I use this to say "XML was the hot when XMPP was created, the way JSON is the hot today, when Matrix is created". I 100% agree with you that using a non-binary-friendly format sucks for pretty much anything that goes beyond plain text messaging:
- encryption
- files/emoticons/voice
- on the server side, any routing stuff
But still, like XMPP I hope this will not be enough to hamper its development.
> jingle for XMPP is pretty much a textbook example of "too much friction -> not fit for purpose and near zero adoption"
Amen to that. XMPP is basically an entity-to-entity messaging protocol, and yet because it can't handle binary there needs to be a negotiation step and yet another connection for binary stuff... blah.
The server-server API is currently just targetting https+json just for expedience in getting started, but nothing to stop us negotiating more efficient transports in future - capn proto has come up a lot in conversation as a possible option. Handling signing is a bit more fun as we currently rely on signing canonical json, but surmountable.
As for binary transfers... well, random blobs are just handled as pure HTTP with a mimetype currently :)
It looks like they did tackle acausality head-on; I like what I see about previous message IDs being included in https://matrix.org/docs/spec/#pdus
Nervous about ever christening JSON "today's technology". JSON has the same problem XML in XMPP does: can't tunnel binary e.g. video without extreme backbending (jingle for XMPP is pretty much a textbook example of "too much friction -> not fit for purpose and near zero adoption"). But it looks like matrix is pluggable on transports, too, so that's potentially a sweet spot for lazy REST clients and powerful performance situations to coexist.
... And I popped into their self-hosted chat room. Observation 1: It works (!). Observation 2: the devs are dogfooding and seem both knowledgeable and friendly :) I haven't taken the leap to self-host yet (will later!); but from preliminaries, matrix is looking remarkably solid and well thought out. I'm going to try to build something with this! Thanks again for the link!