///

### Lifespan function { #lifespan-function }

The first thing to notice, is that we are defining an async function with `yield`. This is very similar to Dependencies with `yield`.

{* ../../docs_src/events/tutorial003.py hl[14:19] *}

The first part of the function, before the `yield`, will be executed **before** the application starts.

    /*
     * This trick allows us to avoid having separate states for "first four ints" and "all other
     * four int chunks."  The state we want after the first four bytes is
     *
     * crc0 = ~int0
     * crc1 = int1
     * crc2 = int2
     * crc3 = int3
     *
     * ...so we set crc0 so that computeForWord(crc0) = -1 and xoring it with the first int

 *
 *  * **b2a**: b2 + 0x80
 *  * **b3a**: b3 + 0x80
 *  * **b2b3**: (b2 << 7) + b3
 *
 * b0
 * --
 *
 * The inclusive start of the range. We get the first 14 bits of this code point from the section
 * and the last 7 bits from this byte.
 *
 * The end of the range is not encoded, but can be inferred by looking at the start of the range
 * that follows.
 *
 * b1
 * --

    /**
     * Extension header set by OkHttp specifying the timestamp when the cached HTTP request was
     * first initiated.
     */
    private var sentRequestMillis = 0L

    /**
     * Extension header set by OkHttp specifying the timestamp when the cached HTTP response was
     * first received.
     */
    private var receivedResponseMillis = 0L

    /** Etag of the cached response. */

OkHttp perseveres when the network is troublesome: it will silently recover from common connection
problems. If your service has multiple IP addresses, OkHttp will attempt alternate addresses if the
first connect fails. This is necessary for IPv4+IPv6 and services hosted in redundant data
centers. OkHttp supports modern TLS features (TLS 1.3, ALPN, certificate pinning). It can be
configured to fall back for broad connectivity.

    }

    @Test
    @DisplayName("close/release manage usage and transport lifecycle")
    void testReleaseLifecycle() {
        SmbSessionImpl session = newSession();

        // First release drops usage to zero and releases transport
        session.release();
        verify(transport, times(1)).release();
        assertFalse(session.isInUse());

        // Next release goes below zero and throws

    * 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 { #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 could be useful if for example you live in a country that restricts some URLs.

### Disable the automatic docs { #disable-the-automatic-docs }

The first step is to disable the automatic docs, as by default, those use the default CDN.

To disable them, set their URLs to `None` when creating your `FastAPI` app:

{* ../../docs_src/custom_docs_ui/tutorial001.py hl[8] *}

        ingesters = newIngesters;
    }

    /**
     * Returns the array of registered ingesters sorted by priority.
     * The returned array contains all ingesters in priority order
     * (lower priority numbers first).
     *
     * @return the sorted array of ingesters
     */
    public Ingester[] getIngesters() {
        return ingesters;
    }

 */
@GwtCompatible
public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
  private @Nullable T nextOrNull;

  /**
   * Creates a new iterator with the given first element, or, if {@code firstOrNull} is null,
   * creates a new empty iterator.
   */
  protected AbstractSequentialIterator(@Nullable T firstOrNull) {
    this.nextOrNull = firstOrNull;
  }

  /**