# writeData(_:) Send a raw byte payload, looping until every byte is written. ``` func writeData(_ data: Data) throws ``` ## Parameters `data` The bytes to write verbatim. ## Discussion Low-level counterpart to [`writeLine(_:)`](/documentation/Tor/ControlSocket/writeLine(_:)). Called when the caller needs to ship a pre-assembled payload (multi-line commands, binary-safe extensions). Loops over `send(2)` until the full `data` has been drained, handling short writes transparently. > Throws: ``doc://Tor/documentation/Tor/TorError/ioError(_:)`` if the FD is closed or any > `send(2)` returns `-1`. > Important: Partial writes are **not** reported to the caller — > swift-tor retries transparently. If `send(2)` fails mid- > payload the caller must treat the socket as compromised and > abandon it; the Tor peer has consumed an unknown prefix of > the intended command.