Add ability to ask external caches to invalidate.

Add a cached_urls method to the Comment, FoiAttachment, InfoRequest,
PublicBody and User models, containing the entries that those models
wish to invalidate when an event is logged via log_event or when the
censor rules change. Entries are either a fixed path to be purged or
a regex beginning with '^' to be banned.

Adds a NotifyCacheJob that for each of the object's cached_urls, for
each locale, for each host in VARNISH_HOSTS, makes BAN or PURGE HTTP
requests to the host, to invalidate the relevant entries.

TODO: www.whatdotheyknow.com is currently hard-coded in the job.

app/jobs/notify_cache_job.rb

@@ -0,0 +1,50 @@
+require 'net/http'
+
+class Net::HTTP::Purge < Net::HTTP::Get
+  METHOD = 'PURGE'
+end
+
+class Net::HTTP::Ban < Net::HTTP::Get
+  METHOD = 'BAN'
+end
+
+##
+# Job to notify a cache of URLs to be purged or banned, given an object
+# (that must have a cached_urls method).
+#
+# Examples:
+#   NotifyCacheJob.perform(InfoRequest.first)
+#   NotifyCacheJob.perform(FoiAttachment.first)
+#   NotifyCacheJob.perform(Comment.first)
+#
+class NotifyCacheJob < ApplicationJob
+  queue_as :default
+
+  def perform(object)
+    urls = object.cached_urls
+    locales = [''] + AlaveteliLocalization.available_locales.map { |locale| '/' + locale }
+    hosts = AlaveteliConfiguration.varnish_hosts
+    locales.each do |locale|
+      hosts.each do |host|
+        Net::HTTP.start('www.whatdotheyknow.com', 80, host, 6081) do |http|
+          urls.each do |url|
+            if url.include? '^'
+              request = Net::HTTP::Ban.new(url)
+            else
+              request = Net::HTTP::Purge.new(url)
+            end
+            response = http.request(request)
+            result = response.code
+            if result == "200"
+              Rails.logger.debug("PURGE: Purged URL #{url} at #{host}: #{result}")
+            else
+              Rails.logger.warn(
+                "PURGE: Unable to purge URL #{url} at #{host}: status #{result}"
+              )
+            end
+          end
+        end
+      end
+    end
+  end
+end

app/models/censor_rule.rb

@@ -75,6 +75,7 @@ def is_global?
   def expire_requests
     if info_request
       InfoRequestExpireJob.perform_later(info_request)
+      NotifyCacheJob.perform_later(info_request)
     elsif user
       InfoRequestExpireJob.perform_later(user, :info_requests)
     elsif public_body

app/models/comment.rb

@@ -193,6 +193,13 @@ def hide(editor:)
     end
   end
 
+  def cached_urls
+    [
+      request_path(info_request),
+      show_user_wall_path(url_name: user.url_name)
+    ]
+  end
+
   private
 
   def check_body_has_content

app/models/foi_attachment.rb

@@ -318,6 +318,12 @@ def body_as_html(dir, opts = {})
     AttachmentToHTML.to_html(self, to_html_opts)
   end
 
+  def cached_urls
+    [
+      request_path(incoming_message.info_request)
+    ]
+  end
+
   private
 
   def text_type?

app/models/info_request.rb

@@ -52,6 +52,7 @@ class InfoRequest < ApplicationRecord
   include InfoRequest::TitleValidation
   include Taggable
   include Notable
+  include LinkToHelper
 
   admin_columns exclude: %i[title url_title],
                 include: %i[rejected_incoming_count]
@@ -1163,6 +1164,15 @@ def log_event(type, params, options = {})
     if !last_event_time || (event.created_at > last_event_time)
       update_column(:last_event_time, event.created_at)
     end
+    if AlaveteliConfiguration.varnish_hosts.present?
+      if %w[comment edit_comment hide_comment].include? type
+        NotifyCacheJob.perform_later(params.comment)
+      elsif type == 'edit_attachment'
+        NotifyCacheJob.perform_later(params.attachment)
+      else
+        NotifyCacheJob.perform_later(self)
+      end
+    end
     event
   end
 
@@ -1758,6 +1768,34 @@ def latest_refusals
     incoming_messages.select(&:refusals?).last&.refusals || []
   end
 
+  def cached_urls
+    feed_request = TrackThing.new(
+      info_request: self,
+      track_type: 'request_updates'
+    )
+    feed_body = TrackThing.new(
+      public_body: public_body,
+      track_type: 'public_body_updates'
+    )
+    feed_user = TrackThing.new(
+      tracked_user: user,
+      track_type: 'user_updates'
+    )
+    [
+      '/',
+      public_body_path(public_body),
+      request_path(self),
+      request_details_path(self),
+      '^/list*',
+      do_track_path(feed_request, feed='feed'),
+      '^/feed/list/*',
+      do_track_path(feed_body, feed='feed'),
+      do_track_path(feed_user, feed='feed'),
+      user_path(user),
+      show_user_wall_path(url_name: user.url_name)
+    ]
+  end
+
   private
 
   def self.add_conditions_from_extra_params(params, extra_params)

app/models/public_body.rb

@@ -35,6 +35,7 @@
 class PublicBody < ApplicationRecord
   include Taggable
   include Notable
+  include LinkToHelper
 
   class ImportCSVDryRun < StandardError; end
 
@@ -911,6 +912,14 @@ def questions
     PublicBodyQuestion.fetch(self)
   end
 
+  def cached_urls
+    [
+      public_body_path(self),
+      list_public_bodies_path,
+      '^/body/list'
+    ]
+  end
+
   private
 
   # If the url_name has changed, then all requested_from: queries will break

app/models/user.rb

@@ -673,6 +673,12 @@ def flipper_id
     "User;#{id}"
   end
 
+  def cached_urls
+    [
+      user_path(self)
+    ]
+  end
+
   private
 
   def set_defaults

config/general.yml-example

@@ -627,6 +627,20 @@ EXCEPTION_NOTIFICATIONS_TO:
 # ---
 MAX_REQUESTS_PER_USER_PER_DAY: 6
 
+# If you're running behind Varnish set this to work out where to send purge
+# requests. Otherwise, don't set it.
+#
+# VARNISH_HOSTS - Array of Strings (default: nil)
+#
+# Examples:
+#
+#   VARNISH_HOSTS:
+#     - host1
+#     - host2
+#
+# ---
+VARNISH_HOSTS: null
+
 # Adding a value here will enable Google Analytics on all non-admin pages for
 # non-admin users.
 #

lib/configuration.rb

@@ -131,6 +131,7 @@ module AlaveteliConfiguration
       USE_MAILCATCHER_IN_DEVELOPMENT: true,
       USER_SIGN_IN_ACTIVITY_RETENTION_DAYS: 0,
       UTILITY_SEARCH_PATH: ['/usr/bin', '/usr/local/bin'],
+      VARNISH_HOSTS: [],
       WORKING_OR_CALENDAR_DAYS: 'working'
     }
     # rubocop:enable Layout/LineLength