give a way to access the stale cache (#216)

* Go defaults to "0"" so in case we want to return
EntryStatus back to the caller "Expired" cannot be differentiated.
Fixing this by default "_" to 0 and incremental RemoveReasons

comment was missing for GetWithInfo api so updated that

test: ran all unit test cases
Change-Id: Ic3e2259630668af0d4b5110125f2d8e43b83081b

* give a way to access the stale cache

Co-authored-by: Jay Gheewala <jgheewala@signalfx.com>

Author: flisky

bigcache.go

@@ -33,13 +33,12 @@ type RemoveReason uint32
 
 const (
 	// Expired means the key is past its LifeWindow.
-	// @TODO: Go defaults to 0 so in case we want to return EntryStatus back to the caller Expired cannot be differentiated
-	Expired RemoveReason = iota
+	Expired = RemoveReason(1)
 	// NoSpace means the key is the oldest and the cache size was at its maximum when Set was called, or the
 	// entry exceeded the maximum shard size.
-	NoSpace
+	NoSpace = RemoveReason(2)
 	// Deleted means Delete was called and this key was removed as a result.
-	Deleted
+	Deleted = RemoveReason(3)
 )
 
 // NewBigCache initialize new instance of BigCache

bigcache_test.go

@@ -995,14 +995,20 @@ func TestBigCache_GetWithInfo(t *testing.T) {
 
 	// when
 	data, resp, err := cache.GetWithInfo(key)
+
+	// then
 	assertEqual(t, []byte(value), data)
 	noError(t, err)
 	assertEqual(t, Response{}, resp)
+
+	// when
 	clock.set(5)
 	data, resp, err = cache.GetWithInfo(key)
-	assertEqual(t, err, ErrEntryIsDead)
+
+	// then
+	assertEqual(t, err, nil)
 	assertEqual(t, Response{EntryStatus: Expired}, resp)
-	assertEqual(t, []byte(nil), data)
+	assertEqual(t, []byte(value), data)
 }
 
 type mockedLogger struct {

entry_not_found_error.go

@@ -5,6 +5,4 @@ import "errors"
 var (
 	// ErrEntryNotFound is an error type struct which is returned when entry was not found for provided key
 	ErrEntryNotFound = errors.New("Entry not found")
-	// ErrEntryIsDead is an error type struct which is returned when entry has past it's life window
-	ErrEntryIsDead = errors.New("entry is dead")
 )

shard.go

@@ -49,16 +49,13 @@ func (s *cacheShard) getWithInfo(key string, hashedKey uint64) (entry []byte, re
 		return nil, resp, ErrEntryNotFound
 	}
 
+	entry = readEntry(wrappedEntry)
 	oldestTimeStamp := readTimestampFromEntry(wrappedEntry)
+	s.lock.RUnlock()
+	s.hit(hashedKey)
 	if currentTime-oldestTimeStamp >= s.lifeWindow {
-		s.lock.RUnlock()
-		// @TODO: when Expired is non-default value return err as nil as the resp will have proper entry status
 		resp.EntryStatus = Expired
-		return nil, resp, ErrEntryIsDead
 	}
-	entry = readEntry(wrappedEntry)
-	s.lock.RUnlock()
-	s.hit(hashedKey)
 	return entry, resp, nil
 }