sync.rs

use std::{
	cmp::Ordering,
	collections::{hash_map::Entry, BTreeMap, BTreeSet, HashMap, HashSet},
	sync::Arc,
	time::Duration,
};

use ruma::{
	api::client::{
		filter::{FilterDefinition, LazyLoadOptions},
		sync::sync_events::{
			self,
			v3::{
				Ephemeral, Filter, GlobalAccountData, InviteState, InvitedRoom, JoinedRoom, LeftRoom, Presence,
				RoomAccountData, RoomSummary, Rooms, State, Timeline, ToDevice,
			},
			v4::SlidingOp,
			DeviceLists, UnreadNotificationsCount,
		},
		uiaa::UiaaResponse,
	},
	events::{
		presence::PresenceEvent,
		room::member::{MembershipState, RoomMemberEventContent},
		StateEventType, TimelineEventType,
	},
	serde::Raw,
	uint, DeviceId, EventId, OwnedDeviceId, OwnedUserId, RoomId, UInt, UserId,
};
use tokio::sync::watch::Sender;
use tracing::{debug, error};

use crate::{
	service::{pdu::EventHash, rooms::timeline::PduCount},
	services, utils, Error, PduEvent, Result, Ruma, RumaResponse,
};

/// # `GET /_matrix/client/r0/sync`
///
/// Synchronize the client's state with the latest state on the server.
///
/// - This endpoint takes a `since` parameter which should be the `next_batch`
///   value from a
/// previous request for incremental syncs.
///
/// Calling this endpoint without a `since` parameter returns:
/// - Some of the most recent events of each timeline
/// - Notification counts for each room
/// - Joined and invited member counts, heroes
/// - All state events
///
/// Calling this endpoint with a `since` parameter from a previous `next_batch`
/// returns: For joined rooms:
/// - Some of the most recent events of each timeline that happened after since
/// - If user joined the room after since: All state events (unless lazy loading
///   is activated) and
/// all device list updates in that room
/// - If the user was already in the room: A list of all events that are in the
///   state now, but were
/// not in the state at `since`
/// - If the state we send contains a member event: Joined and invited member
///   counts, heroes
/// - Device list updates that happened after `since`
/// - If there are events in the timeline we send or the user send updated his
///   read mark: Notification counts
/// - EDUs that are active now (read receipts, typing updates, presence)
/// - TODO: Allow multiple sync streams to support Pantalaimon
///
/// For invited rooms:
/// - If the user was invited after `since`: A subset of the state of the room
///   at the point of the invite
///
/// For left rooms:
/// - If the user left after `since`: `prev_batch` token, empty state (TODO:
///   subset of the state at the point of the leave)
///
/// - Sync is handled in an async task, multiple requests from the same device
///   with the same
/// `since` will be cached
pub(crate) async fn sync_events_route(
	body: Ruma<sync_events::v3::Request>,
) -> Result<sync_events::v3::Response, RumaResponse<UiaaResponse>> {
	let sender_user = body.sender_user.expect("user is authenticated");
	let sender_device = body.sender_device.expect("user is authenticated");
	let body = body.body;

	let mut rx = match services()
		.globals
		.sync_receivers
		.write()
		.await
		.entry((sender_user.clone(), sender_device.clone()))
	{
		Entry::Vacant(v) => {
			let (tx, rx) = tokio::sync::watch::channel(None);

			v.insert((body.since.clone(), rx.clone()));

			tokio::spawn(sync_helper_wrapper(sender_user.clone(), sender_device.clone(), body, tx));

			rx
		},
		Entry::Occupied(mut o) => {
			if o.get().0 != body.since {
				let (tx, rx) = tokio::sync::watch::channel(None);

				o.insert((body.since.clone(), rx.clone()));

				debug!("Sync started for {sender_user}");

				tokio::spawn(sync_helper_wrapper(sender_user.clone(), sender_device.clone(), body, tx));

				rx
			} else {
				o.get().1.clone()
			}
		},
	};

	let we_have_to_wait = rx.borrow().is_none();
	if we_have_to_wait {
		if let Err(e) = rx.changed().await {
			error!("Error waiting for sync: {}", e);
		}
	}

