proxy.js

#!/usr/bin/env node

// Needs `npm install yargs connect request superstatic firebase-tools` as prerequisites.

const stream = require('stream');
const yargs = require('yargs');
const connect = require('connect');
const request = require('request');

const superstatic = require('superstatic');
const firebaseConfig = require('firebase-tools/lib/config').load({ cwd: __dirname });

function createProxyProvider(base) {
    return (_req, path) => {
        const proxyPath = base + path;
        const passThrough = new stream.PassThrough();
        return new Promise((resolve, reject) => {
            request(proxyPath)
            .on('error', (err) => {
                reject(err);
            })
            .on('response', (res) => {
                if (res.statusCode != 200) {
                    resolve(null);
                    console.error(`statusCode ${res.statusCode} for ${proxyPath}`);
                    return;
                }

                const size = res.headers['content-length'];
                const etag = res.headers['etag'];
                const date = res.headers['date'];
                resolve({ stream: passThrough, size, etag, modified: date });
                res.pipe(passThrough);
            });
        });
    }
}

const argv = yargs
.usage('Usage: $0 [options]')
.default({ port: 8081, base: 'http://localhost:8080' })
.alias('p', 'port')
.alias('b', 'base')
.help('h')
.alias('h', 'help')
.argv;

const port = argv.port;
const proxyBase = argv.base;
const app = connect();

app.use(superstatic({
    config: firebaseConfig.data.hosting,
    provider: createProxyProvider(proxyBase)
}));

app.listen(port, () => {
    console.log(`Superstatic proxy is running on port ${port}. Proxy base is ${proxyBase}.`);
});