TCP socket client through proxy on nodejs - node.js

Question

I need to make tcp socket connection to smtp server. Is it possible to connect through proxy server on nodejs? Is there any npm modules available to use? I couldn't find any at all.
var net = require('net');
var HOST = '127.0.0.1';
var PORT = 6969;
var client = new net.Socket();
client.connect(PORT, HOST, function() {
console.log('CONNECTED TO: ' + HOST + ':' + PORT);
client.write('I am here!');
});
// Add a 'data' event handler for the client socket
// data is what the server sent to this socket
client.on('data', function(data) {
console.log('DATA: ' + data);
});
// Add a 'close' event handler for the client socket
client.on('close', function() {
console.log('Connection closed');
});

Answer 1

net.socket, tls.connect and dgram have no proxy support.
The simplest way to use it with proxy is to replace some libc functions with proxychains or something similar.
var client = require('tls')
.connect(443, 'www.facebook.com', function() {
console.log('connected');
client.write('hello');
})
.on('data', function(data) {
console.log('received', data.toString());
})
.on('close', function() {
console.log('closed');
});
proxychains node fit.js
connected
received HTTP/1.1 400 Bad Request
...
closed

Answer 2

Other than 'net' you don't need another module to make a socket connect to a host through a proxy server as long at the proxy server supports HTTPS traffic.
Create a socket connection to the proxy server
Send an HTTP CONNECT message to inform the proxy server of the host and port you want to connect to
If the proxy server responds with an HTTP 200 response then the proxy server established a socket connection to your desired target and is now relaying the traffic between the sockets
If the proxy server responded with any HTTP response other than 200 then the connection was not established.
Even though this process starts with HTTP it doesn't mean it wouldn't work for SMTP traffic. The initial HTTP message is just used to negotiate the connection, after that its just raw traffic. A proxy server might look at the port or host you want to connect to and disallow it. For example, block connections to ports below 80 or below 443 such as port 25 so it really depends on the proxy server if the connection will be allowed.

Answer 3

Yes, it is possible with one of these NPM modules:
http-proxy-agent: An HTTP(s) proxy http.Agent implementation for HTTP endpoints
https-proxy-agent: An HTTP(s) proxy http.Agent implementation for HTTPS endpoints
pac-proxy-agent: A PAC file proxy http.Agent implementation for HTTP and HTTPS
socks-proxy-agent: A SOCKS (v4a) proxy http.Agent implementation for HTTP and HTTPS
HTTPS Proxy Example:
var url = require('url');
var WebSocket = require('ws');
var HttpsProxyAgent = require('https-proxy-agent');
// HTTP/HTTPS proxy to connect to
var proxy = process.env.http_proxy || 'http://168.63.76.32:3128';
console.log('using proxy server %j', proxy);
// WebSocket endpoint for the proxy to connect to
var endpoint = process.argv[2] || 'ws://echo.websocket.org';
var parsed = url.parse(endpoint);
console.log('attempting to connect to WebSocket %j', endpoint);
// create an instance of the `HttpsProxyAgent` class with the proxy server information
var opts = url.parse(proxy);
var agent = new HttpsProxyAgent(opts);
// finally, initiate the WebSocket connection
var socket = new WebSocket(endpoint, { agent: agent });
socket.on('open', function () {
console.log('"open" event!');
socket.send('hello world');
});
socket.on('message', function (data, flags) {
console.log('"message" event! %j %j', data, flags);
socket.close();
});
I hope this helps.