Pause event loop while FETCHing to prevetn EXPUNGE

Changelog.md

@@ -40,6 +40,8 @@ Changelog [format](http://keepachangelog.com/en/1.0.0/)
 * GODT-454 Fix send on closed channel when receiving unencrypted send confirmation from GUI.
 * GODT-597 Duplicate sending when draft creation takes too long
 
+### Changed
+* GODT-462 Pausing event loop while FETCHing to prevent EXPUNGE
 
 ## [v1.3.x] Emma (v1.3.2 beta 2020-08-04, v1.3.3 beta 2020-08-06, v1.3.3 live 2020-08-12)
 

internal/imap/mailbox_messages.go

@@ -383,6 +383,12 @@ func (im *imapMailbox) ListMessages(isUID bool, seqSet *imap.SeqSet, items []ima
 		im.panicHandler.HandlePanic()
 	}()
 
+	// EXPUNGE cannot be sent during listing and can come only from
+	// the event loop, so we prevent any server side update to avoid
+	// the problem.
+	im.storeUser.PauseEventLoop(true)
+	defer im.storeUser.PauseEventLoop(false)
+
 	var markAsReadIDs []string
 	markAsReadMutex := &sync.Mutex{}
 

internal/imap/store.go

@@ -41,6 +41,8 @@ type storeUserProvider interface {
 		attachedPublicKey,
 		attachedPublicKeyName string,
 		parentID string) (*pmapi.Message, []*pmapi.Attachment, error)
+
+	PauseEventLoop(bool)
 }
 
 type storeAddressProvider interface {

internal/store/event_loop.go

@@ -38,7 +38,8 @@ type eventLoop struct {
 	pollCh         chan chan struct{}
 	stopCh         chan struct{}
 	notifyStopCh   chan struct{}
-	isRunning      bool
+	isRunning      bool // The whole event loop is running.
+	isTickerPaused bool // The periodic loop is paused (but the event loop itself is still running).
 	hasInternet    bool
 
 	pollCounter int
@@ -59,6 +60,7 @@ func newEventLoop(cache *Cache, store *Store, user BridgeUser, events listener.L
 		currentEventID: cache.getEventID(user.ID()),
 		pollCh:         make(chan chan struct{}),
 		isRunning:      false,
+		isTickerPaused: false,
 
 		log: eventLog,
 
@@ -68,10 +70,6 @@ func newEventLoop(cache *Cache, store *Store, user BridgeUser, events listener.L
 	}
 }
 
-func (loop *eventLoop) IsRunning() bool {
-	return loop.isRunning
-}
-
 func (loop *eventLoop) client() pmapi.Client {
 	return loop.store.client()
 }
@@ -156,6 +154,10 @@ func (loop *eventLoop) loop() {
 			close(loop.notifyStopCh)
 			return
 		case <-t.C:
+			if loop.isTickerPaused {
+				loop.log.Trace("Event loop paused, skipping")
+				continue
+			}
 			// Randomise periodic calls within range pollInterval ± pollSpread to reduces potential load spikes on API.
 			time.Sleep(time.Duration(rand.Intn(2*int(pollIntervalSpread.Milliseconds()))) * time.Millisecond)
 		case eventProcessedCh = <-loop.pollCh:

internal/store/store.go

@@ -348,6 +348,18 @@ func (store *Store) addAddress(address, addressID string, labels []*pmapi.Label)
 	return
 }
 
+// PauseEventLoop sets whether the ticker is periodically polling or not.
+func (store *Store) PauseEventLoop(pause bool) {
+	store.lock.Lock()
+	defer store.lock.Unlock()
+
+	store.log.WithField("pause", pause).Info("Pausing event loop")
+
+	if store.eventLoop != nil {
+		store.eventLoop.isTickerPaused = pause
+	}
+}
+
 // Close stops the event loop and closes the database to free the file.
 func (store *Store) Close() error {
 	store.lock.Lock()

internal/store/store_test_exports.go

@@ -26,6 +26,10 @@ import (
 	bolt "go.etcd.io/bbolt"
 )
 
+func (loop *eventLoop) IsRunning() bool {
+	return loop.isRunning
+}
+
 // TestSync triggers a sync of the store.
 func (store *Store) TestSync() {
 	store.lock.Lock()