add support for file copy on object storage

app/uploaders/file_uploader.rb

@@ -81,6 +81,13 @@ class FileUploader < GitlabUploader
     apply_context!(uploader_context)
   end
 
+  def initialize_copy(from)
+    super
+
+    @secret = self.class.generate_secret
+    @upload = nil # calling record_upload would delete the old upload if set
+  end
+
   # enforce the usage of Hashed storage when storing to
   # remote store as the FileMover doesn't support OS
   def base_dir(store = nil)
@@ -144,6 +151,25 @@ class FileUploader < GitlabUploader
     @secret ||= self.class.generate_secret
   end
 
+  # return a new uploader with a file copy on another project
+  def self.copy_to(uploader, to_project)
+    moved = uploader.dup.tap do |u|
+      u.model = to_project
+    end
+
+    moved.copy_file(uploader.file)
+    moved
+  end
+
+  def copy_file(file)
+    if file_storage?
+      store!(file)
+    else
+      self.file = file.copy_to(store_path)
+      record_upload # after_store is not triggered
+    end
+  end
+
   private
 
   def apply_context!(uploader_context)

lib/gitlab/gfm/uploads_rewriter.rb

@@ -23,11 +23,8 @@ module Gitlab
           file = find_file(@source_project, $~[:secret], $~[:file])
           break markdown unless file.try(:exists?)
 
-          new_uploader = FileUploader.new(target_project)
-          with_link_in_tmp_dir(file.file) do |open_tmp_file|
-            new_uploader.store!(open_tmp_file)
-          end
-          new_uploader.markdown_link
+          moved = FileUploader.copy_to(file, target_project)
+          moved.markdown_link
         end
       end
 
@@ -48,20 +45,7 @@ module Gitlab
       def find_file(project, secret, file)
         uploader = FileUploader.new(project, secret: secret)
         uploader.retrieve_from_store!(file)
-        uploader.file if uploader.object_store == ObjectStorage::Store::LOCAL
-      end
-
-      # Because the uploaders use 'move_to_store' we must have a temporary
-      # file that is allowed to be (re)moved.
-      def with_link_in_tmp_dir(file)
-        dir = Dir.mktmpdir('UploadsRewriter', File.dirname(file))
-        # The filename matters to Carrierwave so we make sure to preserve it
-        tmp_file = File.join(dir, File.basename(file))
-        File.link(file, tmp_file)
-        # Open the file to placate Carrierwave
-        File.open(tmp_file) { |open_file| yield open_file }
-      ensure
-        FileUtils.rm_rf(dir)
+        uploader
       end
     end
   end

spec/lib/gitlab/gfm/uploads_rewriter_spec.rb

@@ -20,10 +20,11 @@ describe Gitlab::Gfm::UploadsRewriter do
       "Text and #{image_uploader.markdown_link} and #{zip_uploader.markdown_link}"
     end
 
+    shared_examples "files are accessible" do
       describe '#rewrite' do
         let!(:new_text) { rewriter.rewrite(new_project) }
 
-      let(:old_files) { [image_uploader, zip_uploader].map(&:file) }
+        let(:old_files) { [image_uploader, zip_uploader] }
         let(:new_files) do
           described_class.new(new_text, new_project, user).files
         end
@@ -52,6 +53,23 @@ describe Gitlab::Gfm::UploadsRewriter do
           expect(new_paths).not_to include zip_uploader.secret
         end
       end
+    end
+
+    context "file are stored locally" do
+      include_examples "files are accessible"
+    end
+
+    context "files are store remotely" do
+      before do
+        stub_uploads_object_storage(FileUploader)
+
+        old_files.each do |file|
+          file.migrate!(ObjectStorage::Store::REMOTE)
+        end
+      end
+
+      include_examples "files are accessible"
+    end
 
     describe '#needs_rewrite?' do
       subject { rewriter.needs_rewrite? }

spec/uploaders/file_uploader_spec.rb

@@ -80,6 +80,50 @@ describe FileUploader do
     end
   end
 
+  describe 'copy_to' do
+    shared_examples 'returns a valid uploader' do
+      describe 'returned uploader' do
+        let(:new_project) { create(:project) }
+        let(:moved) { described_class.copy_to(subject, new_project) }
+
+        it 'generates a new secret' do
+          expect(subject).to be
+          expect(described_class).to receive(:generate_secret).once.and_call_original
+          expect(moved).to be
+        end
+
+        it 'create new upload' do
+          expect(moved.upload).not_to eq(subject.upload)
+        end
+
+        it 'copies the file' do
+          expect(subject.file).to exist
+          expect(moved.file).to exist
+          expect(subject.file).not_to eq(moved.file)
+          expect(subject.object_store).to eq(moved.object_store)
+        end
+      end
+    end
+
+    context 'files are store locally' do
+      include_examples 'returns a valid uploader'
+
+      before do
+        subject.store!(fixture_file_upload('spec/fixtures/dk.png'))
+      end
+    end
+
+    context 'files are stored remotely' do
+      before do
+        stub_uploads_object_storage
+        subject.store!(fixture_file_upload('spec/fixtures/dk.png'))
+        subject.migrate!(ObjectStorage::Store::REMOTE)
+      end
+
+      include_examples 'returns a valid uploader'
+    end
+  end
+
   describe '#secret' do
     it 'generates a secret if none is provided' do
       expect(described_class).to receive(:generate_secret).and_return('secret')