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.

4 files changed, 34 insertions, 3 deletions

diff --git a/lib/api/entities.rb b/lib/api/entities.rb
index 5954aea8041..01ae2dbd583 100644
--- a/lib/api/entities.rb
+++ b/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
diff --git a/lib/api/settings.rb b/lib/api/settings.rb
index d4d3229f0d1..c7f97ad2aab 100644
--- a/lib/api/settings.rb
+++ b/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)
diff --git a/lib/gitlab/etag_caching/middleware.rb b/lib/gitlab/etag_caching/middleware.rb
index ffbc6e17dc5..9c98f0d1a30 100644
--- a/lib/gitlab/etag_caching/middleware.rb
+++ b/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)
diff --git a/lib/gitlab/polling_interval.rb b/lib/gitlab/polling_interval.rb
new file mode 100644
index 00000000000..c44bb1cd14d
--- /dev/null
+++ b/lib/gitlab/polling_interval.rb
@@ -0,0 +1,22 @@
+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