dhcp4client

package
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 Go to latest Published: Apr 3, 2019 License: BSD-3-Clause Imports: 15 Imported by: 0

Documentation

Overview

Package dhcp4client is a small, minimum-functionality client for DHCPv4.

It only supports the 4-way DHCPv4 Discover-Offer-Request-Ack handshake as well as the Request-Ack renewal process.

Index

Constants

View Source 
const (

	// ClientPort is the port that DHCP clients listen on.
	ClientPort = 68

	// ServerPort is the port that DHCP servers and relay agents listen on.
	ServerPort = 67
)
View Source 
const (
	// IPv4MinimumSize is the minimum size of a valid IPv4 packet.
	IPv4MinimumSize = 20

	// IPv4MaximumHeaderSize is the maximum size of an IPv4 header. Given
	// that there are only 4 bits to represents the header length in 32-bit
	// units, the header cannot exceed 15*4 = 60 bytes.
	IPv4MaximumHeaderSize = 60

	// IPv4AddressSize is the size, in bytes, of an IPv4 address.
	IPv4AddressSize = 4

	// IPv4Version is the version of the ipv4 protocol.
	IPv4Version = 4
)
View Source 
const (
	IPv4FlagMoreFragments = 1 << iota
	IPv4FlagDontFragment
)

Flags that may be set in an IPv4 packet.

Variables

View Source 
var (
	// IPv4Broadcast is the broadcast address of the IPv4 procotol.
	IPv4Broadcast = net.IP{0xff, 0xff, 0xff, 0xff}

	// IPv4Any is the non-routable IPv4 "any" meta address.
	IPv4Any = net.IP{0, 0, 0, 0}
)
View Source 
var (
	BroadcastMac = net.HardwareAddr([]byte{255, 255, 255, 255, 255, 255})
)
View Source 
var (
	// DefaultServers is the address of all link-local DHCP servers and
	// relay agents.
	DefaultServers = &net.UDPAddr{
		IP:   net.IPv4bcast,
		Port: ServerPort,
	}
)

Functions

func Checksum 

func Checksum(buf []byte, initial uint16) uint16

Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the given byte array.

The initial checksum must have been computed on an even number of bytes.

func ChecksumCombine 

func ChecksumCombine(a, b uint16) uint16

ChecksumCombine combines the two uint16 to form their checksum. This is done by adding them and the carry.

Note that checksum a must have been computed on an even number of bytes.

func IPVersion 

func IPVersion(b []byte) int

IPVersion returns the version of IP used in the given packet. It returns -1 if the packet is not large enough to contain the version field.

func IsV4MulticastAddress 

func IsV4MulticastAddress(addr net.IP) bool

IsV4MulticastAddress determines if the provided address is an IPv4 multicast address (range 224.0.0.0 to 239.255.255.255). The four most significant bits will be 1110 = 0xe0.

func NewBroadcastUDPConn 

func NewBroadcastUDPConn(rawPacketConn net.PacketConn, boundAddr *net.UDPAddr) net.PacketConn

NewBroadcastUDPConn returns a PacketConn that marshals and unmarshals UDP packets, sending them to the broadcast MAC at on rawPacketConn.

Calls to ReadFrom will only return packets destined to boundAddr.

func NewIPv4UDPConn 

func NewIPv4UDPConn(iface string, port int) (net.PacketConn, error)

NewIPv4UDPConn returns a UDP connection bound to both the interface and port given based on a IPv4 DGRAM socket. The UDP connection allows broadcasting.

func NewPacketUDPConn 

func NewPacketUDPConn(iface string, port int) (net.PacketConn, error)

NewPacketUDPConn returns a UDP connection bound to the interface and port given based on a raw packet socket. All packets are broadcasted.

func PseudoHeaderChecksum 

func PseudoHeaderChecksum(protocol TransportProtocolNumber, srcAddr net.IP, dstAddr net.IP) uint16

PseudoHeaderChecksum calculates the pseudo-header checksum for the given destination protocol and network address, ignoring the length field. Pseudo-headers are needed by transport layers when calculating their own checksum.

