index.js

require('dotenv').config();

const http = require('http');
const httpProxy = require('http-proxy');
const fs = require('fs/promises');
const path = require('path');

(async () => {
  const proxies = {};
  const plugins = [];

  if (process.env['CURTAIN_PLUGINS']) {
      try {
          const files = await fs.readdir(process.env['CURTAIN_PLUGINS']);
          for (const file of files) {
              try {
                  plugins.push(require(
                      path.resolve(
                          __dirname,
                          path.join(process.env['CURTAIN_PLUGINS'], file)
                      )
                  ));
              } catch (e) {
                  console.error('[error] loading plugin', file, e);
              }
          }
      } catch (e) {
          console.error('[error] loading plugins', e);
      }
  }

  try {
    const proxy = httpProxy.createProxyServer({});

    for (const key of Object.keys(process.env).filter(e => e.startsWith('CURTAIN_URL_'))) {
      proxies[process.env[`CURTAIN_PATH_${key.slice(12)}`]] = {
        target: process.env[key],
        transformers: Object.keys(process.env)
          .sort()
          .filter(e => e.startsWith(`CURTAIN_REGEX_${key.slice(12)}`))
          .map(k => {
            const regex = process.env[k].split('/');
            return [new RegExp(regex[1], regex[3]), regex[2]];
          })
      };
    }

    const server = http.createServer((req, res) => {
      if (proxies[req.url]) {
        proxy.web(req, res, {
          target: proxies[req.url].target,
          selfHandleResponse: true,
          changeOrigin: true,
          ignorePath: true
        }, (e) => console.log(e));
      } else {
        res.writeHead(404, { 'Content-Type': 'text/plain' });
        res.write('Not Found!');
        res.end();
      }
    });

    proxy.on('proxyRes', (proxyRes, req, res) => {
      const chunks = [];
      proxyRes.on('data', (chunk) => chunks.push(chunk));
      proxyRes.on('end', () => {
        let body = Buffer.concat(chunks).toString();
        for (const t of proxies[req.url].transformers) {
          body = body.replace(t[0], t[1]);
        }

        if (plugins.length) {
            const [mainmatter, backmatter] = body.split('END:VCALENDAR', 2);
            let events = mainmatter.split('BEGIN:VEVENT');
            const frontmatter = events.shift();

            events = events.map(e => plugins.reduce((s, p) => p(`BEGIN:VEVENT${s}`, req.url), e));
            body = [frontmatter, events.join(''), 'END:VCALENDAR', backmatter].join('');
        }

        for (const [key, value] of Object.entries(proxyRes.headers)) {
          res.setHeader(key, value);
        }

        res.end(body);
      });
    });

    console.log('listening on port 5050');
    server.listen(5050);
  } catch (e) {
    console.log(e);
  }
})();