This code sets up an Express.js server and creates a reverse proxy middleware to forward requests to a specified host. It also includes error handling and asynchronous function initialization, allowing the server to be started or stopped and handled accordingly.

Run example

npm run import -- "start a proxy on {port}"

start a proxy on {port}

if (typeof server != 'undefined') {
    server.close();
}
var app = express();
app.use('/', function (req, res) {
    var url = host + req.url;
    req.pipe(request(url)).pipe(res);
});

$.async();
try {
    var server = app.listen(port, () => $.done('server up and running on port ' + port));
    server.on('error', (e) => $.done(e));
} catch (e) {
    $.done(e);
}

/**
 * Server setup and teardown.
 * 
 * @requires express
 */

const express = require('express');
const request = require('request');
const $ = require('./async');

// Close the server if it's defined
if (global.server) {
  global.server.close();
}

// Initialize the Express app
const app = express();

// Define the proxy middleware
app.use('/', (req, res) => {
  const url = `${global.host}${req.url}`;
  req.pipe(request(url)).pipe(res);
});

// Start the server
try {
  global.server = app.listen(global.port, () => {
    $.done(`Server up and running on port ${global.port}`);
  });
  // Catch and handle server errors
  global.server.on('error', (e) => {
    $.done(e);
  });
} catch (e) {
  $.done(e);
}

// TODO: Consider implementing proper error handling and logging
// TODO: Review and refactor global variables usage
// TODO: Add support for multiple environments (dev, prod, etc.)

Code Breakdown

Checking for Server Existence

if (typeof server!= 'undefined') {
    server.close();
}

This code checks if a variable server exists and if it's not undefined. If it exists, the server is closed.

Setting Up Express Server

var app = express();

A new instance of the Express.js framework is created and assigned to the app variable.

Creating a Reverse Proxy Middleware

app.use('/', function (req, res) {
    var url = host + req.url;
    req.pipe(request(url)).pipe(res);
});

This code creates a middleware function that acts as a reverse proxy. It adds the value of the host variable to the request URL and forwards the request to the specified URL using the req.pipe() method.

Initializing Async Function

$.async();

This line initializes an asynchronous function called $.async().

Handling Server Start/Stop

try {
    var server = app.listen(port, () => $.done('server up and running on port'+ port));
    server.on('error', (e) => $.done(e));
} catch (e) {
    $.done(e);
}

This code attempts to start the server on the specified port using app.listen(). The callback function is called when the server is successfully started. The server.on('error') event listener is also set to handle any potential errors during server startup. If an error occurs during startup, the catch block is executed, and the error is handled by the $.done() function.