Next.js http2 push test

server.js

const express = require("express");
const next = require("next");
const expressHealthcheck = require("express-healthcheck");
const Sentry = require("@sentry/node");
const fs = require("fs");

const port = parseInt(process.env.PORT, 10) || 3000;
const dev = process.env.NODE_ENV !== "production";
const app = next({dev});
const handle = app.getRequestHandler();
const path = require("path");
const helmet = require("helmet");

Sentry.init({
    dsn: "<DSN>",
    environment: process.env.NODE_ENV || "development",
    release: "VERSION_PLACEHOLDER",
});


function linkFile(name, as) {
    return `<${name}>; as=${as}; rel=preload`;
}

function getFiles(dir, mapping, as) {
    try {
        const files_ = [];
        const files = fs.readdirSync(dir);
        for (const i in files) {
            const name = linkFile(`${mapping}${files[i]}`, as);
            files_.push(name);
        }
        return files_;
    } catch (err) {
        return [];
    }
}

const buildId = !dev
    ? fs.readFileSync("./.next/BUILD_ID", "utf8").toString()
    : "";

const createServer = () => {
    const server = express();

    server.use(helmet());
    // Performance desired in this case
    server.use(helmet.dnsPrefetchControl({allow: true}));
    // Lets not force our summary domain to https
    server.use(helmet.hsts({includeSubDomains: false}));

    server.use(Sentry.Handlers.requestHandler());

    // The error handler must be before any other error middleware
    server.use(Sentry.Handlers.errorHandler());

    server.use("/health", expressHealthcheck());

    server.get("/favicon.ico", (req, res) => {
        app.serveStatic(req, res, path.resolve("./static/icons/favicon.ico"));
    });

    server.get("/service-worker.js", (req, res) => {
        // Don't cache sw as a best practice
        res.set("Cache-Control", "no-store, no-cache, must-revalidate, proxy-revalidate");
        app.serveStatic(req, res, path.resolve("./.next/service-worker.js"));
    });

    const robotsOptions = {
        root: `${__dirname}/static/`,
        headers: {
            "Content-Type": "text/plain;charset=UTF-8",
        },
    };
    server.get("/robots.txt", (req, res) => (
        res.status(200).sendFile("robots.txt", robotsOptions)
    ));


    server.get("/", (req, res) => {
        const allFiles = getFiles("./.next/static/css", "/_next/static/css/", "style")
            .concat(getFiles("./.next/static/chunks", "/_next/static/chunks/", "script"))
            .concat(getFiles("./.next/static/runtime", "/_next/static/runtime/", "script"));

        allFiles.push(linkFile(`/_next/static/${buildId}/pages/_app.js`, "script"));
        allFiles.push(linkFile(`/_next/static/${buildId}/pages/_error.js`, "script"));
        allFiles.push(linkFile(`/_next/static/${buildId}/pages/index.js`, "script"));

        if (allFiles.length > 0) {
            res.set("Link", allFiles.toString());
        }
        
        handle(req, res);
    });


    server.get("*", (req, res) => {
        handle(req, res);
    });


    return server;
};

const server = createServer();

if (!process.env.LAMBDA) {
    app.prepare()
        .then(() => {
            server.listen(port, (err) => {
                if (err) throw err;
                // eslint-disable-next-line
                console.log(`> Ready on http://localhost:${port}`);
            });
        });
}

exports.app = app;
exports.server = server;