sync.rs

					.expect("event is valid, we just created it"),
			)
			.expect("event is valid, we just created it"),
		);
	}

	// Save the state after this sync so we can send the correct state diff next
	// sync
	services()
		.rooms
		.user
		.associate_token_shortstatehash(room_id, next_batch, current_shortstatehash)?;

	Ok(JoinedRoom {
		account_data: RoomAccountData {
			events: services()
				.account_data
				.changes_since(Some(room_id), sender_user, since)?
				.into_iter()
				.filter_map(|(_, v)| {
					serde_json::from_str(v.json().get())
						.map_err(|_| Error::bad_database("Invalid account event in database."))
						.ok()
				})
				.collect(),
		},
		summary: RoomSummary {
			heroes,
			joined_member_count: joined_member_count.map(|n| (n as u32).into()),
			invited_member_count: invited_member_count.map(|n| (n as u32).into()),
		},
		unread_notifications: UnreadNotificationsCount {
			highlight_count,
			notification_count,
		},
		timeline: Timeline {
			limited: limited || joined_since_last_sync,
			prev_batch,
			events: room_events,
		},
		state: State {
			events: state_events
				.iter()
				.map(|pdu| pdu.to_sync_state_event())
				.collect(),
		},
		ephemeral: Ephemeral {
			events: edus,
		},
		unread_thread_notifications: BTreeMap::new(),
	})
}

fn load_timeline(
	sender_user: &UserId, room_id: &RoomId, roomsincecount: PduCount, limit: u64,
) -> Result<(Vec<(PduCount, PduEvent)>, bool), Error> {
	let timeline_pdus;
	let limited;
	if services()
		.rooms
		.timeline
		.last_timeline_count(sender_user, room_id)?
		> roomsincecount
	{
		let mut non_timeline_pdus = services()
			.rooms
			.timeline
			.pdus_until(sender_user, room_id, PduCount::max())?
			.filter_map(|r| {
				// Filter out buggy events
				if r.is_err() {
					error!("Bad pdu in pdus_since: {:?}", r);
				}
				r.ok()
			})
			.take_while(|(pducount, _)| pducount > &roomsincecount);

		// Take the last events for the timeline
		timeline_pdus = non_timeline_pdus
			.by_ref()
			.take(limit as usize)
			.collect::<Vec<_>>()
			.into_iter()
			.rev()
			.collect::<Vec<_>>();

		// They /sync response doesn't always return all messages, so we say the output
		// is limited unless there are events in non_timeline_pdus
		limited = non_timeline_pdus.next().is_some();
	} else {
		timeline_pdus = Vec::new();
		limited = false;
	}
	Ok((timeline_pdus, limited))
}

fn share_encrypted_room(sender_user: &UserId, user_id: &UserId, ignore_room: &RoomId) -> Result<bool> {
	Ok(services()
		.rooms
		.user
		.get_shared_rooms(vec![sender_user.to_owned(), user_id.to_owned()])?
		.filter_map(Result::ok)
		.filter(|room_id| room_id != ignore_room)
		.filter_map(|other_room_id| {
			Some(
				services()
					.rooms
					.state_accessor
					.room_state_get(&other_room_id, &StateEventType::RoomEncryption, "")
					.ok()?
					.is_some(),
			)
		})
		.any(|encrypted| encrypted))
}

/// POST `/_matrix/client/unstable/org.matrix.msc3575/sync`
///
/// Sliding Sync endpoint (future endpoint: `/_matrix/client/v4/sync`)
pub async fn sync_events_v4_route(
	body: Ruma<sync_events::v4::Request>,
) -> Result<sync_events::v4::Response, RumaResponse<UiaaResponse>> {
	let sender_user = body.sender_user.expect("user is authenticated");
	let sender_device = body.sender_device.expect("user is authenticated");
	let mut body = body.body;
	// Setup watchers, so if there's no response, we can wait for them
	let watcher = services().globals.watch(&sender_user, &sender_device);

	let next_batch = services().globals.next_count()?;

	let globalsince = body
		.pos
		.as_ref()
		.and_then(|string| string.parse().ok())
		.unwrap_or(0);

	if globalsince == 0 {
		if let Some(conn_id) = &body.conn_id {
			services().users.forget_sync_request_connection(
				sender_user.clone(),
				sender_device.clone(),
				conn_id.clone(),
			);
		}
	}

