err := tryParse(t, func() {
			parser.Parse()
		})

		switch {
		case err == nil:
			t.Errorf("#%d: %q: want error %q; have none", i, test.input, test.error)
		case !strings.Contains(err.Error(), test.error):
			t.Errorf("#%d: %q: want error %q; have %q", i, test.input, test.error, err)
		}
	}

  override fun getUseClientMode(): Boolean = delegate!!.useClientMode

  override fun setNeedClientAuth(need: Boolean) {
    delegate!!.needClientAuth = need
  }

  override fun setWantClientAuth(want: Boolean) {
    delegate!!.wantClientAuth = want
  }

  override fun getNeedClientAuth(): Boolean = delegate!!.needClientAuth

  override fun getWantClientAuth(): Boolean = delegate!!.wantClientAuth

```Python hl_lines="3" title="app/internal/admin.py"
{!../../docs_src/bigger_applications/app/internal/admin.py!}
```

But we still want to set a custom `prefix` when including the `APIRouter` so that all its *path operations* start with `/admin`, we want to secure it with the `dependencies` we already have for this project, and we want to include `tags` and `responses`.

   *
   * @param reference any array of the desired type
   * @param length the length of the new array
   */
  /*
   * The new array contains nulls, even if the old array did not. If we wanted to be accurate, we
   * would declare a return type of `@Nullable T[]`. However, we've decided not to think too hard
   * about arrays for now, as they're a mess. (We previously discussed this in the review of

In this type of scenario, you probably would want to have **a single (Uvicorn) process per container**, as you would already be handling replication at the cluster level.

So, in this case, you **would not** want to have a multiple workers in the container, for example with the `--workers` command line option.You would want to have just a **single Uvicorn process** per container (but probably multiple containers).

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

## Forbid Extra Headers { #forbid-extra-headers }

In some special use cases (probably not very common), you might want to **restrict** the headers that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

{* ../../docs_src/header_param_models/tutorial002_an_py310.py hl[10] *}

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`.

And you don't need to declare anything else for that parameter, so you don't really need to use `Query`.

But you still need to use `Path` for the `item_id` path parameter. And you don't want to use `Annotated` for some reason.

## Do not Separate Schemas { #do-not-separate-schemas }

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.

# Development - Contributing

First, you might want to see the basic ways to [help FastAPI and get help](help-fastapi.md){.internal-link target=_blank}.

## Developing

If you already cloned the <a href="https://github.com/fastapi/fastapi" class="external-link" target="_blank">fastapi repository</a> and you want to deep dive in the code, here are some guidelines to set up your environment.

### Virtual environment

func bitrotVerify(r io.Reader, wantSize, partSize int64, algo BitrotAlgorithm, want []byte, shardSize int64) error {
	if algo != HighwayHash256S {
		h := algo.New()
		if n, err := io.Copy(h, r); err != nil || n != wantSize {
			// Premature failure in reading the object, file is corrupt.
			return errFileCorrupt
		}
		if !bytes.Equal(h.Sum(nil), want) {
			return errFileCorrupt
		}
		return nil
	}