matrix-bot/docs/jitsi-dev.md

# Jitsi wrapper developer docs

*If you're looking for information on how to set up Jitsi in your Element, see 
[jitsi.md](./jitsi.md) instead.*

These docs are for developers wondering how the different conference buttons work
within Element. If you're not a developer, you're probably looking for [jitsi.md](./jitsi.md).

## Brief introduction to widgets

Widgets are embedded web applications in a room, controlled through state events, and
have a `url` property. They are largely specified by [MSC1236](https://github.com/matrix-org/matrix-doc/issues/1236)
and have extensions proposed under [MSC1286](https://github.com/matrix-org/matrix-doc/issues/1286).

The `url` is typically something we shove into an iframe with sandboxing (see `AppTile`
in the react-sdk), though for some widgets special integration can be done. v2 widgets
have a `data` object which helps achieve that special integration, though v1 widgets
are best iframed and left alone.

Widgets have a `postMessage` API they can use to interact with Element, which also allows
Element to interact with them. Typically this is most used by the sticker picker (an
account-level widget), though widgets like the Jitsi widget will request permissions to
get 'stuck' into the room list during a conference.

Widgets can be added with the `/addwidget <url>` command.

## Brief introduction to integration managers

Integration managers (like Scalar and Dimension) are accessible via the 4 squares in
the top right of the room and provide a simple UI over top of bridges, bots, and other
stuff to plug into a room. They are a separate service to Element and are thus iframed
in a dialog as well. They also have a `postMessage` API they can use to interact with
the client to create things like widgets, give permissions to bridges, and generally
set everything up for the integration the user is working with.

Integration managers do not currently have a spec associated with them, though efforts
are underway in [MSC1286](https://github.com/matrix-org/matrix-doc/issues/1286).

## Widgets configured by integration managers

Integration managers will often "wrap" a widget by using a widget `url` which points
to the integration manager instead of to where the user requested the widget be. For
example, a custom widget added in an integration manager for https://matrix.org will
end up creating a widget with a URL like `https://integrations.example.org?widgetUrl=https%3A%2F%2Fmatrix.org`.

The integration manager's wrapper will typically have another iframe to isolate the
widget from the client by yet another layer. The wrapper often provides other functionality
which might not be available on the embedded site, such as a fullscreen button or the
communication layer with the client (all widgets *should* be talking to the client
over `postMessage`, even if they aren't going to be using the widget APIs).

Widgets added with the `/addwidget` command will *not* be wrapped as they are not going
through an integration manager. The widgets themselves *should* also work outside of
Element. Widgets currently have a "pop out" button which opens them in a new tab and
therefore have no connection back to Riot.

## Jitsi widgets from integration managers

Integration managers will create an entire widget event and send it over `postMessage`
for the client to add to the room. This means that the integration manager gets to 
decide the conference domain, conference name, and other aspects of the widget. As
a result, users can end up with a Jitsi widget that does not use the same conference
server they specified in their config.json - this is expected.

Some integration managers allow the user to change the conference name while others
will generate one for the user. 

## Jitsi widgets generated by Element itself

When the user clicks on the call buttons by the composer, the integration manager is
not involved in the slightest. Instead, Element itself generates a widget event, this time
using the config.json parameters, and publishes that to the room. If there's only two
people in the room, a plain WebRTC call is made instead of using a widget at all - these
are defined in the Matrix specification.

The Jitsi widget created by Element uses a local `jitsi.html` wrapper (or one hosted by
`https://app.element.io` for desktop users or those on non-https domains) as the widget
`url`. The wrapper has some basic functionality for talking to Element to ensure the
required `postMessage` calls are fulfilled.

**Note**: Per [jitsi.md](./jitsi.md) the `preferredDomain` can also come from the server's
client .well-known data. 

## The Jitsi wrapper in Element

Whenever Element sees a Jitsi widget, it ditches the `url` and instead replaces it with
its local wrapper, much like what it would do when creating a widget. However, instead
of using one from [app.element.io](https://app.element.io), it will use one local to the client instead.

The wrapper is used to provide a consistent experience to users, as well as being faster
and less risky to load. The local wrapper URL is populated with the conference information
from the original widget (which could be a v1 or v2 widget) so the user joins the right
call.

Critically, when the widget URL is reconstructed it does *not* take into account the
config.json's `preferredDomain` for Jitsi. If it did this, users would end up on different
conference servers and therefore different calls entirely. 

**Note**: Per [jitsi.md](./jitsi.md) the `preferredDomain` can also come from the server's
client .well-known data.