# `Hostname`

A host: a domain name or an IP address.

Use it for what a server connects to. For a name that must be a real domain, use [`DomainName`](/docs/types/type-domain-name.md). To add a scheme, use [`WebOrigin`](/docs/types/type-web-origin.md).

## Shape

One value, held as text in one set form, with no parts: `2001:db8::1`.

## Example

```jadpo
Hostname("localhost")
```

`Hostname(raw)` checks the text, and text that isn't one breaks the `format` rule.

`text.parse(raw, as: Hostname)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `Example.com`, `[2001:db8::1]` or `2001:DB8::1`.

## Good to know

- It is lower case. An IPv6 address has no brackets, so `[2001:db8::1]` is refused.
- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.

## In JSON

A string, in a request, a response or `json.write`:

```json
"example.com"
"localhost"
"192.0.2.1"
```

## Details

<details>
<summary>Text form, storage, how it is shown, and operations</summary>

`Hostname` is in the group Web and network, and has been in Jadpo since 0.1.0.

### Text form

`text.from` writes one standard text form, the same form `text.parse` reads back: `example.com`, `localhost` and `192.0.2.1`.

### How it is stored

It is stored in one column named for the field, of type `text`. `192.0.2.1` is stored as `'192.0.2.1'`.

### How it is shown to people

`text.format(value, locale:)` shows it to people in their locale.

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `example.com` | `example.com` |
| `localhost` | `localhost` |
| `192.0.2.1` | `192.0.2.1` |
| `2001:db8::1` | `2001:db8::1` |

### Operations

It also takes `text.parse`, `text.from`, `text.format`, `json.read`, `json.write` and `==`. [How every standard type behaves](/docs/every-standard-type-meets-one-contract.md) says how they work.

</details>