	// Get sticky parameters from cache
	let known_rooms =
		services()
			.users
			.update_sync_request_with_cache(sender_user.clone(), sender_device.clone(), &mut body);

	let all_joined_rooms = services()
		.rooms
		.state_cache
		.rooms_joined(&sender_user)
		.filter_map(Result::ok)
		.collect::<Vec<_>>();

	if body.extensions.to_device.enabled.unwrap_or(false) {
		services()
			.users
			.remove_to_device_events(&sender_user, &sender_device, globalsince)?;
	}

	let mut left_encrypted_users = HashSet::new(); // Users that have left any encrypted rooms the sender was in
	let mut device_list_changes = HashSet::new();
	let mut device_list_left = HashSet::new();

	if body.extensions.e2ee.enabled.unwrap_or(false) {
		// Look for device list updates of this account
		device_list_changes.extend(
			services()
				.users
				.keys_changed(sender_user.as_ref(), globalsince, None)
				.filter_map(Result::ok),
		);

		for room_id in &all_joined_rooms {
			let Some(current_shortstatehash) = services().rooms.state.get_room_shortstatehash(room_id)? else {
				error!("Room {} has no state", room_id);
				continue;
			};

			let since_shortstatehash = services()
				.rooms
				.user
				.get_token_shortstatehash(room_id, globalsince)?;

			let since_sender_member: Option<RoomMemberEventContent> = since_shortstatehash
				.and_then(|shortstatehash| {
					services()
						.rooms
						.state_accessor
						.state_get(shortstatehash, &StateEventType::RoomMember, sender_user.as_str())
						.transpose()
				})
				.transpose()?
				.and_then(|pdu| {
					serde_json::from_str(pdu.content.get())
						.map_err(|_| Error::bad_database("Invalid PDU in database."))
						.ok()
				});

			let encrypted_room = services()
				.rooms
				.state_accessor
				.state_get(current_shortstatehash, &StateEventType::RoomEncryption, "")?
				.is_some();

			if let Some(since_shortstatehash) = since_shortstatehash {
				// Skip if there are only timeline changes
				if since_shortstatehash == current_shortstatehash {
					continue;
				}

				let since_encryption = services().rooms.state_accessor.state_get(
					since_shortstatehash,
					&StateEventType::RoomEncryption,
					"",
				)?;

				let joined_since_last_sync =
					since_sender_member.map_or(true, |member| member.membership != MembershipState::Join);

				let new_encrypted_room = encrypted_room && since_encryption.is_none();
				if encrypted_room {
					let current_state_ids = services()
						.rooms
						.state_accessor
						.state_full_ids(current_shortstatehash)
						.await?;
					let since_state_ids = services()
						.rooms
						.state_accessor
						.state_full_ids(since_shortstatehash)
						.await?;

					for (key, id) in current_state_ids {
						if since_state_ids.get(&key) != Some(&id) {
							let Some(pdu) = services().rooms.timeline.get_pdu(&id)? else {
								error!("Pdu in state not found: {}", id);
								continue;
							};
							if pdu.kind == TimelineEventType::RoomMember {
								if let Some(state_key) = &pdu.state_key {
									let user_id = UserId::parse(state_key.clone())
										.map_err(|_| Error::bad_database("Invalid UserId in member PDU."))?;

									if user_id == sender_user {
										continue;
									}

									let new_membership =
										serde_json::from_str::<RoomMemberEventContent>(pdu.content.get())
											.map_err(|_| Error::bad_database("Invalid PDU in database."))?
											.membership;

