Add voters count support (#11917)

* Add voters count to polls

* Add ActivityPub serialization and parsing of voters count

* Add support for voters count in WebUI

* Move incrementation of voters count out of redis lock

* Reword “voters” to “people”

2 files changed, 36 insertions, 5 deletions

diff --git a/app/lib/activitypub/activity/create.rb b/app/lib/activitypub/activity/create.rb
index e69193b71..76bf9b2e5 100644
--- a/app/lib/activitypub/activity/create.rb
+++ b/app/lib/activitypub/activity/create.rb
@@ -232,25 +232,40 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
       items    = @object['oneOf']
     end
 
+    voters_count = @object['votersCount']
+
     @account.polls.new(
       multiple: multiple,
       expires_at: expires_at,
       options: items.map { |item| item['name'].presence || item['content'] }.compact,
-      cached_tallies: items.map { |item| item.dig('replies', 'totalItems') || 0 }
+      cached_tallies: items.map { |item| item.dig('replies', 'totalItems') || 0 },
+      voters_count: voters_count
     )
   end
 
   def poll_vote?
     return false if replied_to_status.nil? || replied_to_status.preloadable_poll.nil? || !replied_to_status.local? || !replied_to_status.preloadable_poll.options.include?(@object['name'])
 
-    unless replied_to_status.preloadable_poll.expired?
-      replied_to_status.preloadable_poll.votes.create!(account: @account, choice: replied_to_status.preloadable_poll.options.index(@object['name']), uri: @object['id'])
-      ActivityPub::DistributePollUpdateWorker.perform_in(3.minutes, replied_to_status.id) unless replied_to_status.preloadable_poll.hide_totals?
-    end
+    poll_vote! unless replied_to_status.preloadable_poll.expired?
 
     true
   end
 
+  def poll_vote!
+    poll = replied_to_status.preloadable_poll
+    already_voted = true
+    RedisLock.acquire(poll_lock_options) do |lock|
+      if lock.acquired?
+        already_voted = poll.votes.where(account: @account).exists?
+        poll.votes.create!(account: @account, choice: poll.options.index(@object['name']), uri: @object['id'])
+      else
+        raise Mastodon::RaceConditionError
+      end
+    end
+    increment_voters_count! unless already_voted
+    ActivityPub::DistributePollUpdateWorker.perform_in(3.minutes, replied_to_status.id) unless replied_to_status.preloadable_poll.hide_totals?
+  end
+
   def resolve_thread(status)
     return unless status.reply? && status.thread.nil? && Request.valid_url?(in_reply_to_uri)
     ThreadResolveWorker.perform_async(status.id, in_reply_to_uri)
@@ -416,7 +431,22 @@ class ActivityPub::Activity::Create < ActivityPub::Activity
     ActivityPub::RawDistributionWorker.perform_async(Oj.dump(@json), replied_to_status.account_id, [@account.preferred_inbox_url])
   end
 
+  def increment_voters_count!
+    poll = replied_to_status.preloadable_poll
+    unless poll.voters_count.nil?
+      poll.voters_count = poll.voters_count + 1
+      poll.save
+    end
+  rescue ActiveRecord::StaleObjectError
+    poll.reload
+    retry
+  end
+
   def lock_options
     { redis: Redis.current, key: "create:#{@object['id']}" }
   end
+
+  def poll_lock_options
+    { redis: Redis.current, key: "vote:#{replied_to_status.poll_id}:#{@account.id}" }
+  end
 end
diff --git a/app/lib/activitypub/adapter.rb b/app/lib/activitypub/adapter.rb
index cb2ac72d4..2a8f72333 100644
--- a/app/lib/activitypub/adapter.rb
+++ b/app/lib/activitypub/adapter.rb
@@ -21,6 +21,7 @@ class ActivityPub::Adapter < ActiveModelSerializers::Adapter::Base
     identity_proof: { 'toot' => 'http://joinmastodon.org/ns#', 'IdentityProof' => 'toot:IdentityProof' },
     blurhash: { 'toot' => 'http://joinmastodon.org/ns#', 'blurhash' => 'toot:blurhash' },
     discoverable: { 'toot' => 'http://joinmastodon.org/ns#', 'discoverable' => 'toot:discoverable' },
+    voters_count: { 'toot' => 'http://joinmastodon.org/ns#', 'votersCount' => 'toot:votersCount' },
   }.freeze
 
   def self.default_key_transform