NPE is used in javax.security.auth.Subject for flowcontrol

[Weijun Wang]

My understanding is by optional you have 2 options while designing the Set:

1. Allow null

2. Not allow null

Now that SecureSet has chosen the 2nd way, it is now in the "this set does not permit null elements" category and therefore it should "@throws NullPointerException if the specified element is null".

--Max

> On Apr 24, 2020, at 6:13 PM, Mkrtchyan, Tigran <tigran.mkrtchyan at desy.de> wrote:
> 
> Hi Max,
> 
> that's right, but java doc as well mentions that this exception is *optional*, and has a corresponding note:
> 
> Some collection implementations have restrictions on the elements that they may contain. For example, some implementations prohibit null elements, and some have restrictions on the types of their elements. Attempting to add an ineligible element throws an unchecked exception, typically NullPointerException or ClassCastException. Attempting to query the presence of an ineligible element may throw an exception, or it may simply return false; some implementations will exhibit the former behavior and some will exhibit the latter. More generally, attempting an operation on an ineligible element whose completion would not result in the insertion of an ineligible element into the collection may throw an exception or it may succeed, at the option of the implementation. Such exceptions are marked as "optional" in the specification for this interface.
> 
> Thus, returning *false* is justified and spec compliant.
> 
> 
> Thanks,
>   Tigran.
> 
> 
> ----- Original Message -----
>> From: "Weijun Wang" <weijun.wang at oracle.com>
>> To: "Tigran Mkrtchyan" <tigran.mkrtchyan at desy.de>
>> Cc: "security-dev" <security-dev at openjdk.java.net>
>> Sent: Friday, April 24, 2020 11:42:41 AM
>> Subject: Re: NPE is used in javax.security.auth.Subject for flowcontrol
> 
>> Hi Tigran,
>> 
>> In java.util.Set, we have:
>> 
>>    * @throws NullPointerException if the specified element is null and this
>>    *         set does not permit null elements
>>    * (<a href="Collection.html#optional-restrictions">optional</a>)
>>    */
>>   boolean contains(Object o);
>> 
>> As an implementation, SecureSet must follow the spec to throw an NPE. If it
>> returns null, some unexpected thing might happen when the contains() method is
>> called somewhere else.
>> 
>> Thanks,
>> Max
>> 
>>> On Apr 24, 2020, at 4:21 PM, Mkrtchyan, Tigran <tigran.mkrtchyan at desy.de> wrote:
>>> 
>>> 
>>> 
>>> 
>>> Dear Java-SE security developers,
>>> 
>>> 
>>> Imagine a following code:
>>> 
>>> ```
>>> Subject s1 = ... ;
>>> 
>>> Subject s2 = ... ;
>>> 
>>> 
>>> s2.getPrincipals().addAll(s1.getPrincipals());
>>> 
>>> ```
>>> 
>>> The Subject's SecureSet.addAll checks that provided Set doesn't contains 'null'
>>> values
>>> by calling collectionNullClean, which calls SecureSet#contains:
>>> 
>>> ```
>>> try {
>>>   hasNullElements = coll.contains(null);
>>> } catch (NullPointerException npe) {
>>> 
>>> ```
>>> 
>>> The SecureSet#contains itself checks for 'null' values, the  NPE is always
>>> generated.
>>> 
>>> This as introduced by commit e680ab7f208e
>>> 
>>> https://hg.openjdk.java.net/jdk/jdk/diff/e680ab7f208e/jdk/src/share/classes/javax/security/auth/Subject.java
>>> 
>>> 
>>> As SecureSet doesn't allow null values, it will be much simpler to return false
>>> right away:
>>> 
>>> ```
>>> 
>>>       public boolean contains(Object o) {
>>>         if (o == null) {
>>>              // null values rejected  by add
>>>              return false;
>>>         }
>>> 
>>>         ...
>>>       }
>>> 
>>> ```
>>> 
>>> 
>>> Thanks in advance,
>>>  Tigran.