Merge pull request #22 from davidalves04/10-create-network-communication-classes

Create network communication classes

main/src/main/java/sd/protocol/MessageProtocol.java

@@ -0,0 +1,41 @@
+package sd.protocol;
+
+import java.io.Serializable;
+import sd.model.MessageType; // Assuming MessageType is in sd.model or sd.protocol
+
+/**
+ * Interface defining the contract for all messages exchanged in the simulator.
+ * Ensures that any message can be identified and routed.
+ * * This interface extends Serializable to allow objects that implement it
+ * to be sent over Sockets (ObjectOutputStream).
+ *
+ */
+public interface MessageProtocol extends Serializable {
+
+    /**
+     * Returns the type of the message, indicating its purpose.
+     * @return The MessageType (e.g., VEHICLE_TRANSFER, STATS_UPDATE).
+     */
+    MessageType getType();
+
+    /**
+     * Returns the data object (payload) that this message carries.
+     * The type of object will depend on the MessageType.
+     * * - If getType() == VEHICLE_TRANSFER, the payload will be a {@link sd.model.Vehicle} object.
+     * - If getType() == STATS_UPDATE, the payload will be a statistics object.
+     * * @return The data object (payload), which must also be Serializable.
+     */
+    Object getPayload();
+
+    /**
+     * Returns the ID of the node (Process) that sent this message.
+     * @return String (e.g., "Cr1", "Cr5", "S").
+     */
+    String getSourceNode();
+
+    /**
+     * Returns the ID of the destination node (Process) for this message.
+     * @return String (e.g., "Cr2", "DashboardServer").
+     */
+    String getDestinationNode();
+}

