matrix-spec-proposals/proposals/3758-expand-push-rule-conditions.md

MSC3758: Add event_property_is push rule condition kind

Currently the only condition used to match event content for push rules is the event_match kind. This compares a glob-style string against a string value within the event dictionary. The event dictionary is flattened before conditions are checked to enable matching nested values.

This approach is currently limited to only checking for string values within the event dictionary (at any level). This MSC proposes a new exact match type for event content that works with all JSON types.

Proposal

Exact matching event data

We propose a new type of condition, event_property_is. Similar to the current event_match (link to spec), this condition takes two parameters: value and key. The exact match compares the value to the event data associated with key exactly. Both type and content (when a string) should be identical (include case). This allows for matching all non-compound JSON types allowed by canonical JSON: i.e. strings, null, true, false and integers. This also provides a simpler exact string matching mechanism (and any associated performance gains on implementation side without globbing).

An example condition may look like (encoded as a JSON object):

{
  "kind": "event_property_is",
  "key": "content.is_something",
  "value": true
}

Alternatives

MSC3862 proposes an alternative solution by converting non-string JSON objects to strings in the event_match condition type.

Security considerations

None.

Future extensions

A future MSC may wish to define the behavior of event_property_is when used with a JSON object or array.

MSC3887 is a related MSC which attempts to define behavior for searching for a value inside of an array.

Unstable prefix

While still not part of the Matrix spec, the new push rule condition should be com.beeper.msc3758.exact_event_match instead of event_property_is, e.g.:

{
  "kind": "com.beeper.msc3758.exact_event_match",
  "key": "..."
}

Dependencies

None.