Does XMPP provide sequential delivery ("delivery on demand")?
Consistent with this discussion about XMPP mode delivery, the XMPP specification guarantees that messages are processed in the order in which they are received, but not necessarily delivered in the order in which they were received.
Even if they are not delivered in received order, does XMPP (regular chat or via the pub-sub extension) ensure that all connected clients receive messages in sequential order?
eg. if three messages are sent A, B, C
and the client C1
receives the stanzas <message>
ok A, C, B
, will the client C2
also get the stanzas ok A, C, B
?
I don't see anything in the standards that guarantee this. This is not the case, do any implementations (like eJabberd) provide this as a side effect of their architecture?
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The linked post is pretty old. XMPP guarantees order processing and therefore delivery stanzas. See RFC 6120 10.1 . Note that this is a different matter if the XMPP implementation actually obeys and enforces this requirement.
The stanzas in your example should be received in the order they are sent, i.e. A
B
C
...
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