Async DNS resolver for ReactPHP

v0.4.12 2018-01-14 10:04 UTC


Build Status

Async DNS resolver for ReactPHP.

The main point of the DNS component is to provide async DNS resolution. However, it is really a toolkit for working with DNS messages, and could easily be used to create a DNS server.

Table of contents

Basic usage

The most basic usage is to just create a resolver through the resolver factory. All you need to give it is a nameserver, then you can start resolving names, baby!

$loop = React\EventLoop\Factory::create();
$factory = new React\Dns\Resolver\Factory();
$dns = $factory->create('', $loop);

$dns->resolve('')->then(function ($ip) {
    echo "Host: $ip\n";


See also the first example.

Note that the factory loads the hosts file from the filesystem once when creating the resolver instance. Ideally, this method should thus be executed only once before the loop starts and not repeatedly while it is running.

Pending DNS queries can be cancelled by cancelling its pending promise like so:

$promise = $resolver->resolve('');


But there's more.


You can cache results by configuring the resolver to use a CachedExecutor:

$loop = React\EventLoop\Factory::create();
$factory = new React\Dns\Resolver\Factory();
$dns = $factory->createCached('', $loop);

$dns->resolve('')->then(function ($ip) {
    echo "Host: $ip\n";


$dns->resolve('')->then(function ($ip) {
    echo "Host: $ip\n";


If the first call returns before the second, only one query will be executed. The second result will be served from an in memory cache. This is particularly useful for long running scripts where the same hostnames have to be looked up multiple times.

See also the third example.

Custom cache adapter

By default, the above will use an in memory cache.

You can also specify a custom cache implementing CacheInterface to handle the record cache instead:

$cache = new React\Cache\ArrayCache();
$loop = React\EventLoop\Factory::create();
$factory = new React\Dns\Resolver\Factory();
$dns = $factory->createCached('', $loop, $cache);

See also the wiki for possible cache implementations.

Advanced Usage

For more advanced usages one can utilize the React\Dns\Query\Executor directly. The following example looks up the IPv6 address for

$loop = Factory::create();

$executor = new Executor($loop, new Parser(), new BinaryDumper(), null);

    new Query($name, Message::TYPE_AAAA, Message::CLASS_IN, time())
)->done(function (Message $message) {
    foreach ($message->answers as $answer) {
        echo 'IPv6: ' . $answer->data . PHP_EOL;
}, 'printf');


See also the fourth example.


Note that the above Executor class always performs an actual DNS query. If you also want to take entries from your hosts file into account, you may use this code:

$hosts = \React\Dns\Config\HostsFile::loadFromPathBlocking();

$executor = new Executor($loop, new Parser(), new BinaryDumper(), null);
$executor = new HostsFileExecutor($hosts, $executor);

    new Query('localhost', Message::TYPE_A, Message::CLASS_IN, time())


The recommended way to install this library is through Composer. New to Composer?

This will install the latest supported version:

$ composer require react/dns:^0.4.12

See also the CHANGELOG for details about version upgrades.

This project aims to run on any platform and thus does not require any PHP extensions and supports running on legacy PHP 5.3 through current PHP 7+ and HHVM. It's highly recommended to use PHP 7+ for this project.


To run the test suite, you first need to clone this repo and then install all dependencies through Composer. Because the test suite contains some circular dependencies, you may have to manually specify the root package version like this:

$ COMPOSER_ROOT_VERSION=`git describe --abbrev=0` composer install

To run the test suite, go to the project root and run:

$ php vendor/bin/phpunit

The test suite also contains a number of functional integration tests that rely on a stable internet connection. If you do not want to run these, they can simply be skipped like this:

$ php vendor/bin/phpunit --exclude-group internet


MIT, see LICENSE file.


  • RFC 1034 Domain Names - Concepts and Facilities
  • RFC 1035 Domain Names - Implementation and Specification