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Randomize roundrobin endpoints #3738

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merged 5 commits into from
Jan 23, 2015
Merged

Randomize roundrobin endpoints #3738

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79a6bfb
Fixes #3640 by shuffling endpoints in the round-robin load balancer
Jan 21, 2015
38241c7
Copies endpoint slices before any sorting
Jan 21, 2015
f7e3cb1
Moves string slice sorting, copying and shuffling into pkg/util/slice
Jan 22, 2015
ab1ede3
Sets year in copyright to 2015
Jan 22, 2015
a186b47
Adds test for slice.ShuffleStrings
Jan 23, 2015
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5 changes: 3 additions & 2 deletions pkg/proxy/roundrobin.go
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,7 @@ import (
"time"

"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
"github.com/GoogleCloudPlatform/kubernetes/pkg/util/slice"
"github.com/golang/glog"
)

Expand Down Expand Up @@ -210,14 +211,14 @@ func (lb *LoadBalancerRR) OnUpdate(endpoints []api.Endpoints) {
for _, endpoint := range endpoints {
existingEndpoints, exists := lb.endpointsMap[endpoint.Name]
validEndpoints := filterValidEndpoints(endpoint.Endpoints)
if !exists || !reflect.DeepEqual(existingEndpoints, validEndpoints) {
if !exists || !reflect.DeepEqual(slice.SortStrings(slice.CopyStrings(existingEndpoints)), slice.SortStrings(validEndpoints)) {
glog.V(3).Infof("LoadBalancerRR: Setting endpoints for %s to %+v", endpoint.Name, endpoint.Endpoints)
updateServiceDetailMap(lb, endpoint.Name, validEndpoints)
// On update can be called without NewService being called externally.
// to be safe we will call it here. A new service will only be created
// if one does not already exist.
lb.NewService(endpoint.Name, api.AffinityTypeNone, 0)
lb.endpointsMap[endpoint.Name] = validEndpoints
lb.endpointsMap[endpoint.Name] = slice.ShuffleStrings(validEndpoints)

// Reset the round-robin index.
lb.rrIndex[endpoint.Name] = 0
Expand Down
205 changes: 115 additions & 90 deletions pkg/proxy/roundrobin_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -75,7 +75,7 @@ func expectEndpoint(t *testing.T, loadBalancer *LoadBalancerRR, service string,
t.Errorf("Didn't find a service for %s, expected %s, failed with: %v", service, expected, err)
}
if endpoint != expected {
t.Errorf("Didn't get expected endpoint for service %s, expected %s, got: %s", service, expected, endpoint)
t.Errorf("Didn't get expected endpoint for service %s client %v, expected %s, got: %s", service, netaddr, expected, endpoint)
}
}

Expand Down Expand Up @@ -109,10 +109,11 @@ func TestLoadBalanceWorksWithMultipleEndpoints(t *testing.T) {
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:3"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", nil)
shuffledEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], nil)
}

func TestLoadBalanceWorksWithMultipleEndpointsAndUpdates(t *testing.T) {
Expand All @@ -127,21 +128,23 @@ func TestLoadBalanceWorksWithMultipleEndpointsAndUpdates(t *testing.T) {
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:3"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", nil)
shuffledEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], nil)
// Then update the configuration with one fewer endpoints, make sure
// we start in the beginning again
endpoints[0] = api.Endpoints{ObjectMeta: api.ObjectMeta{Name: "foo"},
Endpoints: []string{"endpoint:8", "endpoint:9"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:8", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:9", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:8", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:9", nil)
shuffledEndpoints = loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], nil)
// Clear endpoints
endpoints[0] = api.Endpoints{ObjectMeta: api.ObjectMeta{Name: "foo"}, Endpoints: []string{}}
loadBalancer.OnUpdate(endpoints)
Expand All @@ -168,17 +171,19 @@ func TestLoadBalanceWorksWithServiceRemoval(t *testing.T) {
Endpoints: []string{"endpoint:4", "endpoint:5"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", nil)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", nil)

expectEndpoint(t, loadBalancer, "bar", "endpoint:4", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", nil)
shuffledFooEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[2], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[1], nil)

shuffledBarEndpoints := loadBalancer.endpointsMap["bar"]
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], nil)

// Then update the configuration by removing foo
loadBalancer.OnUpdate(endpoints[1:])
Expand All @@ -188,10 +193,10 @@ func TestLoadBalanceWorksWithServiceRemoval(t *testing.T) {
}

