Another big feature required by APIs is <abbr title="reading and converting to Python data">parsing</abbr> data from incoming requests.

Webargs is a tool that was made to provide that on top of several frameworks, including Flask.

It uses Marshmallow underneath to do the data validation. And it was created by the same developers.

It's a great tool and I have used it a lot too, before having **FastAPI**.

Onlar mənbə kodu, sənədləmə, tərcümələr və s. barədə əmək göstərmişlər. 📦

{% if people %}
<div class="user-list user-list-center">
{% for user in people.top_contributors[:50] %}

Kaynak koduna, dökümantasyona, çevirilere ve bir sürü şeye katkıda bulundular. 📦

{% if people %}
<div class="user-list user-list-center">
{% for user in people.top_contributors[:50] %}

* **FastAPI**:
    * The same way that Starlette uses Uvicorn and cannot be faster than it, **FastAPI** uses Starlette, so it cannot be faster than it.

    If there were any background tasks (documented later), they will run *after* all the middleware.

## 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*.

{% endfor %}

</div>
{% endif %}

## Top Contributors

**Top Contributors** を紹介します。👷

彼らは、*マージされた* [最も多くのプルリクエストを作成した](help-fastapi.md#create-a-pull-request){.internal-link target=_blank}ユーザーです。

ソースコード、ドキュメント、翻訳などに貢献してくれました。📦

{% if people %}
<div class="user-list user-list-center">
{% for user in people.top_contributors[:50] %}

"Mounting" means adding a completely "independent" application in a specific path, that then takes care of handling everything under that path, with the _path operations_ declared in that sub-application.

### Top-level application

First, create the main, top-level, **FastAPI** application, and its *path operations*:

```Python hl_lines="3  6-8"
{!../../../docs_src/sub_applications/tutorial001.py!}
```

### Sub-application

{% endfor %}

</div>
{% endif %}

## Top Contributors

Here are the **Top Contributors**. 👷

These users have [created the most Pull Requests](help-fastapi.md#create-a-pull-request){.internal-link target=_blank} that have been *merged*.

# Using Dataclasses

FastAPI is built on top of **Pydantic**, and I have been showing you how to use Pydantic models to declare requests and responses.

But FastAPI also supports using <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> the same way:

```Python hl_lines="1  7-12  19-20"
{!../../../docs_src/dataclasses/tutorial001.py!}
```

## Proxy with a stripped path prefix

Having a proxy with a stripped path prefix, in this case, means that you could declare a path at `/app` in your code, but then, you add a layer on top (the proxy) that would put your **FastAPI** application under a path like `/api/v1`.

In this case, the original path `/app` would actually be served at `/api/v1/app`.