Revert "Revert "Move rand string func to util for reuse""

This reverts commit acebe24bf3.

pkg/api/generate.go

@@ -18,7 +18,8 @@ package api
 
 import (
 	"fmt"
-	"math/rand"
+
+	utilrand "github.com/GoogleCloudPlatform/kubernetes/pkg/util/rand"
 )
 
 // NameGenerator generates names for objects. Some backends may have more information
@@ -59,16 +60,5 @@ func (simpleNameGenerator) GenerateName(base string) string {
 	if len(base) > maxGeneratedNameLength {
 		base = base[:maxGeneratedNameLength]
 	}
-	value := randSeq(randomLength)
-	return fmt.Sprintf("%s%s", base, value)
-}
-
-var letters = []rune("abcdefghijklmnopqrstuvwxyz0123456789")
-
-func randSeq(n int) string {
-	b := make([]rune, n)
-	for i := range b {
-		b[i] = letters[rand.Intn(len(letters))]
-	}
-	return string(b)
+	return fmt.Sprintf("%s%s", base, utilrand.String(randomLength))
 }

pkg/util/rand/rand.go

@@ -0,0 +1,48 @@
+/*
+Copyright 2015 The Kubernetes Authors 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 rand provides utilities related to randomization.
+package rand
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var letters = []rune("abcdefghijklmnopqrstuvwxyz0123456789")
+var numLetters = len(letters)
+var rng = struct {
+	rand *rand.Rand
+	lock sync.Mutex
+}{
+	rand: rand.New(rand.NewSource(time.Now().UTC().UnixNano())),
+}
+
+// String generates a random alphanumeric string n characters long.  This will
+// panic if n is less than zero.
+func String(n int) string {
+	if n < 0 {
+		panic("out-of-bounds value")
+	}
+	b := make([]rune, n)
+	rng.lock.Lock()
+	defer rng.lock.Unlock()
+	for i := range b {
+		b[i] = letters[rng.rand.Intn(numLetters)]
+	}
+	return string(b)
+}

pkg/util/rand/rand_test.go

@@ -0,0 +1,37 @@
+/*
+Copyright 2015 The Kubernetes Authors 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 rand
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestString(t *testing.T) {
+	valid := "0123456789abcdefghijklmnopqrstuvwxyz"
+	for _, l := range []int{0, 1, 2, 10, 123} {
+		s := String(l)
+		if len(s) != l {
+			t.Errorf("expected string of size %d, got %q", l, s)
+		}
+		for _, c := range s {
+			if !strings.ContainsRune(valid, c) {
+				t.Errorf("expected valid charaters, got %v", c)
+			}
+		}
+	}
+}