Introduce "polling_interval_multiplier" as application setting

Implement module for setting "Poll-Interval" response header.
Return 429 in ETag caching middleware when polling is disabled.

app/controllers/admin/application_settings_controller.rb

@@ -134,6 +134,7 @@ class Admin::ApplicationSettingsController < Admin::ApplicationController
       :unique_ips_limit_enabled,
       :version_check_enabled,
       :terminal_max_session_time,
+      :polling_interval_multiplier,
       disabled_oauth_sign_in_sources: [],
       import_sources: [],

app/models/application_setting.rb

@@ -131,6 +131,10 @@ class ApplicationSetting < ActiveRecord::Base
             presence: true,
             numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :polling_interval_multiplier,
+            presence: true,
+            numericality: { greater_than_or_equal_to: 0 }
+
   validates_each :restricted_visibility_levels do |record, attr, value|
     value&.each do |level|
       unless Gitlab::VisibilityLevel.options.has_value?(level)
@@ -233,7 +237,8 @@ class ApplicationSetting < ActiveRecord::Base
       signup_enabled: Settings.gitlab['signup_enabled'],
       terminal_max_session_time: 0,
       two_factor_grace_period: 48,
-      user_default_external: false
+      user_default_external: false,
+      polling_interval_multiplier: 1
     }
   end

app/views/admin/application_settings/_form.html.haml

@@ -558,5 +558,19 @@
           Maximum time for web terminal websocket connection (in seconds).
           0 for unlimited.
+  %fieldset
+    %legend Real-time features
+    .form-group
+      = f.label :polling_interval_multiplier, 'Polling interval multiplier', class: 'control-label col-sm-2'
+      .col-sm-10
+        = f.text_field :polling_interval_multiplier, class: 'form-control'
+        .help-block
+          Change this value to influence how frequently the GitLab UI polls for updates.
+          If you set the value to 2 all polling intervals are multiplied
+          by 2, which means that polling happens half as frequently.
+          The multiplier can also have a decimal value.
+          The default value (1) is a reasonable choice for the majority of GitLab
+          installations. Set to 0 to completely disable polling.
+
   .form-actions
     = f.submit 'Save', class: 'btn btn-save'

changelogs/unreleased/introduce-polling-interval-multiplier.yml

+---
+title: Introduce "polling_interval_multiplier" as application setting
+merge_request: 10280
+author:

db/migrate/20170329124448_add_polling_interval_multiplier_to_application_settings.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddPollingIntervalMultiplierToApplicationSettings < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  disable_ddl_transaction!
+
+  def up
+    add_column_with_default :application_settings, :polling_interval_multiplier, :decimal, default: 1, allow_null: false
+  end
+
+  def down
+    remove_column :application_settings, :polling_interval_multiplier
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
-ActiveRecord::Schema.define(version: 20170317203554) do
+ActiveRecord::Schema.define(version: 20170329124448) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -115,6 +115,7 @@ ActiveRecord::Schema.define(version: 20170317203554) do
     t.integer "unique_ips_limit_per_user"
     t.integer "unique_ips_limit_time_window"
     t.boolean "unique_ips_limit_enabled", default: false, null: false
+    t.decimal "polling_interval_multiplier", default: 1.0, null: false
   end
   create_table "audit_events", force: :cascade do |t|

