async_dns

This is the documentation for v2.x. Click here for 1.x documentation.

• Features
• Prerequisite
• Installation
• CLI
  • Resolver
  • Server
• API
  • Client
  • Routing
• DoH support
• DNS Spoofing
• Test
• Logging
• References

Features

• Built with asyncio in pure Python, no third party dependency is required
• Support DNS over UDP / TCP
• Support DNS over HTTPS
• Support DNS over TLS

Prerequisite

• Python >=3.6

Installation

$ pip3 install async_dns
# or
$ pip3 install git+https://github.com/gera2ld/async_dns.git

CLI

Resolver

usage: python3 -m async_dns.resolver [-h] [-n NAMESERVERS [NAMESERVERS ...]] [-t TYPES [TYPES ...]]
                                     hostnames [hostnames ...]

Async DNS resolver

positional arguments:
  hostnames             the hostnames to query

optional arguments:
  -h, --help            show this help message and exit
  -n NAMESERVERS [NAMESERVERS ...], --nameservers NAMESERVERS [NAMESERVERS ...]
                        name servers
  -t TYPES [TYPES ...], --types TYPES [TYPES ...]
                        query types, default as `any`

Examples:

# Resolve an IP
$ python3 -m async_dns.resolver www.google.com
$ python3 -m async_dns.resolver -t mx -- gmail.com

# Query via TCP
$ python3 -m async_dns.resolver -n tcp://127.0.0.1 -- www.google.com

# Query via TLS
$ python3 -m async_dns.resolver -n tcps://dns.alidns.com -- www.google.com

# Query from non-standard ports
$ python3 -m async_dns.resolver -n udp://127.0.0.1:1053 -- www.google.com

# Query from HTTPS
$ python3 -m async_dns.resolver -n https://dns.alidns.com/dns-query -- www.google.com

Note: -- is required before hostnames if the previous option can have multiple arguments.

Server

usage: python3 -m async_dns.server [-h] [-b BIND] [--hosts HOSTS] [-x [PROXY [PROXY ...]]]

DNS server by Gerald.

optional arguments:
  -h, --help            show this help message and exit
  -b BIND, --bind BIND  the address for the server to bind
  --hosts HOSTS         the path of a hosts file, `none` to disable hosts, `local` to read from
                        local hosts file
  -x [PROXY [PROXY ...]], --proxy [PROXY [PROXY ...]]
                        the proxy DNS servers, `none` to serve as a recursive server, `default` to
                        proxy to default nameservers

Note: TLS and HTTPS are not supported in async_dns server. Consider async-doh for DoH server support.

Examples:

# Start a DNS proxy server on :53
$ python3 -m async_dns.server -b :53 --hosts /etc/hosts

# Start a DNS server over TCP proxy
$ python3 -m async_dns.server -x tcp://114.114.114.114

# Start a DNS recursive server
$ python3 -m async_dns.server -x none

API

import asyncio
from async_dns.core import types
from async_dns.resolver import ProxyResolver

resolver = ProxyResolver()
res, cached = asyncio.run(resolver.query('www.baidu.com', types.A))
print(res)

Client

The client sends a request to a remote server and returns the message directly. Unlike resolvers, client does not have a cache and does not modify the response.

import asyncio
from async_dns.core import types, Address
from async_dns.resolver import DNSClient

async def query():
    client = DNSClient()
    res = await client.query('www.google.com', types.A,
                             Address.parse('8.8.8.8'))
    print(res)
    print(res.aa)

asyncio.run(query())

Routing

ProxyResolver supports routing based on domains:

resolver = ProxyResolver(proxies=[
    ('*.lan', ['192.168.1.1']),                             # query 'udp://192.168.1.1:53' for '*.lan' domains
    (lambda d: d.endswith('.local'), ['tcp://127.0.0.1']),  # query tcp://127.0.0.1:53 for domains ending with '.local'
    '8.8.8.8',                                              # equivalent to (None, ['8.8.8.8']), matches all others
])

DoH support

This library contains a simple implementation of DoH (aka DNS over HTTPS) client with partial HTTP protocol implemented.

If you need a more powerful DoH client based on aiohttp, or a DoH server, consider async-doh.

DNS Spoofing

You can easily add records to the cache with a hosts file or the cache API.

• Start a server with a custom hosts file:

  $ python3 -m async_dns.server -b :53 --hosts /path/to/custom/hosts
  

• Add some additional records to a resolver:

  from async_dns.core import parse_hosts_file, types
  
  for name, qtype, data in parse_hosts_file(hosts):
      resolver.cache.add(name, qtype, data)
  
  resolver.cache.add('www.example.com', types.A, ['127.0.0.1'])
  

Test

$ python3 -m unittest

# Or with tox
$ tox -e py

Logging

Logging does not work out of the box in v2. It requires at least minimal logging configuration.

logging.basicConfig(level=logging.INFO)

You can also add a formatter for the logger:

import logging
from async_dns.core import logger

logger.setLevel(logging.INFO)
handler = logging.StreamHandler()
fmt = logging.Formatter('%(asctime)s %(levelname)s: %(message)s')
handler.setFormatter(fmt)
logger.addHandler(handler)

References

• https://tools.ietf.org/html/rfc1034
• https://tools.ietf.org/html/rfc1035
• https://tools.ietf.org/html/rfc1464 TXT
• https://tools.ietf.org/html/rfc2915 NAPTR