From 9eea26459a79ef76ecb84a49205ba34d11efc905 Mon Sep 17 00:00:00 2001
From: Leander Beernaert <leander.beernaert@proton.ch>
Date: Wed, 18 Oct 2023 14:29:27 +0200
Subject: [PATCH] fix(GODT-3033): Unable to receive new mail

If the IMAP service happened to finish syncing and wanted to reset the
user event service at a time the latter was publishing an event a
deadlock would occur and the user would not receive any new messages.

This change puts the request to revert the event id in a separate
go-routine to avoid this situation from re-occurring. The operational
flow remains unchanged as the event service will only process this
request once the current set of events have been published.
---
 internal/services/imapservice/service.go | 42 ++++++++++++++----------
 1 file changed, 24 insertions(+), 18 deletions(-)

diff --git a/internal/services/imapservice/service.go b/internal/services/imapservice/service.go
index fc178d95..293b86e1 100644
--- a/internal/services/imapservice/service.go
+++ b/internal/services/imapservice/service.go
@@ -22,6 +22,7 @@ import (
 	"errors"
 	"fmt"
 	"path/filepath"
+	"sync/atomic"
 	"time"
 
 	"github.com/ProtonMail/gluon/async"
@@ -94,7 +95,7 @@ type Service struct {
 
 	syncConfigPath     string
 	lastHandledEventID string
-	isSyncing          bool
+	isSyncing          atomic.Bool
 }
 
 func NewService(
@@ -389,23 +390,28 @@ func (s *Service) run(ctx context.Context) { //nolint gocyclo
 					continue
 				}
 
+				// Start a goroutine to wait on event reset as it is possible that the sync received message
+				// was processed during an event publish. This in turn will block the imap service, since the
+				// event service is unable to reply to the request until the events have been processed.
 				s.log.Info("Sync complete, starting API event stream")
-				if err := s.eventProvider.RewindEventID(ctx, s.lastHandledEventID); err != nil {
-					if errors.Is(err, context.Canceled) {
-						continue
+				go func() {
+					if err := s.eventProvider.RewindEventID(ctx, s.lastHandledEventID); err != nil {
+						if errors.Is(err, context.Canceled) {
+							return
+						}
+
+						s.log.WithError(err).Error("Failed to rewind event service")
+						s.eventPublisher.PublishEvent(ctx, events.UserBadEvent{
+							UserID:     s.identityState.UserID(),
+							OldEventID: "",
+							NewEventID: "",
+							EventInfo:  "",
+							Error:      fmt.Errorf("failed to rewind event loop: %w", err),
+						})
 					}
 
-					s.log.WithError(err).Error("Failed to rewind event service")
-					s.eventPublisher.PublishEvent(ctx, events.UserBadEvent{
-						UserID:     s.identityState.UserID(),
-						OldEventID: "",
-						NewEventID: "",
-						EventInfo:  "",
-						Error:      fmt.Errorf("failed to rewind event loop: %w", err),
-					})
-				}
-
-				s.isSyncing = false
+					s.isSyncing.Store(false)
+				}()
 			}
 
 		case request, ok := <-s.syncUpdateApplier.requestCh:
@@ -427,7 +433,7 @@ func (s *Service) run(ctx context.Context) { //nolint gocyclo
 				continue
 			}
 			e.Consume(func(event proton.Event) error {
-				if s.isSyncing {
+				if s.isSyncing.Load() {
 					if err := syncEventHandler.OnEvent(ctx, event); err != nil {
 						return err
 					}
@@ -610,13 +616,13 @@ func (s *Service) setShowAllMail(v bool) {
 }
 
 func (s *Service) startSyncing() {
-	s.isSyncing = true
+	s.isSyncing.Store(true)
 	s.syncHandler.Execute(s.syncReporter, s.labels.GetLabelMap(), s.syncUpdateApplier, s.syncMessageBuilder, syncservice.DefaultRetryCoolDown)
 }
 
 func (s *Service) cancelSync() {
 	s.syncHandler.CancelAndWait()
-	s.isSyncing = false
+	s.isSyncing.Store(false)
 }
 
 type resyncReq struct{}