## 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*.

```Python
from fastapi import FastAPI
from unicorn import UnicornMiddleware

app = FastAPI()

app.add_middleware(UnicornMiddleware, some_config="rainbow")
```

`app.add_middleware()` receives a middleware class as the first argument and any additional arguments to be passed to the middleware.

## Integrated middlewares

**FastAPI** includes several middlewares for common use cases, we'll see next how to use them.

            assert data == "Session cookie or query token value is: some-token"
            data = websocket.receive_text()
            assert data == f"Message text was: {message}, for item ID: bar"
            message = "Message two"
            websocket.send_text(message)
            data = websocket.receive_text()
            assert data == "Session cookie or query token value is: some-token"
            data = websocket.receive_text()

```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():

class User(BaseModel):
    username: str
    email: str


@app.post("/items/", response_model=ResponseMessage, tags=["items"])
async def create_item(item: Item):
    return {"message": "Item received"}


@app.get("/items/", response_model=List[Item], tags=["items"])
async def get_items():
    return [
        {"name": "Plumbus", "price": 3},
        {"name": "Portal Gun", "price": 9001},
    ]

{!../../../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>。

    name: str
    price: float


class ResponseMessage(BaseModel):
    message: str


@app.post("/items/", response_model=ResponseMessage)
async def create_item(item: Item):
    return {"message": "item received"}


@app.get("/items/", response_model=List[Item])
async def get_items():
    return [
        {"name": "Plumbus", "price": 3},
        {"name": "Portal Gun", "price": 9001},

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`

@app.websocket("/ws/{client_id}")
async def websocket_endpoint(websocket: WebSocket, client_id: int):
    await manager.connect(websocket)
    try:
        while True:
            data = await websocket.receive_text()
            await manager.send_personal_message(f"You wrote: {data}", websocket)
            await manager.broadcast(f"Client #{client_id} says: {data}")
    except WebSocketDisconnect: