nclient4

package
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 Go to latest Published: Jul 19, 2019 License: BSD-3-Clause Imports: 18 Imported by: 0

Documentation

Overview

Package nclient4 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 is the broadcast MAC address.
	//
	// Any UDP packet sent to this address is broadcast on the subnet.
	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,
	}
)
View Source 
var (
	// ErrNoResponse is returned when no response packet is received.
	ErrNoResponse = errors.New("no matching response packet received")
)

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 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.

The interface must already be configured.

func NewRawUDPConn 

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

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

The interface can be completely unconfigured.

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 BroadcastRawUDPConn 

type BroadcastRawUDPConn struct {
	// PacketConn is a raw DGRAM socket.
	net.PacketConn
	// contains filtered or unexported fields
}

BroadcastRawUDPConn uses a raw socket to send UDP packets to the broadcast MAC address.

func (*BroadcastRawUDPConn) ReadFrom 

func (upc *BroadcastRawUDPConn) 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 (*BroadcastRawUDPConn) WriteTo 

func (upc *BroadcastRawUDPConn) 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.

type Client 

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

Client is an IPv4 DHCP client.

func New 

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

New returns a client usable with an unconfigured interface.

func NewWithConn 

func NewWithConn(conn net.PacketConn, ifaceHWAddr net.HardwareAddr, opts ...ClientOpt) (*Client, error)

NewWithConn 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 underlying connection.

func (*Client) DiscoverOffer 

func (c *Client) DiscoverOffer(ctx context.Context, modifiers ...dhcpv4.Modifier) (*dhcpv4.DHCPv4, error)

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

func (*Client) Request 

func (c *Client) Request(ctx context.Context, modifiers ...dhcpv4.Modifier) (offer, ack *dhcpv4.DHCPv4, err error)

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

Note that modifiers will be applied *both* to Discover and Request packets.

func (*Client) SendAndRead 

func (c *Client) SendAndRead(ctx context.Context, dest *net.UDPAddr, p *dhcpv4.DHCPv4, match Matcher) (*dhcpv4.DHCPv4, error)

SendAndRead sends a packet p to a destination dest and waits for the first response matching `match` as well as its Transaction ID and ClientHWAddr.

If match is nil, the first packet matching the Transaction ID and ClientHWAddr is returned.

type ClientOpt 

type ClientOpt func(*Client)

ClientOpt is a function that configures the Client.

func WithDebugLogger 

func WithDebugLogger() ClientOpt

WithDebugLogger logs multi-line full DHCPv4 messages when sent & received.

func WithRetry 

func WithRetry(r int) ClientOpt

WithRetry configures the number of retransmissions to attempt.

Default is 3.

func WithServerAddr 

func WithServerAddr(n *net.UDPAddr) ClientOpt

WithServerAddr configures the address to send messages to.

func WithSummaryLogger 

func WithSummaryLogger() ClientOpt

WithSummaryLogger logs one-line DHCPv4 message summarys when sent & received.

func WithTimeout 

func WithTimeout(d time.Duration) ClientOpt

WithTimeout configures the retransmission timeout.

Default is 5 seconds.

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) 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) HeaderLength 

func (b IPv4) HeaderLength() uint8

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

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) SetSourceAddress 

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

SetSourceAddress sets the "source address" 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) 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 Matcher 

type Matcher func(*dhcpv4.DHCPv4) bool

Matcher matches DHCP packets.

func IsMessageType 

func IsMessageType(t dhcpv4.MessageType) Matcher

IsMessageType returns a matcher that checks for the message type.

If t is MessageTypeNone, all packets are matched.

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.

Source Files

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