From a139af414437d150c72562ef765dcb392b58edfa Mon Sep 17 00:00:00 2001
From: Matt Harrison <88399148+mattharr013@users.noreply.github.com>
Date: Tue, 20 Dec 2022 10:31:47 -0500
Subject: [PATCH] Fix LRU to correct evict cache items when replaced (#52)

---
 groupcache_test.go | 15 +++++++++++++++
 lru/lru.go         |  6 +++++-
 lru/lru_test.go    | 26 ++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/groupcache_test.go b/groupcache_test.go
index e87c62a..5eca5e2 100644
--- a/groupcache_test.go
+++ b/groupcache_test.go
@@ -535,3 +535,18 @@ func TestContextDeadlineOnPeer(t *testing.T) {
 		}
 	}
 }
+
+func TestCacheRemovesBytesOfReplacedValues(t *testing.T) {
+	c := cache{}
+
+	const key = "test"
+	keyLen := len(key)
+
+	for _, bytes := range []int{100, 1000, 2000} {
+		c.add(key, ByteView{b: make([]byte, bytes)})
+		expected := int64(bytes + keyLen)
+		if c.nbytes != expected {
+			t.Fatalf("%s: expected %d was %d", t.Name(), expected, c.nbytes)
+		}
+	}
+}
diff --git a/lru/lru.go b/lru/lru.go
index 9e606c0..549122f 100644
--- a/lru/lru.go
+++ b/lru/lru.go
@@ -63,8 +63,12 @@ func (c *Cache) Add(key Key, value interface{}, expire time.Time) {
 		c.ll = list.New()
 	}
 	if ee, ok := c.cache[key]; ok {
+		eee := ee.Value.(*entry)
+		if c.OnEvicted != nil {
+			c.OnEvicted(key, eee.value)
+		}
 		c.ll.MoveToFront(ee)
-		ee.Value.(*entry).value = value
+		eee.value = value
 		return
 	}
 	ele := c.ll.PushFront(&entry{key, value, expire})
diff --git a/lru/lru_test.go b/lru/lru_test.go
index a2e5f0b..4d029c5 100644
--- a/lru/lru_test.go
+++ b/lru/lru_test.go
@@ -46,6 +46,32 @@ var getTests = []struct {
 		complexStruct{1, simpleStruct{2, "three"}}, true},
 }
 
+func TestAdd_evictsOldAndReplaces(t *testing.T) {
+	var evictedKey Key
+	var evictedValue interface{}
+	lru := New(0)
+	lru.OnEvicted = func(key Key, value interface{}) {
+		evictedKey = key
+		evictedValue = value
+	}
+	lru.Add("myKey", 1234, time.Time{})
+	lru.Add("myKey", 1235, time.Time{})
+
+	newVal, ok := lru.Get("myKey")
+	if !ok {
+		t.Fatalf("%s: cache hit = %v; want %v", t.Name(), ok, !ok)
+	}
+	if newVal != 1235 {
+		t.Fatalf("%s: cache hit = %v; want %v", t.Name(), newVal, 1235)
+	}
+	if evictedKey != "myKey" {
+		t.Fatalf("%s: evictedKey = %v; want %v", t.Name(), evictedKey, "myKey")
+	}
+	if evictedValue != 1234 {
+		t.Fatalf("%s: evictedValue = %v; want %v", t.Name(), evictedValue, 1234)
+	}
+}
+
 func TestGet(t *testing.T) {
 	for _, tt := range getTests {
 		lru := New(0)