Cache Events are exposed via the EventListener API.  Typical scenarios are below.

### Cache Hit

In the ideal scenario the cache can fulfill the request without any conditional call to the network.
This will skip the normal events such as DNS, connecting to the network, and downloading the response body.

As recommended by the HTTP RFC the max age of a document is defaulted to 10% of the 

# Extending OpenAPI

There are some cases where you might need to modify the generated OpenAPI schema.

In this section you will see how.

## The normal process

The normal (default) process, is as follows.

A `FastAPI` application (instance) has an `.openapi()` method that is expected to return the OpenAPI schema.

      log.put("normal task running")
      return@schedule -1L
    }

    queue.idleLatch().await(500, TimeUnit.MILLISECONDS)

    assertThat(log.take()).isEqualTo("failing task running")
    assertThat(log.take()).isEqualTo("uncaught exception: java.lang.RuntimeException: boom!")
    assertThat(log.take()).isEqualTo("normal task running")
    assertThat(log).isEmpty()
  }

## HTTPX

Even if your **FastAPI** application uses normal `def` functions instead of `async def`, it is still an `async` application underneath.

    ```Python hl_lines="1  2  12-16"
    {!> ../../../docs_src/extra_data_types/tutorial001.py!}
    ```

Note that the parameters inside the function have their natural data type, and you can, for example, perform normal date manipulations, like:

=== "Python 3.10+"

    ```Python hl_lines="18-19"
    {!> ../../../docs_src/extra_data_types/tutorial001_an_py310.py!}
    ```

=== "Python 3.9+"

    Você o coloca em cima de uma função. Como um chapéu decorativo (acho que é daí que vem o termo).

    Um "decorador" pega a função abaixo e faz algo com ela.

    Em nosso caso, este decorador informa ao **FastAPI** que a função abaixo corresponde a **rota** `/` com uma **operação** `get`.

    É o "**decorador de rota**".

Você também pode usar as outras operações:

* `@app.post()`
* `@app.put()`

  optional string subresource = 1;

  // responseKind describes the group, version, and kind of the serialization schema for the object type this endpoint typically returns.
  // Some subresources do not return normal resources, these will have null return types.
  optional k8s.io.apimachinery.pkg.apis.meta.v1.GroupVersionKind responseKind = 2;

  // acceptedTypes describes the kinds that this endpoint accepts.

## The normal **FastAPI** app

Let's first see how the normal API app would look like before adding the callback.

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you:

        Prefer to use the `Annotated` version if possible.

    ```Python hl_lines="17"
    {!> ../../../docs_src/dependencies/tutorial006.py!}
    ```

These dependencies will be executed/solved the same way as normal dependencies. But their value (if they return any) won't be passed to your *path operation function*.

!!! tip
    Some editors check for unused function parameters, and show them as errors.

# OpenAPI Webhooks

There are cases where you want to tell your API **users** that your app could call *their* app (sending a request) with some data, normally to **notify** of some type of **event**.

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

## Webhooks steps