	let result = match rx
		.borrow()
		.as_ref()
		.expect("When sync channel changes it's always set to some")
	{
		Ok(response) => Ok(response.clone()),
		Err(error) => Err(error.to_response()),
	};

	result
}

async fn sync_helper_wrapper(
	sender_user: OwnedUserId, sender_device: OwnedDeviceId, body: sync_events::v3::Request,
	tx: Sender<Option<Result<sync_events::v3::Response>>>,
) {
	let since = body.since.clone();

	let r = sync_helper(sender_user.clone(), sender_device.clone(), body).await;

	if let Ok((_, caching_allowed)) = r {
		if !caching_allowed {
			match services()
				.globals
				.sync_receivers
				.write()
				.await
				.entry((sender_user, sender_device))
			{
				Entry::Occupied(o) => {
					// Only remove if the device didn't start a different /sync already
					if o.get().0 == since {
						o.remove();
					}
				},
				Entry::Vacant(_) => {},
			}
		}
	}

	_ = tx.send(Some(r.map(|(r, _)| r)));
}

async fn sync_helper(
	sender_user: OwnedUserId,
	sender_device: OwnedDeviceId,
	body: sync_events::v3::Request,
	// bool = caching allowed
) -> Result<(sync_events::v3::Response, bool), Error> {
	// Presence update
	if services().globals.allow_local_presence() {
		services()
			.presence
			.ping_presence(&sender_user, &body.set_presence)?;
	}

	// 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.current_count()?;
	let next_batchcount = PduCount::Normal(next_batch);
	let next_batch_string = next_batch.to_string();

	// Load filter
	let filter = match body.filter {
		None => FilterDefinition::default(),
		Some(Filter::FilterDefinition(filter)) => filter,
		Some(Filter::FilterId(filter_id)) => services()
			.users
			.get_filter(&sender_user, &filter_id)?
			.unwrap_or_default(),
	};

	let (lazy_load_enabled, lazy_load_send_redundant) = match filter.room.state.lazy_load_options {
		LazyLoadOptions::Enabled {
			include_redundant_members: redundant,
		} => (true, redundant),
		LazyLoadOptions::Disabled => (false, false),
	};

	let full_state = body.full_state;

	let mut joined_rooms = BTreeMap::new();
	let since = body
		.since
		.as_ref()
		.and_then(|string| string.parse().ok())
		.unwrap_or(0);
	let sincecount = PduCount::Normal(since);

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

	// Look for device list updates of this account
	device_list_updates.extend(
		services()
			.users
			.keys_changed(sender_user.as_ref(), since, None)
			.filter_map(Result::ok),
	);

	if services().globals.allow_local_presence() {
		process_presence_updates(&mut presence_updates, since, &sender_user).await?;
	}

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

	// Coalesce database writes for the remainder of this scope.
	let _cork = services().globals.db.cork_and_flush()?;

	for room_id in all_joined_rooms {
		let room_id = room_id?;
		if let Ok(joined_room) = load_joined_room(
			&sender_user,
			&sender_device,
			&room_id,
			since,
			sincecount,
			next_batch,
			next_batchcount,
			lazy_load_enabled,
			lazy_load_send_redundant,
			full_state,
			&mut device_list_updates,
			&mut left_encrypted_users,
		)
		.await
		{
			if !joined_room.is_empty() {
				joined_rooms.insert(room_id.clone(), joined_room);
			}
		}
	}

	let mut left_rooms = BTreeMap::new();
	let all_left_rooms: Vec<_> = services()
		.rooms
		.state_cache
		.rooms_left(&sender_user)
		.collect();
	for result in all_left_rooms {
		let (room_id, _) = result?;

		{
			// Get and drop the lock to wait for remaining operations to finish
			let mutex_insert = Arc::clone(
				services()
					.globals
					.roomid_mutex_insert
					.write()
					.await
					.entry(room_id.clone())
					.or_default(),
			);
			let insert_lock = mutex_insert.lock().await;
			drop(insert_lock);
		};

		let left_count = services()
			.rooms
			.state_cache
			.get_left_count(&room_id, &sender_user)?;

