[1] is socket.SocketKind.SOCK_RAW  
    )

print(get_ipv4_by_hostname('localhost'))
print(get_ipv4_by_hostname('google.com'))

---

Answer 4

list( map( lambda x: x[4][0], socket.getaddrinfo( \
     'www.example.com.',22,type=socket.SOCK_STREAM)))

为您提供 www.example.com 的地址列表。 （ipv4 和 ipv6）

Answer 5

此代码适用于返回可能属于特定 URI 的所有 IP 地址。由于许多系统现在处于托管环境（AWS/Akamai/等）中，系统可能会返回多个 IP 地址。 lambda 是从@Peter Silva “借来的”。

def get_ips_by_dns_lookup(target, port=None):
    '''
        this function takes the passed target and optional port and does a dns
        lookup. it returns the ips that it finds to the caller.

        :param target:  the URI that you'd like to get the ip address(es) for
        :type target:   string
        :param port:    which port do you want to do the lookup against?
        :type port:     integer
        :returns ips:   all of the discovered ips for the target
        :rtype ips:     list of strings

    '''
    import socket

    if not port:
        port = 443

    return list(map(lambda x: x[4][0], socket.getaddrinfo('{}.'.format(target),port,type=socket.SOCK_STREAM)))

ips = get_ips_by_dns_lookup(target='google.com')

Answer 6

我发现这种方法可以将扩展为 IP 列表的 DNS RR 主机名扩展为成员主机名列表：

#!/usr/bin/python

def expand_dnsname(dnsname):
    from socket import getaddrinfo
    from dns import reversename, resolver
    namelist = [ ]
    # expand hostname into dict of ip addresses
    iplist = dict()
    for answer in getaddrinfo(dnsname, 80):
        ipa = str(answer[4][0])
        iplist[ipa] = 0
    # run through the list of IP addresses to get hostnames
    for ipaddr in sorted(iplist):
        rev_name = reversename.from_address(ipaddr)
        # run through all the hostnames returned, ignoring the dnsname
        for answer in resolver.query(rev_name, "PTR"):
            name = str(answer)
            if name != dnsname:
                # add it to the list of answers
                namelist.append(name)
                break
    # if no other choice, return the dnsname
    if len(namelist) == 0:
        namelist.append(dnsname)
    # return the sorted namelist
    namelist = sorted(namelist)
    return namelist

namelist = expand_dnsname('google.com.')
for name in namelist:
    print name

当我运行它时，会列出几个 1e100.net 主机名：