dhcp: switch to github.com/rtr7/dhcp4
All existing DHCPv4 packages I looked at were unappealing for one reason or another, so we’re now using a little helper to glue github.com/google/gopacket and github.com/mdlayher/raw together, which suffices for our use-case and gives us more control.
This commit is contained in:
Michael Stapelberg
parent
a6ce446055
commit
14287515bc
272
cmd/dhcp/dhcp.go
272
cmd/dhcp/dhcp.go
@ -9,7 +9,6 @@ package main
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"io/ioutil"
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"log"
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@ -19,101 +18,109 @@ import (
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"syscall"
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"time"
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"golang.org/x/sys/unix"
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"github.com/d2g/dhcp4"
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"github.com/d2g/dhcp4client"
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"github.com/gokrazy/gokrazy/internal/iface"
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"github.com/google/gopacket/layers"
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"github.com/mdlayher/raw"
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"github.com/rtr7/dhcp4"
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"golang.org/x/sys/unix"
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)
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func parseDHCPDuration(b []byte) time.Duration {
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return time.Duration(binary.BigEndian.Uint32(b)) * time.Second
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}
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var (
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defaultDst = net.IP([]byte{0, 0, 0, 0})
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defaultNetmask = net.IPMask([]byte{0, 0, 0, 0})
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hardwareAddr net.HardwareAddr
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)
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func addHostname(p *dhcp4.Packet) {
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var utsname unix.Utsname
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if err := unix.Uname(&utsname); err != nil {
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log.Fatal(err)
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}
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nnb := utsname.Nodename[:bytes.IndexByte(utsname.Nodename[:], 0)]
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p.AddOption(dhcp4.OptionHostName, nnb)
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type client struct {
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hostname string
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hardwareAddr net.HardwareAddr
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generateXID func() uint32
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conn net.PacketConn
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}
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func addClientId(p *dhcp4.Packet) {
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id := make([]byte, len(hardwareAddr)+1)
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id[0] = 1 // hardware type ethernet, https://tools.ietf.org/html/rfc1700
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copy(id[1:], hardwareAddr)
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p.AddOption(dhcp4.OptionClientIdentifier, id)
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func (c *client) packet(xid uint32, opts []layers.DHCPOption) *layers.DHCPv4 {
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return &layers.DHCPv4{
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Operation: layers.DHCPOpRequest,
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HardwareType: layers.LinkTypeEthernet,
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HardwareLen: uint8(len(layers.EthernetBroadcast)),
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HardwareOpts: 0, // TODO: document
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Xid: xid,
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Secs: 0, // TODO: fill in?
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Flags: 0, // TODO: document
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ClientHWAddr: c.hardwareAddr,
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ServerName: nil,
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File: nil,
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Options: opts,
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}
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}
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// dhcpRequest is a copy of (dhcp4client/Client).Request which
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// includes the hostname.
