matrix-spec-proposals/proposals/2540-stricter-event-validation.md

# MSC2540: Stricter event validation: JSON compliance

## Background

There has been [prior discussions](https://github.com/matrix-org/matrix-doc/issues/1646)
about validating events more strictly. This MSC proposes fixing a small piece of
this: JSON compliance.

The [Canonical JSON](https://matrix.org/docs/spec/appendices#canonical-json)
specification requires that numbers that are serialized in JSON are integers in
the range of [-2 ^ 53 + 1, 2 ^ 53 - 1], which matches the requirements of
[section 6 of RFC 7159](https://tools.ietf.org/html/rfc7159). Note that it is
not explicit, but all floats are invalid.

It is worth mentioning that there are common extensions to JSON which produce 
invalid JSON according to the Matrix specification, some programming langauges
even support these by default. One common additional feature is handling
"special" float values: `Infinity`, `-Infinity`, and `NaN`.


## Proposal

In a future room version, Matrix server implementations are to strictly enforce
the JSON compliance of the Canonical JSON specification for events.

The rationale for doing this in a future room version is to avoid a split brain
room -- where some federated servers believe an event is valid and others reject
it as invalid. Rooms will be able to opt into this behavior as part of a room
version upgrade.


## Potential issues

N/A


## Alternatives

It could be argued that this MSC is unnecessary since it does not add any new
requirements for handling of JSON data. Unfortunately starting to enforce these 
requirements in current rooms could cause federation to break as homeservers
will disagree on whether events are valid.


## Security considerations

N/A


## Unstable prefix

A room versions of `org.matrix.strict_canonicaljson` until a future room version
is available. This room version will use
[room version 5](https://matrix.org/docs/spec/rooms/v5) as base and include the
above modifications.