// but bar is still there, and we continue RR from where we left off.
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", nil)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[1], nil)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], nil)
}

func TestStickyLoadBalanceWorksWithSingleEndpoint(t *testing.T) {
Expand Down Expand Up @@ -232,14 +237,15 @@ func TestStickyLoadBalanaceWorksWithMultipleEndpoints(t *testing.T) {
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:3"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
shuffledEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
}

func TestStickyLoadBalanaceWorksWithMultipleEndpointsStickyNone(t *testing.T) {
Expand All @@ -259,14 +265,15 @@ func TestStickyLoadBalanaceWorksWithMultipleEndpointsStickyNone(t *testing.T) {
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:3"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client1)
shuffledEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client1)
}

func TestStickyLoadBalanaceWorksWithMultipleEndpointsRemoveOne(t *testing.T) {
Expand All @@ -289,32 +296,45 @@ func TestStickyLoadBalanaceWorksWithMultipleEndpointsRemoveOne(t *testing.T) {
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:3"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
shuffledEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
client1Endpoint := shuffledEndpoints[0]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
client2Endpoint := shuffledEndpoints[1]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client3)
client3Endpoint := shuffledEndpoints[2]

endpoints[0] = api.Endpoints{
ObjectMeta: api.ObjectMeta{Name: "foo"},
Endpoints: []string{"endpoint:1", "endpoint:2"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client3)
shuffledEndpoints = loadBalancer.endpointsMap["foo"]
if client1Endpoint == "endpoint:3" {
client1Endpoint = shuffledEndpoints[0]
} else if client2Endpoint == "endpoint:3" {
client2Endpoint = shuffledEndpoints[0]
} else if client3Endpoint == "endpoint:3" {
client3Endpoint = shuffledEndpoints[0]
}
expectEndpoint(t, loadBalancer, "foo", client1Endpoint, client1)
expectEndpoint(t, loadBalancer, "foo", client2Endpoint, client2)
expectEndpoint(t, loadBalancer, "foo", client3Endpoint, client3)

endpoints[0] = api.Endpoints{
ObjectMeta: api.ObjectMeta{Name: "foo"},
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:4"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client4)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client5)
expectEndpoint(t, loadBalancer, "foo", "endpoint:4", client6)
shuffledEndpoints = loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", client1Endpoint, client1)
expectEndpoint(t, loadBalancer, "foo", client2Endpoint, client2)
expectEndpoint(t, loadBalancer, "foo", client3Endpoint, client3)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client4)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client5)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client6)
}

func TestStickyLoadBalanceWorksWithMultipleEndpointsAndUpdates(t *testing.T) {
Expand All @@ -334,24 +354,26 @@ func TestStickyLoadBalanceWorksWithMultipleEndpointsAndUpdates(t *testing.T) {
Endpoints: []string{"endpoint:1", "endpoint:2", "endpoint:3"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
shuffledEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[2], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
// Then update the configuration with one fewer endpoints, make sure
// we start in the beginning again
endpoints[0] = api.Endpoints{ObjectMeta: api.ObjectMeta{Name: "foo"},
Endpoints: []string{"endpoint:4", "endpoint:5"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:5", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:5", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:5", client2)
shuffledEndpoints = loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledEndpoints[1], client2)

// Clear endpoints
endpoints[0] = api.Endpoints{ObjectMeta: api.ObjectMeta{Name: "foo"}, Endpoints: []string{}}
Expand Down Expand Up @@ -384,19 +406,21 @@ func TestStickyLoadBalanceWorksWithServiceRemoval(t *testing.T) {
Endpoints: []string{"endpoint:4", "endpoint:5"},
}
loadBalancer.OnUpdate(endpoints)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:3", client3)
expectEndpoint(t, loadBalancer, "foo", "endpoint:1", client1)
expectEndpoint(t, loadBalancer, "foo", "endpoint:2", client2)

expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", client2)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", client2)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
shuffledFooEndpoints := loadBalancer.endpointsMap["foo"]
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[2], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[2], client3)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[1], client2)

shuffledBarEndpoints := loadBalancer.endpointsMap["bar"]
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "foo", shuffledFooEndpoints[0], client1)

// Then update the configuration by removing foo
loadBalancer.OnUpdate(endpoints[1:])
Expand All @@ -406,10 +430,11 @@ func TestStickyLoadBalanceWorksWithServiceRemoval(t *testing.T) {
}

// but bar is still there, and we continue RR from where we left off.
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", client2)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "bar", "endpoint:5", client2)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
expectEndpoint(t, loadBalancer, "bar", "endpoint:4", client1)
shuffledBarEndpoints = loadBalancer.endpointsMap["bar"]
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[1], client2)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], client1)
expectEndpoint(t, loadBalancer, "bar", shuffledBarEndpoints[0], client1)
}
49 changes: 49 additions & 0 deletions pkg/util/slice/slice.go
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,49 @@
/*
Copyright 2015 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package slice provides utility methods for common operations on slices.
package slice

import (
"math/rand"
"sort"
)

// CopyStrings copies the contents of the specified string slice
// into a new slice.
func CopyStrings(s []string) []string {
c := make([]string, len(s))
copy(c, s)
return c
}

// SortStrings sorts the specified string slice in place. It returns the same
// slice that was provided in order to facilitate method chaining.
func SortStrings(s []string) []string {
sort.Strings(s)
return s
}

// ShuffleStrings copies strings from the specified slice into a copy in random
// order. It returns a new slice.
func ShuffleStrings(s []string) []string {
shuffled := make([]string, len(s))
perm := rand.Perm(len(s))
for i, j := range perm {
shuffled[j] = s[i]
}
return shuffled
}