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func dhcpRequest(c *dhcp4client.Client) (bool, dhcp4.Packet, error) {
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discoveryPacket := c.DiscoverPacket()
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addHostname(&discoveryPacket)
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addClientId(&discoveryPacket)
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discoveryPacket.PadToMinSize()
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if err := c.SendPacket(discoveryPacket); err != nil {
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return false, discoveryPacket, err
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func (c *client) discover() (*layers.DHCPv4, error) {
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discover := c.packet(c.generateXID(), []layers.DHCPOption{
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dhcp4.MessageTypeOpt(layers.DHCPMsgTypeDiscover),
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dhcp4.HostnameOpt(c.hostname),
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dhcp4.ClientIDOpt(layers.LinkTypeEthernet, c.hardwareAddr),
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dhcp4.ParamsRequestOpt(
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layers.DHCPOptDNS,
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layers.DHCPOptRouter,
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layers.DHCPOptSubnetMask),
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})
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if err := dhcp4.Write(c.conn, discover); err != nil {
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return nil, err
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}
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offerPacket, err := c.GetOffer(&discoveryPacket)
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// Look for DHCPOFFER packet (TODO: RFC)
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c.conn.SetDeadline(time.Now().Add(5 * time.Second))
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for {
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offer, err := dhcp4.Read(c.conn)
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if err != nil {
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return false, offerPacket, err
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return nil, err
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}
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requestPacket := c.RequestPacket(&offerPacket)
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addHostname(&requestPacket)
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addClientId(&requestPacket)
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requestPacket.PadToMinSize()
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if err := c.SendPacket(requestPacket); err != nil {
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return false, requestPacket, err
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if offer == nil {
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continue // not a DHCPv4 packet
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}
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acknowledgement, err := c.GetAcknowledgement(&requestPacket)
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if err != nil {
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return false, acknowledgement, err
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if offer.Xid != discover.Xid {
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continue // broadcast reply for different DHCP transaction
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}
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acknowledgementOptions := acknowledgement.ParseOptions()
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if dhcp4.MessageType(acknowledgementOptions[dhcp4.OptionDHCPMessageType][0]) != dhcp4.ACK {
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return false, acknowledgement, nil
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if !dhcp4.HasMessageType(offer.Options, layers.DHCPMsgTypeOffer) {
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continue
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}
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return offer, nil
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}
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return true, acknowledgement, nil
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}
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// dhcpRenew is a copy of (dhcp4client/Client).Renew which
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// includes the hostname.
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func dhcpRenew(c *dhcp4client.Client, packet dhcp4.Packet) (bool, dhcp4.Packet, error) {
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addHostname(&packet)
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addClientId(&packet)
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packet.PadToMinSize()
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if err := c.SendPacket(packet); err != nil {
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return false, packet, err
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func (c *client) request(last *layers.DHCPv4) (*layers.DHCPv4, error) {
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// Build a DHCPREQUEST packet:
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request := c.packet(last.Xid, append([]layers.DHCPOption{
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dhcp4.MessageTypeOpt(layers.DHCPMsgTypeRequest),
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dhcp4.RequestIPOpt(last.YourClientIP),
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dhcp4.HostnameOpt(c.hostname),
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dhcp4.ClientIDOpt(layers.LinkTypeEthernet, c.hardwareAddr),
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dhcp4.ParamsRequestOpt(
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layers.DHCPOptDNS,
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layers.DHCPOptRouter,
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layers.DHCPOptSubnetMask),
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}, dhcp4.ServerID(last.Options)...))
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if err := dhcp4.Write(c.conn, request); err != nil {
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return nil, err
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}
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acknowledgement, err := c.GetAcknowledgement(&packet)
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c.conn.SetDeadline(time.Now().Add(10 * time.Second))
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for {
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// Look for DHCPACK packet (described in RFC2131 4.3.1):
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ack, err := dhcp4.Read(c.conn)
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if err != nil {
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return false, acknowledgement, err
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return nil, err
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}
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acknowledgementOptions := acknowledgement.ParseOptions()
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if dhcp4.MessageType(acknowledgementOptions[dhcp4.OptionDHCPMessageType][0]) != dhcp4.ACK {
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return false, acknowledgement, nil
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if ack == nil {
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continue // not a DHCPv4 packet
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}
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if ack.Xid != request.Xid {
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continue // broadcast reply for different DHCP transaction
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}
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if !dhcp4.HasMessageType(ack.Options, layers.DHCPMsgTypeAck) {
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continue
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}
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return ack, nil
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}
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return true, acknowledgement, nil
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}
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func main() {
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@ -122,6 +129,12 @@ func main() {
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// NOTE: cannot gokrazy.WaitForClock() here, since the clock can only be
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// initialized once the network is up.
