[MM-40179] Go into directories when trying to export attachments (#19249)

* MM-40179 traverse directories when trying to export

* fix test

* fix s3 to behabe the same way

* add test for paths way too deep

* test recursion only on localstorage

* make list directories non recursively the default approach

* fix linting error

* fix non-recursive case

Co-authored-by: = <=>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/file.go

@@ -179,11 +179,24 @@ func (s *Server) removeFile(path string) *model.AppError {
 }
 
 func (a *App) ListDirectory(path string) ([]string, *model.AppError) {
-	return a.Srv().listDirectory(path)
+	return a.Srv().listDirectory(path, false)
 }
 
-func (s *Server) listDirectory(path string) ([]string, *model.AppError) {
-	paths, nErr := s.FileBackend().ListDirectory(path)
+func (a *App) ListDirectoryRecursively(path string) ([]string, *model.AppError) {
+	return a.Srv().listDirectory(path, true)
+}
+
+func (s *Server) listDirectory(path string, recursion bool) ([]string, *model.AppError) {
+	backend := s.FileBackend()
+	var paths []string
+	var nErr error
+
+	if recursion {
+		paths, nErr = backend.ListDirectoryRecursively(path)
+	} else {
+		paths, nErr = backend.ListDirectory(path)
+	}
+
 	if nErr != nil {
 		return nil, model.NewAppError("ListDirectory", "api.file.list_directory.app_error", nil, nErr.Error(), http.StatusInternalServerError)
 	}