Function check_send_content 

pub(crate) async fn check_send_content(
    services: &Services,
    sender_user: &UserId,
    room_id: &RoomId,
    event_type: &MessageLikeEventType,
    content: &Raw<AnyMessageLikeEventContent>,
) -> Result

Applies the room’s content rules for sending a message event, under the room lock.

Refuses a duplicate reaction, a call invite in a public room, and a thread rooted at an event that itself carries a relation.