Link existing LFS objects from parent fork during uploads

Previously LFS uploads would always have to be reuploaded to a fork even
if the parent already had received the LFS file, but this is
unnecessary, wasting time and bandwidth. Consider this sequence of
events:

1. Push LFS file `test.bin` to project A.
2. Fork project A to project B.
3. Push LFS file `test2.bin` to project A.
4. Push to project B.

When 4 happens, GitLab should be smart enough to realize that if the
user has access to the parent project, then we should be able to link
the LFS files in A without requesting a reupload of the file.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/297022

Changelog: fixed

app/controllers/repositories/lfs_api_controller.rb

@@ -76,7 +76,10 @@ module Repositories
       existing_oids = project.lfs_objects_oids(oids: objects_oids)
 
       objects.each do |object|
-        object[:actions] = upload_actions(object) unless existing_oids.include?(object[:oid])
+        next if existing_oids.include?(object[:oid])
+        next if should_auto_link? && oids_from_fork.include?(object[:oid]) && link_to_project!(object)
+
+        object[:actions] = upload_actions(object)
       end
 
       objects
@@ -150,6 +153,26 @@ module Repositories
 
       Gitlab::LfsToken.new(user).basic_encoding
     end
+
+    def should_auto_link?
+      return false unless Feature.enabled?(:lfs_auto_link_fork_source, project)
+      return false unless project.forked?
+
+      # Sanity check in case for some reason the user doesn't have access to the parent
+      can?(user, :download_code, project.fork_source)
+    end
+
+    def oids_from_fork
+      @oids_from_fork ||= project.lfs_objects_oids_from_fork_source(oids: objects_oids)
+    end
+
+    def link_to_project!(object)
+      lfs_object = LfsObject.for_oid_and_size(object[:oid], object[:size])
+
+      return unless lfs_object
+
+      LfsObjectsProject.link_to_project!(lfs_object, project)
+    end
   end
 end
 

app/models/lfs_object.rb

@@ -13,6 +13,7 @@ class LfsObject < ApplicationRecord
   scope :with_files_stored_locally, -> { where(file_store: LfsObjectUploader::Store::LOCAL) }
   scope :with_files_stored_remotely, -> { where(file_store: LfsObjectUploader::Store::REMOTE) }
   scope :for_oids, -> (oids) { where(oid: oids) }
+  scope :for_oid_and_size, -> (oid, size) { find_by(oid: oid, size: size) }
 
   validates :oid, presence: true, uniqueness: true
 

app/models/lfs_objects_project.rb

@@ -21,9 +21,19 @@ class LfsObjectsProject < ApplicationRecord
   scope :project_id_in, ->(ids) { where(project_id: ids) }
   scope :lfs_object_in, -> (lfs_objects) { where(lfs_object: lfs_objects) }
 
+  def self.link_to_project!(lfs_object, project)
+    # We can't use an upsert here because there is no uniqueness constraint:
+    # https://gitlab.com/gitlab-org/gitlab/-/issues/347466
+    self.safe_find_or_create_by!(lfs_object_id: lfs_object.id, project_id: project.id) # rubocop:disable Performance/ActiveRecordSubtransactionMethods
+  end
+
+  def self.update_statistics_for_project_id(project_id)
+    ProjectCacheWorker.perform_async(project_id, [], [:lfs_objects_size]) # rubocop:disable CodeReuse/Worker
+  end
+
   private
 
   def update_project_statistics
-    ProjectCacheWorker.perform_async(project_id, [], [:lfs_objects_size])
+    self.class.update_statistics_for_project_id(project_id)
   end
 end

app/models/project.rb

@@ -1569,6 +1569,12 @@ class Project < ApplicationRecord
     oids(lfs_objects, oids: oids)
   end
 
