Twitter Card Proxy

index.js

'use strict';

exports.handler = function(event, context) {
	var agent = event.headers['User-Agent'] || 'None';
	var path = event.path.substring(event.path.indexOf('http'));

	if (agent.startsWith('Twitterbot')) {
		var proxy = require('./proxy');
		proxy(path, (err, status, headers, body) => {
			var response = {
				statusCode: status,
				headers: {
					"content-type": headers["content-type"],
					"content-length": body.length
				},
				body: body
			};
			context.succeed(response);
		});
	} else {
		// redirect
		var response = {
			statusCode: 301,
			headers: {
				"Location": path
			}
		};
		context.succeed(response);
	}
};

package.json

{
  "dependencies": {
    "cheerio": "^0.22.0",
    "request": "^2.79.0"
  }
}

proxy.js

'use strict';
var request = require('request');

module.exports = function(path, callback) {
	request(path, (err, response, body) => {
		var host = path.substring(0, path.indexOf('/',8));
		let cheerio = require('cheerio'), $ = cheerio.load(body);

		let title = $('article.blog h1').text();
		let description = ($('article.blog header').next('p').text()) || '';
		let image = ($('article.blog img').first().attr('src')) || '';
		if (image != '') image = host + image;
		var meta = `
		<meta name="twitter:card" content="summary"/>
		<meta name="twitter:site" content="@ExLibrisGroup"/>
		<meta name="twitter:title" content="${title}"/>
		<meta name="twitter:description" content="${description.substring(0,100)}"/>
		<meta name="twitter:image" content="${image}"/>
		`;

		console.log('meta', meta);
		$('head').append(meta);
		callback(err, response.statusCode, response.headers, $.html());
	});
}

server.js

'use strict';

var http = require('http');

const PORT=8080;

var server = http.createServer((req, resp) => {
	var path = req.url.substring(req.url.indexOf('http'));
	var agent = req.headers['user-agent'] || 'None';
	if (agent.startsWith('Twitterbot')) {
		var proxy = require('./proxy');
		proxy(path, (err, status, headers, body) => {
			resp.writeHead(status, headers);
			resp.end(body);
		});
	} else {
		// redirect
		resp.writeHead(301, { "Location": path} );
		resp.end();
	}
});

server.listen(process.env.PORT || PORT);