		// Left before last sync
		if Some(since) >= left_count {
			continue;
		}

		if !services().rooms.metadata.exists(&room_id)? {
			// This is just a rejected invite, not a room we know
			// Insert a leave event anyways
			let event = PduEvent {
				event_id: EventId::new(services().globals.server_name()).into(),
				sender: sender_user.clone(),
				origin: None,
				origin_server_ts: utils::millis_since_unix_epoch()
					.try_into()
					.expect("Timestamp is valid js_int value"),
				kind: TimelineEventType::RoomMember,
				content: serde_json::from_str(r#"{"membership":"leave"}"#).expect("this is valid JSON"),
				state_key: Some(sender_user.to_string()),
				unsigned: None,
				// The following keys are dropped on conversion
				room_id: room_id.clone(),
				prev_events: vec![],
				depth: uint!(1),
				auth_events: vec![],
				redacts: None,
				hashes: EventHash {
					sha256: String::new(),
				},
				signatures: None,
			};

			left_rooms.insert(
				room_id,
				LeftRoom {
					account_data: RoomAccountData {
						events: Vec::new(),
					},
					timeline: Timeline {
						limited: false,
						prev_batch: Some(next_batch_string.clone()),
						events: Vec::new(),
					},
					state: State {
						events: vec![event.to_sync_state_event()],
					},
				},
			);
			continue;
		}

		let mut left_state_events = Vec::new();

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

		let since_state_ids = match since_shortstatehash {
			Some(s) => services().rooms.state_accessor.state_full_ids(s).await?,
			None => HashMap::new(),
		};

		let Some(left_event_id) = services().rooms.state_accessor.room_state_get_id(
			&room_id,
			&StateEventType::RoomMember,
			sender_user.as_str(),
		)?
		else {
			error!("Left room but no left state event");
			continue;
		};

		let Some(left_shortstatehash) = services()
			.rooms
			.state_accessor
			.pdu_shortstatehash(&left_event_id)?
		else {
			error!("Leave event has no state");
			continue;
		};

		let mut left_state_ids = services()
			.rooms
			.state_accessor
			.state_full_ids(left_shortstatehash)
			.await?;

		let leave_shortstatekey = services()
			.rooms
			.short
			.get_or_create_shortstatekey(&StateEventType::RoomMember, sender_user.as_str())?;

		left_state_ids.insert(leave_shortstatekey, left_event_id);

		let mut i = 0;
		for (key, id) in left_state_ids {
			if full_state || since_state_ids.get(&key) != Some(&id) {
				let (event_type, state_key) = services().rooms.short.get_statekey_from_short(key)?;

				if !lazy_load_enabled
                    || event_type != StateEventType::RoomMember
                    || full_state
                    // TODO: Delete the following line when this is resolved: https://github.com/vector-im/element-web/issues/22565
                    || (cfg!(feature = "element_hacks") && *sender_user == state_key)
				{
					let Some(pdu) = services().rooms.timeline.get_pdu(&id)? else {
						error!("Pdu in state not found: {}", id);
						continue;
					};

					left_state_events.push(pdu.to_sync_state_event());

					i += 1;
					if i % 100 == 0 {
						tokio::task::yield_now().await;
					}
				}
			}
		}

		left_rooms.insert(
			room_id.clone(),
			LeftRoom {
				account_data: RoomAccountData {
					events: Vec::new(),
				},
				timeline: Timeline {
					limited: false,
					prev_batch: Some(next_batch_string.clone()),
					events: Vec::new(),
				},
				state: State {
					events: left_state_events,
				},
			},
		);
	}

	let mut invited_rooms = BTreeMap::new();
	let all_invited_rooms: Vec<_> = services()
		.rooms
		.state_cache
		.rooms_invited(&sender_user)
		.collect();
	for result in all_invited_rooms {
		let (room_id, invite_state_events) = result?;

