/*
* Create DHCP Offer Packet
*/
func (s *Server) OfferPacket(discoverPacket dhcp4.Packet) dhcp4.Packet {
offerPacket := dhcp4.NewPacket(dhcp4.BootReply)
offerPacket.SetXId(discoverPacket.XId())
offerPacket.SetFlags(discoverPacket.Flags())
offerPacket.SetCHAddr(discoverPacket.CHAddr())
offerPacket.SetGIAddr(discoverPacket.GIAddr())
offerPacket.SetSecs(discoverPacket.Secs())
//53
offerPacket.AddOption(dhcp4.OptionDHCPMessageType, []byte{byte(dhcp4.Offer)})
//54
offerPacket.AddOption(dhcp4.OptionServerIdentifier, s.ip.To4())
//51
offerPacket.AddOption(dhcp4.OptionIPAddressLeaseTime, dhcp4.OptionsLeaseTime(s.leaseDuration))
//Other options go in requested order...
discoverPacketOptions := discoverPacket.ParseOptions()
ourOptions := make(dhcp4.Options)
//1
ourOptions[dhcp4.OptionSubnetMask] = s.subnetMask.To4()
//3
ourOptions[dhcp4.OptionRouter] = s.defaultGateway.To4()
//6
ourOptions[dhcp4.OptionDomainNameServer] = dhcp4.JoinIPs(s.dnsServers)
if discoverPacketOptions[dhcp4.OptionParameterRequestList] != nil {
//Loop through the requested options and if we have them add them.
for _, optionCode := range discoverPacketOptions[dhcp4.OptionParameterRequestList] {
if !bytes.Equal(ourOptions[dhcp4.OptionCode(optionCode)], []byte{}) {
offerPacket.AddOption(dhcp4.OptionCode(optionCode), ourOptions[dhcp4.OptionCode(optionCode)])
delete(ourOptions, dhcp4.OptionCode(optionCode))
}
}
}
//Add all the options not requested.
for optionCode, optionValue := range ourOptions {
offerPacket.AddOption(optionCode, optionValue)
}
return offerPacket
}
func (s *Server) ServeDHCP(packet dhcp4.Packet) (dhcp4.Packet, error) {
packetOptions := packet.ParseOptions()
switch dhcp4.MessageType(packetOptions[dhcp4.OptionDHCPMessageType][0]) {
case dhcp4.Discover:
//Discover Received from client
//Lets get the lease we're going to send them
found, lease, err := s.GetLease(packet)
if err != nil {
return dhcp4.Packet{}, err
}
if !found {
log.Println("Warning: It Looks Like Our Leases Are Depleted...")
return dhcp4.Packet{}, nil
}
offerPacket := s.OfferPacket(packet)
offerPacket.SetYIAddr(lease.IP)
//Sort out the packet options
offerPacket.PadToMinSize()
lease.Status = leasepool.Reserved
lease.MACAddress = packet.CHAddr()
//If the lease expires within the next 5 Mins increase the lease expiary (Giving the Client 5 mins to complete)
if lease.Expiry.Before(time.Now().Add(time.Minute * 5)) {
lease.Expiry = time.Now().Add(time.Minute * 5)
}
if packetOptions[dhcp4.OptionHostName] != nil && string(packetOptions[dhcp4.OptionHostName]) != "" {
lease.Hostname = string(packetOptions[dhcp4.OptionHostName])
}
updated, err := s.leasePool.UpdateLease(lease)
if err != nil {
return dhcp4.Packet{}, err
}
if !updated {
//Unable to reserve lease (It's now active else where maybe?)
return dhcp4.Packet{}, errors.New("Unable to Reserve Lease:" + lease.IP.String())
}
return offerPacket, nil
case dhcp4.Request:
//Request Received from client
//Lets get the lease we're going to send them
found, lease, err := s.GetLease(packet)
if err != nil {
return dhcp4.Packet{}, err
}
if !found {
log.Println("Warning: It Looks Like Our Leases Are Depleted...")
return dhcp4.Packet{}, nil
}
//If the lease is not the one requested We should send a NAK..
if len(packetOptions) > 0 && !net.IP(packetOptions[dhcp4.OptionRequestedIPAddress]).Equal(lease.IP) {
//NAK
declinePacket := s.DeclinePacket(packet)
declinePacket.PadToMinSize()
return declinePacket, nil
} else {
lease.Status = leasepool.Active
lease.MACAddress = packet.CHAddr()
lease.Expiry = time.Now().Add(s.leaseDuration)
if packetOptions[dhcp4.OptionHostName] != nil && string(packetOptions[dhcp4.OptionHostName]) != "" {
lease.Hostname = string(packetOptions[dhcp4.OptionHostName])
}
updated, err := s.leasePool.UpdateLease(lease)
if err != nil {
return dhcp4.Packet{}, err
}
if updated {
//ACK
acknowledgementPacket := s.AcknowledgementPacket(packet)
acknowledgementPacket.SetYIAddr(lease.IP)
//Lease time.
acknowledgementPacket.AddOption(dhcp4.OptionIPAddressLeaseTime, dhcp4.OptionsLeaseTime(lease.Expiry.Sub(time.Now())))
acknowledgementPacket.PadToMinSize()
return acknowledgementPacket, nil
} else {
//NAK
declinePacket := s.DeclinePacket(packet)
declinePacket.PadToMinSize()
return declinePacket, nil
}
}
case dhcp4.Decline:
//Decline from the client:
log.Printf("Debug: Decline Message:%v\n", packet)
case dhcp4.Release:
//Decline from the client:
log.Printf("Debug: Release Message:%v\n", packet)
default:
log.Printf("Debug: Unexpected Packet Type:%v\n", dhcp4.MessageType(packetOptions[dhcp4.OptionDHCPMessageType][0]))
}
return dhcp4.Packet{}, nil
}
