Function tcp4syn

wgengine/netstack/netstack_test.go:670–706

(tb testing.TB, src, dst netip.Addr, sport, dport uint16)

}

func tcp4syn(tb testing.TB, src, dst netip.Addr, sport, dport uint16) []byte {
	ip := header.IPv4(make([]byte, header.IPv4MinimumSize+header.TCPMinimumSize))
	ip.Encode(&header.IPv4Fields{
		Protocol:    uint8(header.TCPProtocolNumber),
		TotalLength: header.IPv4MinimumSize + header.TCPMinimumSize,
		TTL:         64,
		SrcAddr:     tcpip.AddrFrom4Slice(src.AsSlice()),
		DstAddr:     tcpip.AddrFrom4Slice(dst.AsSlice()),
	})
	ip.SetChecksum(^ip.CalculateChecksum())
	if !ip.IsChecksumValid() {
		tb.Fatal("test broken; packet has incorrect IP checksum")
	}

	tcp := header.TCP(ip[header.IPv4MinimumSize:])
	tcp.Encode(&header.TCPFields{
		SrcPort:    sport,
		DstPort:    dport,
		SeqNum:     0,
		DataOffset: header.TCPMinimumSize,
		Flags:      header.TCPFlagSyn,
		WindowSize: 65535,
		Checksum:   0,
	})
	xsum := header.PseudoHeaderChecksum(
		header.TCPProtocolNumber,
		tcpip.AddrFrom4Slice(src.AsSlice()),
		tcpip.AddrFrom4Slice(dst.AsSlice()),
		uint16(header.TCPMinimumSize),
	)
	tcp.SetChecksum(^tcp.CalculateChecksum(xsum))
	if !tcp.IsChecksumValid(tcpip.AddrFrom4Slice(src.AsSlice()), tcpip.AddrFrom4Slice(dst.AsSlice()), 0, 0) {
		tb.Fatal("test broken; packet has incorrect TCP checksum")
	}

	return ip
}

// makeHangDialer returns a dialer that notifies the returned channel when a
// connection is dialed and then hangs until the test finishes.