/*
* 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
}
/*
* Create DHCP Decline
*/
func (s *Server) DeclinePacket(requestPacket dhcp4.Packet) dhcp4.Packet {
declinePacket := dhcp4.NewPacket(dhcp4.BootReply)
declinePacket.SetXId(requestPacket.XId())
declinePacket.SetFlags(requestPacket.Flags())
declinePacket.SetGIAddr(requestPacket.GIAddr())
declinePacket.SetCHAddr(requestPacket.CHAddr())
declinePacket.SetSecs(requestPacket.Secs())
declinePacket.AddOption(dhcp4.OptionDHCPMessageType, []byte{byte(dhcp4.NAK)})
declinePacket.AddOption(dhcp4.OptionSubnetMask, s.subnetMask.To4())
declinePacket.AddOption(dhcp4.OptionRouter, s.defaultGateway.To4())
declinePacket.AddOption(dhcp4.OptionDomainNameServer, dhcp4.JoinIPs(s.dnsServers))
declinePacket.AddOption(dhcp4.OptionServerIdentifier, s.ip.To4())
return declinePacket
}
/*
* Create Release Packet For a Release
*/
func (c *Client) ReleasePacket(acknowledgement *dhcp4.Packet) dhcp4.Packet {
messageid := make([]byte, 4)
if _, err := rand.Read(messageid); err != nil {
panic(err)
}
acknowledgementOptions := acknowledgement.ParseOptions()
packet := dhcp4.NewPacket(dhcp4.BootRequest)
packet.SetCHAddr(acknowledgement.CHAddr())
packet.SetXId(messageid)
packet.SetCIAddr(acknowledgement.YIAddr())
packet.AddOption(dhcp4.OptionDHCPMessageType, []byte{byte(dhcp4.Release)})
packet.AddOption(dhcp4.OptionServerIdentifier, acknowledgementOptions[dhcp4.OptionServerIdentifier])
//packet.PadToMinSize()
return packet
}
/*
* Get Lease tries to work out the best lease for the packet supplied.
* Taking into account all Requested IP, Exisitng MACAddresses and Free leases.
*/
func (s *Server) GetLease(packet dhcp4.Packet) (found bool, lease leasepool.Lease, err error) {
packetOptions := packet.ParseOptions()
//Requested an IP
if (len(packetOptions) > 0) &&
packetOptions[dhcp4.OptionRequestedIPAddress] != nil &&
!net.IP(packetOptions[dhcp4.OptionRequestedIPAddress]).Equal(net.IP{}) {
//An IP Has Been Requested Let's Try and Get that One.
found, lease, err = s.leasePool.GetLease(net.IP(packetOptions[dhcp4.OptionRequestedIPAddress]))
if err != nil {
return
}
if found {
if lease.Status == leasepool.Free {
//Lease Is Free you Can Have it.
return
}
if lease.Status != leasepool.Free && bytes.Equal(lease.MACAddress, packet.CHAddr()) {
//Lease isn't free but it's yours
return
}
}
}
//Ok Even if you requested an IP you can't have it.
found, lease, err = s.leasePool.GetLeaseForHardwareAddress(packet.CHAddr())
if found || err != nil {
return
}
//Just get the next free lease if you can.
found, lease, err = s.leasePool.GetNextFreeLease()
return
}
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
}