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”

3 files changed, 34 insertions, 5 deletions

diff --git a/app/services/activitypub/process_poll_service.rb b/app/services/activitypub/process_poll_service.rb
index 2fbce65b9..cb4a0d460 100644
--- a/app/services/activitypub/process_poll_service.rb
+++ b/app/services/activitypub/process_poll_service.rb
@@ -28,6 +28,8 @@ class ActivityPub::ProcessPollService < BaseService
       end
     end
 
+    voters_count = @json['votersCount']
+
     latest_options = items.map { |item| item['name'].presence || item['content'] }
 
     # If for some reasons the options were changed, it invalidates all previous
@@ -39,7 +41,8 @@ class ActivityPub::ProcessPollService < BaseService
         last_fetched_at: Time.now.utc,
         expires_at: expires_at,
         options: latest_options,
-        cached_tallies: items.map { |item| item.dig('replies', 'totalItems') || 0 }
+        cached_tallies: items.map { |item| item.dig('replies', 'totalItems') || 0 },
+        voters_count: voters_count
       )
     rescue ActiveRecord::StaleObjectError
       poll.reload
diff --git a/app/services/post_status_service.rb b/app/services/post_status_service.rb
index 34ec6d504..a0a650d62 100644
--- a/app/services/post_status_service.rb
+++ b/app/services/post_status_service.rb
@@ -174,7 +174,7 @@ class PostStatusService < BaseService
   def poll_attributes
     return if @options[:poll].blank?
 
-    @options[:poll].merge(account: @account)
+    @options[:poll].merge(account: @account, voters_count: 0)
   end
 
   def scheduled_options
diff --git a/app/services/vote_service.rb b/app/services/vote_service.rb
index 0eeb8fd56..cb7dce6e8 100644
--- a/app/services/vote_service.rb
+++ b/app/services/vote_service.rb
@@ -12,12 +12,24 @@ class VoteService < BaseService
     @choices = choices
     @votes   = []
 
-    ApplicationRecord.transaction do
-      @choices.each do |choice|
-        @votes << @poll.votes.create!(account: @account, choice: choice)
+    already_voted = true
+
+    RedisLock.acquire(lock_options) do |lock|
+      if lock.acquired?
+        already_voted = @poll.votes.where(account: @account).exists?
+
+        ApplicationRecord.transaction do
+          @choices.each do |choice|
+            @votes << @poll.votes.create!(account: @account, choice: choice)
+          end
+        end
+      else
+        raise Mastodon::RaceConditionError
       end
     end
 
+    increment_voters_count! unless already_voted
+
     ActivityTracker.increment('activity:interactions')
 
     if @poll.account.local?
@@ -53,4 +65,18 @@ class VoteService < BaseService
   def build_json(vote)
     Oj.dump(serialize_payload(vote, ActivityPub::VoteSerializer))
   end
+
+  def increment_voters_count!
+    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: "vote:#{@poll.id}:#{@account.id}" }
+  end
 end