main/src/main/java/sd/protocol/SocketConnection.java

@@ -0,0 +1,183 @@
+package sd.protocol; 
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.net.ConnectException;
+import java.net.Socket;
+import java.net.SocketTimeoutException;
+import java.net.UnknownHostException;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Wrapper class that simplifies communication via Sockets.
+ * Includes connection retry logic for robustness.
+ */
+public class SocketConnection implements Closeable {
+
+    private final Socket socket;
+    private final ObjectOutputStream outputStream;
+    private final ObjectInputStream inputStream;
+
+    // --- Configuration for Retry Logic ---
+    /** Maximum number of connection attempts. */
+    private static final int MAX_RETRIES = 5; 
+    /** Delay between retry attempts in milliseconds. */
+    private static final long RETRY_DELAY_MS = 1000; 
+
+    /**
+     * Constructor for the "Client" (who initiates the connection).
+     * Tries to connect to a process that is already listening (Server).
+     * Includes retry logic in case of initial connection failure.
+     *
+     * @param host The host address (e.g., "localhost" from your simulation.properties)
+     * @param port The port (e.g., 8001 from your simulation.properties)
+     * @throws IOException If connection fails after all retries.
+     * @throws UnknownHostException If the host is not found (this error usually doesn't need retry).
+     * @throws InterruptedException If the thread is interrupted while waiting between retries.
+     */
+    public SocketConnection(String host, int port) throws IOException, UnknownHostException, InterruptedException {
+        Socket tempSocket = null;
+        IOException lastException = null;
+
+        System.out.printf("[SocketConnection] Attempting to connect to %s:%d...%n", host, port);
+
+        // --- Retry Loop ---
+        for (int attempt = 1; attempt <= MAX_RETRIES; attempt++) {
+            try {
+                // Try to establish the connection
+                tempSocket = new Socket(host, port);
+
+                // If successful, break out of the retry loop
+                System.out.printf("[SocketConnection] Connected successfully on attempt %d.%n", attempt);
+                lastException = null; // Clear last error on success
+                break;
+
+            } catch (ConnectException | SocketTimeoutException e) {
+                // These are common errors indicating the server might not be ready.
+                lastException = e;
+                System.out.printf("[SocketConnection] Attempt %d/%d failed: %s. Retrying in %d ms...%n",
+                        attempt, MAX_RETRIES, e.getMessage(), RETRY_DELAY_MS);
+
+                if (attempt < MAX_RETRIES) {
+                    // Wait before the next attempt
+                    TimeUnit.MILLISECONDS.sleep(RETRY_DELAY_MS);
+                }
+            } catch (IOException e) {
+                // Other IOExceptions might be more permanent, but we retry anyway.
+                 lastException = e;
+                 System.out.printf("[SocketConnection] Attempt %d/%d failed with IOException: %s. Retrying in %d ms...%n",
+                        attempt, MAX_RETRIES, e.getMessage(), RETRY_DELAY_MS);
+                 if (attempt < MAX_RETRIES) {
+                     TimeUnit.MILLISECONDS.sleep(RETRY_DELAY_MS);
+                 }
+            }
+        } // --- End of Retry Loop ---
+
+        // If after all retries tempSocket is still null, it means connection failed permanently.
+        if (tempSocket == null) {
+            System.err.printf("[SocketConnection] Failed to connect to %s:%d after %d attempts.%n", host, port, MAX_RETRIES);
+            if (lastException != null) {
+                 throw lastException; // Throw the last exception encountered
+            } else {
+                 // Should not happen if loop ran, but as a fallback
+                 throw new IOException("Failed to connect after " + MAX_RETRIES + " attempts, reason unknown.");
+            }
+        }
+
+        // If connection was successful, assign to final variable and create streams
+        this.socket = tempSocket;
+        try {
+            // IMPORTANT: The order is crucial. OutputStream first.
+            this.outputStream = new ObjectOutputStream(socket.getOutputStream());
+            this.inputStream = new ObjectInputStream(socket.getInputStream());
+        } catch (IOException e) {
+             // If stream creation fails even after successful socket connection, clean up.
+             System.err.println("[SocketConnection] Failed to create streams after connection: " + e.getMessage());
+             try { socket.close(); } catch (IOException closeEx) { /* ignore */ }
+             throw e; // Re-throw the stream creation exception
+        }
+    }
+
+
+    /**
+     * Constructor for the "Server" (who accepts the connection).
+     * Receives a Socket that has already been accepted by a ServerSocket.
+     * No retry logic needed here as the connection is already established.
+     *
+     * @param acceptedSocket The Socket returned by serverSocket.accept().
+     * @throws IOException If stream creation fails.
+     */
+    public SocketConnection(Socket acceptedSocket) throws IOException {
+        this.socket = acceptedSocket;
+
+        // IMPORTANT: The order is crucial. OutputStream first.
+        this.outputStream = new ObjectOutputStream(socket.getOutputStream());
+        this.inputStream = new ObjectInputStream(socket.getInputStream());
+        System.out.printf("[SocketConnection] Connection accepted from %s:%d.%n",
+            acceptedSocket.getInetAddress().getHostAddress(), acceptedSocket.getPort());
+    }
+
+    /**
+     * Sends (serializes) a MessageProtocol object over the socket.
+     *
+     * @param message The "envelope" (which contains the Vehicle) to be sent.
+     * @throws IOException If writing to the stream fails or socket is not connected.
+     */
+    public void sendMessage(MessageProtocol message) throws IOException {
+        if (!isConnected()) {
+            throw new IOException("Socket is not connected.");
+        }
+        synchronized (outputStream) {
+            outputStream.writeObject(message);
+            outputStream.flush(); // Ensures the message is sent immediately.
+        }
+    }
+
+    /**
+     * Tries to read (deserialize) a MessageProtocol object from the socket.
+     * This call is "blocked" until an object is received.
+     *
+     * @return The "envelope" (MessageProtocol) that was received.
+     * @throws IOException If the connection is lost, the stream is corrupted, or socket is not connected.
+     * @throws ClassNotFoundException If the received object is unknown.
+     */
+    public MessageProtocol receiveMessage() throws IOException, ClassNotFoundException {
+       if (!isConnected()) {
+            throw new IOException("Socket is not connected.");
+        }
+        synchronized (inputStream) {
+            return (MessageProtocol) inputStream.readObject();
+        }
+    }
+
+    /**
+     * Closes the socket and all streams (Input and Output).
+     * It is called automatically if you use 'try-with-resources'.
+     */
+    @Override
+    public void close() throws IOException {
+         System.out.printf("[SocketConnection] Closing connection to %s:%d.%n",
+            socket != null ? socket.getInetAddress().getHostAddress() : "N/A",
+            socket != null ? socket.getPort() : -1);
+        try {
+            if (inputStream != null) inputStream.close();
+        } catch (IOException e) { /* ignore */ }
+
+        try {
+            if (outputStream != null) outputStream.close();
+        } catch (IOException e) { /* ignore */ }
+
+        if (socket != null && !socket.isClosed()) {
+            socket.close();
+        }
+    }
+
+    /**
+     * @return true if the socket is still connected and not closed.
+     */
+    public boolean isConnected() {
+        return socket != null && socket.isConnected() && !socket.isClosed();
+    }
+}