The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

* Memory
* Previous steps before starting

Up to this point, with all the tutorials in the docs, you have probably been running a **server program**, for example, using the `fastapi` command, that runs Uvicorn, running a **single process**.

When deploying applications you will probably want to have some **replication of processes** to take advantage of **multiple cores** and to be able to handle more requests.

 *   <li>While a dependency on Android ought to be easy if it's for annotations only, it will
 *       probably require adding the dep to various ACLs, license files, and Proguard
 *       configurations, and there's always the potential that something will go wrong. It
 *       <i>probably</i> won't, since the deps are needed only in tests (and maybe someday in
 *       testlib), but why bother?

<div class="screenshot">
<img src="/img/tutorial/request-form-models/image01.png">
</div>

## Forbid Extra Form Fields { #forbid-extra-form-fields }

In some special use cases (probably not very common), you might want to **restrict** the form fields to only those declared in the Pydantic model. And **forbid** any **extra** fields.

/// note

This is supported since FastAPI version `0.114.0`. 🤓

///

Now, there are some cases where you might want to have the **same schema for input and output**.

Probably the main use case for this is if you already have some autogenerated client code/SDKs and you don't want to update all the autogenerated client code/SDKs yet, you probably will want to do it at some point, but maybe not right now.

   * could use null, but that messes with our nullness checking, including under J2KT. We could
   * probably work around it by changing how we annotate the J2CL EnumMap, but that's probably more
   * trouble than just using Object.class.)
   *
   * Then we declare the getters for these fields as @GwtIncompatible so that no one can try to use

You send it a token and it returns an authenticated user.

This provider might be charging you per request, and calling it might take some extra time than if you had a fixed mock user for tests.

You probably want to test the external provider once, but not necessarily call it for every test that runs.

///

## Order the parameters as you need { #order-the-parameters-as-you-need }

/// tip

This is probably not as important or necessary if you use `Annotated`.

///

Let's say that you want to declare the query parameter `q` as a required `str`.

      // Enable ALPN.
      sslParameters.applicationProtocols = Platform.alpnProtocolNames(protocols).toTypedArray()

      sslSocket.sslParameters = sslParameters
    } catch (iae: IllegalArgumentException) {
      // probably java.lang.IllegalArgumentException: Invalid input to toASCII from IDN.toASCII
      throw IOException("Android internal error", iae)
    }
  }

  @SuppressSignatureCheck
  companion object {

"thr" = "thr"
"toi" = "toi"

[type.go]
extend-ignore-identifiers-re = [
    # Variants of `typ` used to mean `type` in golang as it is otherwise a
    # keyword - some of these (like typ1 -> type1) can be fixed, but probably
    # not worth the effort.
    "[tT]yp[0-9]*",