Types

type Client 

type Client struct {
	// contains filtered or unexported fields
}

Client is an IPv4 DHCP client.

func New 

func New(iface netlink.Link, opts ...ClientOpt) (*Client, error)

New creates a new DHCP client that sends and receives packets on the given interface.

func (*Client) Close 

func (c *Client) Close() error

Close closes the client connection.

func (*Client) DiscoverOffer 

func (c *Client) DiscoverOffer() (*dhcp4.Packet, error)

DiscoverOffer sends a DHCPDiscover message and returns the first valid offer received.

func (*Client) DiscoverPacket 

func (c *Client) DiscoverPacket() *dhcp4.Packet

DiscoverPacket returns a valid Discover packet for this client.

TODO: Look at RFC and confirm.

func (*Client) Renew 

func (c *Client) Renew(ack *dhcp4.Packet) (*dhcp4.Packet, error)

Renew sends a renewal request packet and waits for the corresponding response.

func (*Client) Request 

func (c *Client) Request() (*dhcp4.Packet, error)

Request completes the 4-way Discover-Offer-Request-Ack handshake.

func (*Client) RequestPacket 

func (c *Client) RequestPacket(offer *dhcp4.Packet) *dhcp4.Packet

RequestPacket returns a valid DHCPRequest packet for the given offer.

TODO: Look at RFC and confirm.

func (*Client) SendAndRead 

func (c *Client) SendAndRead(ctx context.Context, dest *net.UDPAddr, p *dhcp4.Packet, out chan<- *ClientPacket, errCh chan<- *ClientError)

SendAndRead sends the given packet `p` to `dest` and reads responses on the UDP connection. Any valid DHCP reply packet is sent to `out`.

SendAndRead blocks reading response packets until either: - `ctx` is canceled; or - we have exhausted all configured retries and timeouts.

SendAndRead retries sending the packet and receiving responses according to the configured number of c.retry, using a response timeout of c.timeout.

TODO(hugelgupf): Make this a little state machine of packet types. See RFC 2131, Section 4.4, Figure 5.

func (*Client) SendAndReadOne 

func (c *Client) SendAndReadOne(packet *dhcp4.Packet) (*dhcp4.Packet, error)

SendAndReadOne sends one packet and returns the first response returned by any server.

func (*Client) SimpleSendAndRead 

func (c *Client) SimpleSendAndRead(ctx context.Context, dest *net.UDPAddr, p *dhcp4.Packet) (*sync.WaitGroup, <-chan *ClientPacket, <-chan *ClientError)

SimpleSendAndRead broadcasts a DHCP packet and launches a goroutine to read response packets. Those response packets will be sent on the channel returned.

Callers must cancel ctx when they have received the packet they are looking for. Otherwise, the spawned goroutine will keep reading until it times out. More importantly, if you send another packet, the spawned goroutine may read the response faster than the one launched for the other packet.

Callers sending a packet on one interface should use this. Callers intending to send packets on many interface at the same time should look at using SendAndRead instead.

Example Usage: 

func sendRequest(someRequest *Packet...) (*Packet, error) {
  ctx, cancel := context.WithCancel(context.Background())
  defer cancel()

  out, errCh := c.SimpleSendAndRead(ctx, DefaultServers, someRequest)

  for response := range out {
    if response == What You Want {
      // Context cancelation will stop the reading goroutine.
      return response, ...
    }
  }

  if err, ok := <-errCh; ok && err != nil {
    return nil, err
  }
  return nil, fmt.Errorf("got no valid responses")
}

TODO(hugelgupf): since the client only has one connection, maybe it should just have one dedicated goroutine for reading from the UDP socket, and use a request and response queue.

type ClientError 

type ClientError struct {
	Interface netlink.Link
	Err       error
}

ClientError is an error that occured on the associated interface.

func (*ClientError) Error 

func (ce *ClientError) Error() string

Error implements error.

type ClientOpt 

type ClientOpt func(*Client) error

ClientOpt is a function that configures the Client.

func WithConn 

func WithConn(conn net.PacketConn) ClientOpt

WithConn configures the packet connection to use.

func WithRetry 

func WithRetry(r int) ClientOpt

WithRetry configures the number of retransmissions to attempt.

Default is 3.

TODO(hugelgupf): Check RFC for retransmission behavior.

func WithTimeout 

func WithTimeout(d time.Duration) ClientOpt

WithTimeout configures the retransmission timeout.

Default is 10 seconds.

