Question

I have a SocketServer accepting incoming connections. For security reasons I should only allow local connections (connections from the machine on which server is running).

How can I determine if an incoming connection is from another machine? Is the following code safe for this?

Socket socket = someServerSocket.accept();
String remoteAddress = socket .getInetAddress().getHostAddress();
if (!fromThisMachine(remoteAddress)) {
    // Not from this machine.
}

while fromThisMachine() method is like this:

public boolean fromThisMachine(String remoteAddress) {
    try {
        Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
        while (interfaces.hasMoreElements()) {
            NetworkInterface networkInterface = interfaces.nextElement();
            Enumeration<InetAddress> addresses = networkInterface.getInetAddresses();
            while (addresses.hasMoreElements()) {
                InetAddress inetAddress = addresses.nextElement();
                String hostName = inetAddress.getHostName();
                String hostAddr = inetAddress.getHostAddress();
                if (hostName.equals(remoteAddress) || hostAddr.equals(remoteAddress)) {
                    return true;
                }
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
        return false;
    }
    log("Unauthorized request to server from: " + remoteAddress);
    return false;
}

Thanks,
Mohsen

Answer 1

If you want to limit connections from the localhost, then specify that when you open the ServerSocket. If you only listen on localhost, then you’ll only get connections from localhost.

    int port = .....
    SocketAddress socketAddress = new InetSocketAddress("127.0.0.1", port);
    ServerSocket serverSocket = new ServerSocket();
    serverSocket.bind(socketAddress);
    serverSocket.accept();