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How to get correct client IP in java sockets when using sshuttle?

I am using the utility sshuttle to access internet on my computer.
sudo sshuttle --dns -vr user#172.16.30.30 0/0
I have a simple java client server program
Client (My computer running sshuttle)
// client ip is 172.16.23.6
class client {
public static void main(String args[]) {
Socket s = new Socket("172.16.30.20",port); // different server
}
}
The server program, running on 172.16.30.20
class server {
public static void main(String args[]) {
ServerSocket s = new ServerSocket(port);
Socket cl = s.accept();
System.out.println(cl);
}
}
When I run the the server and connect the client, the IP address which the socket cl holds is 172.16.30.30 (IP of server to which I did sshuttle) instead of its own IP which is 172.16.23.6
When I stop sshuttle, the program works fine and the correct IP address is displayed.
I have to run both the programs simultaneously but am unable to do so.

You are out of the luck. sshuttle is like a proxy. The sshuttle server creates completely independent TCP connection from 172.16.30.30 to 172.16.30.20 and it copies incoming data from client connection to this connection. Your server 172.16.30.20 cannot get the information about the real client address because it is present neither in IP nor in TCP header. Your java server is able read sender address from the IP header but it is IP address of host that established the connection and it is 172.16.30.30 (sshuttle server).
Application protocols like HTTP have mechanism how to indicate the real client IP address. HTTP proxy may add HTTP header X-Forwarded-For and server then may learn the client IP from it. But it is possible only if application proxy adds this information to the forwarded data. sshuttle is application protocol independent so it cannot add such information.

Socket connection won't work between smartphone and computer

I have a C# WPF application that uses TCPListener to start a Server in my computer, and an android app that works as a client. It works perfectly when I start the server and emulate the app in my computer, but most of the time it just doesn't work when I use my smartphone to connect to my computer, it only works some times after I restarted my router DHCP and my smartphone.
If you need, here's the connection code
Server:
private static IPAddress ipAd;
private static TcpListener server;
private static TcpClient client;
public static void start() {
//Already tried with both
ipAd = IPAddress.Parse(TCPServer.GetLocalIPAddress());
//ipAd = IPAddress.Parse("127.0.0.1");
server = new TcpListener(ipAd, 1209);
client = default(TcpClient);
try {
server.Start();
Console.WriteLine("Server started");
} catch {
Console.WriteLine("Failed to start server");
}
Client:
Socket socket = null;
String response = new String();
try{
//connect This ipAddress is the same in my desktop
InetAddress ipAd = InetAddress.getByName(ipAddress);
socket = new Socket(ipAd, 1209);
//send
DataOutputStream DOS = new DataOutputStream(socket.getOutputStream());
DOS.write(message.getBytes());
}
...
Thanks for your time, I've should had dedicated more to my Computer Networks class...
Should I redirect some specific port? Have some specific configurations in my router/firewall? I think I'm missing something

This would work when your devices located in the same network in terms of IP routing. However even part of the most simple SOHO grade WiFi routers/AP enable so called device isolation, denying access from wifi devices in the network access between them or to clients, connected with ethernet.
To make this setup work reliably you need to ensure the following:
Use external address of your router in the mobile application. (You can discover it browsing http://whatismyip.org from the server)
Setup port forwarding in your router for particular port to particular IP in your internal network.
As for privided source code, you'd rather use 0.0.0.0 as bind address in the server app, because default .NET implementation will select first available IP address and it may be not the one you're using for connection in the mobile app or not related to the same network. This approach may have security and convenience (coexistence) problems in case of complex networking setup, but will work good for most of the cases.

