Report closed ports as closed on Windows - #498
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Windows retries a SYN answered with a RST for about 2 s before connect() fails with WSAECONNREFUSED. The scanner's default timeout is 500 ms, so every closed port timed out first and read as filtered. Connect through a socket with SYN retransmissions off (SIO_TCP_INITIAL_RTO, MaxSynRetransmissions = TCP_INITIAL_RTO_NO_SYN_RETRANSMISSIONS), which makes the first RST final. Without retransmissions Windows gives up after the initial RTO (1 s by default), so set that to the caller's timeout too. The closed-port test accepted filtered, which is how this went unnoticed; it now requires closed within 500 ms and fails without the ioctl.
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On Windows every closed port came back as filtered. Windows retries a SYN that was answered with a RST for about 2 s before
connect()reports the refusal, and the scanner stops waiting at 500 ms.The scanner now connects through a socket with SYN retransmissions turned off (
SIO_TCP_INITIAL_RTO), so the first RST is final. With no retransmissions Windows gives up after the initial retransmission timeout, 1 s by default, so that is set to the scan timeout as well; otherwise a longer timeout would be cut to 1 s.Measured (Windows 11, release build,
scan -p 1-1024)Single connects to a closed port: 2025 to 2047 ms before, 0 to 5 ms after. A port that drops packets still times out at the requested timeout (checked at 300 ms and 3000 ms).
Tests
The closed-port test allowed
Filtered, which is how this went unnoticed. It now requiresClosedwithin 500 ms. With the ioctl commented out it fails (left: Filtered, right: Closed).Linux and macOS are unchanged apart from the connect going through
TcpSocketinstead ofTcpStream::connect.