Supports [RFC 8484](https://tools.ietf.org/html/rfc8484) POST and GET syntaxes as well as [Google's proprietary JSON DNS format](https://developers.google.com/speed/public-dns/docs/dns-over-https).
In the last example, [domain fronting](https://en.wikipedia.org/wiki/Domain_fronting), useful to bypass censorship in non-free countries: from the outside, it looks like the DoH client is connecting to `https://google.com`, but by sending a custom Host HTTP header to the server after the TLS handshake is finished, the server that actually replies is `https://dns.google.com` (this is only possible if both servers are behind a common CDN that allows domain fronting, like google's CDN).
In normal conditions, it is recommended that you use mozilla+cloudflare's DoH endpoint (`https://mozilla.cloudflare-dns.com/dns-query`), for greater privacy.
Other parameters that can be passed to the DoHConfig constructor are:
```php
public function __construct(array $nameservers, \Amp\Artax\Client $artax = null, \Amp\Dns\Resolver $resolver = null, \Amp\Dns\ConfigLoader $configLoader = null, \Amp\Cache\Cache $cache = null);
```
You can provide a custom HTTP client to use for resolution, or use a custom subresolver (the subresolver is used to make the first and only plaintext DNS request to obtain the address of the DoH nameserver), or use a [custom configuration](https://amphp.org/dns/#configuration) for the DoH client (and the subresolver, too, if the configuration is provided but the resolver isn't).
The last parameter can be a custom async caching object.
To resolve addresses using `dns-over-https` first set the global DNS resolver as explained in the [configuration section](#configuration), or use an instance of `Rfc8484StubResolver` instead of `Rfc1035StubResolver`.
`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 type.
```php
// Example without type restriction. Will return IPv4 and / or IPv6 addresses.
// What's returned depends on what's available for the given hostname.
/** @var Amp\Dns\Record[] $records */
$records = yield Amp\Dns\resolve("github.com");
```
```php
// Example with type restriction. Will throw an exception if there are no A records.
To resolve addresses using `dns-over-https` first set the global DNS resolver as explained in the [configuration section](#configuration), or use an instance of `Rfc8484StubResolver` instead of `Rfc1035StubResolver`.
`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.
The `Rfc8484StubResolver` caches responses by default in an `Amp\Cache\ArrayCache`. You can set any other `Amp\Cache\Cache` implementation by creating a custom instance of `Rfc8484StubResolver` 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`.
The subresolver (which is the resolver set in the `DoHConfig`, `Rfc1035StubResolver` by default) 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.