+  def lfs_objects_oids_from_fork_source(oids: [])
+    return [] unless forked?
+
+    oids(fork_source.lfs_objects, oids: oids)
+  end
+
   def personal?
     !group
   end

config/feature_flags/development/lfs_auto_link_fork_source.yml

+---
+name: lfs_auto_link_fork_source
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/75972
+rollout_issue_url:
+milestone: '14.6'
+type: development
+group: group::source code
+default_enabled: false

spec/models/lfs_objects_project_spec.rb

@@ -25,6 +25,28 @@ RSpec.describe LfsObjectsProject do
     end
   end
 
+  describe '#link_to_project!' do
+    it 'does not throw error when duplicate exists' do
+      subject
+
+      expect do
+        result = described_class.link_to_project!(subject.lfs_object, subject.project)
+        expect(result).to be_a(LfsObjectsProject)
+      end.not_to change { described_class.count }
+    end
+
+    it 'upserts a new entry and updates the project cache' do
+      new_project = create(:project)
+
+      allow(ProjectCacheWorker).to receive(:perform_async).and_call_original
+      expect(ProjectCacheWorker).to receive(:perform_async).with(new_project.id, [], [:lfs_objects_size])
+      expect { described_class.link_to_project!(subject.lfs_object, new_project) }
+        .to change { described_class.count }
+
+      expect(described_class.find_by(lfs_object_id: subject.lfs_object.id, project_id: new_project.id)).to be_present
+    end
+  end
+
   describe '#update_project_statistics' do
     it 'updates project statistics when the object is added' do
       expect(ProjectCacheWorker).to receive(:perform_async)

spec/models/project_spec.rb

@@ -3581,6 +3581,29 @@ RSpec.describe Project, factory_default: :keep do
         expect(project.forks).to contain_exactly(forked_project)
       end
     end
+
+    describe '#lfs_object_oids_from_fork_source' do
+      let_it_be(:lfs_object) { create(:lfs_object) }
+      let_it_be(:another_lfs_object) { create(:lfs_object) }
+
+      let(:oids) { [lfs_object.oid, another_lfs_object.oid] }
+
+      context 'when fork has one of two LFS objects' do
+        before do
+          create(:lfs_objects_project, lfs_object: lfs_object, project: project)
+          create(:lfs_objects_project, lfs_object: another_lfs_object, project: forked_project)
+        end
+
+        it 'returns OIDs of owned LFS objects', :aggregate_failures do
+          expect(forked_project.lfs_objects_oids_from_fork_source(oids: oids)).to eq([lfs_object.oid])
+          expect(forked_project.lfs_objects_oids(oids: oids)).to eq([another_lfs_object.oid])
+        end
+
+        it 'returns empty when project is not a fork' do
+          expect(project.lfs_objects_oids_from_fork_source(oids: oids)).to eq([])
+        end
+      end
+    end
   end
 
   it_behaves_like 'can housekeep repository' do

spec/requests/lfs_http_spec.rb

@@ -518,13 +518,43 @@ RSpec.describe 'Git LFS API and storage' do
                 end
 
                 context 'in source of fork project' do
+                  let(:other_project) { create(:project, :empty_repo) }
                   let(:project) { fork_project(other_project) }
 
                   before do
                     lfs_object.update!(projects: [other_project])
                   end
 
-                  it_behaves_like 'batch upload with existing LFS object'
+                  context 'when user has access to both the parent and fork' do
+                    before do
+                      project.add_developer(user)
+                      other_project.add_developer(user)
+                    end
+
+                    it 'links existing LFS objects to other project' do
+                      expect(json_response['objects']).to be_kind_of(Array)
+                      expect(json_response['objects'].first).to include(sample_object)
+                      expect(json_response['objects'].first).not_to have_key('actions')
+
+                      expect(lfs_object.reload.projects.pluck(:id)).to match_array([other_project.id, project.id])
+                    end
+
+                    context 'when feature flag is disabled' do
+                      before do
+                        stub_feature_flags(lfs_auto_link_fork_source: false)
+                      end
+
+                      it_behaves_like 'batch upload with existing LFS object'
+                    end
+                  end
+
+                  context 'when user does not have access to parent' do
+                    before do
+                      project.add_developer(user)
+                    end
+
+                    it_behaves_like 'batch upload with existing LFS object'
+                  end
                 end
               end