fix(DocumentService): Return 200 steps before saved version in SyncStep2

When replying to a SyncStep1, which the client sends if it detected
a missing step, we now add the 200 steps before the last saved version.

This is done to workaround race conditions where the state with the
missing step got persisted in the document state.

See #7692

Signed-off-by: Jonas <[email protected]>

lib/Db/StepMapper.php

@@ -56,6 +56,25 @@ public function getLatestVersion(int $documentId): ?int {
 		return $data['id'];
 	}
 
+	public function getBeforeVersion(int $documentId, int $version, int $offset): int {
+		$qb = $this->db->getQueryBuilder();
+		$result = $qb->select('id')
+			->from($this->getTableName())
+			->where($qb->expr()->eq('document_id', $qb->createNamedParameter($documentId)))
+			->andWhere($qb->expr()->lt('id', $qb->createNamedParameter($version)))
+			->setMaxResults($offset)
+			->orderBy('id', 'DESC')
+			->executeQuery();
+
+		$rows = $result->fetchAll();
+		$data = end($rows);
+		if ($data === false) {
+			return $version;
+		}
+
+		return $data['id'];
+	}
+
 	public function deleteAll(int $documentId): void {
 		$qb = $this->db->getQueryBuilder();
 		$qb->delete($this->getTableName())

lib/Service/DocumentService.php

@@ -239,8 +239,9 @@ public function addStep(Document $document, Session $session, array $steps, int
 				$stateFile = $this->getStateFile($documentId);
 				$documentState = $stateFile->getContent();
 				$this->logger->debug('Existing document, state file loaded ' . $documentId);
-				// If there were any queries in the steps, send all steps since last save.
-				$getStepsSinceVersion = $document->getLastSavedVersion();
+				// If there were any queries in the steps, send all steps starting 200 steps before last save.
+				// Adding 200 previous steps to workaround race conditions where state with missing step got persisted in the document state. See #7692
+				$getStepsSinceVersion = $this->stepMapper->getBeforeVersion($documentId, $document->getLastSavedVersion(), 200);
 			} catch (NotFoundException $e) {
 				$this->logger->debug('Existing document, but no state file found for ' . $documentId);
 				// If there is no state file, include all the steps.