It would be nice if Telepathy (and Empathy later on) would support message receipts to make IM more reliable. It looks not too complicated to support.
You're quite right, it wasn't that difficult, particularly since I made the executive decision in the attached branch not to provide a way to disable sending receipts. This branch will do nothing visible without changes to Empathy, though. Empathy does have support for showing delivery status information when the protocol /guarantees/ success or failure reports for each message. XEP-0184 is not such a protocol, so Empathy will ignore the reports. Maybe it should do something like WhatsApp, which puts a single tick-mark beside messages which have been delivered and a double tick-mark beside messages which have been read. (A bit of Googling suggests that WhatsApp uses literally this XEP, in fact.)
I've updated this branch to make Gabble actually advertise the cap. (And I also noticed it was missing the cap for jabber:iq:last so added that too.)
Will be in 0.17.2.
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