---
title: "connection(_:didSendBodyData:totalBytesWritten:totalBytesExpectedToWrite:)"
framework: foundation
role: symbol
role_heading: Instance Method
path: "foundation/nsurlconnectiondatadelegate/connection(_:didsendbodydata:totalbyteswritten:totalbytesexpectedtowrite:)"
---

# connection(_:didSendBodyData:totalBytesWritten:totalBytesExpectedToWrite:)

Sent as the body (message data) of a request is transmitted (such as in an HTTP POST request).

## Declaration

```swift
optional func connection(_ connection: NSURLConnection, didSendBodyData bytesWritten: Int, totalBytesWritten: Int, totalBytesExpectedToWrite: Int)
```

## Parameters

- `connection`: The connection sending the message.
- `bytesWritten`: The number of bytes written in the latest write.
- `totalBytesWritten`: The total number of bytes written for this connection.
- `totalBytesExpectedToWrite`: The number of bytes the connection expects to write.

## Discussion

Discussion This method provides an estimate of the progress of a URL upload. The value of totalBytesExpectedToWrite may change during the upload if the request needs to be retransmitted due to a lost connection or an authentication challenge from the server.

## See Also

### Receiving Connection Progress

- [connectionDidFinishLoading(_:)](foundation/nsurlconnectiondatadelegate/connectiondidfinishloading(_:).md)