* Processing data:
    * For example, let's say you receive a file that must go through a slow process, you can return a response of "Accepted" (HTTP 202) and process the file in the background.

## Using `BackgroundTasks`

# `UploadFile` class

You can define *path operation function* parameters to be of the type `UploadFile` to receive files from the request.

You can import it directly from `fastapi`:

```python
from fastapi import UploadFile
```

::: fastapi.UploadFile
    options:
        members:
            - file
            - filename
            - size
            - headers
            - content_type
            - read

# Allgemeines – How-To – Rezepte

Hier finden Sie mehrere Verweise auf andere Stellen in der Dokumentation, für allgemeine oder häufige Fragen.

## Daten filtern – Sicherheit

Um sicherzustellen, dass Sie nicht mehr Daten zurückgeben, als Sie sollten, lesen Sie die Dokumentation unter [Tutorial – Responsemodell – Rückgabetyp](../tutorial/response-model.md){.internal-link target=_blank}.

## Dokumentations-Tags – OpenAPI

    attributes:
      label: Go version
      description: |
        What version of Go are you using (`go version`)?

        Note: we only [support](https://go.dev/doc/devel/release#policy) the two most recent major releases.
      placeholder: ex. go version go1.20.7 darwin/arm64
    validations:
      required: true

  - type: textarea
    id: go-env
    attributes:

		}
		b.fill() // buffer is empty
	}
	c := b.buf[b.r]
	b.r++
	b.lastByte = int(c)
	return c, nil
}

// UnreadByte unreads the last byte. Only the most recently read byte can be unread.
//
// UnreadByte returns an error if the most recent method called on the
// [Reader] was not a read operation. Notably, [Reader.Peek], [Reader.Discard], and [Reader.WriteTo] are not
// considered read operations.

func (m *muxServer) checkSeq(seq uint32) (ok bool) {
	if seq != m.RecvSeq {
		if debugPrint {
			fmt.Printf("expected sequence %d, got %d\n", m.RecvSeq, seq)
		}
		m.disconnect(fmt.Sprintf("receive sequence number mismatch. want %d, got %d", m.RecvSeq, seq), false)
		return false
	}
	m.RecvSeq++
	return true
}

func (m *muxServer) message(msg message) {
	if debugPrint {

1a) Send encrypted data key and master key ID to KMS.
1b) Receive decrypted data key.
2)  Decrypt encrypted object key with the KEK derived from the data key.
3a) Receive new plain data key from the KMS using the master key ID of the server config.
3b) Receive encrypted form of the data key from the KMS.
4)  Derive a new KEK from the new data key and re-encrypt the OEK with it.

## The normal **FastAPI** app

Let's first see how the normal API app would look like before adding the callback.

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"

```

////

//// tab | Python 3.8+

```Python hl_lines="1  14"
{!> ../../docs_src/body_nested_models/tutorial003.py!}
```

////

With this, even if you receive a request with duplicate data, it will be converted to a set of unique items.

And whenever you output that data, even if the source had duplicates, it will be output as a set of unique items.

        original_route_handler = super().get_route_handler()

        async def custom_route_handler(request: Request) -> Response:
            request = GzipRequest(request.scope, request.receive)
            return await original_route_handler(request)

        return custom_route_handler


app = FastAPI()
app.router.route_class = GzipRoute


@app.post("/sum")