Ports the event class to Rust.
The main difference here are:
1. There is now a single event class
2. We now validate a lot more at event construction time than we
previously did (we basically checked nothing before). This required some
changes to the tests, including
https://github.com/matrix-org/sytest/pull/1423
Reviewable commit-by-commit.
### Overview of Event Rust structure
The format of the event struct in Rust is quite different than that in
Python.
The top-level looks like:
```rust
pub struct Event {
/// The parsed event JSON.
fields: FormattedEvent,
/// The event ID. For format v1 this is read directly from the JSON;
/// for v2+ it is computed from the canonical-JSON hash at
/// construction time and cached here.
event_id: Arc<str>,
/// Synapse-internal per-event state that lives outside the federated
/// JSON (e.g. outlier flag, soft-failure, stream positions).
#[pyo3(get)]
internal_metadata: EventInternalMetadata,
/// The room version this event was parsed for.
#[pyo3(get)]
room_version: &'static RoomVersion,
/// `None` for accepted events; otherwise a short reason set by auth
/// when the event was rejected.
rejected_reason: Option<Box<str>>,
}
```
which includes the actual parsed event in `FormattedEvent`, plus the
rest of the event metadata.
```rust
pub struct FormattedEvent<E = Arc<EventFormatEnum>> {
#[serde(default)]
pub signatures: Signatures,
#[serde(default)]
pub unsigned: Unsigned,
#[serde(flatten)]
pub specific_fields: E,
#[serde(flatten)]
pub common_fields: Arc<EventCommonFields>,
}
```
The struct is further split into the common fields, format specific
fields, plus the signatures and unsigned. We split out the signature and
unsigned fields as they are mutable, so when we clone the event we can
still share the common and specific fields and only copy signature and
unsigned.
The `specific_fields` are the fields that depend on the format version.
They can either be a specific format (e.g. `E = EventFormatV1`) or a
type-erased enum `EventFormatEnum` that is across all room versions:
```rust
pub enum EventFormatEnum {
V1(EventFormatV1),
V2V3(EventFormatV2V3),
V4(EventFormatV4),
VMSC4242(EventFormatVMSC4242),
}
```
For example:
```rust
/// Shared flat-list encoding of `auth_events` and `prev_events`, reused
/// by every format from v2/v3 onwards.
#[derive(Serialize, Deserialize)]
pub struct SimpleAuthPrevEvents {
pub auth_events: Vec<String>,
pub prev_events: Vec<String>,
}
/// Version-specific fields for room versions 3-10.
#[derive(Serialize, Deserialize)]
pub struct EventFormatV2V3 {
pub room_id: Box<str>,
#[serde(flatten)]
pub auth_prev_events: SimpleAuthPrevEvents,
}
```
### Dev notes
As discussed in
[`#element-backend-internal:matrix.org`](https://matrix.to/#/!SGNQGPGUwtcPBUotTL:matrix.org/$3gTjDO440GbAz57cXcCawwiyFLiD0crrarvS1uhzKOY?via=jki.re&via=element.io&via=matrix.org)
---------
Co-authored-by: Eric Eastwood <erice@element.io>
When we port the `Event` class to Rust, the constructor will check for
the existence of required fields. To support that, we tidy up the test
code where we construct fake events to add all the required fields.
There should be no behavioural changes.
Review commit-by-commit.
