66 lines
2.1 KiB
Markdown
66 lines
2.1 KiB
Markdown
# MSC3966: `event_property_contains` push rule condition
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[MSC3952](https://github.com/matrix-org/matrix-spec-proposals/pull/3952):
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Intentional mentions requires a way for a push rule condition to search
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for a value in a JSON array of values. This proposes implementing it in a
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generic fashion for re-use with other push rules.
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## Proposal
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A new push rule condition `event_property_contains` is added which acts like
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[`event_match`](https://spec.matrix.org/v1.5/client-server-api/#conditions-1),
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but searches an array for an exact value. The values must match exactly and be a
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non-compound JSON type allowed by [canonical JSON](https://spec.matrix.org/v1.5/appendices/#canonical-json):
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i.e. strings, `null`, `true`, `false` and integers.
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An example condition would look like:
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```json
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{
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"kind": "event_property_contains",
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"key": "content.my_array",
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"value": "foo"
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}
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```
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This would match an event with content:
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```json
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{
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"content": {
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"my_array": ["foo", true]
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}
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}
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```
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And it would not match if `my_array` was empty or did not exist.
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## Potential issues
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None foreseen.
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## Alternatives
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[MSC3887](https://github.com/matrix-org/matrix-spec-proposals/pull/3887) is an
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unfinished alternative which suggests allowing [`event_match`](https://spec.matrix.org/v1.5/client-server-api/#conditions-1)
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to search in arrays without other changes.
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## Security considerations
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It is possible for the event content to contain very large arrays (the
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[maximum event size](https://spec.matrix.org/v1.5/client-server-api/#size-limits)
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is 65,536 bytes, if most of that contains an array of empty strings you get
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somewhere around 20,000 entries). Iterating through arrays of this size should
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not be a problem for modern computers, especially since the push rule searches
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for *exact* matches.
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## Unstable prefix
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During development `org.matrix.msc3966.exact_event_property_contains` shall be
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used in place of `event_property_contains`.
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## Dependencies
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This MSC has similar semantics to [MSC3758](https://github.com/matrix-org/matrix-spec-proposals/pull/3758)
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(and the implementation builds on that), but it does not strictly depend on it.
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