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var utsname unix.Utsname
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if err := unix.Uname(&utsname); err != nil {
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log.Fatal(err)
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}
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hostname := string(utsname.Nodename[:bytes.IndexByte(utsname.Nodename[:], 0)])
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eth0, err := net.InterfaceByName("eth0")
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if err != nil {
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log.Fatal(err)
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@ -148,73 +161,67 @@ func main() {
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time.Sleep(1 * time.Second)
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}
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hardwareAddr = eth0.HardwareAddr
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pktsock, err := dhcp4client.NewPacketSock(eth0.Index)
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if err != nil {
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log.Fatal(err)
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}
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dhcp, err := dhcp4client.New(
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dhcp4client.HardwareAddr(eth0.HardwareAddr),
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dhcp4client.Timeout(5*time.Second),
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dhcp4client.Broadcast(false),
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dhcp4client.Connection(pktsock),
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)
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conn, err := raw.ListenPacket(eth0, syscall.ETH_P_IP, &raw.Config{
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LinuxSockDGRAM: true,
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})
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if err != nil {
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log.Fatal(err)
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}
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ok, ack, err := dhcpRequest(dhcp)
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c := &client{
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hostname: hostname,
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hardwareAddr: eth0.HardwareAddr,
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generateXID: dhcp4.XIDGenerator(eth0.HardwareAddr),
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conn: conn,
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}
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offer, err := c.discover()
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if err != nil {
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log.Fatal(err)
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}
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last := offer
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for {
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last, err = c.request(last)
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if err != nil {
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log.Fatal(err)
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}
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if !ok {
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log.Fatal("received DHCPNAK")
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}
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opts := ack.ParseOptions()
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// DHCPACK (described in RFC2131 4.3.1)
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// - yiaddr: IP address assigned to client
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lease := dhcp4.LeaseFromACK(last)
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// Log the received DHCPACK packet:
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details := []string{
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fmt.Sprintf("IP %v", ack.YIAddr()),
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fmt.Sprintf("IP %v", lease.IP),
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}
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if b, ok := opts[dhcp4.OptionSubnetMask]; ok {
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if len(lease.Netmask) > 0 {
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ipnet := net.IPNet{
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IP: ack.YIAddr(),
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Mask: net.IPMask(b),
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IP: lease.IP,
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Mask: lease.Netmask,
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}
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details[0] = fmt.Sprintf("IP %v", ipnet.String())
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}
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if b, ok := opts[dhcp4.OptionBroadcastAddress]; ok {
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details = append(details, fmt.Sprintf("broadcast %v", net.IP(b)))
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if len(lease.Router) > 0 {
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details = append(details, fmt.Sprintf("router %v", lease.Router))
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}
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if b, ok := opts[dhcp4.OptionRouter]; ok {
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details = append(details, fmt.Sprintf("router %v", net.IP(b)))
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if len(lease.DNS) > 0 {
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details = append(details, fmt.Sprintf("DNS %v", lease.DNS))
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}
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if b, ok := opts[dhcp4.OptionDomainNameServer]; ok {
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details = append(details, fmt.Sprintf("DNS %v", net.IP(b)))
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if len(lease.Broadcast) > 0 {
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details = append(details, fmt.Sprintf("broadcast %v", lease.Broadcast))
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}
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log.Printf("DHCPACK: %v", strings.Join(details, ", "))
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if err := cs.SetAddress(ack.YIAddr()); err != nil {
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// Apply the received settings:
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if err := cs.SetAddress(lease.IP); err != nil {
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log.Fatal(err)
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}
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if b, ok := opts[dhcp4.OptionSubnetMask]; ok {
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if err := cs.SetNetmask(net.IPMask(b)); err != nil {
