91 lines
2.9 KiB
JavaScript
91 lines
2.9 KiB
JavaScript
'use strict';
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const assert = require('assert');
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const { traceFunction } = require('../../tracing/trace-utilities');
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const { DIRECTION } = require('matrix-public-archive-shared/lib/reference-values');
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const timestampToEvent = require('./timestamp-to-event');
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const getMessagesResponseFromEventId = require('./get-messages-response-from-event-id');
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const config = require('../config');
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const matrixServerUrl = config.get('matrixServerUrl');
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assert(matrixServerUrl);
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// Find an event right ahead of where we are trying to look. Then paginate
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// /messages backwards. This makes sure that we can get events for the day when
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// the room started. And it ensures that the `/messages` backfill kicks in
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// properly since it only works to fill in the gaps going backwards.
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//
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// Consider this scenario: dayStart(fromTs) <- msg1 <- msg2 <- msg3 <- dayEnd(toTs)
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// - ❌ If we start from dayStart and look backwards, we will find nothing.
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// - ❌ If we start from dayStart and look forwards, we will find msg1, but
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// federated backfill won't be able to paginate forwards
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// - ✅ If we start from dayEnd and look backwards, we will find msg3 and
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// federation backfill can paginate backwards
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// - ❌ If we start from dayEnd and look forwards, we will find nothing
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//
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// Returns events in reverse-chronological order.
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async function fetchEventsFromTimestampBackwards({ accessToken, roomId, ts, limit }) {
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assert(accessToken);
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assert(roomId);
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assert(ts);
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// Synapse has a max `/messages` limit of 1000
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assert(
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limit <= 1000,
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'We can only get 1000 messages at a time from Synapse. If you need more messages, we will have to implement pagination'
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);
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let eventIdForTimestamp;
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try {
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const { eventId } = await timestampToEvent({
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accessToken,
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roomId,
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ts,
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direction: DIRECTION.backward,
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});
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eventIdForTimestamp = eventId;
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} catch (err) {
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const allowedErrorCodes = [
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// Allow `404: Unable to find event xxx in direction x`
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// so we can just display an empty placeholder with no events.
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404,
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];
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if (!allowedErrorCodes.includes(err?.response?.status)) {
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throw err;
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}
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}
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if (!eventIdForTimestamp) {
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return {
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stateEventMap: {},
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events: [],
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};
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}
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const messageResData = await getMessagesResponseFromEventId({
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accessToken,
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roomId,
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eventId: eventIdForTimestamp,
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// We go backwards because that's the direction that backfills events (Synapse
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// doesn't backfill in the forward direction)
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dir: DIRECTION.backward,
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limit,
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});
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const stateEventMap = {};
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for (const stateEvent of messageResData.state || []) {
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if (stateEvent.type === 'm.room.member') {
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stateEventMap[stateEvent.state_key] = stateEvent;
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}
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}
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const chronologicalEvents = messageResData?.chunk?.reverse() || [];
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return {
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stateEventMap,
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events: chronologicalEvents,
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};
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}
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module.exports = traceFunction(fetchEventsFromTimestampBackwards);
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