FEATURE: allow long polling to go to a different url

Added the site setting long_polling_base_url , this allows you
to farm long polling to a different server.

This setting is very important if a CDN is serving dynamic content.

Gemfile.lock

@@ -163,7 +163,7 @@ GEM
       mime-types (~> 1.16)
       treetop (~> 1.4.8)
     memory_profiler (0.0.4)
-    message_bus (1.0.0)
+    message_bus (1.0.4)
       eventmachine
       rack (>= 1.1.3)
       redis

app/assets/javascripts/discourse/initializers/subscribe-user-notifications.js.es6

@@ -2,7 +2,7 @@
    Subscribes to user events on the message bus
 **/
 export default {
-  name: "subscribe-user-notifications",
+  name: 'subscribe-user-notifications',
   after: 'message-bus',
   initialize: function(container) {
     var user = Discourse.User.current();
@@ -13,14 +13,25 @@ export default {
     var bus = Discourse.MessageBus;
     bus.callbackInterval = siteSettings.anon_polling_interval;
     bus.backgroundCallbackInterval = siteSettings.background_polling_interval;
+    bus.baseUrl = siteSettings.long_polling_base_url;
+
+    if (bus.baseUrl !== '/') {
+      // zepto compatible, 1 param only
+      bus.ajax = function(opts){
+        opts.headers = opts.headers || {};
+        opts.headers['X-Shared-Session-Key'] = $('meta[name=shared_session_key]').attr('content');
+        return $.ajax(opts);
+      };
+    } else {
+      bus.baseUrl = Discourse.getURL('/');
+    }
 
     if (user) {
       bus.callbackInterval = siteSettings.polling_interval;
       bus.enableLongPolling = true;
-      bus.baseUrl = Discourse.getURL("/");
 
       if (user.admin || user.moderator) {
-        bus.subscribe("/flagged_counts", function(data) {
+        bus.subscribe('/flagged_counts', function(data) {
           user.set('site_flagged_posts_count', data.total);
         });
       }

app/helpers/application_helper.rb

@@ -11,6 +11,17 @@ module ApplicationHelper
   include CanonicalURL::Helpers
   include ConfigurableUrls
 
+  def shared_session_key
+    if SiteSetting.long_polling_base_url != '/'.freeze && current_user
+      sk = "shared_session_key"
+      return request.env[sk] if request.env[sk]
+
+      request.env[sk] = key = (session[sk] ||= SecureRandom.hex)
+      $redis.setex "#{sk}_#{key}", 7.days, current_user.id.to_s
+      key
+    end
+  end
+
   def script(*args)
     if SiteSetting.enable_cdn_js_debugging && GlobalSetting.cdn_url
       tags = javascript_include_tag(*args, "crossorigin" => "anonymous")

app/views/layouts/application.html.erb

@@ -10,6 +10,10 @@
     <meta name="fragment" content="!">
     <%- end %>
 
+    <%- if shared_session_key %>
+    <meta name="shared_session_key" content="<%= shared_session_key %>">
+    <%- end %>
+
     <%= script "preload_store" %>
     <%= script "locales/#{I18n.locale}" %>
     <%= script "vendor" %>

config/initializers/04-message_bus.rb

@@ -2,6 +2,14 @@
   RailsMultisite::ConnectionManagement.current_db
 end
 
+MessageBus.extra_response_headers_lookup do |env|
+  {
+    "Access-Control-Allow-Origin" => Discourse.base_url,
+    "Access-Control-Allow-Methods" => "GET, POST",
+    "Access-Control-Allow-Headers" => "X-SILENCE-LOGGER, X-Shared-Session-Key"
+  }
+end
+
 MessageBus.user_id_lookup do |env|
   user = CurrentUser.lookup_from_env(env)
   user.id if user

config/locales/server.en.yml

@@ -698,6 +698,7 @@ en:
     enable_private_messages: "Allow trust level 1 users to create private messages and reply to private messages"
 
     enable_long_polling: "Message bus used for notification can use long polling"
+    long_polling_base_url: "Base URL used for long polling (when a CDN is serving dynamic content, be sure to set this to origin pull) eg: http://origin.site.com"
     long_polling_interval: "Amount of time the server should wait before responding to clients when there is no data to send (logged on users only)"
     polling_interval: "When not long polling, how often should logged on clients poll in milliseconds"
     anon_polling_interval: "How often should anonymous clients poll in milliseconds"

config/site_settings.yml

@@ -616,6 +616,9 @@ developer:
     client: true
     default: true
   long_polling_interval: 25000
+  long_polling_base_url:
+    client: true
+    default: '/'
   background_polling_interval:
     client: true
     default: 60000

lib/auth/default_current_user_provider.rb

@@ -18,6 +18,17 @@ def initialize(env)
   def current_user
     return @env[CURRENT_USER_KEY] if @env.key?(CURRENT_USER_KEY)
 
+    # bypass if we have the shared session header
+    if shared_key = @env['HTTP_X_SHARED_SESSION_KEY']
+      uid = $redis.get("shared_session_key_#{shared_key}")
+      user = nil
+      if uid
+        user = User.find_by(id: uid.to_i)
+      end
+      @env[CURRENT_USER_KEY] = user
+      return user
+    end
+
     request = @request
 
     auth_token = request.cookies[TOKEN_COOKIE]