Error Handling and Recovery

/**
 * Exception indicating a shutdown signal from connection or channel
 */
public class ShutdownSignalException extends RuntimeException {
    /**
     * Get the shutdown reason object
     * @return AMQP method object indicating the reason
     */
    public Object getReason();
    
    /**
     * Check if this is a hard error (connection-level)
     * @return true for connection errors, false for channel errors
     */
    public boolean isHardError();
    
    /**
     * Check if shutdown was initiated by the application
     * @return true if application initiated, false if server initiated
     */
    public boolean isInitiatedByApplication();
    
    /**
     * Get reference to the connection or channel that was shut down
     * @return ShutdownNotifier object (Connection or Channel)
     */
    public ShutdownNotifier getReference();
}

/**
 * Exception for operations on already closed connections or channels
 */
public class AlreadyClosedException extends ShutdownSignalException {
    /**
     * Create exception with shutdown signal
     * @param shutdownSignalException - Original shutdown signal
     */
    public AlreadyClosedException(ShutdownSignalException shutdownSignalException);
}

/**
 * Exception for malformed AMQP frames
 */
public class MalformedFrameException extends IOException {
    /**
     * Create exception with message
     * @param message - Error message
     */
    public MalformedFrameException(String message);
}

/**
 * Exception for missed heartbeats from server
 */
public class MissedHeartbeatException extends IOException {
    /**
     * Create exception with message
     * @param message - Error message
     */
    public MissedHeartbeatException(String message);
}

// Handling shutdown signals
try {
    channel.basicPublish("exchange", "key", null, message.getBytes());
} catch (ShutdownSignalException e) {
    if (e.isHardError()) {
        System.out.println("Connection error: " + e.getReason());
        // Handle connection-level error
        reconnect();
    } else {
        System.out.println("Channel error: " + e.getReason());
        // Handle channel-level error  
        reopenChannel();
    }
} catch (AlreadyClosedException e) {
    System.out.println("Attempted operation on closed resource");
    // Recreate connection/channel
    recreateResources();
}

/**
 * Base class for possible authentication failures
 */
public class PossibleAuthenticationFailureException extends IOException {
    /**
     * Create exception with message
     * @param message - Error message
     */
    public PossibleAuthenticationFailureException(String message);
}

/**
 * Exception for confirmed authentication failures
 */
public class AuthenticationFailureException extends PossibleAuthenticationFailureException {
    /**
     * Create exception with message
     * @param message - Error message
     */
    public AuthenticationFailureException(String message);
}

/**
 * Exception for protocol version mismatches
 */
public class ProtocolVersionMismatchException extends IOException {
    /**
     * Create exception with version information
     * @param clientMajor - Client protocol major version
     * @param clientMinor - Client protocol minor version
     * @param serverMajor - Server protocol major version
     * @param serverMinor - Server protocol minor version
     */
    public ProtocolVersionMismatchException(int clientMajor, int clientMinor, int serverMajor, int serverMinor);
    
    public int getClientMajor();
    public int getClientMinor();
    public int getServerMajor();
    public int getServerMinor();
}

/**
 * Error for unexpected AMQP frames
 */
public class UnexpectedFrameError extends Error {
    /**
     * Create error with frame information
     * @param frame - Unexpected frame object
     * @param expectedFrameType - Expected frame type
     */
    public UnexpectedFrameError(Frame frame, int expectedFrameType);
}

/**
 * Error for unexpected AMQP methods
 */  
public class UnexpectedMethodError extends Error {
    /**
     * Create error with method information
     * @param method - Unexpected method object
     */
    public UnexpectedMethodError(Method method);
}

/**
 * Exception for unknown class or method IDs
 */
public class UnknownClassOrMethodId extends IOException {
    /**
     * Create exception with class and method IDs
     * @param classId - AMQP class ID
     * @param methodId - AMQP method ID
     */
    public UnknownClassOrMethodId(int classId, int methodId);
    
    public int getClassId();
    public int getMethodId();
}

/**
 * Exception for channel RPC operation timeouts
 */
public class ChannelContinuationTimeoutException extends TimeoutException {
    /**
     * Create timeout exception
     */
    public ChannelContinuationTimeoutException();
    
    /**
     * Create timeout exception with message
     * @param message - Error message
     */
    public ChannelContinuationTimeoutException(String message);
}

/**
 * Exception for consumer cancellation
 */
public class ConsumerCancelledException extends RuntimeException {
    /**
     * Create consumer cancellation exception
     */
    public ConsumerCancelledException();
}

