max / makenotwork

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1	//! What the server sends down the stream.
2	//!
3	//! Deliberately four variants. Presence, typing, join, and leave are all absent
4	//! by decision: typing in particular is the largest driver of event volume, and
5	//! both consumers run under a hard 512M cgroup cap where an OOM restarts the
6	//! whole site.
7
8	use serde::{Deserialize, Serialize};
9
10	use crate::ids::{MessageId, UserId};
11	use crate::message::Message;
12
13	/// A single frame on the stream.
14	#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
15	#[serde(tag = "type", rename_all = "snake_case")]
16	pub enum ChatEvent {
17	/// A new message.
18	Message(Message),
19
20	/// One message removed, by its author or by a moderator.
21	Delete { id: MessageId },
22
23	/// Every message from one author removed at once, following a ban.
24	///
25	/// One event rather than N `Delete`s: a ban is issued on a hot path and the
26	/// deletion is a single statement keyed by (room, author), so fanning it out
27	/// per message would put an unbounded burst through every open connection
28	/// for no gain.
29	Purge { author_id: UserId },
30
31	/// The connection fell behind and messages were dropped from the broadcast
32	/// buffer. The client re-fetches from its cursor.
33	///
34	/// Never silently swallowed. SyncKit's SSE can ignore lag because its clients
35	/// re-pull on their own schedule; a chat client that ignored it would show a
36	/// room with a hole in it and no indication anything was missing.
37	Gap,
38	}
39
40	impl ChatEvent {
41	/// The SSE event name for this frame.
42	pub fn name(&self) -> &'static str {
43	match self {
44	Self::Message(_) => "message",
45	Self::Delete { .. } => "delete",
46	Self::Purge { .. } => "purge",
47	Self::Gap => "gap",
48	}
49	}
50
51	/// The cursor a client should record after handling this frame, if any.
52	///
53	/// Only `Message` advances the cursor. A deletion is not a position in the
54	/// room, and reconnecting past a `Gap` is exactly what the cursor is for.
55	pub fn cursor(&self) -> Option<MessageId> {
56	match self {
57	Self::Message(m) => Some(m.id),
58	_ => None,
59	}
60	}
61	}
62
63	#[cfg(test)]
64	mod tests {
65	use super::*;
66	use crate::ids::RoomId;
67	use uuid::Uuid;
68
69	fn message(id: i64) -> Message {
70	Message {
71	id: MessageId(id),
72	room_id: RoomId(Uuid::nil()),
73	author_id: UserId(Uuid::nil()),
74	body_html: "hi".into(),
75	created_at: 0,
76	nonce: None,
77	}
78	}
79
80	#[test]
81	fn only_messages_advance_the_cursor() {
82	assert_eq!(ChatEvent::Message(message(7)).cursor(), Some(MessageId(7)));
83	assert_eq!(ChatEvent::Delete { id: MessageId(7) }.cursor(), None);
84	assert_eq!(
85	ChatEvent::Purge {
86	author_id: UserId(Uuid::nil())
87	}
88	.cursor(),
89	None
90	);
91	assert_eq!(ChatEvent::Gap.cursor(), None);
92	}
93
94	#[test]
95	fn serializes_tagged_for_the_client() {
96	let json = serde_json::to_string(&ChatEvent::Delete { id: MessageId(3) }).unwrap();
97	assert!(json.contains(r#""type":"delete""#), "{json}");
98	}
99
100	#[test]
101	fn nonce_is_omitted_when_absent() {
102	let json = serde_json::to_string(&message(1)).unwrap();
103	assert!(!json.contains("nonce"), "{json}");
104	}
105	}
106