```

**Note:** Execute the commands on all 4 nodes.

![Example-3](https://github.com/minio/minio/blob/master/docs/screenshots/Example-3.jpg?raw=true)

	// Canceling the context will cause the context cancellation error to be returned.
	responses <-chan Response
	cancel    context.CancelCauseFunc

	// Requests sent to the server.
	// If the handler is defined with 0 incoming capacity this will be nil.
	// Channel *must* be closed to signal the end of the stream.
	// If the request context is canceled, the stream will no longer process requests.

    open fun headers(headers: Headers) = commonHeaders(headers)

    /**
     * Sets this request's `Cache-Control` header, replacing any cache control headers already
     * present. If [cacheControl] doesn't define any directives, this clears this request's
     * cache-control headers.
     */
    open fun cacheControl(cacheControl: CacheControl): Builder = commonCacheControl(cacheControl)

      "/job:localhost/replica:0/task:0/device:CPU:0",
      "/job:localhost/replica:0/task:0/device:CPU:1"};
  ParallelDevice parallel_device(devices);
  const FunctionDef assert_and_collective = FunctionDefHelper::Define(
      // Name
      "AssertAndCollective",
      // Args
      {"x: float", "condition: bool"},
      // Return values
      {"y: float"},
      // Attr def
      {},
      // Nodes
      {

{!> ../../docs_src/header_param_models/tutorial001_py310.py!}
```

////

**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs

You can see the required headers in the docs UI at `/docs`:

<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers

  // that are considered authoritative for the behavior of that escaper.

  private static final Escaper HTML_ESCAPER =
      Escapers.builder()
          .addEscape('"', """)
          // Note: "'" is not defined in HTML 4.01.
          .addEscape('\'', "'")
          .addEscape('&', "&")
          .addEscape('<', "&lt;")
          .addEscape('>', "&gt;")
          .build();

  private HtmlEscapers() {}

// Package-wide variables from generator "generated".
option go_package = "k8s.io/api/scheduling/v1beta1";

// DEPRECATED - This group version of PriorityClass is deprecated by scheduling.k8s.io/v1/PriorityClass.
// PriorityClass defines mapping from a priority class name to the priority
// integer value. The value can be any valid integer.
message PriorityClass {
  // Standard object's metadata.

* `expose_headers` - Indica quaisquer cabeçalhos de resposta que devem ser disponibilizados ao navegador. O padrão é `[]`.
* `max_age` - Define um tempo máximo em segundos para os navegadores armazenarem em cache as respostas CORS. O padrão é `600`.

O middleware responde a dois tipos específicos de solicitação HTTP...

### Requisições CORS pré-voo (preflight)

```
http://127.0.0.1:8000/items/foo-item?needy=sooooneedy
```

...this would work:

```JSON
{
    "item_id": "foo-item",
    "needy": "sooooneedy"
}
```

And of course, you can define some parameters as required, some as having a default value, and some entirely optional:

//// tab | Python 3.10+

```Python hl_lines="8"
{!> ../../docs_src/query_params/tutorial006_py310.py!}
```

////

 * high contention, expected throughput of this class is significantly higher, at the expense of
 * higher space consumption.
 *
 * <p>This class extends {@link Number}, but does not define methods such as {@code
 * equals}, {@code hashCode} and {@code compareTo} because instances are expected to be mutated, and
 * so are not useful as collection keys.
 *