swaf/src/components/MaintenanceComponent.ts

import ApplicationComponent from "../ApplicationComponent";
import {NextFunction, Request, Response, Router} from "express";
import {ServiceUnavailableHttpError} from "../HttpError";
import Application from "../Application";
import config from "config";

export default class MaintenanceComponent extends ApplicationComponent {
    private readonly application: Application;
    private readonly canServe: () => boolean;

    constructor(application: Application, canServe: () => boolean) {
        super();
        this.application = application;
        this.canServe = canServe;
    }

    public async handle(router: Router): Promise<void> {
        router.use((req: Request, res: Response, next: NextFunction) => {
            if (res.headersSent) {
                return next();
            }

            if (!this.application.isReady()) {
                res.header({'Retry-After': 60});
                res.locals.refresh_after = 5;
                throw new ServiceUnavailableHttpError(`${config.get('app.name')} is readying up. Please wait a few seconds...`);
            }

            if (!this.canServe()) {
                res.locals.refresh_after = 30;
                throw new ServiceUnavailableHttpError(`${config.get('app.name')} is unavailable due to failure of dependent services.`);
            }

            next();
        });
    }
}