# write(_:timeout:) Writes all bytes in `data` to the socket, awaiting write-readiness. ``` func write(_ data: Data, timeout: Duration? = nil) async throws ``` ## Parameters `data` The bytes to send. `timeout` Maximum time to wait for write-readiness. `nil` (default) waits indefinitely. On expiry the call throws [`SocketError.timeout`](/documentation/Event/SocketError/timeout) without having written any bytes. ## Discussion Registers an `EV_WRITE` event and drives the loop until the descriptor is writable, then issues a single `write(2)` syscall covering the full buffer. > Warning: This implementation does **not** handle partial writes — if the > kernel accepts fewer bytes than requested the remainder is silently > discarded (the callback just reports success). In practice, small writes > on connected TCP sockets complete in one syscall on all supported platforms, > but callers writing large buffers should chunk explicitly until the > planned backpressure helper lands. See . > Throws: ``doc://Event/documentation/Event/SocketError/writeFailed(_:)`` with the errno payload if > `write(2)` returns a negative value (e.g. `EPIPE` when the peer closed), > or ``doc://Event/documentation/Event/SocketError/timeout`` if `timeout` elapses first.