overleaf/services/document-updater/app/coffee/ShareJsUpdateManager.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 ShareJsUpdateManager;
const ShareJsModel = require("./sharejs/server/model");
const ShareJsDB = require("./ShareJsDB");
const logger = require("logger-sharelatex");
const Settings = require('settings-sharelatex');
const Keys = require("./UpdateKeys");
const {EventEmitter} = require("events");
const util = require("util");
const RealTimeRedisManager = require("./RealTimeRedisManager");
const crypto = require("crypto");
const metrics = require('./Metrics');
const Errors = require("./Errors");

ShareJsModel.prototype = {};
util.inherits(ShareJsModel, EventEmitter);

const MAX_AGE_OF_OP = 80;

module.exports = (ShareJsUpdateManager = {
	getNewShareJsModel(project_id, doc_id, lines, version) {
		const db = new ShareJsDB(project_id, doc_id, lines, version);
		const model = new ShareJsModel(db, {maxDocLength: Settings.max_doc_length, maximumAge: MAX_AGE_OF_OP});
		model.db = db;
		return model;
	},

	applyUpdate(project_id, doc_id, update, lines, version, callback) {
		if (callback == null) { callback = function(error, updatedDocLines) {}; }
		logger.log({project_id, doc_id, update}, "applying sharejs updates");
		const jobs = [];
		// record the update version before it is modified
		const incomingUpdateVersion = update.v;
		// We could use a global model for all docs, but we're hitting issues with the
		// internal state of ShareJS not being accessible for clearing caches, and
		// getting stuck due to queued callbacks (line 260 of sharejs/server/model.coffee)
		// This adds a small but hopefully acceptable overhead (~12ms per 1000 updates on
		// my 2009 MBP).
		const model = this.getNewShareJsModel(project_id, doc_id, lines, version);
		this._listenForOps(model);
		const doc_key = Keys.combineProjectIdAndDocId(project_id, doc_id);
		return model.applyOp(doc_key, update, function(error) {
			if (error != null) {
				if (error === "Op already submitted") {
					metrics.inc("sharejs.already-submitted");
					logger.warn({project_id, doc_id, update}, "op has already been submitted");
					update.dup = true;
					ShareJsUpdateManager._sendOp(project_id, doc_id, update);
				} else if (/^Delete component/.test(error)) {
					metrics.inc("sharejs.delete-mismatch");
					logger.warn({project_id, doc_id, update, shareJsErr: error}, "sharejs delete does not match");
					error = new Errors.DeleteMismatchError("Delete component does not match");
					return callback(error);
				} else {
					metrics.inc("sharejs.other-error");
					return callback(error);
				}
			}
			logger.log({project_id, doc_id, error}, "applied update");
			return model.getSnapshot(doc_key, (error, data) => {
				if (error != null) { return callback(error); }
				// only check hash when present and no other updates have been applied 
				if ((update.hash != null) && (incomingUpdateVersion === version)) {
					const ourHash = ShareJsUpdateManager._computeHash(data.snapshot);
					if (ourHash !== update.hash) {
						metrics.inc("sharejs.hash-fail");
						return callback(new Error("Invalid hash"));
					} else {
						metrics.inc("sharejs.hash-pass", 0.001);
					}
				}
				const docLines = data.snapshot.split(/\r\n|\n|\r/);
				return callback(null, docLines, data.v, model.db.appliedOps[doc_key] || []);
			});
		});
	},

	_listenForOps(model) {
		return model.on("applyOp", function(doc_key, opData) {
			const [project_id, doc_id] = Array.from(Keys.splitProjectIdAndDocId(doc_key));
			return ShareJsUpdateManager._sendOp(project_id, doc_id, opData);
		});
	},
	
	_sendOp(project_id, doc_id, op) {
		return RealTimeRedisManager.sendData({project_id, doc_id, op});
	},

	_computeHash(content) {
		return crypto.createHash('sha1')
			.update("blob " + content.length + "\x00")
			.update(content, 'utf8')
			.digest('hex');
	}
});