doc/api/settings.md

@@ -48,7 +48,8 @@ Example response:
    "koding_url": null,
    "plantuml_enabled": false,
    "plantuml_url": null,
-   "terminal_max_session_time": 0
+   "terminal_max_session_time": 0,
+   "polling_interval_multiplier": 1.0
 }
 ```
@@ -88,6 +89,7 @@ PUT /application/settings
 | `plantuml_enabled` | boolean | no | Enable PlantUML integration. Default is `false`. |
 | `plantuml_url` | string | yes (if `plantuml_enabled` is `true`) |  The PlantUML instance URL for integration. |
 | `terminal_max_session_time` | integer | no | Maximum time for web terminal websocket connection (in seconds). Set to 0 for unlimited time. |
+| `polling_interval_multiplier` | decimal | no | Interval multiplier used by endpoints that perform polling. Set to 0 to disable polling. |
 ```bash
 curl --request PUT --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/application/settings?signup_enabled=false&default_project_visibility=internal
@@ -124,6 +126,7 @@ Example response:
   "koding_url": null,
   "plantuml_enabled": false,
   "plantuml_url": null,
-  "terminal_max_session_time": 0
+  "terminal_max_session_time": 0,
+  "polling_interval_multiplier": 1.0
 }
 ```

lib/api/entities.rb

@@ -581,6 +581,7 @@ module API
       expose :plantuml_enabled
       expose :plantuml_url
       expose :terminal_max_session_time
+      expose :polling_interval_multiplier
     end
     class Release < Grape::Entity

lib/api/settings.rb

@@ -110,6 +110,7 @@ module API
         requires :housekeeping_gc_period, type: Integer, desc: "Number of Git pushes after which 'git gc' is run."
       end
       optional :terminal_max_session_time, type: Integer, desc: 'Maximum time for web terminal websocket connection (in seconds). Set to 0 for unlimited time.'
+      optional :polling_interval_multiplier, type: BigDecimal, desc: 'Interval multiplier used by endpoints that perform polling. Set to 0 to disable polling.'
       at_least_one_of :default_branch_protection, :default_project_visibility, :default_snippet_visibility,
                       :default_group_visibility, :restricted_visibility_levels, :import_sources,
                       :enabled_git_access_protocol, :gravatar_enabled, :default_projects_limit,
@@ -125,7 +126,7 @@ module API
                       :akismet_enabled, :admin_notification_email, :sentry_enabled,
                       :repository_storage, :repository_checks_enabled, :koding_enabled, :plantuml_enabled,
                       :version_check_enabled, :email_author_in_body, :html_emails_enabled,
-                      :housekeeping_enabled, :terminal_max_session_time
+                      :housekeeping_enabled, :terminal_max_session_time, :polling_interval_multiplier
     end
     put "application/settings" do
       attrs = declared_params(include_missing: false)

lib/gitlab/etag_caching/middleware.rb

@@ -18,8 +18,7 @@ module Gitlab
         if_none_match = env['HTTP_IF_NONE_MATCH']
         if if_none_match == etag
-          Gitlab::Metrics.add_event(:etag_caching_cache_hit)
-          [304, { 'ETag' => etag }, ['']]
+          handle_cache_hit(etag)
         else
           track_cache_miss(if_none_match, cached_value_present)
@@ -52,6 +51,14 @@ module Gitlab
         %Q{W/"#{value}"}
       end
+      def handle_cache_hit(etag)
+        Gitlab::Metrics.add_event(:etag_caching_cache_hit)
+
+        status_code = Gitlab::PollingInterval.polling_enabled? ? 304 : 429
+
+        [status_code, { 'ETag' => etag }, ['']]
+      end
+
       def track_cache_miss(if_none_match, cached_value_present)
         if if_none_match.blank?
           Gitlab::Metrics.add_event(:etag_caching_header_missing)

lib/gitlab/polling_interval.rb

+module Gitlab
+  class PollingInterval
+    include Gitlab::CurrentSettings
+
+    HEADER_NAME = 'Poll-Interval'.freeze
+
+    def self.set_header(response, interval:)
+      if polling_enabled?
+        multiplier = current_application_settings.polling_interval_multiplier
+        value = (interval * multiplier).to_i
+      else
+        value = -1
+      end
+
+      response.headers[HEADER_NAME] = value
+    end
+
+    def self.polling_enabled?
+      !current_application_settings.polling_interval_multiplier.zero?
+    end
+  end
+end

spec/lib/gitlab/etag_caching/middleware_spec.rb

@@ -99,6 +99,19 @@ describe Gitlab::EtagCaching::Middleware do
       middleware.call(build_env(path, if_none_match))
     end
+
+    context 'when polling is disabled' do
+      before do
+        allow(Gitlab::PollingInterval).to receive(:polling_enabled?).
+          and_return(false)
+      end
+
+      it 'returns status code 429' do
+        status, _, _ = middleware.call(build_env(path, if_none_match))
+
+        expect(status).to eq 429
+      end
+    end
   end
   context 'when If-None-Match header does not match ETag in store' do

spec/lib/gitlab/polling_interval_spec.rb

+require 'spec_helper'
+
+describe Gitlab::PollingInterval, lib: true do
+  let(:polling_interval) { described_class }
+
+  describe '.set_header' do
+    let(:headers) { {} }
+    let(:response) { double(headers: headers) }
+
+    context 'when polling is disabled' do
+      before do
+        stub_application_setting(polling_interval_multiplier: 0)
+      end
+
+      it 'sets value to -1' do
+        polling_interval.set_header(response, interval: 10_000)
+
+        expect(headers['Poll-Interval']).to eq(-1)
+      end
+    end
+
+    context 'when polling is enabled' do
+      before do
+        stub_application_setting(polling_interval_multiplier: 0.33333)
+      end
+
+      it 'applies modifier to base interval' do
+        polling_interval.set_header(response, interval: 10_000)
+
+        expect(headers['Poll-Interval']).to eq(3333)
+      end
+    end
+  end
+end