Permalink to the latest release

Changelog: added

app/controllers/projects/releases_controller.rb

@@ -7,6 +7,7 @@ class Projects::ReleasesController < Projects::ApplicationController
   before_action :authorize_read_release!
   before_action :authorize_update_release!, only: %i[edit update]
   before_action :authorize_create_release!, only: :new
+  before_action :validate_suffix_path, :fetch_latest_tag, only: :latest_permalink
   before_action only: :index do
     push_frontend_feature_flag(:releases_index_apollo_client, project, default_enabled: :yaml)
   end
@@ -26,10 +27,24 @@ class Projects::ReleasesController < Projects::ApplicationController
     redirect_to link.url
   end
 
+  def latest_permalink
+    unless @latest_tag.present?
+      return render_404
+    end
+
+    query_parameters_except_order_by = request.query_parameters.except(:order_by)
+
+    redirect_url = project_release_url(@project, @latest_tag)
+    redirect_url += "/#{params[:suffix_path]}" if params[:suffix_path]
+    redirect_url += "?#{query_parameters_except_order_by.compact.to_param}" if query_parameters_except_order_by.present?
+
+    redirect_to redirect_url
+  end
+
   private
 
-  def releases
-    ReleasesFinder.new(@project, current_user).execute
+  def releases(params = {})
+    ReleasesFinder.new(@project, current_user, params).execute
   end
 
   def authorize_update_release!
@@ -51,4 +66,18 @@ class Projects::ReleasesController < Projects::ApplicationController
   def sanitized_tag_name
     CGI.unescape(params[:tag])
   end
+
+  # Default order_by is 'released_at', which is set in ReleasesFinder.
+  # Also if the passed order_by is invalid, we reject and default to 'released_at'.
+  def fetch_latest_tag
+    allowed_values = ['released_at']
+
+    params.reject! { |key, value| key.to_sym == :order_by && allowed_values.any?(value) }
+
+    @latest_tag = releases(order_by: params[:order_by]).first&.tag
+  end
+
+  def validate_suffix_path
+    Gitlab::Utils.check_path_traversal!(params[:suffix_path]) if params[:suffix_path]
+  end
 end

config/routes/project.rb

@@ -241,6 +241,8 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
           end
         end
 
+        get 'releases/permalink/latest(/)(*suffix_path)', to: 'releases#latest_permalink', as: :latest_release_permalink, format: false
+
         resources :logs, only: [:index] do
           collection do
             get :k8s

spec/controllers/projects/releases_controller_spec.rb

@@ -222,6 +222,166 @@ RSpec.describe Projects::ReleasesController do
     end
   end
 
