```Python hl_lines="13  15  22  25"
{!../../docs_src/background_tasks/tutorial002.py!}
```

Neste exemplo, as mensagens serão gravadas no arquivo `log.txt` _após_ o envio da resposta.

Se houver uma consulta na solicitação, ela será gravada no log em uma tarefa em segundo plano.

* Então ele retorna a **resposta**.

/// note | "Detalhes técnicos"

Se você tiver dependências com `yield`, o código de saída será executado *depois* do middleware.

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.

    plan0.tcpConnectDelayNanos = 280.ms

    val plan1 = routePlanner.addPlan()
    plan1.tcpConnectDelayNanos = 10.ms // Connect at time = 260 ms.
    plan1.tlsConnectDelayNanos = 10.ms // Connect at time = 270 ms.
    plan1.tlsConnectThrowable = IOException("boom!")

    val plan2 = plan1.createConnectTlsNextPlan()
    plan2.tcpConnectDelayNanos = 270.ms // Connect at time = 540 ms.

    val plan3 = plan0.createRetry()

    if (nextPlanIndex >= plans.size && autoGeneratePlans) addPlan()

    require(nextPlanIndex < plans.size) {
      "not enough plans! call addPlan() or set autoGeneratePlans=true in the test to set this up"
    }
    val result = plans[nextPlanIndex++]
    events += "take plan ${result.id}"

    if (result.yieldBeforePlanReturns) {
      taskFaker.yield()
    }

    if (plan is FailedPlan) return plan.result

    // Connect TCP asynchronously.
    tcpConnectsInFlight += plan
    val taskName = "$okHttpName connect ${routePlanner.address.url.redact()}"
    taskRunner.newQueue().schedule(
      object : Task(taskName) {
        override fun runOnce(): Long {
          val connectResult =
            try {
              plan.connectTcp()

 */
interface RoutePlanner {
  val address: Address

  /** Follow-ups for failed plans and plans that lost a race. */
  val deferredPlans: ArrayDeque<Plan>

  fun isCanceled(): Boolean

  /** Returns a plan to attempt. */
  @Throws(IOException::class)
  fun plan(): Plan

  /**
   * Returns true if there's more route plans to try.
   *

  private var routeSelector: RouteSelector? = null
  private var nextRouteToTry: Route? = null

  override val deferredPlans = ArrayDeque<Plan>()

  override fun isCanceled(): Boolean = connectionUser.isCanceled()

  @Throws(IOException::class)
  override fun plan(): Plan {
    val reuseCallConnection = planReuseCallConnection()
    if (reuseCallConnection != null) return reuseCallConnection

  # (Certificates must be obtained before this step.  The --cert-dir flag lets istioctl bypass the Kubernetes API server.)
  istioctl ps --xds-address istio.example.com:15012 --cert-dir ~/.istio-certs

  # Retrieve proxy status information via XDS from specific control plane in multi-control plane in-cluster configuration

  # (This is the usual way to get the control plane version with an out-of-cluster control plane.)
  istioctl x version --xds-address istio.cloudprovider.example.com:15012

  # Retrieve version information via Kubernetes config, using token security
  # (This is the usual way to get the control plane version with an in-cluster control plane.)
  istioctl x version

  # (Select a specific control plane in an in-cluster canary Istio configuration.)
  istioctl x internal-debug syncz --xds-label istio.io/rev=default
`,
		RunE: func(c *cobra.Command, args []string) error {
			kubeClient, err := ctx.CLIClientWithRevision(opts.Revision)
			if err != nil {
				return err
			}
			if len(args) == 0 {