RawController respond with uncached headers

Also small refactor on spec/requests/api/files_spec.rb to use new
uncached response shared example.

app/controllers/projects/raw_controller.rb

@@ -12,6 +12,7 @@ class Projects::RawController < Projects::ApplicationController
   before_action :authorize_download_code!
   before_action :show_rate_limit, only: [:show], unless: :external_storage_request?
   before_action :assign_ref_vars
+  before_action :no_cache_headers, only: [:show]
   before_action :redirect_to_external_storage, only: :show, if: :static_objects_external_storage_enabled?
 
   def show

changelogs/unreleased/security-44-stored-xss-via-svg-file-preview.yml

+---
+title: Prevent SVG XSS via Web IDE
+merge_request:
+author:
+type: security

spec/controllers/projects/raw_controller_spec.rb

@@ -33,6 +33,11 @@ RSpec.describe Projects::RawController do
 
       it_behaves_like 'project cache control headers'
       it_behaves_like 'content disposition headers'
+      it_behaves_like 'uncached response' do
+        before do
+          subject
+        end
+      end
     end
 
     context 'image header' do

spec/requests/api/files_spec.rb

@@ -532,16 +532,13 @@ RSpec.describe API::Files do
         expect(response).to have_gitlab_http_status(:ok)
       end
 
-      it 'sets no-cache headers' do
+      it_behaves_like 'uncached response' do
+        before do
           url = route('.gitignore') + "/raw"
           expect(Gitlab::Workhorse).to receive(:send_git_blob)
 
           get api(url, current_user), params: params
-
-        expect(response.headers["Cache-Control"]).to include("no-store")
-        expect(response.headers["Cache-Control"]).to include("no-cache")
-        expect(response.headers["Pragma"]).to eq("no-cache")
-        expect(response.headers["Expires"]).to eq("Fri, 01 Jan 1990 00:00:00 GMT")
+        end
       end
 
       context 'when mandatory params are not given' do

spec/support/shared_examples/cached_response_shared_examples.rb

+# frozen_string_literal: true
+#
+# Negates lib/gitlab/no_cache_headers.rb
+#
+
+RSpec.shared_examples 'cached response' do
+  it 'defines a cached header response' do
+    expect(response.headers["Cache-Control"]).not_to include("no-store", "no-cache")
+    expect(response.headers["Pragma"]).not_to eq("no-cache")
+    expect(response.headers["Expires"]).not_to eq("Fri, 01 Jan 1990 00:00:00 GMT")
+  end
+end