@hatsa/express/index.js

const express      = require('express');
const get          = require('lodash/get');

const helmet       = require('./middlewares/helmet');
const cors         = require('./middlewares/cors');

const {
    createRequestLogger,
    createErrorLogger,
    loggerMiddleware,
    genStackdriverLogTraceMw
} = require('./log');

const genApp = (opts = {}) => {

    const {
        logger,
        sd_mw
    } = opts;

    const app = express();

    app.use(helmet());
    app.use(cors());

    app.set('trust proxy', true);

    //TODO: make this GAE functionality overwriteable
    //https://cloud.google.com/appengine/docs/standard/nodejs/how-instances-are-managed
    app.use('/_ah/start',  (req, res) => res.json({success: true}));
    app.use('/_ah/stop',   (req, res) => res.json({success: true}));
    app.use('/_ah/warmup', (req, res) => res.json({success: true})); //not for manual or basic scaling instances
    app.use('/_ah/health_check', (req, res) => res.json({success: true}));

    if (logger) {
        app.use(createRequestLogger({logger}));
        app.logger = logger; //global scoped logger req.app.logger

        if (typeof sd_mw !== 'function') {
            app.use(loggerMiddleware({logger}));
        }
    }

    if (typeof sd_mw === 'function')
        app.use(sd_mw); //enables Google Trace + request scoped req.log interface

    if (sd_mw === true)
        return genStackdriverLogTraceMw(logger)
            .then(sd_mw => {
                app.use(sd_mw);
                return app;
            })
        ;

    return app;
};

const addErrorHandler = (app, logger, debug) => {

    const isProduction = process.env.NODE_ENV === 'production';
    const showStack    = !isProduction || process.env.DEBUG || debug;

    //express-winston logger
    if (logger)
        app.use(createErrorLogger({logger}));

    app.use((err, req, res, next) => {

        const log = req.log || logger;

        //log exception to trigger stackdriver push notifications
        const shouldTriggerError = isProduction && (!err.statusCode || err.statusCode >= 500);
        if (log && shouldTriggerError)
            log.error(err.message, err);

        res.status(err.statusCode || 500).json({
            success: false,
            error: {
                message: get(err, 'originalError.message', err.message),
                code:    get(err, 'originalError.code', err.code),
                stack:   showStack ? err.stack.split('\n') : undefined
            }
        });
    });
};

const addApiServiceRoutes = (app, path, routes, serviceName) => {
    //add routes like normal
    app.use(path, routes);

    //if serviceName given, expose routes als as /api/servicename/...
    if (serviceName)
        app.use(`/api/${serviceName}${path}`, routes);
};

module.exports = {
    genApp,
    static: express.static,
    Router: express.Router,
    createErrorLogger,
    addErrorHandler,
    addApiServiceRoutes
};