Fix race condition when processing statuses twice with the same idempotency key (#37879)

app/services/post_status_service.rb

@@ -2,6 +2,7 @@
 
 class PostStatusService < BaseService
   include Redisable
+  include Lockable
   include LanguagesHelper
 
   class UnexpectedMentionsError < StandardError
@@ -39,19 +40,17 @@ class PostStatusService < BaseService
     @in_reply_to = @options[:thread]
     @quoted_status = @options[:quoted_status]
 
-    return idempotency_duplicate if idempotency_given? && idempotency_duplicate?
+    with_idempotency do
+      validate_media!
+      preprocess_attributes!
 
-    validate_media!
+      if scheduled?
-    preprocess_attributes!
+        schedule_status!
-
+      else
-    if scheduled?
+        process_status!
-      schedule_status!
+      end
-    else
-      process_status!
     end
 
-    redis.setex(idempotency_key, 3_600, @status.id) if idempotency_given?
-
     unless scheduled?
       postprocess_status!
       bump_potential_friendship!
@@ -208,6 +207,18 @@ class PostStatusService < BaseService
     @idempotency_duplicate = redis.get(idempotency_key)
   end
 
+  def with_idempotency
+    return yield unless idempotency_given?
+
+    with_redis_lock("idempotency:lock:status:#{@account.id}:#{@options[:idempotency]}") do
+      return idempotency_duplicate if idempotency_duplicate?
+
+      yield
+
+      redis.setex(idempotency_key, 3_600, @status.id)
+    end
+  end
+
   def scheduled_in_the_past?
     @scheduled_at.present? && @scheduled_at <= Time.now.utc
   end