// scan scans the dst IP address of this scanner.
func (s *scanner) scan() error {
// First off, get the MAC address we should be sending packets to.
hwaddr, err := s.getHwAddr()
if err != nil {
return err
}
// Construct all the network layers we need.
eth := layers.Ethernet{
SrcMAC: s.iface.HardwareAddr,
DstMAC: hwaddr,
EthernetType: layers.EthernetTypeIPv4,
}
ip4 := layers.IPv4{
SrcIP: s.src,
DstIP: s.dst,
Version: 4,
TTL: 64,
Protocol: layers.IPProtocolTCP,
}
tcp := layers.TCP{
SrcPort: 54321,
DstPort: 0, // will be incremented during the scan
SYN: true,
}
tcp.SetNetworkLayerForChecksum(&ip4)
// Create the flow we expect returning packets to have, so we can check
// against it and discard useless packets.
ipFlow := gopacket.NewFlow(layers.EndpointIPv4, s.dst, s.src)
start := time.Now()
for {
// Send one packet per loop iteration until we've sent packets
// to all of ports [1, 65535].
if tcp.DstPort < 65535 {
start = time.Now()
tcp.DstPort++
if err := s.send(ð, &ip4, &tcp); err != nil {
log.Printf("error sending to port %v: %v", tcp.DstPort, err)
}
}
// Time out 5 seconds after the last packet we sent.
if time.Since(start) > time.Second*5 {
log.Printf("timed out for %v, assuming we've seen all we can", s.dst)
return nil
}
// Read in the next packet.
data, _, err := s.handle.ReadPacketData()
if err == pcap.NextErrorTimeoutExpired {
continue
} else if err != nil {
log.Printf("error reading packet: %v", err)
continue
}
// Parse the packet. We'd use DecodingLayerParser here if we
// wanted to be really fast.
packet := gopacket.NewPacket(data, layers.LayerTypeEthernet, gopacket.NoCopy)
// Find the packets we care about, and print out logging
// information about them. All others are ignored.
if net := packet.NetworkLayer(); net == nil {
// log.Printf("packet has no network layer")
} else if net.NetworkFlow() != ipFlow {
// log.Printf("packet does not match our ip src/dst")
} else if tcpLayer := packet.Layer(layers.LayerTypeTCP); tcpLayer == nil {
// log.Printf("packet has not tcp layer")
} else if tcp, ok := tcpLayer.(*layers.TCP); !ok {
// We panic here because this is guaranteed to never
// happen.
panic("tcp layer is not tcp layer :-/")
} else if tcp.DstPort != 54321 {
// log.Printf("dst port %v does not match", tcp.DstPort)
} else if tcp.RST {
log.Printf(" port %v closed", tcp.SrcPort)
} else if tcp.SYN && tcp.ACK {
log.Printf(" port %v open", tcp.SrcPort)
} else {
// log.Printf("ignoring useless packet")
}
}
}
