无法在Python中使自定义DNS服务器工作

Question

我在让Python使用自定义DNS服务器时遇到了很大的麻烦。
我按照这个告诉urllib2使用自定义DNS的指南操作。
如果我不指定self.host和self.port，它就会正常运行，不会出现阻塞。

这是我的代码：

import urllib2
import httplib
import socket
class MyHTTPConnection (httplib.HTTPConnection):
    def connect (self):
        if self.host == 'www.porn.com':
            self.host = '208.67.222.123' #OpenDNS FamilyShield
            self.port = 53
        self.sock = socket.create_connection ((self.host, self.port))
class MyHTTPHandler (urllib2.HTTPHandler):
    def http_open (self, req):
        return self.do_open (MyHTTPConnection, req)

opener = urllib2.build_opener(MyHTTPHandler)
urllib2.install_opener (opener)
f = urllib2.urlopen ('http://www.porn.com/videos/anime-toon.html')
data = f.read ()
print data

我一直收到“raise BadStatusLine(line)”这个错误。

错误日志：

Traceback (most recent call last):
  File "K:\Desktop\rte\dns2.py", line 16, in <module>
    f = urllib2.urlopen ('http://www.porn.com/videos/anime-toon.html')
  File "C:\Python27\lib\urllib2.py", line 126, in urlopen
    return _opener.open(url, data, timeout)
  File "C:\Python27\lib\urllib2.py", line 394, in open
    response = self._open(req, data)
  File "C:\Python27\lib\urllib2.py", line 412, in _open
    '_open', req)
  File "C:\Python27\lib\urllib2.py", line 372, in _call_chain
    result = func(*args)
  File "K:\Desktop\rte\dns2.py", line 12, in http_open
    return self.do_open (MyHTTPConnection, req)
  File "C:\Python27\lib\urllib2.py", line 1170, in do_open
    r = h.getresponse(buffering=True)
  File "C:\Python27\lib\httplib.py", line 1027, in getresponse
    response.begin()
  File "C:\Python27\lib\httplib.py", line 407, in begin
    version, status, reason = self._read_status()
  File "C:\Python27\lib\httplib.py", line 371, in _read_status
    raise BadStatusLine(line)
BadStatusLine: ''

编辑：根据isedev的回复，我发现我走错了方向。

似乎urllib2没有识别到对名称服务器的更改。

import dns.resolver
import urllib2

resolver = dns.resolver.Resolver()
resolver.nameservers = ['208.67.222.123']
answer = resolver.query('www.porn.com','A')
web_url = 'http://www.porn.com/videos/anime-toon.html'
req1 = urllib2.Request(web_url)
req1.add_header('User-Agent', 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3')
response1 = urllib2.urlopen(req1)
html=response1.read()
print html

Answer 1

我觉得你可能误解了你提到的“自定义DNS”答案中的内容。那个解决方案中的例子其实并不是在设置一个自定义的DNS服务器——MyResolver类只是作为一个示例，它只是把'news.bbc.co.uk'这个名字硬编码成了一个IP地址。

所以你的代码实际上是在把一个HTTP请求重定向到'www.porn.com'（80端口），然后转到OpenDNS Family Shield的DNS服务器（53端口）……这显然会导致你遇到的错误。

所以你需要做的是把：

if self.host == 'www.porn.com':
    self.host = '208.67.222.123' #OpenDNS FamilyShield
    self.port = 53

替换成能够直接通过选定的DNS服务器解析'www.porn.com'的代码（比如使用dnspython）。

假设你已经安装了dnspython这个包，你可以这样做：

import urllib2
import httplib
import socket
import dns.resolver

class MyHTTPConnection (httplib.HTTPConnection):
    def connect (self):
        if self.host == 'www.porn.com':
            resolver = dns.resolver.Resolver()
            resolver.nameservers = ['208.67.222.123']
            answer = resolver.query(self.host,'A')
            self.host = answer.rrset.items[0].address
        self.sock = socket.create_connection ((self.host, self.port))

class MyHTTPHandler (urllib2.HTTPHandler):
    def http_open (self, req):
        return self.do_open (MyHTTPConnection, req)

opener = urllib2.build_opener(MyHTTPHandler)
urllib2.install_opener (opener)
f = urllib2.urlopen ('http://www.porn.com/videos/anime-toon.html')
data = f.read ()
print data

这段代码返回'404 - 找不到'，网络追踪显示HTTP请求被发送到了'hit-adult.opendns.com'，这就是当使用'208.67.222.123'这个DNS服务器时'www.porn.com'解析到的地址：

dig @208.67.222.123 www.porn.com A
;; ANSWER SECTION:
www.porn.com.           0       IN      A       67.215.65.130

nslookup 67.215.65.130
130.65.215.67.in-addr.arpa      name = hit-adult.opendns.com.

以上只是一个示例。真正的代码还需要进行错误检查等等……