Correctly handle Gitaly being unavailable in more locations

If `GRPC::Unavailable` or `Gitlab::Git::CommandError` is raised in code
outside of a controller action, such as an `around_action`, it can be
executed after a render call inside the controller has completed. When
this happens, ActionController detects it and raises a very unhelpful
`AbstractController::DoubleRenderError`, swallowing the original error.

This code was introduced as part of this MR:
https://gitlab.com/gitlab-org/gitlab-foss/-/merge_requests/114491

Circuit-breakers have since been removed, so it should be safe to
remove this code as well.

app/controllers/application_controller.rb

@@ -103,14 +103,6 @@ class ApplicationController < ActionController::Base
     head :forbidden, retry_after: Gitlab::Auth::UniqueIpsLimiter.config.unique_ips_limit_time_window
   end
 
-  rescue_from GRPC::Unavailable, Gitlab::Git::CommandError do |exception|
-    log_exception(exception)
-
-    headers['Retry-After'] = exception.retry_after if exception.respond_to?(:retry_after)
-
-    render_503
-  end
-
   def redirect_back_or_default(default: root_path, options: {})
     redirect_back(fallback_location: default, **options)
   end
@@ -246,19 +238,6 @@ class ApplicationController < ActionController::Base
     head :unprocessable_entity
   end
 
-  def render_503
-    respond_to do |format|
-      format.html do
-        render(
-          file: Rails.root.join("public", "503"),
-          layout: false,
-          status: :service_unavailable
-        )
-      end
-      format.any { head :service_unavailable }
-    end
-  end
-
   def no_cache_headers
     DEFAULT_GITLAB_NO_CACHE_HEADERS.each do |k, v|
       headers[k] = v

changelogs/unreleased/247477-fix-double-render-errors-in-rescue-from.yml

+---
+title: Correctly handle Gitaly being unavailable in more locations
+merge_request: 51222
+author:
+type: fixed

spec/controllers/projects_controller_spec.rb

@@ -211,21 +211,6 @@ RSpec.describe ProjectsController do
       end
     end
 
-    context 'when the storage is not available', :broken_storage do
-      let_it_be(:project) { create(:project, :broken_storage) }
-
-      before do
-        project.add_developer(user)
-        sign_in(user)
-      end
-
-      it 'renders a 503' do
-        get :show, params: { namespace_id: project.namespace, id: project }
-
-        expect(response).to have_gitlab_http_status(:service_unavailable)
-      end
-    end
-
     context "project with empty repo" do
       let_it_be(:empty_project) { create(:project_empty_repo, :public) }
 

spec/support/shared_examples/controllers/repositories/git_http_controller_shared_examples.rb

@@ -77,30 +77,6 @@ RSpec.shared_examples Repositories::GitHttpController do
         end
       end
     end
-
-    context 'with exceptions' do
-      before do
-        allow(controller).to receive(:authenticate_user).and_return(true)
-        allow(controller).to receive(:verify_workhorse_api!).and_return(true)
-      end
-
-      it 'returns 503 with GRPC Unavailable' do
-        allow(controller).to receive(:access_check).and_raise(GRPC::Unavailable)
-
-        get :info_refs, params: params
-
-        expect(response).to have_gitlab_http_status(:service_unavailable)
-      end
-
-      it 'returns 503 with timeout error' do
-        allow(controller).to receive(:access_check).and_raise(Gitlab::GitAccess::TimeoutError)
-
-        get :info_refs, params: params
-
-        expect(response).to have_gitlab_http_status(:service_unavailable)
-        expect(response.body).to eq 'Gitlab::GitAccess::TimeoutError'
-      end
-    end
   end
 
   describe 'POST #git_upload_pack' do