+  describe 'GET #latest_permalink' do
+    # Uses default order_by=released_at parameter.
+    subject do
+      get :latest_permalink, params: { namespace_id: project.namespace, project_id: project }
+    end
+
+    before do
+      sign_in(user)
+    end
+
+    let(:release) { create(:release, project: project) }
+    let(:tag) { CGI.escape(release.tag) }
+
+    context 'when user is a guest' do
+      let(:project) { private_project }
+      let(:user) { guest }
+
+      it 'proceeds with the redirect' do
+        subject
+
+        expect(response).to have_gitlab_http_status(:redirect)
+      end
+    end
+
+    context 'when user is an external user for the project' do
+      let(:project) { private_project }
+      let(:user) { create(:user) }
+
+      it 'behaves like not found' do
+        subject
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+
+    context 'when there are no releases for the project' do
+      let(:project) { create(:project, :repository, :public) }
+      let(:user) { developer }
+
+      before do
+        project.releases.destroy_all # rubocop: disable Cop/DestroyAll
+      end
+
+      it 'behaves like not found' do
+        subject
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+
+    context 'multiple releases' do
+      let(:user) { developer }
+
+      it 'redirects to the latest release' do
+        create(:release, project: project, released_at: 1.day.ago)
+        latest_release = create(:release, project: project, released_at: Time.current)
+
+        subject
+
+        expect(response).to redirect_to("#{project_releases_path(project)}/#{latest_release.tag}")
+      end
+    end
+
+    context 'suffix path redirection' do
+      let(:user) { developer }
+      let(:suffix_path) { 'downloads/zips/helm-hello-world.zip' }
+      let!(:latest_release) { create(:release, project: project, released_at: Time.current) }
+
+      subject do
+        get :latest_permalink, params: {
+          namespace_id: project.namespace,
+          project_id: project,
+          suffix_path: suffix_path
+        }
+      end
+
+      it 'redirects to the latest release with suffix path and format' do
+        subject
+
+        expect(response).to redirect_to(
+          "#{project_releases_path(project)}/#{latest_release.tag}/#{suffix_path}")
+      end
+
+      context 'suffix path abuse' do
+        let(:suffix_path) { 'downloads/zips/../../../../../../../robots.txt'}
+
+        it 'raises attack error' do
+          expect do
+            subject
+          end.to raise_error(Gitlab::Utils::PathTraversalAttackError)
+        end
+      end
+
+      context 'url parameters' do
+        let(:suffix_path) { 'downloads/zips/helm-hello-world.zip' }
+
+        subject do
+          get :latest_permalink, params: {
+            namespace_id: project.namespace,
+            project_id: project,
+            suffix_path: suffix_path,
+            order_by: 'released_at',
+            param_1: 1,
+            param_2: 2
+          }
+        end
+
+        it 'carries over query parameters without order_by parameter in the redirect' do
+          subject
+
+          expect(response).to redirect_to(
+            "#{project_releases_path(project)}/#{latest_release.tag}/#{suffix_path}?param_1=1&param_2=2")
+        end
+      end
+    end
+
+    context 'order_by parameter' do
+      let!(:latest_release) { create(:release, project: project, released_at: Time.current) }
+
+      shared_examples_for 'redirects to latest release ordered by using released_at' do
+        it do
+          subject
+
+          expect(response).to redirect_to("#{project_releases_path(project)}/#{latest_release.tag}")
+        end
+      end
+
+      before do
+        create(:release, project: project, released_at: 1.day.ago)
+        create(:release, project: project, released_at: 2.days.ago)
+      end
+
+      context 'invalid parameter' do
+        let(:user) { developer }
+
+        subject do
+          get :latest_permalink, params: {
+            namespace_id: project.namespace,
+            project_id: project,
+            order_by: 'unsupported'
+          }
+        end
+
+        it_behaves_like 'redirects to latest release ordered by using released_at'
+      end
+
+      context 'valid parameter' do
+        subject do
+          get :latest_permalink, params: {
+            namespace_id: project.namespace,
+            project_id: project,
+            order_by: 'released_at'
+          }
+        end
+
+        it_behaves_like 'redirects to latest release ordered by using released_at'
+      end
+    end
+  end
+
   # `GET #downloads` is addressed in spec/requests/projects/releases_controller_spec.rb
 
   private

spec/routing/project_routing_spec.rb

@@ -680,6 +680,32 @@ RSpec.describe 'project routing' do
     end
   end
 
+  describe Projects::ReleasesController, 'routing' do
+    it 'to #latest_permalink with a valid permalink path' do
+      expect(get('/gitlab/gitlabhq/-/releases/permalink/latest/downloads/release-binary.zip')).to route_to(
+        'projects/releases#latest_permalink',
+        namespace_id: 'gitlab',
+        project_id: 'gitlabhq',
+        suffix_path: 'downloads/release-binary.zip'
+      )
+
+      expect(get('/gitlab/gitlabhq/-/releases/permalink/latest')).to route_to(
+        'projects/releases#latest_permalink',
+        namespace_id: 'gitlab',
+        project_id: 'gitlabhq'
+      )
+    end
+
+    it 'to #show for the release with tag named permalink' do
+      expect(get('/gitlab/gitlabhq/-/releases/permalink')).to route_to(
+        'projects/releases#show',
+        namespace_id: 'gitlab',
+        project_id: 'gitlabhq',
+        tag: 'permalink'
+      )
+    end
+  end
+
   describe Projects::Registry::TagsController, 'routing' do
     describe '#destroy' do
       it 'correctly routes to a destroy action' do