Smack throws NullPointerException in Roster's presence listener

Question

I'm using Smack with android chatting applications and recently I have updated Smack to version to 4.3.0 and getting some error in fabric. It is a NullPointerException inside of Smack:

Fatal Exception: java.lang.NullPointerException
Attempt to invoke virtual method 'int java.lang.Object.hashCode()' on a null object reference
java.util.concurrent.ConcurrentHashMap.get (ConcurrentHashMap.java:772)
org.jivesoftware.smack.roster.Roster.getPresencesInternal (Roster.java:374)
org.jivesoftware.smack.roster.Roster.getOrCreatePresencesInternal (Roster.java:388)
org.jivesoftware.smack.roster.Roster.access$1100 (Roster.java:94)
org.jivesoftware.smack.roster.Roster$PresencePacketListener$1.run (Roster.java:1502)
org.jivesoftware.smack.AsyncButOrdered$Handler.run (AsyncButOrdered.java:121)
java.util.concurrent.ThreadPoolExecutor.runWorker (ThreadPoolExecutor.java:1113)
java.util.concurrent.ThreadPoolExecutor$Worker.run (ThreadPoolExecutor.java:588)
java.lang.Thread.run (Thread.java:818)

Can you please post your code as well for better understanding ? — Akshay Paliwal, Oct 26 '18 at 10:30
Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — user2004685, Oct 26 '18 at 10:31
Its not about java null pointer exception. Its in smack library crash. — Devganiya Hitesh, Oct 26 '18 at 10:50
`Its not about java null pointer exception` Then your logcat is telling you lies... — Phantômaxx, Oct 26 '18 at 15:18

score 1 · Answer 1 · edited Oct 07 '21 at 11:39

"Use the source, Luke (and study the relevant open standard)" ^{Obi-Wan Kenobi}

Smack is open soure, so let us look at the source: One interesting part is

org.jivesoftware.smack.roster.Roster.getPresencesInternal (Roster.java:374)

which reads

Map<Resourcepart, Presence> entityPresences = presenceMap.get(entity);

^{Source: https://github.com/igniterealtime/Smack/blob/4.3.0/smack-im/src/main/java/org/jivesoftware/smack/roster/Roster.java#L374}

We also find that presenceMap is declared as follows

private final Map<BareJid, Map<Resourcepart, Presence>> presenceMap = new ConcurrentHashMap<>();

^{Source: https://github.com/igniterealtime/Smack/blob/4.3.0/smack-im/src/main/java/org/jivesoftware/smack/roster/Roster.java#L168}

So it is a ConcurrentHashMap, which matches with the stacktrace. It is obvous that entity above is null, which is the cause of the NullPointerException.

Now we need to walk the call stack up (or down, depening on your point of view), to determine where entity origins from. Here the interesting part is

org.jivesoftware.smack.roster.Roster$PresencePacketListener$1.run (Roster.java:1502)

which reads

userPresences = getOrCreatePresencesInternal(key);

^{Source: https://github.com/igniterealtime/Smack/blob/4.3.0/smack-im/src/main/java/org/jivesoftware/smack/roster/Roster.java#L1562}

so enitty is key here. Which is declare and define just a few lines above

final BareJid key = from != null ? from.asBareJid() : null;

^{Source: https://github.com/igniterealtime/Smack/blob/4.3.0/smack-im/src/main/java/org/jivesoftware/smack/roster/Roster.java#L1562}

So in case from is null, keywill also be null. Which later causes theNullPointerException. Looking at the code, we find that this is caused by a presence XMPP stanza without a from` attribute set.

The question is now if those stanzas are legal in XMPP. To determine that, we need to have a look at the specification. The relevant part is [RFC 6120 § 8.1.2.1 4.],1, which states

When the server generates a stanza from the server for delivery to the client on behalf of the account of the connected client (e.g., in the context of data storage services provided by the server on behalf of the client), the stanza MUST either (a) not include a 'from' attribute or (b) include a 'from' attribute whose value is the account's bare JID (localpart@domainpart).

So a missing 'from' attribute is generally allowed and is equal to the "account's bare JID".

Now the question is: Are there any presence stanzas specified send from the server to the client which do not have a 'from' attribute? I could not find any while reading the related RFC 6121. And I am not aware when this should ever happen (I possibly could be missing someting). But right now this appears to be a bug in the entity which creates those presence stanzas, which is the used XMPP server implementation.

(What XMPP server implementation do you use?).

Hi @Flow, thanks for you answer, But i got to know that main issue is coming from server, and its related to https://stackoverflow.com/questions/53005782/openfire-chatting-unexpected-behavior. — Devganiya Hitesh, Nov 02 '18 at 05:02

Smack throws NullPointerException in Roster's presence listener

1 Answers1