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log.Fatalf("setNetmask(%v): %v", net.IPMask(b), err)
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if len(lease.Netmask) > 0 {
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if err := cs.SetNetmask(lease.Netmask); err != nil {
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log.Fatalf("setNetmask(%v): %v", lease.Netmask, err)
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}
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}
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if b, ok := opts[dhcp4.OptionBroadcastAddress]; ok {
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if err := cs.SetBroadcast(net.IP(b)); err != nil {
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log.Fatalf("setBroadcast(%v): %v", net.IP(b), err)
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if b := lease.Broadcast; len(b) > 0 {
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if err := cs.SetBroadcast(b); err != nil {
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log.Fatalf("setBroadcast(%v): %v", b, err)
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}
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}
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@ -222,22 +229,22 @@ func main() {
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log.Fatal(err)
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}
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if b, ok := opts[dhcp4.OptionRouter]; ok {
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if errno := cs.AddRoute(defaultDst, net.IP(b), defaultNetmask); errno != 0 {
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if r := lease.Router; len(r) > 0 {
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if errno := cs.AddRoute(defaultDst, r, defaultNetmask); errno != 0 {
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if errno == syscall.EEXIST {
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if errno := cs.DelRoute(defaultDst, net.IP(b), defaultNetmask); errno != 0 {
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log.Printf("delRoute(%v): %v", net.IP(b), errno)
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if errno := cs.DelRoute(defaultDst, r, defaultNetmask); errno != 0 {
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log.Printf("delRoute(%v): %v", r, errno)
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}
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if errno := cs.AddRoute(defaultDst, net.IP(b), defaultNetmask); errno != 0 {
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log.Fatalf("addRoute(%v): %v", net.IP(b), errno)
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if errno := cs.AddRoute(defaultDst, r, defaultNetmask); errno != 0 {
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log.Fatalf("addRoute(%v): %v", r, errno)
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}
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} else {
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log.Fatalf("addRoute(%v): %v", net.IP(b), errno)
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log.Fatalf("addRoute(%v): %v", r, errno)
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}
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}
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}
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if b, ok := opts[dhcp4.OptionDomainNameServer]; ok {
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if len(lease.DNS) > 0 {
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resolvConf := "/etc/resolv.conf"
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if dest, err := os.Readlink("/etc/resolv.conf"); err == nil && dest == "/tmp/resolv.conf" {
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resolvConf = "/tmp/resolv.conf"
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@ -247,11 +254,13 @@ func main() {
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log.Fatalf("resolv.conf: %v", err)
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}
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var lines []string
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if domain, ok := opts[dhcp4.OptionDomainName]; ok {
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lines = append(lines, fmt.Sprintf("domain %s", string(domain)))
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lines = append(lines, fmt.Sprintf("search %s", string(domain)))
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if domain := lease.Domain; domain != "" {
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lines = append(lines, fmt.Sprintf("domain %s", domain))
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lines = append(lines, fmt.Sprintf("search %s", domain))
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}
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for _, ns := range lease.DNS {
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lines = append(lines, fmt.Sprintf("nameserver %v", ns))
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}
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lines = append(lines, fmt.Sprintf("nameserver %v", net.IP(b)))
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if err := ioutil.WriteFile(resolvConf, []byte(strings.Join(lines, "\n")+"\n"), 0644); err != nil {
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log.Fatalf("resolv.conf: %v", err)
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}
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@ -263,19 +272,6 @@ func main() {
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log.Printf("send SIGHUP to init: %v", err)
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}
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leaseTime := 10 * time.Minute // seems sensible as a fallback
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if b, ok := opts[dhcp4.OptionIPAddressLeaseTime]; ok && len(b) == 4 {
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leaseTime = parseDHCPDuration(b)
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}
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// As per RFC 2131 section 4.4.5:
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// renewal time defaults to 50% of the lease time
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renewalTime := time.Duration(float64(leaseTime) * 0.5)
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if b, ok := opts[dhcp4.OptionRenewalTimeValue]; ok && len(b) == 4 {
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renewalTime = parseDHCPDuration(b)
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}
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time.Sleep(renewalTime)
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ok, ack, err = dhcpRenew(dhcp, dhcp.RenewalRequestPacket(&ack))
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time.Sleep(lease.RenewalTime)
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}
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}
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Loading…
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Reference in New Issue
Block a user