ejabberd APIs and modules can be reused in MQTT

[rallep71]

Hello, I have a question regarding my understanding.

In the documentation https://docs.ejabberd.im/admin/guide/mqtt/#benefits, point 2 explains that the ejabberd API can be used with MQTT, meaning it can do everything that I can do externally via the API. Is that correct? Or am I fundamentally misunderstanding something?

I cannot find anywhere how to configure the connection from MQTT to the API. MQTT is enabled on port 8883, uses TLS, and I can connect to it without any problems as an ejabberd user, set topics, subscribe, etc. But where is the connection to the API to use the API via MQTT as ejabberd admin?

thx

[badlop]

Or am I fundamentally misunderstanding something?

Short answer: Right, that sentence in the documentation is confusing and should be corrected.

The Good

When support for MQTT was first announced, the ejabberd 19.02 release notes explained this with precise words:

MQTT support in ejabberd benefits from all the code infrastructure in place in ejabberd for clustering, plugins, etc. For example, the authentication mechanism is the same. Leveraging 16 years of work on our clustering engine and optimization of our stack, our MQTT server is able to reach millions of concurrent online users and is already among the top most scalable MQTT servers available.

When implementing a feature in the mod_mqtt (or in other module that provides a feature for MQTT), it is possible to reuse code from ejabberd by calling those erlang functions, the same way that any ejabberd module can call erlang functions from Erlang/OTP libraries, functions from xmpp library and all the other dependencies.

This is a benefit of using mod_mqtt instead of a standalone MQTT server.

The Bad

Sometime later, a new page for the ejabberd documentation site was written covering MQTT, and it said (and still says):

The ejabberd APIs and modules can be reused in MQTT. Authentication, virtual hosting, database backends, ... They both work with XMPP and MQTT. You can also share your security policy, as defined in the configuration file between the two protocols.

Using the term "ejabberd API" is confusing here, because instead of referring to "the exported erlang functions", it can be understood as "the ejabberd ReST API".

But as you noticed, mod_mqtt does not include any support for that in the source code, not mentioned anywhere in the mod_mqtt/MQTT documentation, and mod_mqtt is not mentioned as an "API Frontend"

The Solution

The sentence in https://docs.ejabberd.im/admin/guide/mqtt/#benefits should be rewritten to not refer to "ejabberd API". Maybe something like this:

The MQTT service can use ejabberd features and modules: authentication, virtual hosting, database backends, ... They both work with XMPP and MQTT. You can also share your security policy, as defined in the configuration file between the two protocols.

[rallep71]

Thank you for the clarification, I could already guess that.

Thx