Crate ruma_events contains serializable types for the events in the Matrix specification that can be shared by client and server code.

All data exchanged over Matrix is expressed as an event. Different event types represent different actions, such as joining a room or sending a message. Events are stored and transmitted as simple JSON structures. While anyone can create a new event type for their own purposes, the Matrix specification defines a number of event types which are considered core to the protocol, and Matrix clients and servers must understand their semantics. ruma-events contains Rust types for each of the event types defined by the specification and facilities for extending the event system for custom event types.

ruma-events includes a Rust enum called EventType , which provides a simple enumeration of all the event types defined by the Matrix specification. Matrix event types are serialized to JSON strings in reverse domain name notation, although the core event types all use the special "m" TLD, e.g. m.room.message. EventType also includes a variant called Custom , which is a catch-all that stores a string containing the name of any event type that isn't part of the specification. EventType is used throughout ruma-events to identify and differentiate between events of different types.

Matrix defines three "kinds" of events:

Events, which are arbitrary JSON structures that have two required keys: type , which specifies the event's type

, which specifies the event's type content , which is a JSON object containing the "payload" of the event Room events, which are a superset of events and represent actions that occurred within the context of a Matrix room. They have at least the following additional keys: event_id , which is a unique identifier for the event

, which is a unique identifier for the event room_id , which is a unique identifier for the room in which the event occurred

, which is a unique identifier for the room in which the event occurred sender , which is the unique identifier of the Matrix user who created the event

, which is the unique identifier of the Matrix user who created the event Optionally, unsigned , which is a JSON object containing arbitrary additional metadata that is not digitally signed by Matrix homeservers. State events, which are a superset of room events and represent persistent state specific to a room, such as the room's member list or topic. Within a single room, state events of the same type and with the same "state key" will effectively "replace" the previous one, updating the room's state. They have at least the following additional keys: state_key , a string which serves as a sort of "sub-type." The state key allows a room to persist multiple state events of the same type. You can think of a room's state events as being a BTreeMap where the keys are the tuple (event_type, state_key) .

, a string which serves as a sort of "sub-type." The state key allows a room to persist multiple state events of the same type. You can think of a room's state events as being a where the keys are the tuple . Optionally, prev_content , a JSON object containing the content object from the previous event of the given (event_type, state_key) tuple in the given room.

ruma-events represents these three event kinds as traits, allowing any Rust type to serve as a Matrix event so long as it upholds the contract expected of its kind.

ruma-events includes Rust types for every one of the event types in the Matrix specification. To better organize the crate, these types live in separate modules with a hierarchy that matches the reverse domain name notation of the event type. For example, the m.room.message event lives at ruma_events::room::message::MessageEvent . Each type's module also contains a Rust type for that event type's content field, and any other supporting types required by the event's other fields.

Although any Rust type that implements Event , RoomEvent , or StateEvent can serve as a Matrix event type, ruma-events also includes a few convenience types for representing events that are not covered by the spec and not otherwise known by the application. CustomEvent , CustomRoomEvent , and CustomStateEvent are simple implementations of their respective event traits whose content field is simply a serde_json::Value value, which represents arbitrary JSON.

All concrete event types in ruma-events can be serialized via the Serialize trait from serde and can be deserialized from as EventJson<EventType> . In order to handle incoming data that may not conform to ruma-events ' strict definitions of event structures, deserialization will return EventJson::Err on error. This error covers both structurally invalid JSON data as well as structurally valid JSON that doesn't fulfill additional constraints the matrix specification defines for some event types. The error exposes the deserialized serde_json::Value so that developers can still work with the received event data. This makes it possible to deserialize a collection of events without the entire collection failing to deserialize due to a single invalid event. The "content" type for each event also implements Serialize and either TryFromRaw (enabling usage as EventJson<ContentType> for dedicated content types) or Deserialize (when the content is a type alias), allowing content to be converted to and from JSON indepedently of the surrounding event structure, if needed.

With the trait-based approach to events, it's easy to write generic collection types like Vec<Box<R: RoomEvent>> . However, there are APIs in the Matrix specification that involve heterogeneous collections of events, i.e. a list of events of different event types. Because Rust does not have a facility for arrays, vectors, or slices containing multiple concrete types, ruma-events provides special collection types for this purpose. The collection types are enums which effectively "wrap" each possible event type of a particular event "kind."

Because of the hierarchical nature of event kinds in Matrix, these collection types are divied into two modules, ruma_events::collections::all and ruma_events::collections::only . The "all" versions include every event type that implements the relevant event trait as well as more specific event traits. The "only" versions include only the event types that implement "at most" the relevant event trait.