MSC3914: Matrix native group call push rule

proposals/3914-call-notif.md

@@ -0,0 +1,64 @@
+# MSC3914: Matrix native group call push rule
+
+[MSC3401](https:/matrix-org/matrix-spec-proposals/pull/3401) defines
+how group calls can happen over Matrix. It adds a an `m.call` state event with
+an `m.intent` field which, if it has a value of `m.ring` or `m.prompt`, should
+cause a notification should be shown to the user. This MSC defines a new push
+rule for this scenario.
+
+## Proposal
+
+A new push-rule condition is added with the name `call_started`. For this
+condition to be met the following conditions have to be met:
+
+- `m.intent` must either be `m.ring` or `m.prompt`
+- `m.terminated` must _not_ be in the content
+- the `prev_content` is either missing or includes `m.terminated`
+
+This is a new push condition since the current push-rule system is not flexible
+enough for this to be built out of existing rules.
+
+A new [default underride
+rule](https://spec.matrix.org/v1.2/client-server-api/#default-underride-rules) is
+to be added:
+
+```json
+{
+ "rule_id": ".m.rule.room.call",
+ "default": true,
+ "enabled": true,
+ "conditions": [
+ {
+ "kind": "event_match",
+ "key": "type",
+ "pattern": "m.call"
+ },
+ {
+ "kind": "call_started"
+ }
+ ],
+ "actions": [
+ "notify", 
+ {"set_tweak": "sound", "value": "default"}
+ ]
+}
+```
+
+This new push rule is inserted immediately after `.m.rule.call`.
+
+## Potential issues
+
+Once we have state event E2EE all notifications will have to be handled
+client-side as the server won't see the content of events.
+
+## Alternatives
+
+This could be implemented entirely client-side without any push rule though this
+presents an issue for mobile devices which can't sync all the time and therefore
+need to receive push notifications.
+
+## Unstable prefix
+
+During development, `.org.matrix.msc3914.rule.room.call` and
+`org.matrix.msc3914.call_started` is to be used instead of `.m.rule.room.call`
+and `call_started` respectively.