* Then it returns the **response**.

!!! note "Technical Details"
    If you have dependencies with `yield`, the exit code will run *after* the middleware.

    If there were any background tasks (documented later), they will run *after* all the middleware.

## Create a middleware

To create a middleware you use the decorator `@app.middleware("http")` on top of a function.

The middleware function receives:

* The `request`.

    And Pydantic's `Field` returns an instance of `FieldInfo` as well.

    `Body` also returns objects of a subclass of `FieldInfo` directly. And there are others you will see later that are subclasses of the `Body` class.

    Remember that when you import `Query`, `Path`, and others from `fastapi`, those are actually functions that return special classes.

!!! tip

    * Si estás comparando Starlette, compáralo con Sanic, Flask, Django, etc. Frameworks web (o microframeworks).
* **FastAPI**:
    * De la misma manera que Starlette usa Uvicorn y no puede ser más rápido que él, **FastAPI** usa Starlette, por lo que no puede ser más rápido que él.

# Parámetros de Cookie

Puedes definir parámetros de Cookie de la misma manera que defines parámetros de `Query` y `Path`.

## Importar `Cookie`

Primero importa `Cookie`:

=== "Python 3.10+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/cookie_params/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    ```Python hl_lines="3"
    {!> ../../../docs_src/cookie_params/tutorial001_an_py39.py!}
    ```

## Dependencies for groups of *path operations*

    * A "token" is just a string with some content that we can use later to verify this user.
    * Normally, a token is set to expire after some time.
        * So, the user will have to log in again at some point later.
        * And if the token is stolen, the risk is less. It is not like a permanent key that will work forever (in most of the cases).

It is compatible with:

* PostgreSQL
* MySQL
* SQLite

In this example, we'll use **SQLite**, because it uses a single file and Python has integrated support. So, you can copy this example and run it as is.

Later, for your production application, you might want to use a database server like **PostgreSQL**.

!!! tip

For now, don't pay attention to the rest, only the imports:

```Python hl_lines="3-5"
{!../../../docs_src/nosql_databases/tutorial001.py!}
```

## Define a constant to use as a "document type"

We will use it later as a fixed field `type` in our documents.

This is not required by Couchbase, but is a good practice that will help you afterwards.

```Python hl_lines="9"
{!../../../docs_src/nosql_databases/tutorial001.py!}
```

    {!> ../../../docs_src/body_multiple_params/tutorial004.py!}
    ```

!!! info
    `Body` also has all the same extra validation and metadata parameters as `Query`,`Path` and others you will see later.

## Embed a single body parameter

Let's say you only have a single `item` body parameter from a Pydantic model `Item`.

By default, **FastAPI** will then expect its body directly.

# Headers de Respuesta

## Usar un parámetro `Response`

Puedes declarar un parámetro de tipo `Response` en tu *función de operación de path* (de manera similar como se hace con las cookies).

Y entonces, podrás configurar las cookies en ese objeto de response *temporal*.

```Python hl_lines="1  7-8"
{!../../../docs_src/response_headers/tutorial002.py!}
```