raise HTTPException(status_code=400, detail="X-Token header invalid")


async def get_query_token(token: str):
    if token != "jessica":

But at some point, there was no other option than creating something that provided all these features, taking the best ideas from previous tools, and combining them in the best way possible, using language features that weren't even available before (Python 3.6+ type hints).

</blockquote>

## Investigation

There are some cases where you might need to convert a data type (like a Pydantic model) to something compatible with JSON (like a `dict`, `list`, etc).

For example, if you need to store it in a database.

For that, **FastAPI** provides a `jsonable_encoder()` function.

## Using the `jsonable_encoder`

Let's imagine that you have a database `fake_db` that only receives JSON compatible data.

    hashed_password: str


def get_user(db, username: str):
    if username in db:
        user_dict = db[username]
        return UserInDB(**user_dict)


def fake_decode_token(token):
    # This doesn't provide any security at all
    # Check the next version
    user = get_user(fake_users_db, token)
    return user


async def get_current_user(token: str = Depends(oauth2_scheme)):
    user = fake_decode_token(token)

<img src="/img/tutorial/response-status-code/image02.png">

!!! note "Technical Details"
    You could also use `from starlette import status`.

    **FastAPI** provides the same `starlette.status` as `fastapi.status` just as a convenience for you, the developer. But it comes directly from Starlette.

## Changing the default

# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL THE

    The `Union` in `Union[str, None]` will allow your editor to give you better support and detect errors.

## Additional validation

We are going to enforce that even though `q` is optional, whenever it is provided, **its length doesn't exceed 50 characters**.

### Import `Query` and `Annotated`

To achieve that, first import:

* `Query` from `fastapi`

    * It depends on the `query_extractor`, and assigns the value returned by it to the parameter `q`.
* It also declares an optional `last_query` cookie, as a `str`.
    * If the user didn't provide any query `q`, we use the last query used, which we saved to a cookie before.

## Use the dependency

Then we can use the dependency with:

=== "Python 3.10+"

    ```Python hl_lines="23"

```Python hl_lines="1  46-47"
{!../../../docs_src/websockets/tutorial001.py!}
```

!!! note "Technical Details"
    You could also use `from starlette.websockets import WebSocket`.

    **FastAPI** provides the same `WebSocket` directly just as a convenience for you, the developer. But it comes directly from Starlette.

## Await for messages and send messages

In your WebSocket route you can `await` for messages and send messages.

* Collect the money.
* Send a notification back to the API user (the external developer).
    * 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

Let's first see how the normal API app would look like before adding the callback.