Add API endpoint to trigger Group Structure Export

- Introduce 2 new API endpoints for Group Structure Export
- POST /groups/:id/export
- GET /groups/:id/export/download

- Add new API endpoint to trigger Group Relations export
- Similar to Project Export, relations only

app/models/group.rb

@@ -451,6 +451,14 @@ class Group < Namespace
     false
   end
 
+  def export_file_exists?
+    export_file&.file
+  end
+
+  def export_file
+    import_export_upload&.export_file
+  end
+
   private
 
   def update_two_factor_requirement

changelogs/unreleased/georgekoltsov-group-structure-export-api-endp.yml

+---
+title: Add API endpoint to trigger Group Structure Export
+merge_request: 19779
+author:
+type: added

lib/api/api.rb

@@ -113,6 +113,7 @@ module API
     mount ::API::Files
     mount ::API::GroupBoards
     mount ::API::GroupClusters
+    mount ::API::GroupExport
     mount ::API::GroupLabels
     mount ::API::GroupMilestones
     mount ::API::Groups

lib/api/group_export.rb

+# frozen_string_literal: true
+
+module API
+  class GroupExport < Grape::API
+    before do
+      authorize! :admin_group, user_group
+    end
+
+    params do
+      requires :id, type: String, desc: 'The ID of a group'
+    end
+    resource :groups, requirements: { id: %r{[^/]+} } do
+      desc 'Download export' do
+        detail 'This feature was introduced in GitLab 12.5.'
+      end
+      get ':id/export/download' do
+        if user_group.export_file_exists?
+          present_carrierwave_file!(user_group.export_file)
+        else
+          render_api_error!('404 Not found or has expired', 404)
+        end
+      end
+
+      desc 'Start export' do
+        detail 'This feature was introduced in GitLab 12.5.'
+      end
+      post ':id/export' do
+        GroupExportWorker.perform_async(current_user.id, user_group.id, params)
+
+        accepted!
+      end
+    end
+  end
+end

spec/requests/api/group_export_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe API::GroupExport do
+  let_it_be(:group) { create(:group) }
+  let_it_be(:user) { create(:user) }
+
+  let(:path) { "/groups/#{group.id}/export" }
+  let(:download_path) { "/groups/#{group.id}/export/download" }
+
+  let(:export_path) { "#{Dir.tmpdir}/group_export_spec" }
+
+  before do
+    allow_next_instance_of(Gitlab::ImportExport) do |import_export|
+      expect(import_export).to receive(:storage_path).and_return(export_path)
+    end
+  end
+
+  after do
+    FileUtils.rm_rf(export_path, secure: true)
+  end
+
+  describe 'GET /groups/:group_id/export/download' do
+    let(:upload) { ImportExportUpload.new(group: group) }
+
+    before do
+      stub_uploads_object_storage(ImportExportUploader)
+
+      group.add_owner(user)
+    end
+
+    context 'when export file exists' do
+      before do
+        upload.export_file = fixture_file_upload('spec/fixtures/group_export.tar.gz', "`/tar.gz")
+        upload.save!
+      end
+
+      it 'downloads exported group archive' do
+        get api(download_path, user)
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+
+      context 'when export_file.file does not exist' do
+        before do
+          expect_next_instance_of(ImportExportUploader) do |uploader|
+            expect(uploader).to receive(:file).and_return(nil)
+          end
+        end
+
+        it 'returns 404' do
+          get api(download_path, user)
+
+          expect(response).to have_gitlab_http_status(404)
+        end
+      end
+    end
+
+    context 'when export file does not exist' do
+      it 'returns 404' do
+        get api(download_path, user)
+
+        expect(response).to have_gitlab_http_status(404)
+      end
+    end
+  end
+
+  describe 'POST /groups/:group_id/export' do
+    context 'when user is a group owner' do
+      before do
+        group.add_owner(user)
+      end
+
+      it 'accepts download' do
+        post api(path, user)
+
+        expect(response).to have_gitlab_http_status(202)
+      end
+    end
+
+    context 'when user is not a group owner' do
+      before do
+        group.add_developer(user)
+      end
+
+      it 'forbids the request' do
+        post api(path, user)
+
+        expect(response).to have_gitlab_http_status(403)
+      end
+    end
+  end
+end