### ユースケース: 外部サービス { #use-cases-external-service }

例として、呼び出す必要がある外部の認証プロバイダがあるとします。

トークンを送ると、認証済みユーザーが返ってきます。

このプロバイダはリクエストごとに課金されるかもしれず、テスト用に固定のモックユーザーを使う場合に比べて呼び出しに余分な時間がかかるかもしれません。

外部プロバイダ自体の動作は一度はテストしたいでしょうが、実行されるすべてのテストで毎回呼び出す必要はありません。

この場合、そのプロバイダを呼び出す依存関係をオーバーライドし、テストのときだけモックユーザーを返すカスタムの依存関係を使えます。

### app.dependency_overrides 属性を使う { #use-the-app-dependency-overrides-attribute }

在某些情况下，你可能想要重写 `Request` 和 `APIRoute` 类使用的逻辑。

尤其是，当你本来会把这些逻辑放到中间件里时，这是一个不错的替代方案。

例如，如果你想在应用处理之前读取或操作请求体。

/// danger | 危险

这是一个“高级”特性。

如果你刚开始使用 **FastAPI**，可以先跳过本节。

///

## 使用场景 { #use-cases }

一些使用场景包括：

* 将非 JSON 的请求体转换为 JSON（例如 [`msgpack`](https://msgpack.org/index.html)）。
* 解压缩使用 gzip 压缩的请求体。
* 自动记录所有请求体日志。

## 处理自定义请求体编码 { #handling-custom-request-body-encodings }

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

 *  @license MIT
 */

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

/*
 * Copyright 2012-2025 CodeLibs Project and the Others.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,

import org.junit.jupiter.api.Test
import java.util.LinkedList

/*
 * Copyright 2024 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software