# Hostname Validator

`Zend\Validator\Hostname` allows you to validate a hostname against a set of
known specifications. It is possible to check for three different types of
hostnames: a DNS Hostname (i.e. `domain.com`), IP address (i.e. 1.2.3.4), and
Local hostnames (i.e. localhost). By default, only DNS hostnames are matched.

## Supported options

The following options are supported for `Zend\Validator\Hostname`:

- `allow`: Defines the sort of hostname which is allowed to be used.
  [See below](#validating-different-types-of-hostnames) for details.
- `idn`: Defines if IDN domains are allowed or not. This option defaults to
  `true`.
- `ip`: Allows defining a custom IP validator. This option defaults to a new
  instance of `Zend\Validator\Ip`.
- `tld`: Defines if TLDs are validated. This option defaults to `true`.

## Basic usage

```php
$validator = new Zend\Validator\Hostname();

if ($validator->isValid($hostname)) {
    // hostname appears to be valid
} else {
    // hostname is invalid; print the reasons
    foreach ($validator->getMessages() as $message) {
        echo "$message\n";
    }
}
```

This will match the hostname `$hostname` and on failure populate `getMessages()`
with useful error messages.

## Validating different types of hostnames

You may find you also want to match IP addresses, Local hostnames, or a
combination of all allowed types. This can be done by passing a parameter to
`Zend\Validator\Hostname` when you instantiate it. The parameter should be an
integer which determines what types of hostnames are allowed. You are encouraged
to use the `Zend\Validator\Hostname` constants to do this.

The `Zend\Validator\Hostname` constants are:

- `ALLOW_DNS`, to allow only DNS hostnames
- `ALLOW_IP` to allow IP addresses
- `ALLOW_LOCAL` to allow local network names
- `ALLOW_URI` to allow [RFC3986](http://tools.ietf.org/html/rfc3986)-compliant addresses
- `ALLOW_ALL` to allow all four above types

> ### Additional Information on `ALLOW_URI`
>
> `ALLOW_URI` allows checking hostnames according to
> [RFC3986](http://tools.ietf.org/html/rfc3986). These are registered names
> which are used by WINS, NetInfo and also local hostnames like those defined
> within your `hosts` file.

To check for IP addresses only, you can use the example below:

```php
use Zend\Validator\Hostname;

$validator = new Hostname(Hostname::ALLOW_IP);

if ($validator->isValid($hostname)) {
    // hostname appears to be valid
} else {
    // hostname is invalid; print the reasons
    foreach ($validator->getMessages() as $message) {
        echo "$message\n";
    }
}
```

As well as using `ALLOW_ALL` to accept all common hostnames types, you can
combine these types to allow for combinations. For example, to accept DNS and
Local hostnames:

```php
use Zend\Validator\Hostname;

$validator = new Hostname(Hostname::ALLOW_DNS | Hostname::ALLOW_IP);
```

## Validating International Domains Names

Some Country Code Top Level Domains (ccTLDs), such as 'de' (Germany), support
international characters in domain names. These are known as International
Domain Names (IDN). These domains can be matched by `Zend\Validator\Hostname`
via extended characters that are used in the validation process.

At the time of writing, more than 50 ccTLDs support IDN domains.

The `Hostname` validator matches IDN domains by default.  If you wish to disable
IDN validation, either pass a parameter to the `Zend\Validator\Hostname`
constructor or call the `setValidateIdn()` method.

You can disable IDN validation by passing a second parameter to the
`Zend\Validator\Hostname` constructor in the following way.

```php
$validator = new Zend\Validator\Hostname([
    'allow' => Zend\Validator\Hostname::ALLOW_DNS,
    'useIdnCheck'   => false,
]);
```

Alternatively you can either pass `true` or `false` to `setValidateIdn()` to
enable or disable IDN validation. If you are trying to match an IDN hostname
which isn't currently supported, it is likely it will fail validation if it has
any international characters in it. Where a ccTLD file doesn't exist in
`Zend/Validator/Hostname` specifying the additional characters, a normal hostname
validation is performed.

Please note that IDNs are only validated if you allow DNS hostnames to be
validated.

## Validating Top Level Domains

By default, a hostname will be verified against a list of known TLDs. If this
functionality is not required, it can be disabled in much the same way as
disabling IDN support. You can disable TLD validation by passing a third
parameter to the `Zend\Validator\Hostname` constructor. In the example below we
are supporting IDN validation via the second parameter.

```php
use Zend\Validator\Hostname;

$validator = new Hostname([
    'allow' => Hostname::ALLOW_DNS,
    'useIdnCheck'   => true,
    'useTldCheck'   => false,
]);
```

Alternatively you can either pass `true` or `false` to `setValidateTld()` to
enable or disable TLD validation.

Please note, TLDs are only validated if you allow DNS hostnames to be validated.