		{
			// Get and drop the lock to wait for remaining operations to finish
			let mutex_insert = Arc::clone(
				services()
					.globals
					.roomid_mutex_insert
					.write()
					.await
					.entry(room_id.clone())
					.or_default(),
			);
			let insert_lock = mutex_insert.lock().await;
			drop(insert_lock);
		};

		let invite_count = services()
			.rooms
			.state_cache
			.get_invite_count(&room_id, &sender_user)?;

		// Invited before last sync
		if Some(since) >= invite_count {
			continue;
		}

		invited_rooms.insert(
			room_id.clone(),
			InvitedRoom {
				invite_state: InviteState {
					events: invite_state_events,
				},
			},
		);
	}

	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);
		}
	}

	// Remove all to-device events the device received *last time*
	services()
		.users
		.remove_to_device_events(&sender_user, &sender_device, since)?;

	let response = sync_events::v3::Response {
		next_batch: next_batch_string,
		rooms: Rooms {
			leave: left_rooms,
			join: joined_rooms,
			invite: invited_rooms,
			knock: BTreeMap::new(), // TODO
		},
		presence: Presence {
			events: presence_updates
				.into_values()
				.map(|v| Raw::new(&v).expect("PresenceEvent always serializes successfully"))
				.collect(),
		},
		account_data: GlobalAccountData {
			events: services()
				.account_data
				.changes_since(None, &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(),
		},
		device_lists: DeviceLists {
			changed: device_list_updates.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)?,
		to_device: ToDevice {
			events: services()
				.users
				.get_to_device_events(&sender_user, &sender_device)?,
		},
		// Fallback keys are not yet supported
		device_unused_fallback_key_types: None,
	};

	// TODO: Retry the endpoint instead of returning
	if !full_state
		&& response.rooms.is_empty()
		&& response.presence.is_empty()
		&& response.account_data.is_empty()
		&& response.device_lists.is_empty()
		&& response.to_device.is_empty()
	{
		// Hang a few seconds so requests are not spammed
		// Stop hanging if new info arrives
		let mut duration = body.timeout.unwrap_or_default();
		if duration.as_secs() > 30 {
			duration = Duration::from_secs(30);
		}
		_ = tokio::time::timeout(duration, watcher).await;
		Ok((response, false))
	} else {
		Ok((response, since != next_batch)) // Only cache if we made progress
	}
}

async fn process_presence_updates(
	presence_updates: &mut HashMap<OwnedUserId, PresenceEvent>, since: u64, syncing_user: &OwnedUserId,
) -> Result<()> {
	// Take presence updates
	for (user_id, _, presence_bytes) in services().presence.presence_since(since) {
		if !services()
			.rooms
			.state_cache
			.user_sees_user(syncing_user, &user_id)?
		{
			continue;
		}

		use crate::service::presence::Presence;
		let presence_event = Presence::from_json_bytes_to_event(&presence_bytes, &user_id)?;
		match presence_updates.entry(user_id) {
			Entry::Vacant(slot) => {
				slot.insert(presence_event);
			},
			Entry::Occupied(mut slot) => {
				let curr_event = slot.get_mut();
				let curr_content = &mut curr_event.content;
				let new_content = presence_event.content;

				// Update existing presence event with more info
				curr_content.presence = new_content.presence;
				curr_content.status_msg = new_content
					.status_msg
					.or_else(|| curr_content.status_msg.take());
				curr_content.last_active_ago = new_content.last_active_ago.or(curr_content.last_active_ago);
				curr_content.displayname = new_content
					.displayname
					.or_else(|| curr_content.displayname.take());
				curr_content.avatar_url = new_content
					.avatar_url
					.or_else(|| curr_content.avatar_url.take());
				curr_content.currently_active = new_content
					.currently_active
					.or(curr_content.currently_active);
			},
		}
	}

