plugin/bind: exclude interface or ip address (#4543)

* plugin/bind: exclude interface or ip address

Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

* fix README.md

Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

* Apply suggestions, Fix test

Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

* Apply suggestions, move errs to setup

Signed-off-by: Mohammad Yosefpor <myusefpur@gmail.com>

plugin/bind/setup.go

@@ -1,6 +1,7 @@
 package bind
 
 import (
+	"errors"
 	"fmt"
 	"net"
 
@@ -10,48 +11,101 @@ import (
 )
 
 func setup(c *caddy.Controller) error {
-	config := dnsserver.GetConfig(c)
 
+	config := dnsserver.GetConfig(c)
 	// addresses will be consolidated over all BIND directives available in that BlocServer
 	all := []string{}
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return plugin.Error("bind", fmt.Errorf("failed to get interfaces list: %s", err))
+	}
+
 	for c.Next() {
-		args := c.RemainingArgs()
-		if len(args) == 0 {
-			return plugin.Error("bind", fmt.Errorf("at least one address or interface name is expected"))
-		}
-
-		ifaces, err := net.Interfaces()
+		b, err := parse(c)
 		if err != nil {
-			return plugin.Error("bind", fmt.Errorf("failed to get interfaces list"))
+			return plugin.Error("bind", err)
 		}
 
-		var isIface bool
-		for _, arg := range args {
-			isIface = false
-			for _, iface := range ifaces {
-				if arg == iface.Name {
-					isIface = true
-					addrs, err := iface.Addrs()
-					if err != nil {
-						return plugin.Error("bind", fmt.Errorf("failed to get the IP addresses of the interface: %q", arg))
-					}
-					for _, addr := range addrs {
-						if ipnet, ok := addr.(*net.IPNet); ok {
-							if ipnet.IP.To4() != nil || (!ipnet.IP.IsLinkLocalMulticast() && !ipnet.IP.IsLinkLocalUnicast()) {
-								all = append(all, ipnet.IP.String())
-							}
+		ips, err := listIP(b.addrs, ifaces)
+		if err != nil {
+			return plugin.Error("bind", err)
+		}
+
+		except, err := listIP(b.except, ifaces)
+		if err != nil {
+			return plugin.Error("bind", err)
+		}
+
+		for _, ip := range ips {
+			if !isIn(ip, except) {
+				all = append(all, ip)
+			}
+		}
+	}
+
+	config.ListenHosts = all
+	return nil
+}
+
+func parse(c *caddy.Controller) (*bind, error) {
+	b := &bind{}
+	b.addrs = c.RemainingArgs()
+	if len(b.addrs) == 0 {
+		return nil, errors.New("at least one address or interface name is expected")
+	}
+	for c.NextBlock() {
+		switch c.Val() {
+		case "except":
+			b.except = c.RemainingArgs()
+			if len(b.except) == 0 {
+				return nil, errors.New("at least one address or interface must be given to except subdirective")
+			}
+		default:
+			return nil, fmt.Errorf("invalid option %q", c.Val())
+		}
+	}
+	return b, nil
+}
+
+// listIP returns a list of IP addresses from a list of arguments which can be either IP-Address or Interface-Name.
+func listIP(args []string, ifaces []net.Interface) ([]string, error) {
+	all := []string{}
+	var isIface bool
+	for _, a := range args {
+		isIface = false
+		for _, iface := range ifaces {
+			if a == iface.Name {
+				isIface = true
+				addrs, err := iface.Addrs()
+				if err != nil {
+					return nil, fmt.Errorf("failed to get the IP addresses of the interface: %q", a)
+				}
+				for _, addr := range addrs {
+					if ipnet, ok := addr.(*net.IPNet); ok {
+						if ipnet.IP.To4() != nil || (!ipnet.IP.IsLinkLocalMulticast() && !ipnet.IP.IsLinkLocalUnicast()) {
+							all = append(all, ipnet.IP.String())
 						}
 					}
 				}
 			}
-			if !isIface {
-				if net.ParseIP(arg) == nil {
-					return plugin.Error("bind", fmt.Errorf("not a valid IP address or interface name: %q", arg))
-				}
-				all = append(all, arg)
+		}
+		if !isIface {
+			if net.ParseIP(a) == nil {
+				return nil, fmt.Errorf("not a valid IP address or interface name: %q", a)
 			}
+			all = append(all, a)
 		}
 	}
-	config.ListenHosts = all
-	return nil
+	return all, nil
+}
+
+// isIn checks if a string array contains an element
+func isIn(s string, list []string) bool {
+	is := false
+	for _, l := range list {
+		if s == l {
+			is = true
+		}
+	}
+	return is
 }