"""
    Create an invoice.

    This will (let's imagine) let the API user (some external developer) create an
    invoice.

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.
    * Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the

 * entries may be counted in {@link Cache#size}, but will never be visible to read or write
 * operations.
 *
 * <p>Certain cache configurations will result in the accrual of periodic maintenance tasks which
 * will be performed during write operations, or during occasional read operations in the absence of
 * writes. The {@link Cache#cleanUp} method of the returned cache will also perform maintenance, but

   * returned from {@link #asMapOfRanges} will be different if there were existing entries which
   * connect to the given range and value.
   *
   * <p>Even if the input range is empty, if it is connected on both sides by ranges mapped to the
   * same value those two ranges will be coalesced.
   *

{* ../../docs_src/json_base64_bytes/tutorial001_py310.py ln[1:9,29:35] hl[9] *}

If you check the `/docs`, they will show that the field `data` expects base64 encoded bytes:

<div class="screenshot">
<img src="/img/tutorial/json-base64-bytes/image01.png">
</div>

     * mirror, its URL and ID will be updated to match the values from the mirror specification. Repositories without a
     * matching mirror will pass through unchanged. Note: This method must be called before
     * {@link #injectAuthentication(List, List)} or the repositories will end up with the wrong credentials.
     *

Now, every request under the path `/v1/` will be handled by the Flask application.

And the rest will be handled by **FastAPI**.

If you run it and go to [http://localhost:8000/v1/](http://localhost:8000/v1/) you will see the response from Flask:

```txt
Hello, World from Flask!
```

And if you go to [http://localhost:8000/v2](http://localhost:8000/v2) you will see the response from FastAPI:

```JSON
{

          projects:
            - name: elastic+elasticsearch+%BRANCH%+multijob+platform-support-darwin
              kill-phase-on: NEVER
              current-parameters: true
              git-revision: true
            - name: elastic+elasticsearch+%BRANCH%+multijob+platform-support-unix
              kill-phase-on: NEVER
              current-parameters: true
              git-revision: true

Also, before that, in previous versions, the `request` object was passed as part of the key-value pairs in the context for Jinja2.

///

/// tip

By declaring `response_class=HTMLResponse` the docs UI will be able to know that the response will be HTML.

///

/// note | Technical Details

You could also use `from starlette.templating import Jinja2Templates`.

   * and column pair, they will be combined with the specified merging function in encounter order.
   *
   * <p>The returned {@code Collector} will throw a {@code NullPointerException} at collection time
   * if the row, column, value, or merging functions return null on any input.
   *
   * @since 33.2.0 (available since 21.0 in guava-jre)
   */
  @IgnoreJRERequirement // Users will use this only if they're already using streams.

```

</div>

Open your browser at [http://127.0.0.1:8000](http://127.0.0.1:8000).

You will see a simple page like:

<img src="/img/tutorial/websockets/image01.png">

You can type messages in the input box, and send them:

<img src="/img/tutorial/websockets/image02.png">

And your **FastAPI** application with WebSockets will respond back:

<img src="/img/tutorial/websockets/image03.png">