Uniqueness check is not safe for concurrent modifications

[Olle Törnström]

So the use of a local reference to the value held in any of the concurrent maps, for example a set of string values for the email addresses of some user UUID, is not guarded against concurrent modifications.

contargo-types/src/main/java/net/contargo/types/contactinfo/validation/ReactiveUniquenessValidator.java

Lines 239 to 255 in 27376ee

 if (dataToCheck.containsKey(key)) { 
     Set<String> values = dataToCheck.get(key); 
  
     // only one presence and mapped to the requester's userUUID 
     if (!values.isEmpty()) { // there are values for this key 
  
         if (values.size() == 1 && values.contains(value)) { // only one value equals to the requested value: unique 
             return true; 
         } else { // more values or one not equal to the requested one: not unique 
             logger().info("detected non-unique value {}. claimed by {} but already taken by {}.", key, value, 
                 String.join(",", values)); 
  
             return false; 
         } 
     } else { 
         return true; 
     } 

I believe the checks may fail between the if-statements, in case the set is changed in an unpredictible way. We've just recorded log-statements where the non-unique value is empty, hinting at it being cleared after the check of it being empty.

I'll try to address this in a fix.