									match new_membership {
										MembershipState::Join => {
											// A new user joined an encrypted room
											if !share_encrypted_room(&sender_user, &user_id, room_id)? {
												device_list_changes.insert(user_id);
											}
										},
										MembershipState::Leave => {
											// Write down users that have left encrypted rooms we are in
											left_encrypted_users.insert(user_id);
										},
										_ => {},
									}
								}
							}
						}
					}
					if joined_since_last_sync || new_encrypted_room {
						// If the user is in a new encrypted room, give them all joined users
						device_list_changes.extend(
							services()
								.rooms
								.state_cache
								.room_members(room_id)
								.flatten()
								.filter(|user_id| {
									// Don't send key updates from the sender to the sender
									&sender_user != user_id
								})
								.filter(|user_id| {
									// Only send keys if the sender doesn't share an encrypted room with the target
									// already
									!share_encrypted_room(&sender_user, user_id, room_id).unwrap_or(false)
								}),
						);
					}
				}
			}
			// Look for device list updates in this room
			device_list_changes.extend(
				services()
					.users
					.keys_changed(room_id.as_ref(), globalsince, None)
					.filter_map(Result::ok),
			);
		}
		for user_id in left_encrypted_users {
			let dont_share_encrypted_room = services()
				.rooms
				.user
				.get_shared_rooms(vec![sender_user.clone(), user_id.clone()])?
				.filter_map(Result::ok)
				.filter_map(|other_room_id| {
					Some(
						services()
							.rooms
							.state_accessor
							.room_state_get(&other_room_id, &StateEventType::RoomEncryption, "")
							.ok()?
							.is_some(),
					)
				})
				.all(|encrypted| !encrypted);
			// If the user doesn't share an encrypted room with the target anymore, we need
			// to tell them
			if dont_share_encrypted_room {
				device_list_left.insert(user_id);
			}
		}
	}

	let mut lists = BTreeMap::new();
	let mut todo_rooms = BTreeMap::new(); // and required state

	for (list_id, list) in body.lists {
		if list.filters.and_then(|f| f.is_invite).unwrap_or(false) {
			continue;
		}

		let mut new_known_rooms = BTreeSet::new();

		lists.insert(
			list_id.clone(),
			sync_events::v4::SyncList {
				ops: list
					.ranges
					.into_iter()
					.map(|mut r| {
						r.0 =
							r.0.clamp(uint!(0), UInt::from(all_joined_rooms.len() as u32 - 1));
						r.1 =
							r.1.clamp(r.0, UInt::from(all_joined_rooms.len() as u32 - 1));
						let room_ids = all_joined_rooms[(u64::from(r.0) as usize)..=(u64::from(r.1) as usize)].to_vec();
						new_known_rooms.extend(room_ids.iter().cloned());
						for room_id in &room_ids {
							let todo_room = todo_rooms
								.entry(room_id.clone())
								.or_insert((BTreeSet::new(), 0, u64::MAX));
							let limit = list
								.room_details
								.timeline_limit
								.map_or(10, u64::from)
								.min(100);
							todo_room
								.0
								.extend(list.room_details.required_state.iter().cloned());
							todo_room.1 = todo_room.1.max(limit);
							// 0 means unknown because it got out of date
							todo_room.2 = todo_room.2.min(
								known_rooms
									.get(&list_id)
									.and_then(|k| k.get(room_id))
									.copied()
									.unwrap_or(0),
							);
						}
						sync_events::v4::SyncOp {
							op: SlidingOp::Sync,
							range: Some(r),
							index: None,
							room_ids,
							room_id: None,
						}
					})
					.collect(),
				count: UInt::from(all_joined_rooms.len() as u32),
			},
		);

		if let Some(conn_id) = &body.conn_id {
			services().users.update_sync_known_rooms(
				sender_user.clone(),
				sender_device.clone(),
				conn_id.clone(),
				list_id,
				new_known_rooms,
				globalsince,
			);
		}
	}

