Added Server classes and modified Database class

src/main/java/controllers/Database.java

@@ -9,7 +9,7 @@ import java.math.BigInteger;
 import java.sql.*;
 
 public class Database {
-    public static boolean register(String username, String password, BigInteger e, BigInteger d, BigInteger n) {
+    public static boolean registerAccount(String username, String password, BigInteger e, BigInteger d, BigInteger n) {
         try (Connection connection = getConnection()) {
             if (connection == null) return false;
 
@@ -38,7 +38,7 @@ public class Database {
         }
     }
 
-    public static Account login(String username, CharSequence password) {
+    public static Account getAccount(String username, CharSequence password) {
         try (Connection connection = getConnection()) {
             if (connection == null) return null;
 
@@ -70,6 +70,28 @@ public class Database {
         }
     }
 
+    public static int getIdFromUsername(String username) {
+        try (Connection connection = getConnection()) {
+            if (connection == null) return -1;
+
+            try (PreparedStatement statement = connection.prepareStatement("""
+            SELECT id
+            FROM accounts
+            WHERE username = ?
+        """)) {
+                statement.setString(1, username);
+                ResultSet resultSet = statement.executeQuery();
+                if (resultSet.next()) {
+                    return resultSet.getInt(1);
+                }
+                return -1;
+            }
+        } catch (SQLException e) {
+            System.err.println("Error while trying to retrieve the id from the username");
+            return -1;
+        }
+    }
+
     private static Connection getConnection() throws SQLException {
         return DriverManager.getConnection(
                 System.getenv("db_url"),

src/main/java/controllers/MessageForwarder.java

@@ -0,0 +1,20 @@
+package controllers;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class MessageForwarder {
+    private static final Map<Integer, ServerThread> idThread;
+
+    static {
+        idThread = new HashMap<>();
+    }
+
+    public static void addUser(int id, ServerThread thread) {
+        idThread.put(id, thread);
+    }
+
+    public static void sendTo(int id, String message, int senderId) {
+        idThread.get(id).sendMessage(message, senderId);
+    }
+}

src/main/java/controllers/Server.java

@@ -0,0 +1,18 @@
+package controllers;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+public class Server {
+    public static void main(String[] args) {
+        try (ServerSocket serverSocket = new ServerSocket(21324)) {
+            Socket socket = serverSocket.accept();
+            ServerThread serverThread = new ServerThread(socket);
+            serverThread.start();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+    }
+}

src/main/java/controllers/ServerThread.java

@@ -0,0 +1,136 @@
+package controllers;
+
+import models.Account;
+import models.Rsa;
+
+import java.io.BufferedReader;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.math.BigInteger;
+import java.net.Socket;
+
+import static controllers.Database.getAccount;
+import static controllers.Database.registerAccount;
+
+public class ServerThread extends Thread {
+    private final Socket client;
+    private BufferedReader fromClient;
+    private DataOutputStream toClient;
+    private final Rsa rsa;
+    private BigInteger clientE, clientN;
+    private int clientId;
+
+    public ServerThread (Socket socket) {
+        this.client = socket;
+        rsa = new Rsa(1024);
+    }
+
+    public void run() {
+        try {
+            fromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));
+            toClient = new DataOutputStream(client.getOutputStream());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        try {
+            toClient.writeBytes(rsa.getE().toString());
+            toClient.writeBytes(rsa.getN().toString());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        try {
+            clientE = new BigInteger(fromClient.readLine());
+            clientN = new BigInteger(fromClient.readLine());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        for (;;) {
+            String operation;
+            try {
+                operation = rsa.decrypt(new BigInteger(fromClient.readLine()));
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+
+            String username, password;
+
+            try {
+                username = rsa.decrypt(new BigInteger(fromClient.readLine()));
+                password = rsa.decrypt(new BigInteger(fromClient.readLine()));
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+
+
+            try {
+                if ("LOGIN".equals(operation)) {
+                    if (login(username, password)) {
+                        toClient.writeBytes(rsa.encrypt("SUCCESS", clientE, clientN).toString());
+                        break;
+                    }
+                } else if ("REGISTER".equals(operation)) {
+                    if (register(username, password)) {
+                        toClient.writeBytes(rsa.encrypt("SUCCESS", clientE, clientN).toString());
+                        break;
+                    }
+                } else {
+                    toClient.writeBytes(rsa.encrypt("FAIL", clientE, clientN).toString());
+                }
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+        }
+
+        MessageForwarder.addUser(clientId, this);
+
+        int recipientId;
+        String message;
+
+        for (;;) {
+            try {
+                recipientId = Integer.parseInt(rsa.decrypt(new BigInteger(fromClient.readLine())));
+                message = rsa.decrypt(new BigInteger(fromClient.readLine()));
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+
+            if (message == null || "DISCONNECT".equals(message)) break;
+
+            MessageForwarder.sendTo(recipientId, message, clientId);
+        }
+    }
+
+    private boolean login(String username, String password) {
+        Account account = getAccount(username, password);
+        return account != null;
+    }
+
+    public boolean register(String username, String password) {
+        BigInteger clientD;
+
+        try {
+            clientD = new BigInteger(fromClient.readLine());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+
+        if (!registerAccount(username, password, clientE, clientD, clientN)) return false;
+
+        clientId = Database.getIdFromUsername(username);
+        return clientId != -1;
+    }
+
+    public void sendMessage(String message, int sender) {
+        try {
+            toClient.writeBytes("INCOMING");
+            toClient.writeInt(sender);
+            toClient.writeBytes(message);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}