TODO(hugelgupf): Check RFC for retransmission behavior.

type ClientPacket 

type ClientPacket struct {
	Interface netlink.Link
	Packet    *dhcp4.Packet
}

ClientPacket is a DHCP packet and the interface it corresponds to.

type IPv4 

type IPv4 []byte

IPv4 represents an ipv4 header stored in a byte array. Most of the methods of IPv4 access to the underlying slice without checking the boundaries and could panic because of 'index out of range'. Always call IsValid() to validate an instance of IPv4 before using other methods.

func (IPv4) CalculateChecksum 

func (b IPv4) CalculateChecksum() uint16

CalculateChecksum calculates the checksum of the ipv4 header.

func (IPv4) Checksum 

func (b IPv4) Checksum() uint16

Checksum returns the checksum field of the ipv4 header.

func (IPv4) DestinationAddress 

func (b IPv4) DestinationAddress() net.IP

DestinationAddress returns the "destination address" field of the ipv4 header.

func (IPv4) Encode 

func (b IPv4) Encode(i *IPv4Fields)

Encode encodes all the fields of the ipv4 header.

func (IPv4) EncodePartial 

func (b IPv4) EncodePartial(partialChecksum, totalLength uint16)

EncodePartial updates the total length and checksum fields of ipv4 header, taking in the partial checksum, which is the checksum of the header without the total length and checksum fields. It is useful in cases when similar packets are produced.

func (IPv4) Flags 

func (b IPv4) Flags() uint8

Flags returns the "flags" field of the ipv4 header.

func (IPv4) FragmentOffset 

func (b IPv4) FragmentOffset() uint16

FragmentOffset returns the "fragment offset" field of the ipv4 header.

func (IPv4) HeaderLength 

func (b IPv4) HeaderLength() uint8

HeaderLength returns the value of the "header length" field of the ipv4 header.

func (IPv4) ID 

func (b IPv4) ID() uint16

ID returns the value of the identifier field of the ipv4 header.

func (IPv4) IsValid 

func (b IPv4) IsValid(pktSize int) bool

IsValid performs basic validation on the packet.

func (IPv4) Payload 

func (b IPv4) Payload() []byte

Payload implements Network.Payload.

func (IPv4) PayloadLength 

func (b IPv4) PayloadLength() uint16

PayloadLength returns the length of the payload portion of the ipv4 packet.

func (IPv4) Protocol 

func (b IPv4) Protocol() uint8

Protocol returns the value of the protocol field of the ipv4 header.

func (IPv4) SetChecksum 

func (b IPv4) SetChecksum(v uint16)

SetChecksum sets the checksum field of the ipv4 header.

func (IPv4) SetDestinationAddress 

func (b IPv4) SetDestinationAddress(addr net.IP)

SetDestinationAddress sets the "destination address" field of the ipv4 header.

func (IPv4) SetFlagsFragmentOffset 

func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16)

SetFlagsFragmentOffset sets the "flags" and "fragment offset" fields of the ipv4 header.

func (IPv4) SetID 

func (b IPv4) SetID(v uint16)

SetID sets the identification field.

func (IPv4) SetSourceAddress 

func (b IPv4) SetSourceAddress(addr net.IP)

SetSourceAddress sets the "source address" field of the ipv4 header.

func (IPv4) SetTOS 

func (b IPv4) SetTOS(v uint8, _ uint32)

SetTOS sets the "type of service" field of the ipv4 header.

func (IPv4) SetTotalLength 

func (b IPv4) SetTotalLength(totalLength uint16)

SetTotalLength sets the "total length" field of the ipv4 header.

func (IPv4) SourceAddress 

func (b IPv4) SourceAddress() net.IP

SourceAddress returns the "source address" field of the ipv4 header.

func (IPv4) TOS 

func (b IPv4) TOS() (uint8, uint32)

TOS returns the "type of service" field of the ipv4 header.

func (IPv4) TTL 

func (b IPv4) TTL() uint8

TTL returns the "TTL" field of the ipv4 header.

func (IPv4) TotalLength 

func (b IPv4) TotalLength() uint16

TotalLength returns the "total length" field of the ipv4 header.

func (IPv4) TransportProtocol 

func (b IPv4) TransportProtocol() TransportProtocolNumber

TransportProtocol implements Network.TransportProtocol.

type IPv4Fields 

type IPv4Fields struct {
	// IHL is the "internet header length" field of an IPv4 packet.
	IHL uint8

