Download LFS-files from object storage for exports

Downloading the stream directly to the archive. In order to avoid
conflicts with the cache.

changelogs/unreleased/bvl-export-import-lfs.yml

+---
+title: Support LFS objects when importing/exporting GitLab project archives
+merge_request: 18115
+author:
+type: added

lib/gitlab/import_export/lfs_saver.rb

@@ -28,7 +28,16 @@ module Gitlab
         if lfs_object.local_store?
           copy_file_for_lfs_object(lfs_object)
         else
-          raise NotImplementedError.new "Exporting files from object storage is not yet supported"
+          download_file_for_lfs_object(lfs_object)
+        end
+      end
+
+      def download_file_for_lfs_object(lfs_object)
+        destination = destination_path_for_object(lfs_object)
+        mkdir_p(File.dirname(destination))
+
+        File.open(destination, 'w') do |file|
+          IO.copy_stream(URI.parse(lfs_object.file.url).open, file)
         end
       end
 

spec/lib/gitlab/import_export/lfs_saver_spec.rb

@@ -17,7 +17,7 @@ describe Gitlab::ImportExport::LfsSaver do
   end
 
   describe '#save' do
-    context 'when the project has LFS objects' do
+    context 'when the project has LFS objects locally stored' do
       let(:lfs_object) { create(:lfs_object, :with_file) }
 
       before do
@@ -36,5 +36,27 @@ describe Gitlab::ImportExport::LfsSaver do
         expect(File).to exist("#{shared.export_path}/lfs-objects/#{lfs_object.oid}")
       end
     end
+
+    context 'when the LFS objects are stored in object storage' do
+      let(:lfs_object) { create(:lfs_object, :object_storage) }
+
+      before do
+        allow(LfsObjectUploader).to receive(:object_store_enabled?).and_return(true)
+        allow(lfs_object.file).to receive(:url).and_return('http://my-object-storage.local')
+        project.lfs_objects << lfs_object
+      end
+
+      it 'downloads the file to include in an archive' do
+        fake_uri = double
+        exported_file_path = "#{shared.export_path}/lfs-objects/#{lfs_object.oid}"
+
+        expect(fake_uri).to receive(:open).and_return(StringIO.new('LFS file content'))
+        expect(URI).to receive(:parse).with('http://my-object-storage.local').and_return(fake_uri)
+
+        saver.save
+
+        expect(File.read(exported_file_path)).to eq('LFS file content')
+      end
+    end
   end
 end