Adding embedded PuSH server

app/controllers/api/push_controller.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+class Api::PushController < ApiController
+  def update
+    mode          = params['hub.mode']
+    topic         = params['hub.topic']
+    callback      = params['hub.callback']
+    lease_seconds = params['hub.lease_seconds']
+    secret        = params['hub.secret']
+
+    case mode
+    when 'subscribe'
+      response, status = Pubsubhubbub::SubscribeService.new.call(topic_to_account(topic), callback, secret, lease_seconds)
+    when 'unsubscribe'
+      response, status = Pubsubhubbub::UnsubscribeService.new.call(topic_to_account(topic), callback)
+    else
+      response = "Unknown mode: #{mode}"
+      status   = 422
+    end
+
+    render plain: response, status: status
+  end
+
+  private
+
+  def topic_to_account(topic_url)
+    return if topic_url.blank?
+
+    uri    = Addressable::URI.parse(topic_url)
+    params = Rails.application.routes.recognize_path(uri.path)
+    domain = uri.host + (uri.port ? ":#{uri.port}" : '')
+
+    return unless TagManager.instance.local_domain?(domain) && params[:controller] == 'accounts' && params[:action] == 'show' && params[:format] == 'atom'
+
+    Account.find_local(params[:username])
+  end
+end