Fix GroupsAsSubDomains option for Mesos and Marathon (#868)

* Fix GroupsAsSubDomains option for Mesos and Marathon
* Refactor reverseStringSlice function

provider/marathon.go

@@ -3,7 +3,6 @@ package provider
 import (
 	"errors"
 	"net/url"
-	"sort"
 	"strconv"
 	"strings"
 	"text/template"
@@ -419,7 +418,7 @@ func (provider *Marathon) getFrontendBackend(application marathon.Application) s
 func (provider *Marathon) getSubDomain(name string) string {
 	if provider.GroupsAsSubDomains {
 		splitedName := strings.Split(strings.TrimPrefix(name, "/"), "/")
-		sort.Sort(sort.Reverse(sort.StringSlice(splitedName)))
+		reverseStringSlice(&splitedName)
 		reverseName := strings.Join(splitedName, ".")
 		return reverseName
 	}

provider/marathon_test.go

@@ -1280,3 +1280,33 @@ func TestMarathonGetBackend(t *testing.T) {
 		}
 	}
 }
+
+func TestMarathonGetSubDomain(t *testing.T) {
+	providerGroups := &Marathon{GroupsAsSubDomains: true}
+	providerNoGroups := &Marathon{GroupsAsSubDomains: false}
+
+	apps := []struct {
+		path     string
+		expected string
+		provider *Marathon
+	}{
+		{"/test", "test", providerNoGroups},
+		{"/test", "test", providerGroups},
+		{"/a/b/c/d", "d.c.b.a", providerGroups},
+		{"/b/a/d/c", "c.d.a.b", providerGroups},
+		{"/d/c/b/a", "a.b.c.d", providerGroups},
+		{"/c/d/a/b", "b.a.d.c", providerGroups},
+		{"/a/b/c/d", "a-b-c-d", providerNoGroups},
+		{"/b/a/d/c", "b-a-d-c", providerNoGroups},
+		{"/d/c/b/a", "d-c-b-a", providerNoGroups},
+		{"/c/d/a/b", "c-d-a-b", providerNoGroups},
+	}
+
+	for _, a := range apps {
+		actual := a.provider.getSubDomain(a.path)
+
+		if actual != a.expected {
+			t.Errorf("expected %q, got %q", a.expected, actual)
+		}
+	}
+}

provider/mesos.go

@@ -7,6 +7,8 @@ import (
 	"text/template"
 
 	"fmt"
+	"time"
+
 	"github.com/BurntSushi/ty/fun"
 	"github.com/cenk/backoff"
 	"github.com/containous/traefik/job"
@@ -20,8 +22,6 @@ import (
 	"github.com/mesosphere/mesos-dns/records"
 	"github.com/mesosphere/mesos-dns/records/state"
 	"github.com/mesosphere/mesos-dns/util"
-	"sort"
-	"time"
 )
 
 var _ Provider = (*Mesos)(nil)
@@ -435,7 +435,7 @@ func Ignore(f ErrorFunction) {
 func (provider *Mesos) getSubDomain(name string) string {
 	if provider.GroupsAsSubDomains {
 		splitedName := strings.Split(strings.TrimPrefix(name, "/"), "/")
-		sort.Sort(sort.Reverse(sort.StringSlice(splitedName)))
+		reverseStringSlice(&splitedName)
 		reverseName := strings.Join(splitedName, ".")
 		return reverseName
 	}

provider/mesos_test.go

@@ -1,11 +1,12 @@
 package provider
 
 import (
+	"reflect"
+	"testing"
+
 	"github.com/containous/traefik/log"
 	"github.com/containous/traefik/types"
 	"github.com/mesosphere/mesos-dns/records/state"
-	"reflect"
-	"testing"
 )
 
 func TestMesosTaskFilter(t *testing.T) {
@@ -244,6 +245,36 @@ func TestMesosLoadConfig(t *testing.T) {
 	}
 }
 
+func TestMesosGetSubDomain(t *testing.T) {
+	providerGroups := &Mesos{GroupsAsSubDomains: true}
+	providerNoGroups := &Mesos{GroupsAsSubDomains: false}
+
+	apps := []struct {
+		path     string
+		expected string
+		provider *Mesos
+	}{
+		{"/test", "test", providerNoGroups},
+		{"/test", "test", providerGroups},
+		{"/a/b/c/d", "d.c.b.a", providerGroups},
+		{"/b/a/d/c", "c.d.a.b", providerGroups},
+		{"/d/c/b/a", "a.b.c.d", providerGroups},
+		{"/c/d/a/b", "b.a.d.c", providerGroups},
+		{"/a/b/c/d", "a-b-c-d", providerNoGroups},
+		{"/b/a/d/c", "b-a-d-c", providerNoGroups},
+		{"/d/c/b/a", "d-c-b-a", providerNoGroups},
+		{"/c/d/a/b", "c-d-a-b", providerNoGroups},
+	}
+
+	for _, a := range apps {
+		actual := a.provider.getSubDomain(a.path)
+
+		if actual != a.expected {
+			t.Errorf("expected %q, got %q", a.expected, actual)
+		}
+	}
+}
+
 // test helpers
 
 type (

provider/provider.go

@@ -101,6 +101,12 @@ func normalize(name string) string {
 	return strings.Join(strings.FieldsFunc(name, fargs), "-")
 }
 
+func reverseStringSlice(slice *[]string) {
+	for i, j := 0, len(*slice)-1; i < j; i, j = i+1, j-1 {
+		(*slice)[i], (*slice)[j] = (*slice)[j], (*slice)[i]
+	}
+}
+
 // ClientTLS holds TLS specific configurations as client
 // CA, Cert and Key can be either path or file contents
 type ClientTLS struct {