}

	// lets drain the buf channel first before we validate invalid buffers.
	for i := uint64(0); i < size; i++ {
		bp.Get() // discard
	}

	// Try putting some invalid buffers into pool
	bp.Put(make([]byte, bp.w, bp.wcap-1)) // wrong capacity is rejected (less)
	bp.Put(make([]byte, bp.w, bp.wcap+1)) // wrong capacity is rejected (more)

Deploying a **FastAPI** application is relatively easy.

## What Does Deployment Mean

To **deploy** an application means to perform the necessary steps to make it **available to the users**.

For a **web API**, it normally involves putting it in a **remote machine**, with a **server program** that provides good performance, stability, etc, so that your **users** can **access** the application efficiently and without interruptions or problems.

# Additional Status Codes

By default, **FastAPI** will return the responses using a `JSONResponse`, putting the content you return from your *path operation* inside of that `JSONResponse`.

It will use the default status code or the one you set in your *path operation*.

## Additional status codes

  // The webhook cares about an operation if it matches _any_ Rule.
  // However, in order to prevent ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks
  // from putting the cluster in a state which cannot be recovered from without completely
  // disabling the plugin, ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks are never called

We create an async function `lifespan()` with `yield` like this:

```Python hl_lines="16  19"
{!../../docs_src/events/tutorial003.py!}
```

Here we are simulating the expensive *startup* operation of loading the model by putting the (fake) model function in the dictionary with machine learning models before the `yield`. This code will be executed **before** the application **starts taking requests**, during the *startup*.

  // The webhook cares about an operation if it matches _any_ Rule.
  // However, in order to prevent ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks
  // from putting the cluster in a state which cannot be recovered from without completely
  // disabling the plugin, ValidatingAdmissionWebhooks and MutatingAdmissionWebhooks are never called

```

////

### `Union` in Python 3.10

In this example we pass `Union[PlaneItem, CarItem]` as the value of the argument `response_model`.

Because we are passing it as a **value to an argument** instead of putting it in a **type annotation**, we have to use `Union` even in Python 3.10.

If it was in a type annotation we could have used the vertical bar, as:

```Python
some_variable: PlaneItem | CarItem
```

* It should not be client-specific.
  * In Istio sidecars, historically we had a lot of client-specific xDS. For example, putting the xDS-client's IP back into the xDS response. This makes efficient control plane implementation (most notably, caching), extremely challenging.

## Alternative (old): `Query` as the default value

Previous versions of FastAPI (before <abbr title="before 2023-03">0.95.0</abbr>) required you to use `Query` as the default value of your parameter, instead of putting it in `Annotated`, there's a high chance that you will see code using it around, so I'll explain it to you.

/// tip

///

## Type Hints with Metadata Annotations

Python also has a feature that allows putting **additional <abbr title="Data about the data, in this case, information about the type, e.g. a description.">metadata</abbr>** in these type hints using `Annotated`.

//// tab | Python 3.9+