Can't get Custom DNS server working in Python

Question

I'm having real trouble getting python to use a custom dns server. I have followed this Tell urllib2 to use custom DNS If I don't specify a self.host and self.port, it will go through without blocking.

Here is the code:

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

I keep getting a "raise BadStatusLine(line)" error

Error log:

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: ''

EDIT: Going on isedev response, that I was going about it the wrong way.

It doesn't seem to register with urllib2 the changes to the namesservers

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

I think you've misunderstood what's being done in the "Custom DNS" answer you refer to. The example given in that solution is not in fact setting up a custom DNS server - the MyResolver class is given as example only and performs a hard-coded name-to-IP for 'news.bbc.co.uk'.

So what your code is actually doing is redirecting an HTTP request to 'www.porn.com' (port 80) to the OpenDNS Family Shield DNS server (on port 53)... which will obviously lead to the error you're getting.

So what you need to do is replace:

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

with code that actually resolves 'www.porn.com' against the chosen DNS server directly (using dnspython for instance).

Assuming you've got the dnspython package installed, you could do something like:

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

This code returns '404 - not found' and network trace shows HTTP request to 'hit-adult.opendns.com', which is what 'www.porn.com' resolves to when using the '208.67.222.123' nameserver:

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.

The above is an example only. Real code would require error checking, etc...