Let's say you have a *path operation* with a path `/files/{file_path}`.

But you need `file_path` itself to contain a *path*, like `home/johndoe/myfile.txt`.

So, the URL for that file would be something like: `/files/home/johndoe/myfile.txt`.

### OpenAPI support

OpenAPI doesn't support a way to declare a *path parameter* to contain a *path* inside, as that could lead to scenarios that are difficult to test and define.

| `contact` | `dict` | The contact information for the exposed API. It can contain several fields. <details><summary><code>contact</code> fields</summary><table><thead><tr><th>Parameter</th><th>Type</th><th>Description</th></tr></thead><tbody><tr><td><code>name</code></td><td><code>str</code></td><td>The identifying name of the contact person/organization.</td></tr><tr><td><code>url</code></td><td><code>str</code></td><td>The...

## 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 part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip

    description=description,
    summary="Deadpool's favorite app. Nuff said.",
    version="0.0.1",
    terms_of_service="http://example.com/terms/",
    contact={
        "name": "Deadpoolio the Amazing",
        "url": "http://x-force.example.com/contact/",
        "email": "******@****.***",
    },
    license_info={
        "name": "Apache 2.0",
        "identifier": "MIT",
    },
)

The first `"/static"` refers to the sub-path this "sub-application" will be "mounted" on. So, any path that starts with `"/static"` will be handled by it.

The `directory="static"` refers to the name of the directory that contains your static files.

The `name="static"` gives it a name that can be used internally by **FastAPI**.

All these parameters can be different than "`static`", adjust them with the needs and specific details of your own application.

5. You can use other standard type annotations with dataclasses as the request body.

    In this case, it's a list of `Item` dataclasses.

6. Here we are returning a dictionary that contains `items` which is a list of dataclasses.

    FastAPI is still capable of <abbr title="converting the data to a format that can be transmitted">serializing</abbr> the data to JSON.

| `description` | `str` | 📏 📛 🛠️. ⚫️ 💪 ⚙️ ✍. |
| `version` | `string` | ⏬ 🛠️. 👉 ⏬ 👆 👍 🈸, 🚫 🗄. 🖼 `2.5.0`. |
| `terms_of_service` | `str` | 📛 ⚖ 🐕‍🦺 🛠️. 🚥 🚚, 👉 ✔️ 📛. |

```

</div>

That would work for most of the cases. 😎

You could use that command for example to start your **FastAPI** app in a container, in a server, etc.

## ASGI Servers

Let's go a little deeper into the details.

                It is UTF-8-encoded data. The interpretation of the reason is up to the
                application, it is not specified by the WebSocket specification.

                It could contain text that could be human-readable or interpretable
                by the client code, etc.
                """
            ),
        ] = None,
    ) -> None:
        super().__init__(code=code, reason=reason)

    The correct place is:

    * In the key `content`, that has as value another JSON object (`dict`) that contains:
        * A key with the media type, e.g. `application/json`, that contains as value another JSON object, that contains:
            * A key `schema`, that has as the value the JSON Schema from the model, here's the correct place.