[Standards] Stanza Size Limits (was Re: [jdev] Communicate between two client instances of the same ID)

Justin Karneges justin-keyword-jabber.093179 at affinix.com
Wed Sep 3 03:21:06 UTC 2008

Dragging this over from jdev:

> > > Hmm. XMPP is not optimized for sending around 100k+ messages.
> >
> > Would 64KB chunks a reasonable thing to do?
> That's probably still too high.  There is currently no specified maximum
> size for XMPP stanzas, but individual implementations may enforce different
> values.  The original jabberd 1.0 server had around a 10KB maximum.  The
> general consensus is that stanzas should be "small", and this is largely in
> part because large stanzas block transmission of other stanzas (you cannot
> send many stanzas in parallel over one stream).

Right now it's fuzzy as to how small you should chunk your data for maximum 
compatibility.  I think we should define the largest stanza size that must be 
supported by clients and servers.  We could just make this value 10000 bytes, 
from the opening '<' to the final '>' of the stanza.  The text should go into 
RFC 3920bis as a SHOULD.

This way, stanzas 10000 bytes or smaller are guaranteed to succeed in 
transmission.  Stanzas larger than 10000 bytes would still be transmittable, 
but without any guarantees that the other side will accept it (which is not 
any worse than the situation today).

A question: which stanza error are we supposed to use to reject a stanza that 
is too large?  Such an error would be very useful to determine the MTU.


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