Expire method

cache.go

@@ -922,6 +922,21 @@ func (c *cache) delete(k string) (interface{}, bool) {
 	return nil, false
 }
 
+// Expire overrides the expiry tim of an existing item. If the duration is 0
+// (DefaultExpiration), the cache's default expiration time is used. If it is -1
+// (NoExpiration), the item never expires.
+func (c *cache) Expire(k string, d time.Duration) error {
+	c.mu.Lock()
+	item, found := c.items[k]
+	if !found || (item.Expiration > 0 && time.Now().UnixNano() > item.Expiration) {
+		c.mu.Unlock()
+		return fmt.Errorf("Item %s doesn't exist", k)
+	}
+	c.set(k, item.Object, d)
+	c.mu.Unlock()
+	return nil
+}
+
 type keyAndValue struct {
 	key   string
 	value interface{}

cache_test.go

@@ -1378,7 +1378,7 @@ func TestFileSerialization(t *testing.T) {
 	tc := New(DefaultExpiration, 0)
 	tc.Add("a", "a", DefaultExpiration)
 	tc.Add("b", "b", DefaultExpiration)
-	f, err := ioutil.TempFile("", "go-cache-cache.dat")
+	f, err := ioutil.TempFile("", "go-cache-1-cache.dat")
 	if err != nil {
 		t.Fatal("Couldn't create cache file:", err)
 	}
@@ -1769,3 +1769,36 @@ func TestGetWithExpiration(t *testing.T) {
 		t.Error("expiration for e is in the past")
 	}
 }
+
+func TestExpire(t *testing.T) {
+	var (
+		ct = time.Now()
+		tc = New(DefaultExpiration, 0)
+	)
+	tc.Set("a", 1, time.Second)
+	if err := tc.Expire("a", time.Second); err != nil {
+		t.Error("expected err to be nil; value", err)
+	}
+
+	_, expiration, found := tc.GetWithExpiration("a")
+	if !found {
+		t.Error("e was not found while getting e2")
+	}
+	if expiration.IsZero() {
+		t.Error("expected expiration not to be zero")
+	}
+	if d := expiration.Sub(ct); d <= time.Second {
+		t.Error("expected difference to be lesser than or equal to one second", d)
+	}
+	if err := tc.Expire("a", DefaultExpiration); err != nil {
+		t.Error("expected err to be nil; value", err)
+	}
+
+	_, expiration, found = tc.GetWithExpiration("a")
+	if !found {
+		t.Error("e was not found while getting e2")
+	}
+	if !expiration.IsZero() {
+		t.Error("expected expiration to be zero")
+	}
+}