假设要触发的自定义异常叫作 `UnicornException`。

且需要 FastAPI 实现全局处理该异常。

此时，可以用 `@app.exception_handler()` 添加自定义异常控制器：

```Python hl_lines="5-7  13-18  24"
{!../../../docs_src/handling_errors/tutorial003.py!}

```

请求 `/unicorns/yolo` 时，路径操作会触发 `UnicornException`。

但该异常将会被 `unicorn_exception_handler` 处理。

接收到的错误信息清晰明了，HTTP 状态码为 `418`，JSON 内容如下：

```JSON

& 👆 💚 🍵 👉 ⚠ 🌐 ⏮️ FastAPI.

👆 💪 🚮 🛃 ⚠ 🐕‍🦺 ⏮️ `@app.exception_handler()`:

```Python hl_lines="5-7  13-18  24"
{!../../../docs_src/handling_errors/tutorial003.py!}
```

📥, 🚥 👆 📨 `/unicorns/yolo`, *➡ 🛠️* 🔜 `raise` `UnicornException`.

✋️ ⚫️ 🔜 🍵 `unicorn_exception_handler`.

, 👆 🔜 📨 🧹 ❌, ⏮️ 🇺🇸🔍 👔 📟 `418` & 🎻 🎚:

```JSON

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

### 创建自定义 `GzipRoute` 类

接下来，创建使用 `GzipRequest` 的 `fastapi.routing.APIRoute  ` 的自定义子类。

此时，这个自定义子类会覆盖 `APIRoute.get_route_handler()`。

`APIRoute.get_route_handler()` 方法返回的是函数，并且返回的函数接收请求并返回响应。

本例用它根据原始请求创建 `GzipRequest`。

```Python hl_lines="18-26"
{!../../../docs_src/custom_request_and_route/tutorial001.py!}
```

!!! note "技术细节"

# Advanced Security

## Additional Features

There are some extra features to handle security apart from the ones covered in the [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

!!! tip
    The next sections are **not necessarily "advanced"**.

    And it's possible that for your use case, the solution is in one of them.

## Read the Tutorial first

* Restarts
* Replication (the number of processes running)
* Memory
* Previous steps before starting

    opt raise
        dep -->> handler: Raise HTTPException
        handler -->> client: HTTP error response
        dep -->> dep: Raise other exception
    end
    dep ->> operation: Run dependency, e.g. DB session
    opt raise
        operation -->> dep: Raise HTTPException
        dep -->> handler: Auto forward exception
        handler -->> client: HTTP error response

## Accessing the request body in an exception handler

!!! tip
    To solve this same problem, it's probably a lot easier to use the `body` in a custom handler for `RequestValidationError` ([Handling Errors](../tutorial/handling-errors.md#use-the-requestvalidationerror-body){.internal-link target=_blank}).

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

### ✍ 🛃 `GzipRoute` 🎓

⏭, 👥 ✍ 🛃 🏿 `fastapi.routing.APIRoute` 👈 🔜 ⚒ ⚙️ `GzipRequest`.

👉 🕰, ⚫️ 🔜 📁 👩‍🔬 `APIRoute.get_route_handler()`.

👉 👩‍🔬 📨 🔢. & 👈 🔢 ⚫️❔ 🔜 📨 📨 & 📨 📨.

📥 👥 ⚙️ ⚫️ ✍ `GzipRequest` ⚪️➡️ ⏮️ 📨.

```Python hl_lines="18-26"
{!../../../docs_src/custom_request_and_route/tutorial001.py!}
```

The `password` "flow" is one of the ways ("flows") defined in OAuth2, to handle security and authentication.

OAuth2 was designed so that the backend or API could be independent of the server that authenticates the user.

But in this case, the same **FastAPI** application will handle the API and the authentication.

So, let's review it from that simplified point of view:

That way, the sub-application will know to use that path prefix for the docs UI.

And the sub-application could also have its own mounted sub-applications and everything would work correctly, because FastAPI handles all these `root_path`s automatically.