[OTR-dev] Pidgin + Yahoo not support SMP?

[Ian Goldberg]

On Wed, Aug 05, 2009 at 09:21:05PM -0700, chris-tuchs at hushmail.com wrote:
> I just tested SMP interoperation between the GreenLife 
> implementation
> of OTR and the Pidgin implementation.  With one issue, I am able to
> complete the SMP protocol in both directions.  However the issue I
> encountered may explain the problems with Pidgin <--yahoo--> Pidgin
> SMP problems I have experienced.  Yahoo does not maintain order of
> IM's in every case.  Below is a message coming from Pidgin via Yahoo
> to the official Yahoo IM client, which doesn't have OTR.  I was 
> doing
> Avy1(OTR) <--SL--> Avy2(no OTR) <--cut-n-paste--> User1(yahoo no 
> OTR)
> <--yahoo--> User2(pidgin with OTR).  I arbitrarily cut the lines off
> at 64 characters cause all that matters really is demonstrating the
> out of order delivery.
> 
> ?OTR,00002,00004,OCTiVspdIkxpqKlACVXDfCp/lFiI345aBsx60GgPF/vL1XP
> ?OTR,00001,00004,?OTR:AAIDAQAAAAMAAAAEAAAAwEIH2lnX+NPoHtYYXuDIvf
> ?OTR,00004,00004,Z+vhQwKssDnBB18z1nFURGZz3k2I2jaOqJek3U8/XkDlVd7
> ?OTR,00003,00004,84StZgo+6T/vqtG+9OD4x3tHO1DirnzOih3A2Zg/j+I8CeG
> 
> This is unfortunately a problem I also see in Second Life -- the IM
> system does not maintain order of fragments under some situations.
> Also when I send long messages (256KByte) Second Life is arbitrarily
> dropping some fragments.
> 
> I am not sure what the 'right' solution is, but the existing message
> fragmentation re-assembly code in the released source does not 
> handle
> out of order fragments or missing fragments.  Is there more recent
> code which handles some of these problems?
> 
> To be clear, SMP does work in GreenLife now, when SL doesn't drop
> or re-order fragments.  I assume SMP would work Pidgin to Pidgin
> over Yahoo if Yahoo didn't reorder the fragments, but I have not
> tested that.

That's bizarre.  The OTR protocol specifically assumes that messages,
although they may be dropped if the network flakes, will be delivered in
the right order if they're delivered at all.  An IM network that doesn't
deliver messages in order would seem to be pretty poor for conversation,
wouldn't it?  Does GreenLife (or is it Yahoo?) really scramble the order
of messages you send?

   - Ian