	// TOS is the "type of service" field of an IPv4 packet.
	TOS uint8

	// TotalLength is the "total length" field of an IPv4 packet.
	TotalLength uint16

	// ID is the "identification" field of an IPv4 packet.
	ID uint16

	// Flags is the "flags" field of an IPv4 packet.
	Flags uint8

	// FragmentOffset is the "fragment offset" field of an IPv4 packet.
	FragmentOffset uint16

	// TTL is the "time to live" field of an IPv4 packet.
	TTL uint8

	// Protocol is the "protocol" field of an IPv4 packet.
	Protocol uint8

	// Checksum is the "checksum" field of an IPv4 packet.
	Checksum uint16

	// SrcAddr is the "source ip address" of an IPv4 packet.
	SrcAddr net.IP

	// DstAddr is the "destination ip address" of an IPv4 packet.
	DstAddr net.IP
}

IPv4Fields contains the fields of an IPv4 packet. It is used to describe the fields of a packet that needs to be encoded.

type TransportProtocolNumber 

type TransportProtocolNumber uint32

TransportProtocolNumber is the number of a transport protocol. 

const (
	// UDPMinimumSize is the minimum size of a valid UDP packet.
	UDPMinimumSize = 8

	// UDPProtocolNumber is UDP's transport protocol number.
	UDPProtocolNumber TransportProtocolNumber = 17
)

type UDP 

type UDP []byte

UDP represents a UDP header stored in a byte array.

func (UDP) CalculateChecksum 

func (b UDP) CalculateChecksum(partialChecksum uint16, totalLen uint16) uint16

CalculateChecksum calculates the checksum of the udp packet, given the total length of the packet and the checksum of the network-layer pseudo-header (excluding the total length) and the checksum of the payload.

func (UDP) Checksum 

func (b UDP) Checksum() uint16

Checksum returns the "checksum" field of the udp header.

func (UDP) DestinationPort 

func (b UDP) DestinationPort() uint16

DestinationPort returns the "destination port" field of the udp header.

func (UDP) Encode 

func (b UDP) Encode(u *UDPFields)

Encode encodes all the fields of the udp header.

func (UDP) Length 

func (b UDP) Length() uint16

Length returns the "length" field of the udp header.

func (UDP) Payload 

func (b UDP) Payload() []byte

Payload returns the data contained in the UDP datagram.

func (UDP) SetChecksum 

func (b UDP) SetChecksum(checksum uint16)

SetChecksum sets the "checksum" field of the udp header.

func (UDP) SetDestinationPort 

func (b UDP) SetDestinationPort(port uint16)

SetDestinationPort sets the "destination port" field of the udp header.

func (UDP) SetSourcePort 

func (b UDP) SetSourcePort(port uint16)

SetSourcePort sets the "source port" field of the udp header.

func (UDP) SourcePort 

func (b UDP) SourcePort() uint16

SourcePort returns the "source port" field of the udp header.

type UDPFields 

type UDPFields struct {
	// SrcPort is the "source port" field of a UDP packet.
	SrcPort uint16

	// DstPort is the "destination port" field of a UDP packet.
	DstPort uint16

	// Length is the "length" field of a UDP packet.
	Length uint16

	// Checksum is the "checksum" field of a UDP packet.
	Checksum uint16
}

UDPFields contains the fields of a UDP packet. It is used to describe the fields of a packet that needs to be encoded.

type UDPPacketConn 

type UDPPacketConn struct {
	net.PacketConn
	// contains filtered or unexported fields
}

UDPPacketConn implements net.PacketConn and marshals and unmarshals UDP packets.

func (*UDPPacketConn) ReadFrom 

func (upc *UDPPacketConn) ReadFrom(b []byte) (int, net.Addr, error)

ReadFrom implements net.PacketConn.ReadFrom.

ReadFrom reads raw IP packets and will try to match them against upc.boundAddr. Any matching packets are returned via the given buffer.

func (*UDPPacketConn) WriteTo 

func (upc *UDPPacketConn) WriteTo(b []byte, addr net.Addr) (int, error)

WriteTo implements net.PacketConn.WriteTo and broadcasts all packets at the raw socket level.

WriteTo wraps the given packet in the appropriate UDP and IP header before sending it on the packet conn.

Source Files

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