The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

## Design

Then I spent some time designing the developer "API" I wanted to have as a user (as a developer using FastAPI).

I tested several ideas in the most popular Python editors: PyCharm, VS Code, Jedi based editors.

By the last <a href="https://www.jetbrains.com/research/python-developers-survey-2018/#development-tools" class="external-link" target="_blank">Python Developer Survey</a>, that covers about 80% of the users.

    """
    Create an invoice.

    This will (let's imagine) let the API user (some external developer) create an
    invoice.

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.
    * Send a notification back to the API user (the external developer), as a callback.
        * At this point is that the API will somehow send a POST request to the

    And as the `Response` can be used frequently to set headers and cookies, **FastAPI** also provides it at `fastapi.Response`.

## Custom Headers

# CORS (Cross-Origin Resource Sharing)

<a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS" class="external-link" target="_blank">Понятие CORS или "Cross-Origin Resource Sharing"</a> относится к ситуациям, при которых запущенный в браузере фронтенд содержит JavaScript-код, который взаимодействует с бэкендом, находящимся на другом "источнике" ("origin").

## Источник

    ✋️ 🕐❔ 📨 🔌 📁, ⚫️ 🗜 `multipart/form-data`. 👆 🔜 ✍ 🔃 🚚 📁 ⏭ 📃.

    🚥 👆 💚 ✍ 🌖 🔃 👉 🔢 &amp; 📨 🏑, 👳 <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST" class="external-link" target="_blank"><abbr title="Mozilla Developer Network">🏇</abbr> 🕸 🩺 <code>POST</code></a>.

!!! warning

# ⚜ (✖️-🇨🇳 ℹ 🤝)

<a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS" class="external-link" target="_blank">⚜ ⚖️ "✖️-🇨🇳 ℹ 🤝"</a> 🔗 ⚠ 🕐❔ 🕸 🏃‍♂ 🖥 ✔️ 🕸 📟 👈 🔗 ⏮️ 👩‍💻, &amp; 👩‍💻 🎏 "🇨🇳" 🌘 🕸.

## 🇨🇳

🇨🇳 🌀 🛠️ (`http`, `https`), 🆔 (`myapp.com`, `localhost`, `localhost.tiangolo.com`), &amp; ⛴ (`80`, `443`, `8080`).

, 🌐 👫 🎏 🇨🇳:

* `http://localhost`
* `https://localhost`
* `http://localhost:8080`

!!! note "Technical Details"
    You could also use `from starlette.middleware.cors import CORSMiddleware`.

!!! tip "Tipp"
    Um mehr über Statuscodes zu lernen, und welcher wofür verwendet wird, lesen Sie die <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Status" class="external-link" target="_blank"><abbr title="Mozilla Developer Network – Mozilla-Entwickler-Netzwerk">MDN</abbr> Dokumentation über HTTP-Statuscodes</a>.

## Abkürzung, um die Namen zu erinnern

!!! tip "Dica"
    Para saber mais sobre cada código de status e qual código serve para quê, verifique o <a href="https://developer.mozilla.org/pt-BR/docs/Web/HTTP/Status" class="external-link" target="_blank"><abbr title="Mozilla Developer Network">MDN</abbr> documentação sobre códigos de status HTTP</a>.

## Atalho para lembrar os nomes

Vamos ver o exemplo anterior novamente:

```Python hl_lines="6"