From dc3cf9d49553eb748b60786dbc351c94ba682738 Mon Sep 17 00:00:00 2001
From: Burak Sezer <burak.sezer.developer@gmail.com>
Date: Wed, 9 Nov 2022 23:39:25 +0300
Subject: [PATCH] fix: AverageLoad() function panics with "divide by zero" when
 no members are in the hash ring #19

---
 consistent.go      | 15 +++++++++++++--
 consistent_test.go | 30 ++++++++++++++++++++----------
 2 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/consistent.go b/consistent.go
index e468a25..77b89f3 100644
--- a/consistent.go
+++ b/consistent.go
@@ -136,7 +136,7 @@ func New(members []Member, config Config) *Consistent {
 	return c
 }
 
-// GetMembers returns a thread-safe copy of members.
+// GetMembers returns a thread-safe copy of members. If there are no members, it returns an empty slice of Member.
 func (c *Consistent) GetMembers() []Member {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
@@ -151,12 +151,23 @@ func (c *Consistent) GetMembers() []Member {
 
 // AverageLoad exposes the current average load.
 func (c *Consistent) AverageLoad() float64 {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+
+	return c.averageLoad()
+}
+
+func (c *Consistent) averageLoad() float64 {
+	if len(c.members) == 0 {
+		return 0
+	}
+
 	avgLoad := float64(c.partitionCount/uint64(len(c.members))) * c.config.Load
 	return math.Ceil(avgLoad)
 }
 
 func (c *Consistent) distributeWithLoad(partID, idx int, partitions map[int]*Member, loads map[string]float64) {
-	avgLoad := c.AverageLoad()
+	avgLoad := c.averageLoad()
 	var count int
 	for {
 		count++
diff --git a/consistent_test.go b/consistent_test.go
index bd11f68..d4a7fce 100644
--- a/consistent_test.go
+++ b/consistent_test.go
@@ -95,22 +95,32 @@ func TestConsistentRemove(t *testing.T) {
 }
 
 func TestConsistentLoad(t *testing.T) {
-	members := []Member{}
+	var members []Member
 	for i := 0; i < 8; i++ {
 		member := testMember(fmt.Sprintf("node%d.olric", i))
 		members = append(members, member)
 	}
 	cfg := newConfig()
-	c := New(members, cfg)
-	if len(c.GetMembers()) != len(members) {
-		t.Fatalf("inserted member count is different")
-	}
-	maxLoad := c.AverageLoad()
-	for member, load := range c.LoadDistribution() {
-		if load > maxLoad {
-			t.Fatalf("%s exceeds max load. Its load: %f, max load: %f", member, load, maxLoad)
+
+	t.Run("Average load should be greater than the member's load", func(t *testing.T) {
+		c := New(members, cfg)
+		if len(c.GetMembers()) != len(members) {
+			t.Fatalf("inserted member count is different")
 		}
-	}
+		maxLoad := c.AverageLoad()
+		for member, load := range c.LoadDistribution() {
+			if load > maxLoad {
+				t.Fatalf("%s exceeds max load. Its load: %f, max load: %f", member, load, maxLoad)
+			}
+		}
+	})
+
+	t.Run("Average load should equal to zero if there are no members", func(t *testing.T) {
+		c := New(nil, cfg)
+		if c.AverageLoad() != 0 {
+			t.Fatalf("AverageLoad should equal to zero")
+		}
+	})
 }
 
 func TestConsistentLocateKey(t *testing.T) {