overleaf/services/document-updater/app/coffee/RealTimeRedisManager.js

/*
 * decaffeinate suggestions:
 * DS101: Remove unnecessary use of Array.from
 * DS102: Remove unnecessary code created because of implicit returns
 * DS207: Consider shorter variations of null checks
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
let RealTimeRedisManager;
const Settings = require('settings-sharelatex');
const rclient = require("redis-sharelatex").createClient(Settings.redis.documentupdater);
const pubsubClient = require("redis-sharelatex").createClient(Settings.redis.pubsub);
const Keys = Settings.redis.documentupdater.key_schema;
const logger = require('logger-sharelatex');
const os = require("os");
const crypto = require("crypto");
const metrics = require('./Metrics');

const HOST = os.hostname();
const RND = crypto.randomBytes(4).toString('hex'); // generate a random key for this process
let COUNT = 0;

const MAX_OPS_PER_ITERATION = 8; // process a limited number of ops for safety

module.exports = (RealTimeRedisManager = {
	getPendingUpdatesForDoc(doc_id, callback){
		const multi = rclient.multi();
		multi.lrange(Keys.pendingUpdates({doc_id}), 0, (MAX_OPS_PER_ITERATION-1));
		multi.ltrim(Keys.pendingUpdates({doc_id}), MAX_OPS_PER_ITERATION, -1);
		return multi.exec(function(error, replys) {
			let jsonUpdate;
			if (error != null) { return callback(error); }
			const jsonUpdates = replys[0];
			for (jsonUpdate of Array.from(jsonUpdates)) {
				// record metric for each update removed from queue
				metrics.summary("redis.pendingUpdates", jsonUpdate.length, {status: "pop"});
			}
			const updates = [];
			for (jsonUpdate of Array.from(jsonUpdates)) {
				var update;
				try {
					update = JSON.parse(jsonUpdate);
				} catch (e) {
					return callback(e);
				}
				updates.push(update);
			}
			return callback(error, updates);
		});
	},

	getUpdatesLength(doc_id, callback){
		return rclient.llen(Keys.pendingUpdates({doc_id}), callback);
	},

	sendData(data) {
		// create a unique message id using a counter
		const message_id = `doc:${HOST}:${RND}-${COUNT++}`;
		if (data != null) {
			data._id = message_id;
		}

		const blob = JSON.stringify(data);
		metrics.summary("redis.publish.applied-ops", blob.length);

		// publish on separate channels for individual projects and docs when
		// configured (needs realtime to be configured for this too).
		if (Settings.publishOnIndividualChannels) {
			return pubsubClient.publish(`applied-ops:${data.doc_id}`, blob);
		} else {
			return pubsubClient.publish("applied-ops", blob);
		}
	}
});