	Ok(())
}

#[allow(clippy::too_many_arguments)]
async fn load_joined_room(
	sender_user: &UserId, sender_device: &DeviceId, room_id: &RoomId, since: u64, sincecount: PduCount,
	next_batch: u64, next_batchcount: PduCount, lazy_load_enabled: bool, lazy_load_send_redundant: bool,
	full_state: bool, device_list_updates: &mut HashSet<OwnedUserId>, left_encrypted_users: &mut HashSet<OwnedUserId>,
) -> Result<JoinedRoom> {
	{
		// Get and drop the lock to wait for remaining operations to finish
		// This will make sure the we have all events until next_batch
		let mutex_insert = Arc::clone(
			services()
				.globals
				.roomid_mutex_insert
				.write()
				.await
				.entry(room_id.to_owned())
				.or_default(),
		);
		let insert_lock = mutex_insert.lock().await;
		drop(insert_lock);
	};

	let (timeline_pdus, limited) = load_timeline(sender_user, room_id, sincecount, 10)?;

	let send_notification_counts = !timeline_pdus.is_empty()
		|| services()
			.rooms
			.user
			.last_notification_read(sender_user, room_id)?
			> since;

	let mut timeline_users = HashSet::new();
	for (_, event) in &timeline_pdus {
		timeline_users.insert(event.sender.as_str().to_owned());
	}

	services()
		.rooms
		.lazy_loading
		.lazy_load_confirm_delivery(sender_user, sender_device, room_id, sincecount)
		.await?;

	// Database queries:

	let Some(current_shortstatehash) = services().rooms.state.get_room_shortstatehash(room_id)? else {
		error!("Room {} has no state", room_id);
		return Err(Error::BadDatabase("Room has no state"));
	};

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

	let (heroes, joined_member_count, invited_member_count, joined_since_last_sync, state_events) =
		if timeline_pdus.is_empty() && since_shortstatehash == Some(current_shortstatehash) {
			// No state changes
			(Vec::new(), None, None, false, Vec::new())
		} else {
			// Calculates joined_member_count, invited_member_count and heroes
			let calculate_counts = || {
				let joined_member_count = services()
					.rooms
					.state_cache
					.room_joined_count(room_id)?
					.unwrap_or(0);
				let invited_member_count = services()
					.rooms
					.state_cache
					.room_invited_count(room_id)?
					.unwrap_or(0);

				// Recalculate heroes (first 5 members)
				let mut heroes = Vec::new();

				if joined_member_count + invited_member_count <= 5 {
					// Go through all PDUs and for each member event, check if the user is still
					// joined or invited until we have 5 or we reach the end

					for hero in services()
					.rooms
					.timeline
					.all_pdus(sender_user, room_id)?
					.filter_map(Result::ok) // Ignore all broken pdus
					.filter(|(_, pdu)| pdu.kind == TimelineEventType::RoomMember)
					.map(|(_, pdu)| {
						let content: RoomMemberEventContent = serde_json::from_str(pdu.content.get())
							.map_err(|_| Error::bad_database("Invalid member event in database."))?;

						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."))?;

							// The membership was and still is invite or join
							if matches!(content.membership, MembershipState::Join | MembershipState::Invite)
								&& (services().rooms.state_cache.is_joined(&user_id, room_id)?
									|| services().rooms.state_cache.is_invited(&user_id, room_id)?)
							{
								Ok::<_, Error>(Some(state_key.clone()))
							} else {
								Ok(None)
							}
						} else {
							Ok(None)
						}
					})
					// Filter out buggy users
					.filter_map(Result::ok)
					// Filter for possible heroes
					.flatten()
					{
						if heroes.contains(&hero) || hero == sender_user.as_str() {
							continue;
						}

						heroes.push(hero);
					}
				}

				Ok::<_, Error>((Some(joined_member_count), Some(invited_member_count), heroes))
			};

