[forty]

I really wanted to like XMPP back in the days, but honestly I always ended up feeling that the protocol is just bad. This idea of opening an XML document at the beginning of the stream, then only allowing a subset of XML and all the mess with the xmlns, all that bringing really nothing to the table except complexity.

I think ideally in a good protocol, the server should not have to parse the content for the messages that are not targetted to itself (only the metadata useful for routing). the XML mess makes it impossible to do that since you have to validate the full document.

At the time I think this page was a good summary of the issues https://about.psyc.eu/XMPP No idea if this is still relevant though.

[icedchai]

I've built an XMPP client for an internal application. My impression was the protocol was overly complex, starting with the lower level problems you describe ("streaming XML.")

It's been years since I've looked at. Maybe things are better now.

[dwaite]

There were several members of the core team, pre-XMPP effort in IETF, who wanted to change it to have framing. If not a length-prefixed model, a nil-separated one.

There were ideas to separate out the addressing/routing from the actual messaging, so that servers did not need to process XML and so that messages did not necessarily need to be XML.

There were even some very preliminary ideas on using the servers to potentially negotiate peer connections for arbitrary traffic.

Back in the early 2000s there were a _lot_ of self-hosted Jabber servers though, and there was push-back from early commercial interests on any protocol-breaking changes resetting adoption to zero. This resulted in Jabber 1.0 pretty much becoming the basis of the XMPP RFC, with XMPP adding new authentication techniques and internationalized JIDs.

Later on, there were efforts to establish alternative transports to accomplish some of these alternative transports and forms - HTTP endpoints to poll for messages, JSON mappings of the core messages, etc.

I would argue against PSYC's claims (or would have, back in the day) that the usage of XML in XMPP is not proper, however. Its proper, it just wasn't the best idea.

[Yoric]

Well, I guess it kinda makes sense? Beats having to reinvent a tokenization format from scratch?

Of course, smaller messages (à la Matrix) probbably make more sense.

[jandrese]

Ultimately the issue is that XML is a document markup language, not a purpose built streaming protocol. You can kind of force it into that role, but the parser ends up being overly complex and issue prone. It's like basing a chat app around creating a MS Word document of every message and sending it across the network.