95 lines
1.6 KiB
Go
95 lines
1.6 KiB
Go
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package dhcp
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import (
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"context"
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"errors"
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"math/rand"
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"net"
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"github.com/insomniacslk/dhcp/dhcpv4"
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)
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var (
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ErrNotResponding = errors.New("DHCP not responding")
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ErrNotFound = errors.New("DNS option not found")
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)
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func ResolveDNSFromDHCP(context context.Context, ifaceName string) ([]net.IP, error) {
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conn, err := ListenDHCPClient(context, ifaceName)
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if err != nil {
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return nil, err
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}
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defer conn.Close()
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result := make(chan []net.IP, 1)
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discovery, err := dhcpv4.NewDiscovery(randomHardware(), dhcpv4.WithBroadcast(true), dhcpv4.WithRequestedOptions(dhcpv4.OptionDomainNameServer))
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if err != nil {
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return nil, err
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}
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go receiveOffer(conn, discovery.TransactionID, result)
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_, err = conn.WriteTo(discovery.ToBytes(), &net.UDPAddr{IP: net.IPv4bcast, Port: 67})
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if err != nil {
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return nil, err
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}
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select {
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case r, ok := <-result:
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if !ok {
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return nil, ErrNotFound
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}
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return r, nil
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case <-context.Done():
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return nil, ErrNotResponding
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}
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}
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func receiveOffer(conn net.PacketConn, id dhcpv4.TransactionID, result chan<- []net.IP) {
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defer close(result)
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buf := make([]byte, dhcpv4.MaxMessageSize)
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for {
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n, _, err := conn.ReadFrom(buf)
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if err != nil {
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return
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}
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pkt, err := dhcpv4.FromBytes(buf[:n])
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if err != nil {
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continue
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}
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if pkt.MessageType() != dhcpv4.MessageTypeOffer {
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continue
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}
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if pkt.TransactionID != id {
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continue
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}
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dns := pkt.DNS()
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if len(dns) == 0 {
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return
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}
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result <- dns
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return
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}
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}
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func randomHardware() net.HardwareAddr {
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addr := make(net.HardwareAddr, 6)
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addr[0] = 0xff
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for i := 1; i < len(addr); i++ {
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addr[i] = byte(rand.Intn(254) + 1)
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}
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return addr
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}
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