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Don't write events earlier than the latest event

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This commit is contained in:
Kegan Dougal 2021-12-15 17:55:36 +00:00
parent 131d255180
commit 882bc86195
1 changed files with 31 additions and 0 deletions
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31
src/matrix/room/timeline/persistence/SyncWriter.js
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@ -42,12 +42,16 @@ export class SyncWriter {
this._relationWriter = relationWriter;
this._fragmentIdComparer = fragmentIdComparer;
this._lastLiveKey = null;
this._lastEventId = null;
}
async load(txn, log) {
const liveFragment = await txn.timelineFragments.liveFragment(this._roomId);
if (liveFragment) {
const [lastEvent] = await txn.timelineEvents.lastEvents(this._roomId, liveFragment.id, 1);
if (lastEvent && lastEvent.event) {
this._lastEventId = lastEvent.event.event_id;
}
// fall back to the default event index in case the fragment was somehow written but no events
// we should only create fragments when really writing timeline events now
// (see https://github.com/vector-im/hydrogen-web/issues/112) but can't hurt to be extra robust.
@ -148,12 +152,39 @@ export class SyncWriter {
async _writeTimeline(timelineEvents, timeline, memberSync, currentKey, txn, log) {
const entries = [];
const updatedEntries = [];
timelineEvents = timelineEvents || [];
// Sync v3 hack:
// Events can come in multiple times currently in the following situation:
// - Click on room A, makes a room subscription, fetches most recent 20 events.
// - Click on room B, unsubs from room A and subs on room B.
// - Click on room A, remakes a room sub, fetches the same most recent 20 events.
// This confuses H which then thinks there are timeline fragments and it inserts events into
// the wrong places. To hack around this, we track the latest event in the room and drop all
// events <= this event ID to ensure we don't see duplicates. We can still get timeline
// fragments (e.g in busy rooms when you re-click on the room there may be >20 events) but
// this should guard against having dupes.
// NB: It is critical that the sliding window request has `timeline_limit: 0`, and ONLY the
// room subscription has `timeline_limit: N`. Failure to do this means when you click on a
// room you are actually getting _scrollback_ (if originally you want 1 event then want 20)
// and this results in dropped events due to not having the correct event key ordering.
let lastEventIndex = -1;
for (let i = 0; i < timelineEvents.length; i++) {
if (timelineEvents[i].event_id === this._lastEventId) {
lastEventIndex = i;
break;
}
}
if (lastEventIndex >= 0) {
timelineEvents.splice(0, lastEventIndex+1);
}
if (timelineEvents?.length) {
// only create a fragment when we will really write an event
currentKey = await this._ensureLiveFragment(currentKey, entries, timeline, txn, log);
log.set("timelineEvents", timelineEvents.length);
let timelineStateEventCount = 0;
for(const event of timelineEvents) {
this._lastEventId = event.event_id;
// store event in timeline
currentKey = currentKey.nextKey();
const storageEntry = createEventEntry(currentKey, this._roomId, event);