## Create a middleware

To create a middleware you use the decorator `@app.middleware("http")` on top of a function.

The middleware function receives:

* The `request`.
* A function `call_next` that will receive the `request` as a parameter.
    * This function will pass the `request` to the corresponding *path operation*.
    * Then it returns the `response` generated by the corresponding *path operation*.

```JSON
{"item_id":3}
```

!!! check
    Notice that the value your function received (and returned) is `3`, as a Python `int`, not a string `"3"`.

    client = TestClient(app)
    with client.websocket_connect("/") as websocket:
        data = json.loads(websocket.receive_text())
        assert data == ["app", "index"]


def test_routerindex():
    client = TestClient(app)
    with client.websocket_connect("/router") as websocket:
        data = json.loads(websocket.receive_text())
        assert data == ["app", "router2", "router", "routerindex"]


def test_routerprefixindex():

{!../../../docs_src/custom_request_and_route/tutorial001.py!}
```

!!! note "技术细节"

    `Request` 的 `request.scope` 属性是包含关联请求元数据的字典。

    `Request` 的 `request.receive` 方法是**接收**请求体的函数。

    `scope` 字典与 `receive` 函数都是 ASGI 规范的内容。

    `scope` 与 `receive` 也是创建新的 `Request` 实例所需的。

    `Request` 的更多内容详见 <a href="https://www.starlette.io/requests/" class="external-link" target="_blank">Starlette 官档 - 请求</a>。

In that case, it would mean the JSON attributes, and data types they have, etc.

#### OpenAPI and JSON Schema

OpenAPI defines an API schema for your API. And that schema includes definitions (or "schemas") of the data sent and received by your API using **JSON Schema**, the standard for JSON data schemas.

#### Check the `openapi.json`

    ```

!!! note
    Notice that `response_model` is a parameter of the "decorator" method (`get`, `post`, etc). Not of your *path operation function*, like all the parameters and body.

`response_model` receives the same type you would declare for a Pydantic model field, so, it can be a Pydantic model, but it can also be, e.g. a `list` of Pydantic models, like `List[Item]`.

!!! info
    Note that the `TestClient` receives data that can be converted to JSON, not Pydantic models.

`get_current_user` will have a dependency with the same `oauth2_scheme` we created before.

The same as we were doing before in the *path operation* directly, our new dependency `get_current_user` will receive a `token` as a `str` from the sub-dependency `oauth2_scheme`:

=== "Python 3.10+"

    ```Python hl_lines="25"
    {!> ../../../docs_src/security/tutorial002_an_py310.py!}
    ```

=== "Python 3.9+"

### API Docs

If you go to the API docs, you will see that it has the **schemas** for the data to be sent in requests and received in responses:

<img src="/img/tutorial/generate-clients/image01.png">

You can see those schemas because they were declared with the models in the app.

Falcon is another high performance Python framework, it is designed to be minimal, and work as the foundation of other frameworks like Hug.