[rtnl] add RouteGet method

Signed-off-by: Pablo Mazzini <pmazzini@gmail.com>

rtnl/route.go

@@ -1,6 +1,7 @@
 package rtnl
 
 import (
+	"errors"
 	"net"
 
 	"github.com/jsimonetti/rtnetlink/internal/unix"
@@ -8,6 +9,12 @@ import (
 	"github.com/jsimonetti/rtnetlink"
 )
 
+// Route represents a route table entry
+type Route struct {
+	Gateway   net.IP
+	Interface *net.Interface
+}
+
 // generating route message
 func genRouteMessage(ifc *net.Interface, dst net.IPNet, gw net.IP, options ...RouteOption) (rm *rtnetlink.RouteMessage, err error) {
 
@@ -93,3 +100,35 @@ func (c *Conn) RouteDel(ifc *net.Interface, dst net.IPNet) error {
 	}
 	return c.Conn.Route.Delete(tx)
 }
+
+// RouteGet gets a single route to the given destination address.
+func (c *Conn) RouteGet(dst net.IP) (*Route, error) {
+	af, err := addrFamily(dst)
+	if err != nil {
+		return nil, err
+	}
+	attr := rtnetlink.RouteAttributes{
+		Dst: dst,
+	}
+	tx := &rtnetlink.RouteMessage{
+		Family:     uint8(af),
+		Table:      unix.RT_TABLE_MAIN,
+		Attributes: attr,
+	}
+	rx, err := c.Conn.Route.Get(tx)
+	if err != nil {
+		return nil, err
+	}
+	if len(rx) == 0 {
+		return nil, errors.New("route wrong length")
+	}
+	ifindex := int(rx[0].Attributes.OutIface)
+	iface, err := c.LinkByIndex(ifindex)
+	if err != nil {
+		return nil, err
+	}
+	return &Route{
+		Gateway:   rx[0].Attributes.Gateway,
+		Interface: iface,
+	}, nil
+}