From 75b30c22100af8956f27b9f388d8fa6a2250db02 Mon Sep 17 00:00:00 2001
From: Seth Hoenig <shoenig@duck.com>
Date: Thu, 8 Sep 2022 09:13:35 -0500
Subject: [PATCH] helper: guard against negative inputs into random stagger

This PR modifies RandomStagger to protect against negative input
values. If the given interval is negative, the value returned will
be somewhere in the stratosphere. Instead, treat negative inputs
like zero, returning zero.
---
 .changelog/14497.txt   |  3 +++
 helper/cluster.go      |  7 +++----
 helper/cluster_test.go | 29 +++++++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 4 deletions(-)
 create mode 100644 .changelog/14497.txt
 create mode 100644 helper/cluster_test.go

diff --git a/.changelog/14497.txt b/.changelog/14497.txt
new file mode 100644
index 000000000..4b233f0ac
--- /dev/null
+++ b/.changelog/14497.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+helpers: Fixed a bug where random stagger func did not protect against negative inputs
+```
diff --git a/helper/cluster.go b/helper/cluster.go
index e3fda8b23..1abca1481 100644
--- a/helper/cluster.go
+++ b/helper/cluster.go
@@ -1,4 +1,3 @@
-// These functions are coming from consul/lib/cluster.go
 package helper
 
 import (
@@ -13,11 +12,11 @@ const (
 )
 
 // RandomStagger returns an interval between 0 and the duration
-func RandomStagger(intv time.Duration) time.Duration {
-	if intv == 0 {
+func RandomStagger(interval time.Duration) time.Duration {
+	if interval <= 0 {
 		return 0
 	}
-	return time.Duration(uint64(rand.Int63()) % uint64(intv))
+	return time.Duration(uint64(rand.Int63()) % uint64(interval))
 }
 
 // RateScaledInterval is used to choose an interval to perform an action in
diff --git a/helper/cluster_test.go b/helper/cluster_test.go
new file mode 100644
index 000000000..028db0b46
--- /dev/null
+++ b/helper/cluster_test.go
@@ -0,0 +1,29 @@
+package helper
+
+import (
+	"testing"
+	"time"
+
+	"github.com/shoenig/test/must"
+)
+
+func TestCluster_RandomStagger(t *testing.T) {
+	cases := []struct {
+		name  string
+		input time.Duration
+	}{
+		{name: "positive", input: 1 * time.Second},
+		{name: "negative", input: -1 * time.Second},
+		{name: "zero", input: 0},
+	}
+
+	abs := func(d time.Duration) time.Duration {
+		return Max(d, -d)
+	}
+
+	for _, tc := range cases {
+		result := RandomStagger(tc.input)
+		must.GreaterEq(t, result, 0)
+		must.LessEq(t, result, abs(tc.input))
+	}
+}