Java Socket connecting to a public ip-address

I need to make a server and client that connects to the server.
Problem: "the server works. the client can only connect to localhost, it cannot connect to a server on the internet. I want the client to connect to the server, via a public ip-address that the server is hosted on."
First of all, I have made sure that the port is forwarded and reachable i have tested the port, secondly i have disabled firewall completely from the server machine.
below is the test code i am using:
The Server: nothing fancy just simple - terminates if a client is connected, else just awaits a connection.
public class Server {
public static void main(String args[]) {
try {
ServerSocket srvr = new ServerSocket(52000);
srvr.accept();
}
catch(Exception e) {
e.printStackTrace();
}
}
}
The Client: I have used no-ip.com to mask the ip of the server to "biogenserver2.noip.me".
Using .getCanonicalHostName(); will return the ip.
public class Client {
public static void main(String args[]) {
try {
String ip = Inet4Address.getByName("somets.noip.com").getCanonicalHostName();
InetSocketAddress sa = new InetSocketAddress(ip, 52000);
//Socket skt = new Socket("0.0.0.0", 52000); //local - this works fine.
Socket skt = new Socket();
skt.connect(sa);
}
catch(Exception e) {
e.printStackTrace();
}
}
}
When i run this the server connects fine, but the client returns a "connection timeout" exception
Any help will be appreciated. Thanks.

Answer:
"Just for clarity: You have checked the port is open via public IP as returned by no-ip and the server will quit without exception when you run that little testclient (on a machine that is not the server machine) - is that correct?" – Fildor
TL:DR
Don't run the client and server on the same machine and the same network trying to connect to your server through your public ip then to your own local network will result in a client timeout exception
I was running the client and server on the same machine and also the same network. This caused the client timeout exception. I tried running the Client on a different machine and a different network and i was able to connect successfully.

What version of IP protocol your application uses? On linux, you may figure it out with netstat -tunap | grep 52000 and watching whether first field is tcp or tcp6. If latter, then it is possible that problem with IPv6 connectivity exists and you may want to prefer using IPv4 to IPv6 by specifying -Djava.net.preferIPv4Stack=true to JVM.

How to run a simple socket server that allows incoming connections?

I am trying to build a very simple socket server in JAVA that my Flash application can listen to. I am using this tutorial. Everything seems to be working - the JAVA code is compiled and the server is running.
My question is: how can external applications send messages to this server using just an IP address and a port number? My goal is that flash can listen to socket messages sent by an external application.
The Java code:
import java.io.*;
import java.net.*;
class SimpleServer {
private static SimpleServer server;
ServerSocket socket;
Socket incoming;
BufferedReader readerIn;
PrintStream printOut;
public static void main(String[] args) {
int port = 8080;
try {
port = Integer.parseInt(args[0]);
} catch (ArrayIndexOutOfBoundsException e) {
// Catch exception and keep going.
}
server = new SimpleServer(port);
}
private SimpleServer(int port) {
System.out.println(">> Starting SimpleServer");
try {
socket = new ServerSocket(port);
incoming = socket.accept();
readerIn = new BufferedReader(
new InputStreamReader(
incoming.getInputStream()));
printOut = new PrintStream(incoming.getOutputStream());
printOut.println("Enter EXIT to exit.\r");
out("Enter EXIT to exit.\r");
boolean done = false;
while (!done) {
String str = readerIn.readLine();
if (str == null) {
done = true;
} else {
out("Echo: " + str + "\r");
if(str.trim().equals("EXIT"))
done = true;
}
incoming.close();
}
} catch (Exception e) {
System.out.println(e);
}
}
private void out(String str) {
printOut.println(str);
System.out.println(str);
}
}

Maybe I don't understand correctly your problem description, but if you create the server in Java, it listens to its port and not your Flash application. If you want your Flash application to wait for messages from other applications, it must have a server role and listen to a TCP port the same way as this Java server does.
You can connect to and test the given Java server easily by telnet program (available in all operating systems) by providing a host name or an IP address and a port as parameters:
telnet 127.0.0.1 8080
Any other application can connect in a similar way, using just a hostname/IP address and a port. For example in Java, you can create a client socket:
Socket clientSocket = new Socket("localhost", 8080);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

