@@ -261,12 +261,22 @@ const readableWebStream = response.body

const readableNodeStream = Readable.fromWeb(readableWebStream)

```

#### Specification Compliance

## Specification Compliance

This section documents parts of the [Fetch Standard](https://fetch.spec.whatwg.org) that Undici does

This section documents parts of the [HTTP/1.1](https://www.rfc-editor.org/rfc/rfc9110.html) and [Fetch Standard](https://fetch.spec.whatwg.org) that Undici does

not support or does not fully implement.

##### Garbage Collection

#### CORS

Unlike browsers, Undici does not implement CORS (Cross-Origin Resource Sharing) checks by default. This means:

- No preflight requests are automatically sent for cross-origin requests

- No validation of `Access-Control-Allow-Origin` headers is performed

- Requests to any origin are allowed regardless of the source

This behavior is intentional for server-side environments where CORS restrictions are typically unnecessary. If your application requires CORS-like protections, you will need to implement these checks manually.

#### Garbage Collection

* https://fetch.spec.whatwg.org/#garbage-collection

@@ -307,7 +317,7 @@ const headers = await fetch(url, { method: 'HEAD' })

.then(res => res.headers)

```

##### Forbidden and Safelisted Header Names

#### Forbidden and Safelisted Header Names

* https://fetch.spec.whatwg.org/#cors-safelisted-response-header-name

* https://fetch.spec.whatwg.org/#forbidden-header-name

@@ -316,7 +326,7 @@ const headers = await fetch(url, { method: 'HEAD' })

The [Fetch Standard](https://fetch.spec.whatwg.org) requires implementations to exclude certain headers from requests and responses. In browser environments, some headers are forbidden so the user agent remains in full control over them. In Undici, these constraints are removed to give more control to the user.

### `undici.upgrade([url, options]): Promise`

#### `undici.upgrade([url, options]): Promise`

Upgrade to a different protocol. See [MDN - HTTP - Protocol upgrade mechanism](https://developer.mozilla.org/en-US/docs/Web/HTTP/Protocol_upgrade_mechanism) for more details.

@@ -378,20 +388,15 @@ Returns: `URL`

* **protocol** `string` (optional)

* **search** `string` (optional)

## Specification Compliance

This section documents parts of the HTTP/1.1 specification that Undici does

not support or does not fully implement.

### Expect

#### Expect

Undici does not support the `Expect` request header field. The request

body is always immediately sent and the `100 Continue` response will be

ignored.

Refs: https://tools.ietf.org/html/rfc7231#section-5.1.1

### Pipelining

#### Pipelining

Undici will only use pipelining if configured with a `pipelining` factor

greater than `1`. Also it is important to pass `blocking: false` to the

@@ -412,7 +417,7 @@ aborted.

* Refs: https://tools.ietf.org/html/rfc2616#section-8.1.2.2

* Refs: https://tools.ietf.org/html/rfc7230#section-6.3.2

### Manual Redirect

#### Manual Redirect

Since it is not possible to manually follow an HTTP redirect on the server-side,

Undici returns the actual response instead of an `opaqueredirect` filtered one

@@ -421,9 +426,9 @@ implementations in Deno and Cloudflare Workers.

Refs: https://fetch.spec.whatwg.org/#atomic-http-redirect-handling

## Workarounds

### Workarounds

### Network address family autoselection.

#### Network address family autoselection.

If you experience problem when connecting to a remote server that is resolved by your DNS servers to a IPv6 (AAAA record)

first, there are chances that your local router or ISP might have problem connecting to IPv6 networks. In that case