	let mut known_subscription_rooms = BTreeSet::new();
	for (room_id, room) in &body.room_subscriptions {
		if !services().rooms.metadata.exists(room_id)? {
			continue;
		}
		let todo_room = todo_rooms
			.entry(room_id.clone())
			.or_insert((BTreeSet::new(), 0, u64::MAX));
		let limit = room.timeline_limit.map_or(10, u64::from).min(100);
		todo_room.0.extend(room.required_state.iter().cloned());
		todo_room.1 = todo_room.1.max(limit);
		// 0 means unknown because it got out of date
		todo_room.2 = todo_room.2.min(
			known_rooms
				.get("subscriptions")
				.and_then(|k| k.get(room_id))
				.copied()
				.unwrap_or(0),
		);
		known_subscription_rooms.insert(room_id.clone());
	}

	for r in body.unsubscribe_rooms {
		known_subscription_rooms.remove(&r);
		body.room_subscriptions.remove(&r);
	}

	if let Some(conn_id) = &body.conn_id {
		services().users.update_sync_known_rooms(
			sender_user.clone(),
			sender_device.clone(),
			conn_id.clone(),
			"subscriptions".to_owned(),
			known_subscription_rooms,
			globalsince,
		);
	}

	if let Some(conn_id) = &body.conn_id {
		services().users.update_sync_subscriptions(
			sender_user.clone(),
			sender_device.clone(),
			conn_id.clone(),
			body.room_subscriptions,
		);
	}

	let mut rooms = BTreeMap::new();
	for (room_id, (required_state_request, timeline_limit, roomsince)) in &todo_rooms {
		let roomsincecount = PduCount::Normal(*roomsince);

		let (timeline_pdus, limited) = load_timeline(&sender_user, room_id, roomsincecount, *timeline_limit)?;

		if roomsince != &0 && timeline_pdus.is_empty() {
			continue;
		}

		let prev_batch = timeline_pdus
			.first()
			.map_or(Ok::<_, Error>(None), |(pdu_count, _)| {
				Ok(Some(match pdu_count {
					PduCount::Backfilled(_) => {
						error!("timeline in backfill state?!");
						"0".to_owned()
					},
					PduCount::Normal(c) => c.to_string(),
				}))
			})?
			.or_else(|| {
				if roomsince != &0 {
					Some(roomsince.to_string())
				} else {
					None
				}
			});

		let room_events: Vec<_> = timeline_pdus
			.iter()
			.map(|(_, pdu)| pdu.to_sync_room_event())
			.collect();

		let required_state = required_state_request
			.iter()
			.map(|state| {
				services()
					.rooms
					.state_accessor
					.room_state_get(room_id, &state.0, &state.1)
			})
			.filter_map(Result::ok)
			.flatten()
			.map(|state| state.to_sync_state_event())
			.collect();

		// Heroes
		let heroes = services()
			.rooms
			.state_cache
			.room_members(room_id)
			.filter_map(Result::ok)
			.filter(|member| member != &sender_user)
			.map(|member| {
				Ok::<_, Error>(
					services()
						.rooms
						.state_accessor
						.get_member(room_id, &member)?
						.map(|memberevent| {
							(
								memberevent
									.displayname
									.unwrap_or_else(|| member.to_string()),
								memberevent.avatar_url,
							)
						}),
				)
			})
			.filter_map(Result::ok)
			.flatten()
			.take(5)
			.collect::<Vec<_>>();
		let name = match heroes.len().cmp(&(1_usize)) {
			Ordering::Greater => {
				let last = heroes[0].0.clone();
				Some(
					heroes[1..]
						.iter()
						.map(|h| h.0.clone())
						.collect::<Vec<_>>()
						.join(", ") + " and " + &last,
				)
			},
			Ordering::Equal => Some(heroes[0].0.clone()),
			Ordering::Less => None,
		};

