{!> ../../docs_src/background_tasks/tutorial002.py!}
```

////

In obigem Beispiel werden die Nachrichten, *nachdem* die Response gesendet wurde, in die Datei `log.txt` geschrieben.

Wenn im Request ein Query-Parameter enthalten war, wird dieser in einem Hintergrundtask in das Log geschrieben.

Und dann schreibt ein weiterer Hintergrundtask, der in der *Pfadoperation-Funktion* erstellt wird, eine Nachricht unter Verwendung des Pfad-Parameters `email`.

	pilotxds "istio.io/istio/pilot/pkg/xds"
	"istio.io/istio/pkg/log"
)

var configDumpFile string

func readConfigFile(filename string) ([]byte, error) {
	file := os.Stdin
	if filename != "-" {
		var err error
		file, err = os.Open(filename)
		if err != nil {
			return nil, err
		}
	}
	defer func() {
		if err := file.Close(); err != nil {
			log.Errorf("failed to close %s: %s", filename, err)
		}
	}()

	}
	type Item struct {
		gorm.Model
		Logo     string        `gorm:"not null;type:varchar(50)"`
		Contents []ItemContent `gorm:"foreignKey:ItemID"`
	}

	tx := DB.Session(&gorm.Session{})
	tx.Migrator().DropTable(&ItemContent{}, &Item{})
	tx.AutoMigrate(&ItemContent{}, &Item{})

	item := Item{
		Logo: "logo",
		Contents: []ItemContent{
			{Name: "name", LanguageCode: "en"},

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

	"istio.io/istio/istioctl/pkg/cli"
	"istio.io/istio/istioctl/pkg/clioptions"
	"istio.io/istio/istioctl/pkg/util"
	"istio.io/istio/pkg/kube"
	"istio.io/istio/pkg/log"
)

var (
	listenPort     = 0
	controlZport   = 0
	promPort       = 0
	grafanaPort    = 0
	kialiPort      = 0
	jaegerPort     = 0
	zipkinPort     = 0
	skywalkingPort = 0

	bindAddress = ""

	if err != nil {
		return kubeconfig{}, err
	}
	// Convert to v1 schema which has proper encoding
	fullYaml, err := yaml.Marshal(lcfg)
	if err != nil {
		return kubeconfig{}, err
	}

	// Log with redaction
	if err := api.RedactSecrets(kcfg); err != nil {
		return kubeconfig{}, err
	}
	for _, c := range kcfg.Clusters {
		// Not actually sensitive, just annoyingly verbose.

	close(target.quitCh)
	if target.updateStmt != nil {
		// FIXME: log returned error. ignore time being.
		_ = target.updateStmt.Close()
	}

	if target.deleteStmt != nil {
		// FIXME: log returned error. ignore time being.
		_ = target.deleteStmt.Close()
	}

	if target.insertStmt != nil {
		// FIXME: log returned error. ignore time being.
		_ = target.insertStmt.Close()
	}

				z.rebalMeta.PoolStats[poolIdx].Info.EndTime = now
				z.rebalMu.Unlock()

			case <-timer.C:
				traceMsg = fmt.Sprintf("saved at %s", time.Now())
			}

			stopFn := globalRebalanceMetrics.log(rebalanceMetricSaveMetadata, poolIdx, traceMsg)
			err := z.saveRebalanceStats(GlobalContext, poolIdx, rebalSaveStats)
			stopFn(0, err)
			rebalanceLogIf(GlobalContext, err)

			if quit {
				return
			}

	// QueueLength is the queue length if any messages are queued.
	QueueLength int

	// TotalMessages is the total number of messages sent in the lifetime of the target
	TotalMessages int64

	// FailedMessages should log message count that failed to send.
	FailedMessages int64

  private static final Logger logger = Logger.getLogger(SloppyTearDown.class.getName());

  @Override
  public final void tearDown() {
    try {
      sloppyTearDown();
    } catch (Throwable t) {
      logger.log(Level.INFO, "exception thrown during tearDown: " + t.getMessage(), t);
    }
  }

  public abstract void sloppyTearDown() throws Exception;

Se houver alguma tarefa em segundo plano (documentada posteriormente), ela será executada *depois* de todo o middleware.

///

## Criar um middleware

Para criar um middleware, use o decorador `@app.middleware("http")` logo acima de uma função.

A função middleware recebe:

* A `request`.
* Uma função `call_next` que receberá o `request` como um parâmetro.
    * Esta função passará a `request` para a *operação de rota* correspondente.