FEATURE: Allow selection of highlight js languages

PERF: stop loading highlight js on load

To get latest highlight js run bin/rake highlightjs:update

app/controllers/highlight_js_controller.rb

@@ -0,0 +1,26 @@
+class HighlightJsController < ApplicationController
+  skip_before_filter :redirect_to_login_if_required, :check_xhr, :verify_authenticity_token, only: [:show]
+
+  def show
+    RailsMultisite::ConnectionManagement.with_hostname(params[:hostname]) do
+
+      current_version = HighlightJs.version(SiteSetting.highlighted_languages)
+
+      if current_version != params[:version]
+        return redirect_to path(HighlightJs.path)
+      end
+
+      # note, this can be slightly optimised by caching the bundled file, it cuts down on N reads
+      # our nginx config caches this so in practical terms it does not really matter and keeps
+      # code simpler
+      highlight_js = HighlightJs.bundle(SiteSetting.highlighted_languages.split("|"))
+
+      response.headers["Last-Modified"] = 10.years.ago.httpdate
+      response.headers["Content-Length"] = highlight_js.bytesize.to_s
+      expires_in 1.year, public: true
+
+      render text: highlight_js, disposition: nil, content_type: 'application/javascript'
+    end
+  end
+end
+