bot: prevent concurrent logins

src/bot.ts

@@ -565,12 +565,30 @@ export class Mwn {
 
 	/************** CORE FUNCTIONS *******************/
 
+	private loginInProgress: Promise<ApiResponse> = null;
+
 	/**
 	 * Executes a Login
 	 * @see https://www.mediawiki.org/wiki/API:Login
 	 * @returns {Promise}
 	 */
 	async login(loginOptions?: { username?: string; password?: string; apiUrl?: string }): Promise<ApiResponse> {
+		// Avoid multiple logins taking place concurrently, for instance when session loss occurs
+		// in the middle of a batch operation.
+		if (!this.loginInProgress) {
+			this.loginInProgress = this.loginInternal(loginOptions);
+			this.loginInProgress.then(() => {
+				this.loginInProgress = null;
+			});
+		}
+		return this.loginInProgress;
+	}
+
+	private async loginInternal(loginOptions?: {
+		username?: string;
+		password?: string;
+		apiUrl?: string;
+	}): Promise<ApiResponse> {
 		this.options = merge(this.options, loginOptions);
 		if (!this.options.username || !this.options.password || !this.options.apiUrl) {
 			return rejectWithError({

tests/login.bot.test.js

@@ -1,6 +1,7 @@
 'use strict';
 
 const { Mwn, expect, verifyTokenAndSiteInfo } = require('./base/test_base');
+const { bot: localBot, sinon } = require('./base/local_wiki');
 
 const testwiki = require('./mocking/loginCredentials.js');
 
@@ -17,6 +18,20 @@ describe('login', async function () {
 		});
 	});
 
+	it('avoids concurrent logins', async function () {
+		const spy = sinon.spy(localBot, 'loginInternal');
+		const [mainPage, serverTime] = await Promise.all([localBot.read('Main Page'), localBot.getServerTime()]);
+		expect(spy).to.have.been.calledOnce;
+		sinon.restore();
+		expect(serverTime).to.be.a('string');
+		expect(mainPage).to.be.a('object');
+
+		await localBot.logout();
+		expect(localBot.loggedIn).to.be.false;
+		await localBot.login();
+		expect(localBot.loggedIn).to.be.true;
+	});
+
 	let bot = new Mwn();
 	it('successfully logs in through init', async function () {
 		bot = await Mwn.init(testwiki.account1);