// It does not encrypt empty ETags because such ETags indicate
// that the S3 client hasn't sent an ETag = MD5(object) and
// the backend can pick an ETag value.
func (key ObjectKey) SealETag(etag []byte) []byte {
	if len(etag) == 0 { // don't encrypt empty ETag - only if client sent ETag = MD5(object)
		return etag
	}
	var buffer bytes.Buffer
	mac := hmac.New(sha256.New, key[:])

	responses <-chan Response
	cancel    context.CancelCauseFunc

	// Requests sent to the server.
	// If the handler is defined with 0 incoming capacity this will be nil.
	// Channel *must* be closed to signal the end of the stream.
	// If the request context is canceled, the stream will no longer process requests.
	// Requests sent cannot be used any further by the called.
	Requests chan<- []byte

	muxID uint64

from fastapi import Depends, FastAPI

app = FastAPI()


def get_username():
    try:
        yield "Rick"
    finally:
        print("Cleanup up before response is sent")


@app.get("/users/me")
def get_user_me(username: str = Depends(get_username, scope="function")):

You can declare a parameter in a *path operation function* or dependency function with the type `BackgroundTasks`, and then you can use it to schedule the execution of background tasks after the response is sent.

You can import it directly from `fastapi`:

```python
from fastapi import BackgroundTasks
```

@app.post("/send-notification/{email}")
async def send_notification(email: str, background_tasks: BackgroundTasks):
    background_tasks.add_task(write_notification, email, message="some notification")

-rwxrwxrwx 1 nobody nobody           45 Apr  1 06:13 chunkdocs/metadata
226 Closing data connection, sent 75 bytes
ftp> get
(remote-file) runner/chunkdocs/metadata
(local-file) test
local: test remote: runner/chunkdocs/metadata
229 Entering Extended Passive Mode (|||37785|)
150 Data transfer starting 45 bytes
	45        3.58 KiB/s
226 Closing data connection, sent 45 bytes
45 bytes received in 00:00 (3.55 KiB/s)
...
```

  private var failed = false

  /** Total number of pings sent by this web socket. */
  private var sentPingCount = 0

  /** Total number of pings received by this web socket. */
  private var receivedPingCount = 0

  /** Total number of pongs received by this web socket. */
  private var receivedPongCount = 0

  /** True if we have sent a ping that is still awaiting a reply. */
  private var awaitingPong = false

    email: str, background_tasks: BackgroundTasks, q: Annotated[str, Depends(get_query)]
):
    message = f"message to {email}\n"
    background_tasks.add_task(write_log, message)

        os.remove(log)  # pragma: no cover
    response = client.post("/send-notification/******@****.***")
    assert response.status_code == 200, response.text
    assert response.json() == {"message": "Notification sent in the background"}
    with open("./log.txt") as f:

Make sure you create a [virtual environment](../virtual-environments.md), activate it, and then install it, for example:

```console
$ pip install python-multipart
```

This is because uploaded files are sent as "form data".

///

## Import `File` { #import-file }

Import `File` and `UploadFile` from `fastapi`:

{* ../../docs_src/request_files/tutorial001_an_py310.py hl[3] *}