By not specifying an IP address for your socket, it will listen on 0.0.0.0 (all interfaces).
In fact, that will usually be your computer's IP / the server's IP.
Assuming that your application runs on your computer at home, there are three cases that cover most of the connection situations:
Connecting from the same machine:
Use 127.0.0.1:8080
Connecting from the same LAN (e.g. your brother's PC):
Use your LAN IP (e.g. 192.168.1.4:8080)
Connecting from WAN (outside your routers LAN) (internet e.g.):
Use your WAN IP.(e.g. 84.156.74.194). There are plenty websites, that tell you your WAN IP like this
You may have to setup your router, to forward the port 8080 to your PC
For simple connection tests, one could use a telnet client.

I think you are missing the point of client/server socket applications.
If you are building the socket server (with whatever programming language you chose), you will then need to connect with (a) socket client(s) to this server. After a connection is successfully established (persistent) between the client and the server, you can start what ever kind of communication you have implemented between them.
The server always acts as the passive, the client as active part in a socket server/client constellation.

I was checking the link that you are referring to. In that, the procedure to create a stand-alone server is mentioned which is the code that you have pasted as well.
According to the link, the application acts as the client and uses the XMLSocket methods to connect to this server. This application is the flash application that you are talking about. As mentioned in the link, by using the following code any flash application can connect and talk to the server:
var xmlsock:XMLSocket = new XMLSocket();
xmlsock.connect("127.0.0.1", 8080);
xmlsock.send(xmlFormattedData);
When you mention
My goal is that flash can listen to socket messages sent by an external application.
its actually the flash application that is the client and it cannot listen unless programmed to act as a server. I hope this provides some clarity!

Java Networking: Connection refused - Yes, my server is running

I'm getting following error when my client tries to connect to my server socket:
java.net.ConnectException: Connection refused: connect
But, my server is really running, on the same machine. I try to connect to it by using the external IP of my router. But when I try to connect with "localhost", it works. And, yes I did port forwarding correcly in my router. Even canyouseeme.org can connect to my server (The site says: "success" and in my server-log appears that someone connected with the server.)
So, is it for one or another reason impossible to connect to the same machine (or to a machine in the same network) via an external IP? Or is this something typical for Windows? (Normally, I use Linux)
I also tried to completely disable Windows Firewall.
ServerSocket:
public ServerSocket ssocket;
public List<ClientHandler> handlers;
public Server(int port) { // Constructor
try {
ssocket = new ServerSocket(port);
this.handlers = new ArrayList<ClientHandler>();
IpSharingManager.uploadData(Utilities.getPublicIp(), port);
} catch (Exception e) {
e.printStackTrace();
System.exit(-1);
}
}
Client:
public InvisibleClient(String host, int port) {
try {
System.out.println("Trying to connect to " + host + ":" + port);
this.host = host;
this.socket = new Socket(host, port);
this.bis = new BufferedInputStream(this.socket.getInputStream());
this.bos = new BufferedOutputStream(this.socket.getOutputStream());
this.console = new RemoteConsole(this.socket);
initializeCommunication();
System.out.println("Successfully connected!");
new Thread(this, "Client Thread").start();
} catch (Exception e) {
e.printStackTrace();
System.out.println("No server available");
}
}
Thanks

Some routers doesn't allow the internal network to connect to the external IP address of the router.
You can try to use telnet to connect to your server socket. If telnet isn't able to establish a connection, it's likely a networking problem.

Add the java.exe process and the port to your firewall exception list?
edit: Just read you already tried that. All I can suggest is make sure the network is not blocking that port. (routers)

Have You tried running it with JVM option: java.net.preferIPv4Stack=true ?

For what I see in your code, you missed the part where you accept the conection, after instantiating the server socket you need ssocket.accept() to accept conections and then you have to start reading the outputstrem from the socket