Fix HostPortOrFile to support IPv6 addresses with zone (#3527)

1. The HostPortOrFile tests don't have any IPv6 tests. This adds some.
2. The HostPortOrFile breaks if any of the addresses have IPv6 zone
defined. ParseIP does not handle %zone anymore.
Signed-off-by: Brad P. Crochet <brad@redhat.com>

plugin/pkg/parse/host.go

@@ -4,12 +4,23 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"strings"
 
 	"github.com/coredns/coredns/plugin/pkg/transport"
 
 	"github.com/miekg/dns"
 )
 
+// Strips the zone, but preserves any port that comes after the zone
+func stripZone(host string) string {
+	if strings.Contains(host, "%") {
+		lastPercent := strings.LastIndex(host, "%")
+		newHost := host[:lastPercent]
+		return newHost
+	}
+	return host
+}
+
 // HostPortOrFile parses the strings in s, each string can either be a
 // address, [scheme://]address:port or a filename. The address part is checked
 // and in case of filename a resolv.conf like file is (assumed) and parsed and
@@ -21,10 +32,11 @@ func HostPortOrFile(s ...string) ([]string, error) {
 		trans, host := Transport(h)
 
 		addr, _, err := net.SplitHostPort(host)
+
 		if err != nil {
 			// Parse didn't work, it is not a addr:port combo
-			if net.ParseIP(host) == nil {
-				// Not an IP address.
+			hostNoZone := stripZone(host)
+			if net.ParseIP(hostNoZone) == nil {
 				ss, err := tryFile(host)
 				if err == nil {
 					servers = append(servers, ss...)
@@ -47,8 +59,7 @@ func HostPortOrFile(s ...string) ([]string, error) {
 			continue
 		}
 
-		if net.ParseIP(addr) == nil {
-			// Not an IP address.
+		if net.ParseIP(stripZone(addr)) == nil {
 			ss, err := tryFile(host)
 			if err == nil {
 				servers = append(servers, ss...)

plugin/pkg/parse/host_test.go

@@ -34,6 +34,26 @@ func TestHostPortOrFile(t *testing.T) {
 			"127.0.0.1:53",
 			false,
 		},
+		{
+			"fe80::1",
+			"[fe80::1]:53",
+			false,
+		},
+		{
+			"fe80::1%ens3",
+			"[fe80::1%ens3]:53",
+			false,
+		},
+		{
+			"[fd01::1]:153",
+			"[fd01::1]:153",
+			false,
+		},
+		{
+			"[fd01::1%ens3]:153",
+			"[fd01::1%ens3]:153",
+			false,
+		},
 	}
 
 	err := ioutil.WriteFile("resolv.conf", []byte("nameserver 127.0.0.1\n"), 0600)