add upload manager and spec

lib/gitlab/import_export/uploads_manager.rb

+module Gitlab
+  module ImportExport
+    class UploadsManager
+      include Gitlab::ImportExport::CommandLineUtil
+
+      def initialize(project:, shared:, relative_export_path: 'uploads', from: nil)
+        @project = project
+        @shared = shared
+        @relative_export_path = relative_export_path
+        @from = from || default_uploads_path
+      end
+
+      def copy
+        copy_files(@from, uploads_export_path) if File.directory?(@from)
+
+        copy_from_object_storage
+      end
+
+      private
+
+      def copy_from_object_storage
+        return unless Gitlab::ImportExport.object_storage?
+        return if uploads.empty?
+
+        mkdir_p(uploads_export_path)
+
+        uploads.each do |upload_model|
+          next unless upload_model.file
+          next if upload_model.upload.local? # Already copied
+
+          download_and_copy(upload_model)
+        end
+      end
+
+      def default_uploads_path
+        FileUploader.absolute_base_dir(@project)
+      end
+
+      def uploads_export_path
+        @uploads_export_path ||= File.join(@shared.export_path, @relative_export_path)
+      end
+
+      def uploads
+        @uploads ||= begin
+          if @relative_export_path == 'avatar'
+            [@project.avatar].compact
+          else
+            (@project.uploads - [@project.avatar&.upload]).map(&:build_uploader)
+          end
+        end
+      end
+
+      def download_and_copy(upload)
+        upload_path = File.join(uploads_export_path, upload.filename)
+
+        File.open(upload_path, 'w') do |file|
+          IO.copy_stream(URI.parse(upload.file.url).open, file)
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/import_export/uploads_manager_spec.rb

+require 'spec_helper'
+
+describe Gitlab::ImportExport::UploadsManager do
+  let(:shared) { project.import_export_shared }
+  let(:export_path) { "#{Dir.tmpdir}/project_tree_saver_spec" }
+  let(:project) { create(:project) }
+
+  subject(:manager) { described_class.new(project: project, shared: shared) }
+
+  before do
+    allow_any_instance_of(Gitlab::ImportExport).to receive(:storage_path).and_return(export_path)
+    FileUtils.mkdir_p(shared.export_path)
+  end
+
+  after do
+    FileUtils.rm_rf(shared.export_path)
+  end
+
+  describe '#copy' do
+    context 'when the project has uploads locally stored' do
+      let(:upload) { create(:upload) }
+
+      before do
+        project.uploads << upload
+      end
+
+      it 'does not cause errors' do
+        manager.copy
+
+        expect(shared.errors).to be_empty
+      end
+
+      it 'copies the file in the correct location when there is an upload' do
+        manager.copy
+
+        expect(File).to exist("#{shared.export_path}/uploads/#{File.basename(upload.path)}")
+      end
+    end
+  end
+end