mobile-proxy/server.js

#!/usr/bin/env node

"use strict";

const Promise = require("bluebird");
const React = require("react");
const ReactDOMServer = require("react-dom/server");
const bhttp = require("bhttp");
const express = require("express");
const expressPromiseRouter = require("express-promise-router");
const { expression } = require("dataprog");
const url = require("url");
const createError = require("create-error");
const objectPick = require("object.pick");
const cheerio = require("cheerio");
const defaultValue = require("default-value");
const whatwgMimeType = require("whatwg-mimetype");

const rewriteHtmlUrls = require("./rewrite-html-urls");
const config = require("./load-config")(defaultValue(process.argv[2], "./config.jsx"));

let ConfigError = createError("ConfigError");

function stripWWW(hostname) {
	return hostname.replace(/^www\./, "");
}

let app = express();

app.set("trust proxy", "loopback");

let router = expressPromiseRouter();

router.use((req, res) => {
	let siteConfiguration = config.hosts[req.hostname];

	if (siteConfiguration == null) {
		res.status(404).send(`No configuration exists for host '${req.hostname}'`);
	} else {
		let filter = siteConfiguration.filters.find((filter) => {
			if (filter.matchPath != null) {
				if (typeof filter.matchPath === "string") {
					return (filter.matchPath === req.path);
				} else if (filter.matchPath instanceof RegExp) {
					return filter.matchPath.test(req.path);
				} else {
					console.warn(`Unrecognized URL filter type while handling path '${req.path}'`);
					return false;
				}
			} else {
				return true;
			}
		});

		let newUrl = expression(() => {
			if (filter.mapUrl == null) {
				throw new ConfigError(`No URL mapper specified for path '${req.path}'`);
			} else if (typeof filter.mapUrl === "function") {
				return filter.mapUrl(url.parse(req.originalUrl));
			} else if (typeof filter.mapUrl === "string") {
				return filter.mapUrl;
			} else {
				throw new ConfigError(`Unrecognized URL filter type while handling path '${req.path}'`);
			}
		});

		return Promise.try(() => {
			return bhttp.get(newUrl, { headers: { "user-agent": "mobile proxy (questions/comments: admin@cryto.net)" } });
		}).then((response) => {
			res.set(objectPick(response.headers, [ "content-type" ]));
			
			let mimeType = new whatwgMimeType(response.headers["content-type"]);

			if (mimeType.isHTML()) {
				let $ = cheerio.load(response.body);

				rewriteHtmlUrls($, (path) => {
					let parsedOrigin = url.parse(newUrl);
					let parsedPath = url.parse(path);

					if (!["http:", "https:"].includes(parsedPath.protocol)) {
						return path;
					} else if (parsedPath.host == null) {
						return url.resolve(req.hostname, path);
					} else if (stripWWW(parsedPath.host) === stripWWW(parsedOrigin.host)) {
						/* Internal absolute URL */
						return url.resolve(req.hostname, parsedPath.path);
					} else {
						/* External absolute URL */
						return path;
					}
				});

				/* Strips any target="_blank" attributes, which mess up some mobile readers */
				$("a").attr("target", null);

				let prefix = (siteConfiguration.prefix != null)
					? ReactDOMServer.renderToStaticMarkup(React.createElement(siteConfiguration.prefix))
					: "";

				res.send(prefix + filter.mapContent($));
			} else {
				res.send(response.body);
			}
		});
	}
});

router.use((err, req, res, next) => {
	if (err instanceof ConfigError) {
		console.warn("Configuration error:", err.message);
		res.status(500).send("Could not handle your request");
	} else {
		throw err;
	}
});

app.use(router);
app.listen(config.port, () => {
	console.log(`Listening on port ${config.port}`);
});