From df478cfa8f42c459da7fd3e357815a95c0e8670c Mon Sep 17 00:00:00 2001
From: zouliehao <zouliehao@bytedance.com>
Date: Sat, 23 Jul 2022 16:42:25 +0800
Subject: [PATCH] Feature get the value but not update the expiration time
 (#57)

---
 cache_test.go | 43 +++++++++++++++++++++++++++++++++++++++++++
 cacheitem.go  |  7 +++++++
 cachetable.go | 27 +++++++++++++++++++++++++++
 3 files changed, 77 insertions(+)

diff --git a/cache_test.go b/cache_test.go
index e195e93..1c7234a 100644
--- a/cache_test.go
+++ b/cache_test.go
@@ -168,6 +168,49 @@ func TestCacheKeepAlive(t *testing.T) {
 	}
 }
 
+func TestPeek(t *testing.T) {
+	// add an expiring item
+	table := Cache("TestPeek")
+	_ = table.Add(k, 250*time.Millisecond, v)
+	_ = table.Add(k+"_", 250*time.Millisecond, v)
+
+	// test peek item
+	time.Sleep(150 * time.Millisecond)
+	p, _ := table.Peek(k)
+	if p.Data() != v {
+		t.Error("Error peek item")
+	}
+
+	// test k is expired
+	time.Sleep(150 * time.Millisecond)
+	if table.Exists(k) {
+		t.Error("Error peek but expired time updated")
+	}
+
+	// test peek nil
+	_, err := table.Peek(k)
+	if err != ErrKeyNotFound {
+		t.Error("Error peek nil value but not return ErrKeyNotFound")
+	}
+
+	// test DataLoader
+	table.SetDataLoader(func(key interface{}, args ...interface{}) *CacheItem {
+		if key == k {
+			return NewCacheItem(key, 150*time.Millisecond, "new value")
+		}
+		return nil
+	})
+	p, _ = table.Peek(k)
+	if p.Data() != "new value" {
+		t.Error("Error peek DataLoader callback did not take effect")
+	}
+
+	_, err = table.Peek(k + "_")
+	if err != ErrKeyNotFoundOrLoadable {
+		t.Error("Error peek DataLoader err")
+	}
+}
+
 func TestDelete(t *testing.T) {
 	// add an item to the cache
 	table := Cache("testDelete")
diff --git a/cacheitem.go b/cacheitem.go
index 4046be2..4e1ef32 100644
--- a/cacheitem.go
+++ b/cacheitem.go
@@ -61,6 +61,13 @@ func (item *CacheItem) KeepAlive() {
 	item.accessCount++
 }
 
+// AddAccessCount only add one access count.
+func (item *CacheItem) AddAccessCount() {
+	item.Lock()
+	defer item.Unlock()
+	item.accessCount++
+}
+
 // LifeSpan returns this item's expiration duration.
 func (item *CacheItem) LifeSpan() time.Duration {
 	// immutable
diff --git a/cachetable.go b/cachetable.go
index 1fa75ad..05433d4 100644
--- a/cachetable.go
+++ b/cachetable.go
@@ -303,6 +303,33 @@ func (table *CacheTable) Value(key interface{}, args ...interface{}) (*CacheItem
 	return nil, ErrKeyNotFound
 }
 
+// Peek returns an item from the cache, but does not mark its active status, i.e. does not update the active time.
+// You can also pass additional arguments to your DataLoader callback function.
+func (table *CacheTable) Peek(key interface{}, args ...interface{}) (*CacheItem, error) {
+	table.RLock()
+	r, ok := table.items[key]
+	loadData := table.loadData
+	table.RUnlock()
+
+	if ok {
+		r.AddAccessCount()
+		return r, nil
+	}
+
+	// Item doesn't exist in cache. Try and fetch it with a data-loader.
+	if loadData != nil {
+		item := loadData(key, args...)
+		if item != nil {
+			table.Add(key, item.lifeSpan, item.data)
+			return item, nil
+		}
+
+		return nil, ErrKeyNotFoundOrLoadable
+	}
+
+	return nil, ErrKeyNotFound
+}
+
 // Flush deletes all items from this cache table.
 func (table *CacheTable) Flush() {
 	table.Lock()