ReturnLastGood bool

	// If CacheError is set, errors will be cached as well
	// and not continuously try to update.
	// Should not be combined with ReturnLastGood.
	CacheError bool

	// If NoWait is set, Get() will return the last good value,
	// if TTL has expired but 2x TTL has not yet passed,
	// but will fetch a new value in the background.
	NoWait bool
}

// corresponding increase or decrease in Mantissa) such that:
//
// - No precision is lost
// - No fractional digits will be emitted
// - The exponent (or suffix) is as large as possible.
//
// The sign will be omitted unless the number is negative.
//
// Examples:
//
// - 1.5 will be serialized as "1500m"
// - 1.5Gi will be serialized as "1536Mi"
//

   * future to finish, and when it completes, run the listeners. This implementation will wait on
   * the source future indefinitely, so if the source future never completes, the adapter will never
   * complete either.
   *
   * <p>If the delegate future is interrupted or throws an unexpected unchecked exception, the
   * listeners will not be invoked.
   */

    If you are starting with **FastAPI**, you might not need this.

You can declare additional responses, with additional status codes, media types, descriptions, etc.

Those additional responses will be included in the OpenAPI schema, so they will also appear in the API docs.

But for those additional responses you have to make sure you return a `Response` like `JSONResponse` directly, with your status code and content.

And then you can return any object you need, as you normally would (a `dict`, a database model, etc).

And if you declared a `response_model`, it will still be used to filter and convert the object you returned.

**FastAPI** will use that *temporal* response to extract the cookies (also headers and status code), and will put them in the final response that contains the value you returned, filtered by any `response_model`.

   * loaded entries; it will never contain null keys or values.
   *
   * <p>Caches loaded by a {@link CacheLoader} will issue a single request to {@link
   * CacheLoader#loadAll} for all keys which are not already present in the cache. All entries
   * returned by {@link CacheLoader#loadAll} will be stored in the cache, over-writing any
   * previously cached values. This method will throw an exception if {@link CacheLoader#loadAll}

{!../../../docs_src/wsgi/tutorial001.py!}
```

## Check it

Now, every request under the path `/v1/` will be handled by the Flask application.

And the rest will be handled by **FastAPI**.

If you run it and go to <a href="http://localhost:8000/v1/" class="external-link" target="_blank">http://localhost:8000/v1/</a> you will see the response from Flask:

```txt
Hello, World from Flask!
```

    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").

## 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.

// If the call is canceled through the context,
// the appropriate error will be returned.
type Stream struct {
	// responses from the remote server.
	// Channel will be closed after error or when remote closes.
	// All responses *must* be read by the caller until either an error is returned or the channel is closed.
	// Canceling the context will cause the context cancellation error to be returned.
	responses <-chan Response

}

// CronJobSpec describes how the job execution will look like and when it will actually run.
message CronJobSpec {
  // The schedule in Cron format, see https://en.wikipedia.org/wiki/Cron.
  optional string schedule = 1;

  // The time zone name for the given schedule, see https://en.wikipedia.org/wiki/List_of_tz_database_time_zones.
  // If not specified, this will default to the time zone of the kube-controller-manager process.