Develop Reference

TCP socket connection over internet

I am doing a project for which connection between server and client is required.
I did it by adding TCP sockets.
Here is the code fraction :
Server:
ServerSocket welcomeSocket = new ServerSocket(80);
while(true)
{
Socket connectionSocket = welcomeSocket.accept();
WorkerThread wt = new WorkerThread(connectionSocket, id);
Thread t = new Thread(wt);
t.start();
workerThreadCount++;
}
Client :
Socket skt = new Socket("192.168.0.108", 80); // The IP address is from cmd->ipconfig/all-> IPv4 Address
outToServer = new PrintWriter(skt.getOutputStream(), true);
inFromServer = new BufferedReader(new InputStreamReader(skt.getInputStream()));
It all works when both ends are in same device/under same WiFi.But I don't understand what to do for creating connection over internet.
Please help with clear steps.

Here:
Socket skt = new Socket("192.168.0.108", 80);
That is local address. If you want to have a server that is reachable on the internet, then that server needs to have its global public IP address!
In other words: you have to make sure that the server can be reached from the internet somehow. For example by turning to some service provider that hosts servers that you can then equip with your code!
The whole purpose of 192.168 addresses is to be defined only in a local subnet.
Alternatively, you have to check if your ISP has a service where the ISP assigns an IP address to your connection, and that allows calls from the internet to go to your "place".
Meaning: when you want to receive phone calls, you need a phone that is connected to the phone net!

In order to connect to a socket over WAN, you must port forward that port to your local device. This can be done in your routers' settings.
192.168.0.108 --> That's your local IP-address.
This can be used on your local network without any requirements for port forwarding whatsoever. However, to use it over WAN, execute the following steps:
Step 1: Search for your routers' model number and port forwarding on Google on how-to forward port 80 to your local IP-address. Warning: use a static IP-address on your local device to prevent your IP from changing after a reboot.
Step 2: Go to a website like IP Chicken and find your external IP-address.
You can then connect to your socket using:
Socket skt = new Socket("[EXTERNALIP]", 80);
Please be noticed: unless you have a business network, your external IP-address will probably change from time to time.

How does a "proxy server" work

I'm trying to implement a simple ProxyServer to analyze traffix between a connected device and the outside world.
The iPhone (for example) is configured to use a proxy to 192.168.1.10:8080.
My proxy server (on 192.168.1.10) will be listening on the port 8080.
The iPhone tries to connect to http://google.com:80, or ftp://somehost.com:21/ it sends a request to the proxy server (port 8080), which is supposed to contact google.com at port 80 and somehost at post 21.
So I figured it would be something like this:
//Accept incoming
ServerSocket serverSocket = new ServerSocket(8080);
Socket socket = serverSocket.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
//Log incoming requests
//Send to remote server on behalf of my device
Socket remote = new Socket(remoteHost, remotePort);
//forward the same data to remote client..
//wait for the reply
//send to my device
How to know the remote port/host to forward the request to?
What did I miss?
Thank you

Connect with a Swift client to a Java server using sockets

How do I connect a Swift client to a Java server using sockets?
How can I send different data types between the client and the server?
ServerSocket serverSocket = new ServerSocket(12345);
while(true) {
Socket socket = serverSocket.accept();
System.out.println(new BufferedReader(new InputStreamReader(socket.getInputStream())).readLine());
}

You can use the SocketRocket ObjC framework bridged to Swift
https://github.com/square/SocketRocket
Then you just create an instance of the class and use it in Swift, i.e.:
var socket = SRWebSocket(...)
socket.open()
socket.send()
socket.close()
Example:
You create a NSURLRequest:
var urlRequest = NSURLRequest(URL: NSURL(string: "http://host.com"))
then init the socket with it
socket = SRWebSocket(URLRequest: urlRequest)
No need to link the framework, just import the files

Client-Server application on different computers

I want to modify my code to make the clients connect to the server if the server is hosted on a different machine. This is the code I have now:
Server:
int port = 5000;
ServerSocket server = new ServerSocket(port);
Socket socket = server.accept();
output/input streams....
Client:
String host = "localhost";
int port = 5000;
Socket socket = new Socket(host, port);
OutputStream out = socket.getOutputStream();
InputStream in = socket.getInputStream();
I am aware of the inetAddress and that's what I need help with, I don't know how to use it correctly, I don't want any complicated methods just enough to connect them together. Also I want to know if it is possible to use DNS for this or if I need a web server or something similar (of course DNS is purely curiosity).

To connect to a remote machine you need that machines IP address or hostname, then you can use InetAddress.getByName(String).
You'd use the IP address if there's no DNS server available to resolve the IP from the hostname, like this:
Socket socket = new Socket(InetAddress.getByName("1.2.3.4"), 5000);
Or is there's is a DNS server, then you can just pass the servers hostname like this:
Socket socket = new Socket(InetAddress.getByName("myserver"), 5000);

Read data from a particular port and specified IP using java

I would like to read the messages from a particular port.For example the IP is 1.2.3.4 and the port is 1000. Already the IP is used for receiving some messages. What I would like to do is to listen to that particular IP and receive all the messages using a java program. Will
SocketServer do the purpose??
ServerSocket ss = new ServerSocket(1000);
Socket socket = new Socket("1.2.3.4",1000);
socket = ss.accept();
Is it possible to read every contents that are being received by the particular IP and port?

To listen to a specific address you have to create a ServerSocket like this
ServerSocket ss = new ServerSocket(); // Unbound socket
ss.bind(new InetSocketAddress("1.2.3.4", 1000)); // Bind the socket to a specific interface
Socket client = ss.accept();
This way the server socket is bound to a specific network interface and will only receive incoming connections from it.