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
- Variables
- func Checksum(buf []byte, initial uint16) uint16
- func ChecksumCombine(a, b uint16) uint16
- func NewBroadcastUDPConn(rawPacketConn net.PacketConn, boundAddr *net.UDPAddr) net.PacketConn
- func NewRawUDPConn(iface string, port int) (net.PacketConn, error)
- func PseudoHeaderChecksum(protocol TransportProtocolNumber, srcAddr net.IP, dstAddr net.IP) uint16
- type BroadcastRawUDPConn
- type Client
- func (c *Client) Close() error
- func (c *Client) DiscoverOffer(ctx context.Context, modifiers ...dhcpv4.Modifier) (*dhcpv4.DHCPv4, error)
- func (c *Client) Request(ctx context.Context, modifiers ...dhcpv4.Modifier) (offer, ack *dhcpv4.DHCPv4, err error)
- func (c *Client) SendAndRead(ctx context.Context, dest *net.UDPAddr, p *dhcpv4.DHCPv4, match Matcher) (*dhcpv4.DHCPv4, error)
- type ClientOpt
- type IPv4
- func (b IPv4) CalculateChecksum() uint16
- func (b IPv4) DestinationAddress() net.IP
- func (b IPv4) Encode(i *IPv4Fields)
- func (b IPv4) HeaderLength() uint8
- func (b IPv4) Payload() []byte
- func (b IPv4) PayloadLength() uint16
- func (b IPv4) Protocol() uint8
- func (b IPv4) SetChecksum(v uint16)
- func (b IPv4) SetDestinationAddress(addr net.IP)
- func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16)
- func (b IPv4) SetSourceAddress(addr net.IP)
- func (b IPv4) SetTotalLength(totalLength uint16)
- func (b IPv4) SourceAddress() net.IP
- func (b IPv4) TotalLength() uint16
- func (b IPv4) TransportProtocol() TransportProtocolNumber
- type IPv4Fields
- type Matcher
- type TransportProtocolNumber
- type UDP
- func (b UDP) CalculateChecksum(partialChecksum uint16, totalLen uint16) uint16
- func (b UDP) Checksum() uint16
- func (b UDP) DestinationPort() uint16
- func (b UDP) Encode(u *UDPFields)
- func (b UDP) Length() uint16
- func (b UDP) Payload() []byte
- func (b UDP) SetChecksum(checksum uint16)
- func (b UDP) SetDestinationPort(port uint16)
- func (b UDP) SetSourcePort(port uint16)
- func (b UDP) SourcePort() uint16
- type UDPFields
Constants ¶
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 )
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 )
const ( IPv4FlagMoreFragments = 1 << iota IPv4FlagDontFragment )
Flags that may be set in an IPv4 packet.
Variables ¶
var ( // IPv4Broadcast is the broadcast address of the IPv4 protocol. IPv4Broadcast = net.IP{0xff, 0xff, 0xff, 0xff} // IPv4Any is the non-routable IPv4 "any" meta address. IPv4Any = net.IP{0, 0, 0, 0} )
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}) )
var ( // DefaultServers is the address of all link-local DHCP servers and // relay agents. DefaultServers = &net.UDPAddr{ IP: net.IPv4bcast, Port: ServerPort, } )
var ( // ErrNoResponse is returned when no response packet is received. ErrNoResponse = errors.New("no matching response packet received") )
Functions ¶
func Checksum ¶
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 ¶
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 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 ¶
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 ¶
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.
type Client ¶
type Client struct {
// contains filtered or unexported fields
}
Client is an IPv4 DHCP client.
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) 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 WithServerAddr ¶
WithServerAddr configures the address to send messages to.
func WithSummaryLogger ¶
func WithSummaryLogger() ClientOpt
WithSummaryLogger logs one-line DHCPv4 message summarys when sent & received.
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 ¶
CalculateChecksum calculates the checksum of the ipv4 header.
func (IPv4) DestinationAddress ¶
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 ¶
HeaderLength returns the value of the "header length" field of the ipv4 header.
func (IPv4) PayloadLength ¶
PayloadLength returns the length of the payload portion of the ipv4 packet.
func (IPv4) SetChecksum ¶
SetChecksum sets the checksum field of the ipv4 header.
func (IPv4) SetDestinationAddress ¶
SetDestinationAddress sets the "destination address" field of the ipv4 header.
func (IPv4) SetFlagsFragmentOffset ¶
SetFlagsFragmentOffset sets the "flags" and "fragment offset" fields of the ipv4 header.
func (IPv4) SetSourceAddress ¶
SetSourceAddress sets the "source address" field of the ipv4 header.
func (IPv4) SetTotalLength ¶
SetTotalLength sets the "total length" field of the ipv4 header.
func (IPv4) SourceAddress ¶
SourceAddress returns the "source address" field of the ipv4 header.
func (IPv4) TotalLength ¶
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 ¶
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 ¶
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) DestinationPort ¶
DestinationPort returns the "destination port" field of the udp header.
func (UDP) SetChecksum ¶
SetChecksum sets the "checksum" field of the udp header.
func (UDP) SetDestinationPort ¶
SetDestinationPort sets the "destination port" field of the udp header.
func (UDP) SetSourcePort ¶
SetSourcePort sets the "source port" field of the udp header.
func (UDP) SourcePort ¶
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.