# `UserAgent`

What an HTTP client says it is: `curl/8.7.1`.

Use it to record how a request was made, such as in an audit log. A client can claim anything, so don't use it to decide what someone may do.

## Shape

One value, held as text in one set form, with no parts: `ExampleBot/1.0 (+https://example.com/bot)`.

## Example

```jadpo
UserAgent("curl/8.7.1")
```

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

`text.parse(raw, as: UserAgent)` reads one from text that comes from outside. Text that isn't one at all fails `malformed`, such as `(compatible)`, `curl /8.7.1` or `Mozilla/5.0  (X11)`.

## Good to know

- `==` tells you whether two are the same. `<` and `list.sort_by` don't take it.
- A field that holds one counts as personal data (`online`), so you don't mark it yourself.

## In JSON

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

```json
"curl/8.7.1"
"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36"
"ExampleBot/1.0 (+https://example.com/bot)"
```

## Details

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

`UserAgent` 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: `curl/8.7.1`, `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36` and `ExampleBot/1.0 (+https://example.com/bot)`.

### How it is stored

It is stored in one column named for the field, of type `text`. `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36` is stored as `'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36'`.

### How it is shown to people

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

With `locale: Locale.en_gb`:

| Value | Shown |
|---|---|
| `curl/8.7.1` | `curl/8.7.1` |
| `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36` | `Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36` |
| `ExampleBot/1.0 (+https://example.com/bot)` | `ExampleBot/1.0 (+https://example.com/bot)` |

### 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>