fix(GODT-2822): Sync Cache

When the sync fail, store the previously downloaded data in memory so
that on next retry we don't have to re-download everything.

internal/user/sync_message_cache.go

@@ -0,0 +1,98 @@
+// Copyright (c) 2023 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge.  If not, see <https://www.gnu.org/licenses/>.
+
+package user
+
+import (
+	"sync"
+
+	"github.com/ProtonMail/go-proton-api"
+)
+
+type SyncDownloadCache struct {
+	messageLock    sync.RWMutex
+	messages       map[string]proton.Message
+	attachmentLock sync.RWMutex
+	attachments    map[string][]byte
+}
+
+func newSyncDownloadCache() *SyncDownloadCache {
+	return &SyncDownloadCache{
+		messages:    make(map[string]proton.Message, 64),
+		attachments: make(map[string][]byte, 64),
+	}
+}
+
+func (s *SyncDownloadCache) StoreMessage(message proton.Message) {
+	s.messageLock.Lock()
+	defer s.messageLock.Unlock()
+
+	s.messages[message.ID] = message
+}
+
+func (s *SyncDownloadCache) StoreAttachment(id string, data []byte) {
+	s.attachmentLock.Lock()
+	defer s.attachmentLock.Unlock()
+
+	s.attachments[id] = data
+}
+
+func (s *SyncDownloadCache) DeleteMessages(id ...string) {
+	s.messageLock.Lock()
+	defer s.messageLock.Unlock()
+
+	for _, id := range id {
+		delete(s.messages, id)
+	}
+}
+
+func (s *SyncDownloadCache) DeleteAttachments(id ...string) {
+	s.attachmentLock.Lock()
+	defer s.attachmentLock.Unlock()
+
+	for _, id := range id {
+		delete(s.attachments, id)
+	}
+}
+
+func (s *SyncDownloadCache) GetMessage(id string) (proton.Message, bool) {
+	s.messageLock.RLock()
+	defer s.messageLock.RUnlock()
+
+	v, ok := s.messages[id]
+
+	return v, ok
+}
+
+func (s *SyncDownloadCache) GetAttachment(id string) ([]byte, bool) {
+	s.attachmentLock.RLock()
+	defer s.attachmentLock.RUnlock()
+
+	v, ok := s.attachments[id]
+
+	return v, ok
+}
+
+func (s *SyncDownloadCache) Clear() {
+	s.messageLock.Lock()
+	s.messages = make(map[string]proton.Message, 64)
+	s.messageLock.Unlock()
+
+	s.attachmentLock.Lock()
+	s.attachments = make(map[string][]byte, 64)
+	s.attachmentLock.Unlock()
+}