[#126] pool: Store access time in the session token cache

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pool/cache.go

@@ -2,6 +2,7 @@ package pool
 
 import (
 	"strings"
+	"time"
 
 	lru "github.com/hashicorp/golang-lru"
 	"github.com/nspcc-dev/neofs-sdk-go/session"
@@ -11,6 +12,11 @@ type SessionCache struct {
 	cache *lru.Cache
 }
 
+type cacheValue struct {
+	atime time.Time
+	token *session.Token
+}
+
 func NewCache() (*SessionCache, error) {
 	cache, err := lru.New(100)
 	if err != nil {
@@ -21,15 +27,31 @@ func NewCache() (*SessionCache, error) {
 }
 
 func (c *SessionCache) Get(key string) *session.Token {
-	tokenRaw, ok := c.cache.Get(key)
+	valueRaw, ok := c.cache.Get(key)
 	if !ok {
 		return nil
 	}
-	return tokenRaw.(*session.Token)
+
+	value := valueRaw.(*cacheValue)
+	value.atime = time.Now()
+
+	return value.token
+}
+
+func (c *SessionCache) GetAccessTime(key string) (time.Time, bool) {
+	valueRaw, ok := c.cache.Peek(key)
+	if !ok {
+		return time.Time{}, false
+	}
+
+	return valueRaw.(*cacheValue).atime, true
 }
 
 func (c *SessionCache) Put(key string, token *session.Token) bool {
-	return c.cache.Add(key, token)
+	return c.cache.Add(key, &cacheValue{
+		atime: time.Now(),
+		token: token,
+	})
 }
 
 func (c *SessionCache) DeleteByPrefix(prefix string) {

pool/cache_test.go

@@ -0,0 +1,31 @@
+package pool
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSessionCache_GetAccessTime(t *testing.T) {
+	const key = "Foo"
+
+	cache, err := NewCache()
+	require.NoError(t, err)
+
+	cache.Put(key, nil)
+
+	t1, ok := cache.GetAccessTime(key)
+	require.True(t, ok)
+
+	time.Sleep(10 * time.Millisecond)
+
+	t2, ok := cache.GetAccessTime(key)
+	require.True(t, ok)
+	require.Equal(t, t1, t2)
+
+	_ = cache.Get(key)
+	t3, ok := cache.GetAccessTime(key)
+	require.True(t, ok)
+	require.NotEqual(t, t1, t3)
+}