Make consecutive random pickings for zones

Author: davidz627

pkg/gce-cloud-provider/compute/fake-gce.go

@@ -49,7 +49,7 @@ func FakeCreateCloudProvider(project, zone string) (*FakeCloudProvider, error) {
 }
 
 func (cloud *FakeCloudProvider) ListZones(ctx context.Context, region string) ([]string, error) {
-	return []string{cloud.zone, "fake-second-zone"}, nil
+	return []string{cloud.zone, "country-region-fakesecondzone"}, nil
 }
 
 // Disk Methods

pkg/gce-pd-csi-driver/controller.go

@@ -17,6 +17,7 @@ package gceGCEDriver
 import (
 	"fmt"
 	"math/rand"
+	"sort"
 	"strings"
 
 	csi "github.com/container-storage-interface/spec/lib/go/csi/v0"
@@ -532,7 +533,7 @@ func pickZonesFromTopology(top *csi.TopologyRequirement, numZones int) ([]string
 		}
 		// Add the remaining number of zones into the set
 		// TODO: Maybe we should pick a random set to get
-		nSlice, err := pickRandNFromSlice(remainingZones.List(), remainingNumZones)
+		nSlice, err := pickRandAndConsecutive(remainingZones.List(), remainingNumZones)
 		if err != nil {
 			return nil, err
 		}
@@ -684,14 +685,16 @@ func createSingleZoneDisk(ctx context.Context, cloudProvider gce.GCECompute, nam
 	return disk, nil
 }
 
-func pickRandNFromSlice(slice []string, n int) ([]string, error) {
+func pickRandAndConsecutive(slice []string, n int) ([]string, error) {
 	if n > len(slice) {
 		return nil, fmt.Errorf("n: %v is greater than length of provided slice: %v", n, slice)
 	}
-	permed := rand.Perm(len(slice))
+	sort.Strings(slice)
+	start := rand.Intn(len(slice))
 	ret := []string{}
 	for i := 0; i < n; i++ {
-		ret = append(ret, slice[permed[i]])
+		idx := (start + i) % len(slice)
+		ret = append(ret, slice[idx])
 	}
 	return ret, nil
 }

pkg/gce-pd-csi-driver/controller_test.go

@@ -16,8 +16,11 @@ package gceGCEDriver
 
 import (
 	"fmt"
+	"math/rand"
 	"reflect"
+	"sort"
 	"testing"
+	"time"
 
 	"golang.org/x/net/context"
 	compute "google.golang.org/api/compute/v1"
@@ -333,7 +336,7 @@ func TestCreateVolumeArguments(t *testing.T) {
 						Segments: map[string]string{common.TopologyKeyZone: metadataservice.FakeZone},
 					},
 					{
-						Segments: map[string]string{common.TopologyKeyZone: "fake-second-zone"},
+						Segments: map[string]string{common.TopologyKeyZone: "country-region-fakesecondzone"},
 					},
 				},
 			},
@@ -945,7 +948,8 @@ func TestPickZonesFromTopology(t *testing.T) {
 	}
 }
 
-func TestPickRandNFromSlice(t *testing.T) {
+func TestPickRandAndConsecutive(t *testing.T) {
+	rand.Seed(time.Now().UnixNano())
 	testCases := []struct {
 		name   string
 		slice  []string
@@ -977,8 +981,9 @@ func TestPickRandNFromSlice(t *testing.T) {
 	for _, tc := range testCases {
 		t.Logf("test case: %s", tc.name)
 		tot := sets.String{}
+		sort.Strings(tc.slice)
 		for i := 0; i < 25; i++ {
-			theslice, err := pickRandNFromSlice(tc.slice, tc.n)
+			theslice, err := pickRandAndConsecutive(tc.slice, tc.n)
 			if err != nil && !tc.expErr {
 				t.Errorf("Did not expect error but got: %v", err)
 			}
@@ -991,6 +996,23 @@ func TestPickRandNFromSlice(t *testing.T) {
 			if len(theslice) != tc.n {
 				t.Errorf("expected the resulting slice to be length %v, but got %v instead", tc.n, theslice)
 			}
+			// Find where it is in the slice
+			var idx = -1
+			for j, elem := range tc.slice {
+				if elem == theslice[0] {
+					idx = j
+					break
+				}
+			}
+			if idx == -1 {
+				t.Errorf("could not find %v in the original slice %v", theslice[0], tc.slice)
+			}
+			for j := 0; j < tc.n; j++ {
+				if theslice[j] != tc.slice[(idx+j)%len(tc.slice)] {
+					t.Errorf("did not pick sorted consecutive values from the slice")
+				}
+			}
+
 			tot.Insert(theslice...)
 		}
 		if !tot.Equal(sets.NewString(tc.slice...)) {