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# MSC2540: Stricter event validation: JSON compliance
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## Background
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There has been [prior discussions](https://github.com/matrix-org/matrix-doc/issues/1646)
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about validating events more strictly. This MSC proposes fixing a small piece of
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this: JSON compliance.
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The [Canonical JSON](https://matrix.org/docs/spec/appendices#canonical-json)
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specification requires that numbers that are serialized in JSON are integers in
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the inclusive range of `[-(2^53) + 1, (2^53) - 1]`, which matches the requirements of
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[section 6 of RFC 7159](https://tools.ietf.org/html/rfc7159). Note that it is
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not explicit, but all floats are invalid.
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It is worth mentioning that there are common extensions to JSON which produce
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invalid JSON according to the Matrix specification; some programming languages
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even support these by default. One common additional feature is handling
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"special" float values: `Infinity`, `-Infinity`, and `NaN`.
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## Proposal
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In a future room version, homeserver implementations are to strictly enforce
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the JSON compliance of the Canonical JSON specification for events.
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Non-compliant events should be treated like any other malformed event,
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for example by rejecting the request with an HTTP 400 error with `M_BAD_JSON`,
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or by discarding the event.
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The rationale for doing this in a future room version is to avoid a split brain
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room -- where some federated servers believe an event is valid and others reject
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it as invalid. Rooms will be able to opt into this behavior as part of a room
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version upgrade.
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Homeserver implementations are not to strictly enforce this JSON compliance in
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[room versions 1, 2, 3, 4, and 5](https://matrix.org/docs/spec/#complete-list-of-room-versions).
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The rationale is essentially the same as why a future room version is necessary:
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this ensures that all federated servers treat the same events as valid.
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## Potential issues
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Homeserver implementations might include JSON parsers which are stricter than
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others. It may not be worthwhile or reasonable to loosen those restrictions for
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stable room versions.
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## Alternatives
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It could be argued that this MSC is unnecessary since it does not add any new
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requirements for handling of JSON data. Unfortunately starting to enforce these
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requirements in current rooms could cause federation to break as homeservers
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will disagree on whether events are valid.
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## Security considerations
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N/A
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## Unstable prefix
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A room version of `org.matrix.strict_canonicaljson` until a future room version
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is available. This room version will use
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[room version 5](https://matrix.org/docs/spec/rooms/v5) as base and include the
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above modifications.
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