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74 lines
3.6 KiB
Markdown
74 lines
3.6 KiB
Markdown
---
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title: Asynchronous DNS Resolution
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permalink: /
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---
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`amphp/dns` provides asynchronous DNS name resolution for [Amp](http://amphp.org/amp).
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## Installation
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```bash
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composer require amphp/dns
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```
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## Usage
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### Configuration
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`amphp/dns` automatically detects the system configuration and uses it. On Unix-like systems it reads `/etc/resolv.conf` and respects settings for nameservers, timeouts, and attempts. On Windows it looks up the correct entries in the Windows Registry and takes the listed nameservers. You can pass a custom `ConfigLoader` instance to `BasicResolver` to load another configuration, such as a static config.
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It respects the system's hosts file on Unix and Windows based systems, so it works just fine in environments like Docker with named containers.
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The package uses a global default resolver with can be accessed and changed via `Amp\Dns\resolver()`. If an argument other than `null` is given, the given resolver is used as global instance. The instance is automatically bound to the current event loop. If you replace the event loop via `Amp\Loop::set()`, then you have to set a new global resolver.
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Usually you don't have to change the resolver. If you want to use a custom configuration for a certain request, you just create a new resolver instance and use that instead of changing the global one.
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### Address Resolution
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`Amp\Dns\resolve` provides hostname to IP address resolution. It returns an array of IPv4 and IPv6 addresses by default. The type of IP addresses returned can be restricted by passing a second argument with the respective time.
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```php
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// Example without type restriction. Will return IPv4 and / or IPv6 addresses.
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// What's returned depends on what's available for the given hostname.
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/** @var Amp\Dns\Record[] $records */
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$records = yield Amp\Dns\resolve("github.com");
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```
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```php
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// Example with type restriction. Will throw an exception if there are no A records.
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/** @var Amp\Dns\Record[] $records */
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$records = yield Amp\Dns\resolve("github.com", Amp\Dns\Record::A);
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```
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### Custom Queries
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`Amp\Dns\query` supports the various other DNS record types such as `MX`, `PTR`, or `TXT`. It automatically rewrites passed IP addresses for `PTR` lookups.
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```php
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/** @var Amp\Dns\Record[] $records */
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$records = Amp\Dns\query("google.com", Amp\Dns\Record::MX);
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```
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```php
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/** @var Amp\Dns\Record[] $records */
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$records = Amp\Dns\query("8.8.8.8", Amp\Dns\Record::PTR);
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```
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### Caching
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The `BasicResolver` caches responses by default in an `Amp\Cache\ArrayCache`. You can set any other `Amp\Cache\Cache` implementation by creating a custom instance of `BasicResolver` and setting that via `Amp\Dns\resolver()`, but it's usually unnecessary. If you have a lot of very short running scripts, you might want to consider using a local DNS resolver with a cache instead of setting a custom cache implementation, such as `dnsmasq`.
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### Reloading Configuration
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The `BasicResolver` (which is the default resolver shipping with that package) will cache the configuration of `/etc/resolv.conf` / the Windows Registry and the read host files by default. If you wish to reload them, you can set a periodic timer that requests a background reload of the configuration.
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```php
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Loop::repeat(60000, function () use ($resolver) {
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yield Amp\Dns\resolver()->reloadConfig();
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});
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```
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{:.note}
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> The above code relies on the resolver not being changed. `reloadConfig` is specific to `BasicResolver` and is not part of the `Resolver` interface. You might want to guard the reloading with an `instanceof` check or manually set a `BasicResolver` instance on startup to be sure it's an instance of `BasicResolver`.
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