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aiodns provides a simple way for doing asynchronous DNS resolutions using pycares <https://github.com/saghul/pycares>_.

.. code:: python

import asyncio
import aiodns

loop = asyncio.get_event_loop()
resolver = aiodns.DNSResolver(loop=loop)

async def query(name, query_type):
    return await resolver.query(name, query_type)

coro = query('google.com', 'A')
result = loop.run_until_complete(coro)

The following query types are supported: A, AAAA, ANY, CAA, CNAME, MX, NAPTR, NS, PTR, SOA, SRV, TXT.

The API is pretty simple, the following functions are provided in the DNSResolver class:

• query(host, type): Do a DNS resolution of the given type for the given hostname. It returns an instance of asyncio.Future. The actual result of the DNS query is taken directly from pycares. As of version 1.0.0 of aiodns (and pycares, for that matter) results are always namedtuple-like objects with different attributes. Please check the documentation <http://pycares.readthedocs.org/en/latest/channel.html#pycares.Channel.query>_ for the result fields.
• gethostbyname(host, socket_family): Do a DNS resolution for the given hostname and the desired type of address family (i.e. socket.AF_INET). While query() always performs a request to a DNS server, gethostbyname() first looks into /etc/hosts and thus can resolve local hostnames (such as localhost). Please check the documentation <http://pycares.readthedocs.io/en/latest/channel.html#pycares.Channel.gethostbyname>_ for the result fields. The actual result of the call is a asyncio.Future.
• gethostbyaddr(name): Make a reverse lookup for an address.
• cancel(): Cancel all pending DNS queries. All futures will get DNSError exception set, with ARES_ECANCELLED errno.
• close(): Close the resolver. This releases all resources and cancels any pending queries. It must be called when the resolver is no longer needed (e.g., application shutdown). The resolver should only be closed from the event loop that created the resolver.

While not recommended for typical use cases, DNSResolver can be used as an async context manager for scenarios where automatic cleanup is desired:

.. code:: python

async with aiodns.DNSResolver() as resolver:
    result = await resolver.query('example.com', 'A')
    # resolver.close() is called automatically when exiting the context

Important: This pattern is discouraged for most applications because DNSResolver instances are designed to be long-lived and reused for many queries. Creating and destroying resolvers frequently adds unnecessary overhead. Use the context manager pattern only when you specifically need automatic cleanup for short-lived resolver instances, such as in tests or one-off scripts.

This library requires the use of an asyncio.SelectorEventLoop or winloop on Windows only when using a custom build of pycares that links against a system- provided c-ares library without thread-safety support. This is because non-thread-safe builds of c-ares are incompatible with the default ProactorEventLoop on Windows.

If you're using the official prebuilt pycares wheels on PyPI (version 4.7.0 or later), which include a thread-safe version of c-ares, this limitation does not apply and can be safely ignored.

The default event loop can be changed as follows (do this very early in your application):

.. code:: python

asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

This may have other implications for the rest of your codebase, so make sure to test thoroughly.

To run the test suite: python tests.py

Saúl Ibarra Corretgé s@saghul.net

aiodns uses the MIT license, check LICENSE file.

If you'd like to contribute, fork the project, make a patch and send a pull request. Have a look at the surrounding code and please, make yours look alike :-)