consul: adding randomStagger util method

consul/util.go

@@ -4,12 +4,14 @@ import (
 	crand "crypto/rand"
 	"encoding/binary"
 	"fmt"
+	"math/rand"
 	"net"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/hashicorp/serf/serf"
 )
@@ -222,3 +224,8 @@ func generateUUID() string {
 		buf[8:10],
 		buf[10:16])
 }
+
+// Returns a random stagger interval between 0 and the duration
+func randomStagger(intv time.Duration) time.Duration {
+	return time.Duration(uint64(rand.Int63()) % uint64(intv))
+}

consul/util_test.go

@@ -4,6 +4,7 @@ import (
 	"net"
 	"regexp"
 	"testing"
+	"time"
 
 	"github.com/hashicorp/serf/serf"
 )
@@ -124,3 +125,13 @@ func TestGenerateUUID(t *testing.T) {
 		}
 	}
 }
+
+func TestRandomStagger(t *testing.T) {
+	intv := time.Minute
+	for i := 0; i < 10; i++ {
+		stagger := randomStagger(intv)
+		if stagger < 0 || stagger >= intv {
+			t.Fatalf("Bad: %v", stagger)
+		}
+	}
+}