WebSocketServer.java

import java.io.*;
import java.net.*;
import java.security.MessageDigest;
import java.util.*;
import java.util.Base64;

public class WebSocketServer {
    
    private static List<String> messages = new ArrayList<>();
    
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8080);
            System.out.println("WebSocket Server is running on port 8080...");
            
            while (true) {
                Socket clientSocket = serverSocket.accept();
                System.out.println("Client connected: " + clientSocket.getInetAddress());
                
                new Thread(() -> handleClient(clientSocket)).start();
            }
        } catch (IOException e) {
            System.err.println("Server error: " + e.getMessage());
            e.printStackTrace();
        }
    }
    
    private static void handleClient(Socket clientSocket) {
        try {
            InputStream in = clientSocket.getInputStream();
            OutputStream out = clientSocket.getOutputStream();
            
            // Perform WebSocket handshake
            BufferedReader reader = new BufferedReader(new InputStreamReader(in));
            String data = reader.readLine();
            String key = "";
            
            while (!data.isEmpty()) {
                if (data.startsWith("Sec-WebSocket-Key:")) {
                    key = data.substring(19).trim();
                }
                data = reader.readLine();
            }
            
            // Send handshake response
            String accept = Base64.getEncoder().encodeToString(
                MessageDigest.getInstance("SHA-1").digest(
                    (key + "258EAFA5-E914-47DA-95CA-C5AB0DC85B11").getBytes()
                )
            );
            
            String response = "HTTP/1.1 101 Switching Protocols\r\n" +
                            "Upgrade: websocket\r\n" +
                            "Connection: Upgrade\r\n" +
                            "Sec-WebSocket-Accept: " + accept + "\r\n\r\n";
            out.write(response.getBytes());
            
            System.out.println("WebSocket handshake completed");
            
            // Handle messages
            while (true) {
                String message = receiveMessage(in);
                if (message == null) break;
                
                System.out.println("Received: " + message);
                String result = processRequest(message);
                sendMessage(out, result);
            }
            
            clientSocket.close();
            System.out.println("Client disconnected");
            
        } catch (Exception e) {
            System.err.println("Client handler error: " + e.getMessage());
        }
    }
    
    private static String receiveMessage(InputStream in) throws IOException {
        int b = in.read();
        if (b == -1) return null;
        
        int opcode = b & 0x0F;
        if (opcode == 8) return null; // Close frame
        
        b = in.read();
        int length = b & 0x7F;
        
        byte[] masks = new byte[4];
        in.read(masks);
        
        byte[] data = new byte[length];
        in.read(data);
        
        for (int i = 0; i < data.length; i++) {
            data[i] = (byte) (data[i] ^ masks[i % 4]);
        }
        
        return new String(data);
    }
    
    private static void sendMessage(OutputStream out, String message) throws IOException {
        byte[] data = message.getBytes();
        out.write(0x81); // Text frame
        out.write(data.length);
        out.write(data);
        out.flush();
    }
    
    private static String processRequest(String request) {
        String[] parts = request.split("\\|", 2);
        String method = parts[0];
        
        switch (method) {
            case "HELLO":
                String name = parts.length > 1 ? parts[1] : "Guest";
                return "Hello, " + name + "!";
                
            case "ADD":
                String[] numbers = parts[1].split(",");
                int a = Integer.parseInt(numbers[0]);
                int b = Integer.parseInt(numbers[1]);
                return String.valueOf(a + b);
                
            case "SEND":
                String message = parts.length > 1 ? parts[1] : "";
                messages.add(message);
                System.out.println("Message stored: " + message);
                return "Message received";
                
            case "GETALL":
                if (messages.isEmpty()) {
                    return "No messages";
                }
                return String.join(";;", messages);
                
            default:
                return "Unknown method";
        }
    }
}