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

			if since_shortstatehash.is_none() || joined_since_last_sync {
				// Probably since = 0, we will do an initial sync

				let (joined_member_count, invited_member_count, heroes) = calculate_counts()?;

				let current_state_ids = services()
					.rooms
					.state_accessor
					.state_full_ids(current_shortstatehash)
					.await?;

				let mut state_events = Vec::new();
				let mut lazy_loaded = HashSet::new();

				let mut i = 0;
				for (shortstatekey, id) in current_state_ids {
					let (event_type, state_key) = services()
						.rooms
						.short
						.get_statekey_from_short(shortstatekey)?;

					if event_type != StateEventType::RoomMember {
						let Some(pdu) = services().rooms.timeline.get_pdu(&id)? else {
							error!("Pdu in state not found: {}", id);
							continue;
						};
						state_events.push(pdu);

						i += 1;
						if i % 100 == 0 {
							tokio::task::yield_now().await;
						}
					} else if !lazy_load_enabled
                || full_state
                || timeline_users.contains(&state_key)
                // TODO: Delete the following line when this is resolved: https://github.com/vector-im/element-web/issues/22565
                || (cfg!(feature = "element_hacks") && *sender_user == state_key)
					{
						let Some(pdu) = services().rooms.timeline.get_pdu(&id)? else {
							error!("Pdu in state not found: {}", id);
							continue;
						};

						// This check is in case a bad user ID made it into the database
						if let Ok(uid) = UserId::parse(&state_key) {
							lazy_loaded.insert(uid);
						}
						state_events.push(pdu);

						i += 1;
						if i % 100 == 0 {
							tokio::task::yield_now().await;
						}
					}
				}

				// Reset lazy loading because this is an initial sync
				services()
					.rooms
					.lazy_loading
					.lazy_load_reset(sender_user, sender_device, room_id)?;

				// The state_events above should contain all timeline_users, let's mark them as
				// lazy loaded.
				services()
					.rooms
					.lazy_loading
					.lazy_load_mark_sent(sender_user, sender_device, room_id, lazy_loaded, next_batchcount)
					.await;

				(heroes, joined_member_count, invited_member_count, true, state_events)
			} else {
				// Incremental /sync
				let since_shortstatehash = since_shortstatehash.unwrap();

				let mut state_events = Vec::new();
				let mut lazy_loaded = HashSet::new();

				if since_shortstatehash != current_shortstatehash {
					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 full_state || 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 {
								match UserId::parse(
									pdu.state_key
										.as_ref()
										.expect("State event has state key")
										.clone(),
								) {
									Ok(state_key_userid) => {
										lazy_loaded.insert(state_key_userid);
									},
									Err(e) => error!("Invalid state key for member event: {}", e),
								}
							}

							state_events.push(pdu);
							tokio::task::yield_now().await;
						}
					}
				}

				for (_, event) in &timeline_pdus {
					if lazy_loaded.contains(&event.sender) {
						continue;
					}

					if !services().rooms.lazy_loading.lazy_load_was_sent_before(
						sender_user,
						sender_device,
						room_id,
						&event.sender,
					)? || lazy_load_send_redundant
					{
						if let Some(member_event) = services().rooms.state_accessor.room_state_get(
							room_id,
							&StateEventType::RoomMember,
							event.sender.as_str(),
						)? {
							lazy_loaded.insert(event.sender.clone());
							state_events.push(member_event);
						}
					}
				}

				services()
					.rooms
					.lazy_loading
					.lazy_load_mark_sent(sender_user, sender_device, room_id, lazy_loaded, next_batchcount)
					.await;

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

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

				// Calculations:
				let new_encrypted_room = encrypted_room && since_encryption.is_none();

				let send_member_count = state_events
					.iter()
					.any(|event| event.kind == TimelineEventType::RoomMember);

				if encrypted_room {
					for state_event in &state_events {
						if state_event.kind != TimelineEventType::RoomMember {
							continue;
						}

						if let Some(state_key) = &state_event.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>(state_event.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_updates.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 && encrypted_room || new_encrypted_room {
					// If the user is in a new encrypted room, give them all joined users
					device_list_updates.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)
							}),
					);
				}

				let (joined_member_count, invited_member_count, heroes) = if send_member_count {
					calculate_counts()?
				} else {
					(None, None, Vec::new())
				};

				(
					heroes,
					joined_member_count,
					invited_member_count,
					joined_since_last_sync,
					state_events,
				)
			}
		};

	// Look for device list updates in this room
	device_list_updates.extend(
		services()
			.users
			.keys_changed(room_id.as_ref(), since, None)
			.filter_map(Result::ok),
	);