		let heroes_avatar = if heroes.len() == 1 {
			heroes[0].1.clone()
		} else {
			None
		};

		rooms.insert(
			room_id.clone(),
			sync_events::v4::SlidingSyncRoom {
				name: services().rooms.state_accessor.get_name(room_id)?.or(name),
				avatar: if let Some(heroes_avatar) = heroes_avatar {
					ruma::JsOption::Some(heroes_avatar)
				} else {
					match services().rooms.state_accessor.get_avatar(room_id)? {
						ruma::JsOption::Some(avatar) => ruma::JsOption::from_option(avatar.url),
						ruma::JsOption::Null => ruma::JsOption::Null,
						ruma::JsOption::Undefined => ruma::JsOption::Undefined,
					}
				},
				initial: Some(roomsince == &0),
				is_dm: None,
				invite_state: None,
				unread_notifications: UnreadNotificationsCount {
					highlight_count: Some(
						services()
							.rooms
							.user
							.highlight_count(&sender_user, room_id)?
							.try_into()
							.expect("notification count can't go that high"),
					),
					notification_count: Some(
						services()
							.rooms
							.user
							.notification_count(&sender_user, room_id)?
							.try_into()
							.expect("notification count can't go that high"),
					),
				},
				timeline: room_events,
				required_state,
				prev_batch,
				limited,
				joined_count: Some(
					(services()
						.rooms
						.state_cache
						.room_joined_count(room_id)?
						.unwrap_or(0) as u32)
						.into(),
				),
				invited_count: Some(
					(services()
						.rooms
						.state_cache
						.room_invited_count(room_id)?
						.unwrap_or(0) as u32)
						.into(),
				),
				num_live: None, // Count events in timeline greater than global sync counter
				timestamp: None,
			},
		);
	}

	if rooms
		.iter()
		.all(|(_, r)| r.timeline.is_empty() && r.required_state.is_empty())
	{
		// Hang a few seconds so requests are not spammed
		// Stop hanging if new info arrives
		let mut duration = body.timeout.unwrap_or(Duration::from_secs(30));
		if duration.as_secs() > 30 {
			duration = Duration::from_secs(30);
		}
		_ = tokio::time::timeout(duration, watcher).await;
	}

	Ok(sync_events::v4::Response {
		initial: globalsince == 0,
		txn_id: body.txn_id.clone(),
		pos: next_batch.to_string(),
		lists,
		rooms,
		extensions: sync_events::v4::Extensions {
			to_device: if body.extensions.to_device.enabled.unwrap_or(false) {
				Some(sync_events::v4::ToDevice {
					events: services()
						.users
						.get_to_device_events(&sender_user, &sender_device)?,
					next_batch: next_batch.to_string(),
				})
			} else {
				None
			},
			e2ee: sync_events::v4::E2EE {
				device_lists: DeviceLists {
					changed: device_list_changes.into_iter().collect(),
					left: device_list_left.into_iter().collect(),
				},
				device_one_time_keys_count: services()
					.users
					.count_one_time_keys(&sender_user, &sender_device)?,
				// Fallback keys are not yet supported
				device_unused_fallback_key_types: None,
			},
			account_data: sync_events::v4::AccountData {
				global: if body.extensions.account_data.enabled.unwrap_or(false) {
					services()
						.account_data
						.changes_since(None, &sender_user, globalsince)?
						.into_iter()
						.filter_map(|(_, v)| {
							serde_json::from_str(v.json().get())
								.map_err(|_| Error::bad_database("Invalid account event in database."))
								.ok()
						})
						.collect()
				} else {
					Vec::new()
				},
				rooms: BTreeMap::new(),
			},
			receipts: sync_events::v4::Receipts {
				rooms: BTreeMap::new(),
			},
			typing: sync_events::v4::Typing {
				rooms: BTreeMap::new(),
			},
		},
		delta_token: None,
	})
}