import time

from fastapi import FastAPI, Request

app = FastAPI()


@app.middleware("http")
async def add_process_time_header(request: Request, call_next):
    start_time = time.time()
    response = await call_next(request)
    process_time = time.time() - start_time
    response.headers["X-Process-Time"] = str(process_time)

                return await app(scope, receive, send)  # pragma: no cover

            async def call_next():
                return await app(scope, receive, send)

            websocket = WebSocket(scope, receive=receive, send=send)
            return await middleware_func(websocket, call_next)

        return wrapped_app

    return middleware_constructor


def test_depend_validation():

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:
        request.state.db = SessionLocal()
        response = await call_next(request)
    finally:
        request.state.db.close()
    return response


# Dependency
def get_db(request: Request):

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:
        request.state.db = SessionLocal()
        response = await call_next(request)
    finally:
        request.state.db.close()
    return response


# Dependency
def get_db(request: Request):

models.Base.metadata.create_all(bind=engine)

app = FastAPI()


@app.middleware("http")
async def db_session_middleware(request: Request, call_next):
    response = Response("Internal server error", status_code=500)
    try:
        request.state.db = SessionLocal()
        response = await call_next(request)
    finally:
        request.state.db.close()
    return response


# Dependency
def get_db(request: Request):

    yield request_state
    legacy_request_state_context_var.reset(contextvar_token)


@app.middleware("http")
async def custom_middleware(
    request: Request, call_next: Callable[[Request], Awaitable[Response]]
):
    response = await call_next(request)
    response.headers["custom"] = "foo"
    return response


@app.get("/user", dependencies=[Depends(set_up_request_state_dependency)])
def get_user():

    🚥 👆 ✔️ 🔗 ⏮️ `yield`, 🚪 📟 🔜 🏃 *⏮️* 🛠️.

    🚥 📤 🙆 🖥 📋 (📄 ⏪), 👫 🔜 🏃 *⏮️* 🌐 🛠️.

## ✍ 🛠️

✍ 🛠️ 👆 ⚙️ 👨‍🎨 `@app.middleware("http")` 🔛 🔝 🔢.

🛠️ 🔢 📨:

*  `request`.
* 🔢 `call_next` 👈 🔜 📨 `request` 🔢.
    * 👉 🔢 🔜 🚶‍♀️ `request` 🔗 *➡ 🛠️*.
    * ⤴️ ⚫️ 📨 `response` 🏗 🔗 *➡ 🛠️*.
* 👆 💪 ⤴️ 🔀 🌅 `response` ⏭ 🛬 ⚫️.

```Python hl_lines="8-9  11  14"

## Erstellung einer Middleware

Um eine Middleware zu erstellen, verwenden Sie den Dekorator `@app.middleware("http")` über einer Funktion.

Die Middleware-Funktion erhält:

* Den `request`.
* Eine Funktion `call_next`, die den `request` als Parameter erhält.
    * Diese Funktion gibt den `request` an die entsprechende *Pfadoperation* weiter.
    * Dann gibt es die von der entsprechenden *Pfadoperation* generierte `response` zurück.

## 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*.

!!! note "技术细节"
    如果你使用了 `yield` 关键字依赖, 依赖中的退出代码将在执行中间件*后*执行.

    如果有任何后台任务(稍后记录), 它们将在执行中间件*后*运行.

## 创建中间件

要创建中间件你可以在函数的顶部使用装饰器 `@app.middleware("http")`.

中间件参数接收如下参数:

* `request`.
* 一个函数 `call_next` 它将接收 `request` 作为参数.
    * 这个函数将 `request` 传递给相应的 *路径操作*.
    * 然后它将返回由相应的*路径操作*生成的 `response`.
* 然后你可以在返回 `response` 前进一步修改它.

```Python hl_lines="8-9  11  14"
{!../../../docs_src/middleware/tutorial001.py!}
```