clash/component/dhcp/dhcp.go

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