- dhcp: CheckIfOtherDHCPServersPresent: fix

Sometimes request from DHCP server couldn't be received
 because we were bound to a specific IP address.

dhcpd/check_other_dhcp.go

@@ -7,12 +7,13 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"runtime"
 	"time"
 
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/insomniacslk/dhcp/dhcpv4"
+	"github.com/insomniacslk/dhcp/dhcpv4/nclient4"
 	"github.com/insomniacslk/dhcp/iana"
-	"golang.org/x/net/ipv4"
 )
 
 // CheckIfOtherDHCPServersPresent sends a DHCP request to the specified network interface,
@@ -29,6 +30,10 @@ func CheckIfOtherDHCPServersPresent(ifaceName string) (bool, error) {
 		return false, fmt.Errorf("couldn't find IPv4 address of interface %s %+v", ifaceName, iface)
 	}
 
+	if runtime.GOOS == "darwin" {
+		return false, fmt.Errorf("Can't find DHCP server: not supported on macOS")
+	}
+
 	srcIP := ifaceIPNet[0]
 	src := net.JoinHostPort(srcIP.String(), "68")
 	dst := "255.255.255.255:67"
@@ -60,7 +65,7 @@ func CheckIfOtherDHCPServersPresent(ifaceName string) (bool, error) {
 
 	// bind to 0.0.0.0:68
 	log.Tracef("Listening to udp4 %+v", udpAddr)
-	c, err := newBroadcastPacketConn(net.IPv4(0, 0, 0, 0), 68, ifaceName)
+	c, err := nclient4.NewRawUDPConn(ifaceName, 68)
 	if c != nil {
 		defer c.Close()
 	}
@@ -69,8 +74,7 @@ func CheckIfOtherDHCPServersPresent(ifaceName string) (bool, error) {
 	}
 
 	// send to 255.255.255.255:67
-	cm := ipv4.ControlMessage{}
+	_, err = c.WriteTo(req.ToBytes(), dstAddr)
-	_, err = c.WriteTo(req.ToBytes(), &cm, dstAddr)
 	if err != nil {
 		return false, wrapErrPrint(err, "Couldn't send a packet to %s", dst)
 	}
@@ -81,9 +85,10 @@ func CheckIfOtherDHCPServersPresent(ifaceName string) (bool, error) {
 		// TODO: replicate dhclient's behaviour of retrying several times with progressively bigger timeouts
 		b := make([]byte, 1500)
 		_ = c.SetReadDeadline(time.Now().Add(defaultDiscoverTime))
-		n, _, _, err := c.ReadFrom(b)
+		n, _, err := c.ReadFrom(b)
 		if isTimeout(err) {
 			// timed out -- no DHCP servers
+			log.Debug("DHCPv4: didn't receive DHCP response")
 			return false, nil
 		}
 		if err != nil {

dhcpd/os_linux.go

@@ -1,45 +0,0 @@
-package dhcpd
-
-import (
-	"net"
-	"os"
-	"syscall"
-
-	"golang.org/x/net/ipv4"
-)
-
-// Create a socket for receiving broadcast packets
-func newBroadcastPacketConn(bindAddr net.IP, port int, ifname string) (*ipv4.PacketConn, error) {
-	s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, syscall.IPPROTO_UDP)
-	if err != nil {
-		return nil, err
-	}
-
-	if err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1); err != nil {
-		return nil, err
-	}
-	if err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1); err != nil {
-		return nil, err
-	}
-	if err := syscall.SetsockoptString(s, syscall.SOL_SOCKET, syscall.SO_BINDTODEVICE, ifname); err != nil {
-		return nil, err
-	}
-
-	addr := syscall.SockaddrInet4{Port: port}
-	copy(addr.Addr[:], bindAddr.To4())
-	err = syscall.Bind(s, &addr)
-	if err != nil {
-		syscall.Close(s)
-		return nil, err
-	}
-
-	f := os.NewFile(uintptr(s), "")
-	c, err := net.FilePacketConn(f)
-	f.Close()
-	if err != nil {
-		return nil, err
-	}
-
-	p := ipv4.NewPacketConn(c)
-	return p, nil
-}

dhcpd/os_unix.go

@@ -1,44 +0,0 @@
-// +build aix darwin dragonfly freebsd netbsd openbsd solaris
-
-package dhcpd
-
-import (
-	"net"
-	"os"
-	"syscall"
-
-	"golang.org/x/net/ipv4"
-)
-
-// Create a socket for receiving broadcast packets
-func newBroadcastPacketConn(bindAddr net.IP, port int, ifname string) (*ipv4.PacketConn, error) {
-	s, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_DGRAM, syscall.IPPROTO_UDP)
-	if err != nil {
-		return nil, err
-	}
-
-	if err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1); err != nil {
-		return nil, err
-	}
-	if err := syscall.SetsockoptInt(s, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1); err != nil {
-		return nil, err
-	}
-
-	addr := syscall.SockaddrInet4{Port: port}
-	copy(addr.Addr[:], bindAddr.To4())
-	err = syscall.Bind(s, &addr)
-	if err != nil {
-		syscall.Close(s)
-		return nil, err
-	}
-
-	f := os.NewFile(uintptr(s), "")
-	c, err := net.FilePacketConn(f)
-	f.Close()
-	if err != nil {
-		return nil, err
-	}
-
-	p := ipv4.NewPacketConn(c)
-	return p, nil
-}