```JSON
{
    "message": "Hello World",
    "root_path": "/api/v1"
}
```

### 在 FastAPI 应用里设置 `root_path`

还有一种方案，如果不能提供 `--root-path` 或等效的命令行选项，则在创建 FastAPI 应用时要设置 `root_path` 参数。

```Python hl_lines="3"
{!../../docs_src/behind_a_proxy/tutorial002.py!}
```

传递 `root_path` 给 `FastAPI` 与传递 `--root-path` 命令行选项给 Uvicorn 或 Hypercorn 一样。

### 关于 `root_path`

注意，服务器（Uvicorn）只是把 `root_path` 传递给应用。

```

</div>

🚥 👆 ⚙️ Hypercorn, ⚫️ ✔️ 🎛 `--root-path`.

/// note | "📡 ℹ"

🔫 🔧 🔬 `root_path` 👉 ⚙️ 💼.

 &amp; `--root-path` 📋 ⏸ 🎛 🚚 👈 `root_path`.

///

### ✅ ⏮️ `root_path`

👆 💪 🤚 ⏮️ `root_path` ⚙️ 👆 🈸 🔠 📨, ⚫️ 🍕 `scope` 📖 (👈 🍕 🔫 🔌).

📥 👥 ✅ ⚫️ 📧 🎦 🎯.

```Python hl_lines="8"
{!../../docs_src/behind_a_proxy/tutorial001.py!}
```

Se você usar Hypercorn, ele também tem a opção `--root-path`.

/// note | "Detalhes Técnicos"

A especificação ASGI define um `root_path` para esse caso de uso.

E a opção de linha de comando `--root-path` fornece esse `root_path`.

///

### Verificando o `root_path` atual

Você pode obter o `root_path` atual usado pela sua aplicação para cada solicitação, ele faz parte do dicionário `scope` (que faz parte da especificação ASGI).

/// note | "Technische Details"

Die ASGI-Spezifikation definiert einen `root_path` für diesen Anwendungsfall.

Und die Kommandozeilenoption `--root-path` stellt diesen `root_path` bereit.

///

### Überprüfen des aktuellen `root_path`

<img src="/img/tutorial/sub-applications/image02.png">

两个用户界面都可以正常运行，因为浏览器能够与每个指定的应用或子应用会话。

### 技术细节：`root_path`

以上述方式挂载子应用时，FastAPI 使用 ASGI 规范中的 `root_path` 机制处理挂载子应用路径之间的通信。

这样，子应用就可以为自动文档使用路径前缀。

并且子应用还可以再挂载子应用，一切都会正常运行，FastAPI 可以自动处理所有 `root_path`。

### Technische Details: `root_path`

Wenn Sie eine Unteranwendung wie oben beschrieben mounten, kümmert sich FastAPI darum, den Mount-Pfad für die Unteranwendung zu kommunizieren, mithilfe eines Mechanismus aus der ASGI-Spezifikation namens `root_path`.

If you use Hypercorn, it also has the option `--root-path`.

/// note | "Technical Details"

The ASGI specification defines a `root_path` for this use case.

And the `--root-path` command line option provides that `root_path`.

///

### Checking the current `root_path`

You can get the current `root_path` used by your application for each request, it is part of the `scope` dictionary (that's part of the ASGI spec).

from fastapi.testclient import TestClient

from docs_src.behind_a_proxy.tutorial001 import app

client = TestClient(app, root_path="/api/v1")


def test_main():
    response = client.get("/app")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World", "root_path": "/api/v1"}


def test_openapi():
    response = client.get("/openapi.json")
    assert response.status_code == 200

@app.get("/app")
def read_main(request: Request):
    return {"message": "Hello World", "root_path": request.scope.get("root_path")}


client = TestClient(app)


def test_main():
    response = client.get("/app")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World", "root_path": "/api/v1"}


def test_openapi():
    response = client.get("/openapi.json")

🚥 👆 🔄 🔗 ⏮️ 🙆 2️⃣ 👩‍💻 🔢, 👫 🔜 👷 ☑, ↩️ 🖥 🔜 💪 💬 🔠 🎯 📱 ⚖️ 🎧-📱.

### 📡 ℹ: `root_path`

🕐❔ 👆 🗻 🎧-🈸 🔬 🔛, FastAPI 🔜 ✊ 💅 🔗 🗻 ➡ 🎧-🈸 ⚙️ 🛠️ ⚪️➡️ 🔫 🔧 🤙 `root_path`.

👈 🌌, 🎧-🈸 🔜 💭 ⚙️ 👈 ➡ 🔡 🩺 🎚.

& 🎧-🈸 💪 ✔️ 🚮 👍 📌 🎧-🈸 & 🌐 🔜 👷 ☑, ↩️ FastAPI 🍵 🌐 👉 `root_path`Ⓜ 🔁.