* Bu, external geliştiricinin sağladığı bir *external API*'ye (sizin API'nizden) bir POST request gönderilerek yapılır (işte bu "callback"tir).

## Normal **FastAPI** uygulaması { #the-normal-fastapi-app }

Önce callback eklemeden önce normal API uygulamasının nasıl görüneceğine bakalım.

Bir `Invoice` body alacak bir *path operation*'ı ve callback için URL'yi taşıyacak `callback_url` adlı bir query parametresi olacak.

     * builder after this call. This does not change semantics, but may improve performance if
     * {@code expectedValuesPerKey} is a good estimate.
     *
     * <p>This may be called more than once; each newly added key will use the most recent call to
     * {@link #expectedValuesPerKey} as its hint.
     *
     * @throws IllegalArgumentException if {@code expectedValuesPerKey} is negative
     * @since 33.3.0

     * be output to the latest value referenced by System.out/err variables. By setting this parameter to true,
     * the output stream will be cached, i.e. assigned once at initialization time and re-used independently of
     * the current value referenced by System.out/err.
     *
     * @since 4.0.0
     */
    @Config(type = "java.lang.Boolean", defaultValue = "false")

            )

        # Handle on_startup/on_shutdown locally since Starlette removed support
        # Ref: https://github.com/Kludex/starlette/pull/3117
        # TODO: deprecate this once the lifespan (or alternative) interface is improved
        self.on_startup: list[Callable[[], Any]] = (
            [] if on_startup is None else list(on_startup)
        )

        }
        for (int i = count; i < size; i++) {
          array[i] = null; // for GWT
        }

        List<@Nullable T> list = unmodifiableList(asList(array));
        // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
        if (pad || count == size) {
          return list;
        } else {
          return list.subList(0, count);
        }
      }
    };
  }

  /**

        }
        for (int i = count; i < size; i++) {
          array[i] = null; // for GWT
        }

        List<@Nullable T> list = unmodifiableList(asList(array));
        // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
        if (pad || count == size) {
          return list;
        } else {
          return list.subList(0, count);
        }
      }
    };
  }

  /**

     * an I/O error, or if the target entry is evicted while this editor is active. In either case
     * we delete the editor's created files and prevent new files from being created. Note that once
     * an editor has been detached it is possible for another editor to edit the entry.
     */
    internal fun detach() {
      if (entry.currentEditor == this) {
        if (civilizedFileSystem) {

Aynı anda aşçı da olan birden fazla (8 diyelim) kasiyerin, senden önceki insanların siparişlerini aldığı bir sırada bekliyorsun.

Senden önceki herkes, tezgâhtan ayrılmadan önce burgerlerinin hazırlanmasını bekliyor; çünkü 8 kasiyerin her biri bir sonraki siparişe geçmeden önce burgeri hemen gidip hazırlıyor.

<img src="/img/async/parallel-burgers/parallel-burgers-01.png" class="illustration">

* The alternative documentation will also reflect the new query parameter and body:

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Recap

In summary, you declare **once** the types of parameters, body, etc. as function parameters.

You do that with standard modern Python types.

You don't have to learn a new syntax, the methods or classes of a specific library, etc.

	cred, errCode := doesPolicySignatureMatch(formValues)
	if errCode != ErrNone {
		writeErrorResponse(ctx, w, errorCodes.ToAPIErr(errCode), r.URL)
		return
	}

	if len(fanOutEntries) > 0 {
		// Once signature is validated, check if the user has
		// explicit permissions for the user.
		if !globalIAMSys.IsAllowed(policy.Args{
			AccountName:     cred.AccessKey,
			Groups:          cred.Groups,