> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tai42.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Network guard (tai42_kit.net)

> The URL guard and safe fetch helpers.

SSRF-guarded server-side URL fetching.

The SSRF guard (`tai42_kit.net.url_guard`) resolves and validates each target
host, and `fetch_url` is the httpx download built on it: while the guard is
enabled (the default) that download is DNS-rebinding-safe, redirect-safe, and
size-capped. The guard is reusable on its own by any caller that fetches a
caller-supplied URL server-side over its own HTTP client.

## UrlGuardError

`tai42_kit.net.url_guard.UrlGuardError`

```python theme={null}
class UrlGuardError(Exception)
```

Raised when a target host cannot be resolved or is rejected as non-public, or when a
response exceeds the guard's size cap or its redirect chain exceeds `max_redirects`.

## UrlGuardSettings

`tai42_kit.net.url_guard.UrlGuardSettings`

```python theme={null}
class UrlGuardSettings(TaiBaseSettings)
```

Policy for the SSRF guard on server-side URL fetches.

**Attributes**

| Attribute            | Type        |
| -------------------- | ----------- |
| `model_config`       | —           |
| `enabled`            | `bool`      |
| `allow_cidrs`        | `list[str]` |
| `max_response_bytes` | `int`       |
| `max_redirects`      | `int`       |

## enforce\_size

`tai42_kit.net.url_guard.enforce_size`

```python theme={null}
enforce_size(nbytes: int) -> None
```

Raise `UrlGuardError` when `nbytes` exceeds the configured cap.
A no-op when the guard is disabled. Never truncates — an over-cap response is
refused loudly.

**Parameters**

| Parameter | Type  | Default | Description |
| --------- | ----- | ------- | ----------- |
| `nbytes`  | `int` | —       | —           |

## fetch\_url

`tai42_kit.net.fetch_url.fetch_url`

```python theme={null}
async fetch_url(url: str) -> tuple[bytes, str | None]
```

Fetch the URL's body and return `(bytes, mime)`.

`mime` is the response `Content-Type` header (`None` when absent). When
the guard is enabled the request runs over `_PinningTransport`, which
validates and pins every connection (initial request and each redirect hop
that opens a new connection), and the body is size-capped while streaming.
Raises rather than truncating an over-cap body or reaching a non-public host.
When the guard is disabled a plain client is used, which caps nothing, pins
nothing, and lets httpx follow redirects.

Under the guard, redirects are followed one hop at a time rather than by
httpx, which reads each intermediate body into memory in full before chasing
`Location`. A hop carrying a body large enough to exhaust memory would slip
past the cap that way, so each redirect response is closed unread — forgoing
connection reuse for that hop — and only the terminal body is streamed and
counted.

**Parameters**

| Parameter | Type  | Default | Description |
| --------- | ----- | ------- | ----------- |
| `url`     | `str` | —       | —           |

## guard\_enabled

`tai42_kit.net.url_guard.guard_enabled`

```python theme={null}
guard_enabled() -> bool
```

Return whether the SSRF guard is enabled (`TAI_URL_GUARD_ENABLED`).

## resolve\_and\_validate

`tai42_kit.net.url_guard.resolve_and_validate`

```python theme={null}
async resolve_and_validate(host: str) -> str
```

Resolve `host`, reject it if any resolved address is non-public, and
return the first validated address to connect to (the "pin").

Resolving once and connecting to the returned address closes DNS-rebinding:
the same lookup that is validated is the one the connection uses, so an
attacker cannot answer public during the check and internal at connect time.
Raises `UrlGuardError` if resolution fails or any address is blocked.

**Parameters**

| Parameter | Type  | Default | Description |
| --------- | ----- | ------- | ----------- |
| `host`    | `str` | —       | —           |

## url\_guard\_settings

`tai42_kit.net.url_guard.url_guard_settings`

```python theme={null}
url_guard_settings() -> UrlGuardSettings
```

Return the process-wide `UrlGuardSettings`, cached after first load.