FIX: serve category images from the CDN

app/serializers/basic_category_serializer.rb

@@ -40,4 +40,14 @@ class BasicCategorySerializer < ApplicationSerializer
   def notification_level
     object.notification_level
   end
+
+  def logo_url
+    url = object.logo_url
+    url.present? && UrlHelper.is_local(url) ? UrlHelper.schemaless(UrlHelper.absolute(url)) : url
+  end
+
+  def background_url
+    url = object.background_url
+    url.present? && UrlHelper.is_local(url) ? UrlHelper.schemaless(UrlHelper.absolute(url)) : url
+  end
 end

spec/serializers/basic_category_serializer_spec.rb

@@ -0,0 +1,40 @@
+require "rails_helper"
+require_dependency "category"
+
+describe BasicCategorySerializer do
+
+  let(:cdn) { "//my.awesome.cdn" }
+  let(:upload) { Fabricate(:upload) }
+  let(:json) { BasicCategorySerializer.new(category, scope: Guardian.new, root: false).as_json }
+
+  describe "logo_url" do
+
+    let(:category) { Fabricate(:category, logo_url: upload.url) }
+
+    it "uses absolute schemaless URL" do
+      expect(json[:logo_url]).to eq("//test.localhost#{upload.url}")
+    end
+
+    it "uses CDN when available" do
+      Discourse.stubs(:asset_host).returns(cdn)
+      expect(json[:logo_url]).to eq("#{cdn}#{upload.url}")
+    end
+
+  end
+
+  describe "background_url" do
+
+    let(:category) { Fabricate(:category, background_url: upload.url) }
+
+    it "uses absolute schemaless URL" do
+      expect(json[:background_url]).to eq("//test.localhost#{upload.url}")
+    end
+
+    it "uses CDN when available" do
+      Discourse.stubs(:asset_host).returns(cdn)
+      expect(json[:background_url]).to eq("#{cdn}#{upload.url}")
+    end
+
+  end
+
+end