## 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:

// current scale target (e.g. CPU or memory).  The values will be averaged
// together before being compared to the target.  Such metrics are built in to
// Kubernetes, and have special scaling options on top of those available to
// normal per-pod metrics using the "pods" source.  Only one "target" type
// should be set.
message ContainerResourceMetricSource {
  // name is the name of the resource in question.
  optional string name = 1;

// current scale target (e.g. CPU or memory).  The values will be averaged
// together before being compared to the target.  Such metrics are built in to
// Kubernetes, and have special scaling options on top of those available to
// normal per-pod metrics using the "pods" source.  Only one "target" type
// should be set.
message ContainerResourceMetricSource {
  // name is the name of the resource in question.
  optional string name = 1;

    Se você tem algum conhecimento técnico (corrotinas, threads, blocking etc) e está curioso sobre como o FastAPI controla o `async def` vs normal `def`, vá em frente.

### Funções de operação de rota

Quando você declara uma *função de operação de rota* com `def` normal ao invés de `async def`, ela é rodada em uma threadpool externa que então é aguardada, ao invés de ser chamada diretamente (ela poderia bloquear o servidor).

# 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

### Other utility functions

Any other utility function that you call directly can be created with normal `def` or `async def` and FastAPI won't affect the way you call it.

    return AnalysisApiFe10TestConfiguratorFactory.INSTANCE.createConfigurator(
      new AnalysisApiTestConfiguratorFactoryData(
        FrontendKind.Fe10,
        TestModuleKind.Source,
        AnalysisSessionMode.Normal,
        AnalysisApiMode.Ide
      )
    );
  }

  @Test
  public void testAllFilesPresentInBuiltins() {

    return AnalysisApiFe10TestConfiguratorFactory.INSTANCE.createConfigurator(
      new AnalysisApiTestConfiguratorFactoryData(
        FrontendKind.Fe10,
        TestModuleKind.Source,
        AnalysisSessionMode.Normal,
        AnalysisApiMode.Ide
      )
    );
  }

  @Test
  public void testAllFilesPresentInHaveCommonSubtype() {

    return AnalysisApiFe10TestConfiguratorFactory.INSTANCE.createConfigurator(
      new AnalysisApiTestConfiguratorFactoryData(
        FrontendKind.Fe10,
        TestModuleKind.Source,
        AnalysisSessionMode.Normal,
        AnalysisApiMode.Ide
      )
    );
  }

  @Test
  public void testAllFilesPresentInSymbolRestoreFromDifferentModule() {

    return AnalysisApiFe10TestConfiguratorFactory.INSTANCE.createConfigurator(
      new AnalysisApiTestConfiguratorFactoryData(
        FrontendKind.Fe10,
        TestModuleKind.Source,
        AnalysisSessionMode.Normal,
        AnalysisApiMode.Ide
      )
    );
  }

  @Test
  public void testAllFilesPresentInTypeParameter() {