/**
 * Exception for unroutable RPC requests
 */
public class UnroutableRpcRequestException extends IOException {
    /**
     * Create exception for unroutable RPC request
     * @param message - Error message
     */
    public UnroutableRpcRequestException(String message);
}

/**
 * Exception during topology recovery process
 */
public class TopologyRecoveryException extends Exception {
    /**
     * Create recovery exception with cause
     * @param cause - Underlying cause of recovery failure
     */
    public TopologyRecoveryException(Throwable cause);
    
    /**
     * Create recovery exception with message and cause
     * @param message - Error message
     * @param cause - Underlying cause
     */
    public TopologyRecoveryException(String message, Throwable cause);
}

/**
 * Interface for objects that support recovery
 */
public interface Recoverable {
    /**
     * Add a recovery listener
     * @param listener - Listener to notify on recovery events
     */
    void addRecoveryListener(RecoveryListener listener);
    
    /**
     * Remove a recovery listener
     * @param listener - Listener to remove
     */
    void removeRecoveryListener(RecoveryListener listener);
}

/**
 * Listener interface for recovery events
 */
public interface RecoveryListener {
    /**
     * Called when recovery completes successfully
     * @param recoverable - Object that was recovered
     */
    void handleRecovery(Recoverable recoverable);
    
    /**
     * Called when recovery process starts
     * @param recoverable - Object being recovered
     */
    void handleRecoveryStarted(Recoverable recoverable);
}

/**
 * Interface for handling recovery delays
 */
public interface RecoveryDelayHandler {
    /**
     * Get delay before next recovery attempt
     * @param recoveryAttempts - Number of recovery attempts so far
     * @return Delay in milliseconds before next attempt
     */
    long getDelay(int recoveryAttempts);
}

// Custom recovery listener
RecoveryListener recoveryListener = new RecoveryListener() {
    @Override
    public void handleRecovery(Recoverable recoverable) {
        if (recoverable instanceof Connection) {
            System.out.println("Connection recovered successfully");
            // Notify application components
            notifyConnectionRecovered();
        } else if (recoverable instanceof Channel) {
            System.out.println("Channel recovered successfully");
            // Restart consumers if needed
            restartConsumers();
        }
    }
    
    @Override
    public void handleRecoveryStarted(Recoverable recoverable) {
        System.out.println("Recovery started for: " + recoverable);
        // Pause message processing during recovery
        pauseProcessing();
    }
};

// Add to recoverable connection
ConnectionFactory factory = new ConnectionFactory();
factory.setAutomaticRecoveryEnabled(true);
RecoverableConnection connection = (RecoverableConnection) factory.newConnection();
connection.addRecoveryListener(recoveryListener);

// Custom recovery delay handler with exponential backoff
RecoveryDelayHandler delayHandler = new RecoveryDelayHandler() {
    @Override
    public long getDelay(int recoveryAttempts) {
        // Exponential backoff: 1s, 2s, 4s, 8s, max 30s
        long delay = Math.min(1000L * (1L << recoveryAttempts), 30000L);
        System.out.println("Recovery attempt " + recoveryAttempts + ", waiting " + delay + "ms");
        return delay;
    }
};

ConnectionFactory factory = new ConnectionFactory();
factory.setRecoveryDelayHandler(delayHandler);
factory.setAutomaticRecoveryEnabled(true);

/**
 * Interface for handling exceptions in consumers and connections
 */
public interface ExceptionHandler {
    /**
     * Handle unexpected exception in connection driver
     * @param conn - Connection where exception occurred
     * @param exception - Exception that occurred
     */
    void handleUnexpectedConnectionDriverException(Connection conn, Throwable exception);
    
    /**
     * Handle exception in return listener
     * @param channel - Channel where exception occurred
     * @param exception - Exception that occurred
     */
    void handleReturnListenerException(Channel channel, Throwable exception);
    
    /**
     * Handle exception in flow listener
     * @param channel - Channel where exception occurred
     * @param exception - Exception that occurred
     */
    void handleFlowListenerException(Channel channel, Throwable exception);
    
    /**
     * Handle exception in confirm listener
     * @param channel - Channel where exception occurred
     * @param exception - Exception that occurred
     */
    void handleConfirmListenerException(Channel channel, Throwable exception);
    
    /**
     * Handle exception in blocked listener
     * @param connection - Connection where exception occurred
     * @param exception - Exception that occurred
     */
    void handleBlockedListenerException(Connection connection, Throwable exception);
    
    /**
     * Handle exception in consumer
     * @param channel - Channel where exception occurred
     * @param exception - Exception that occurred
     * @param consumer - Consumer that threw exception
     * @param consumerTag - Consumer tag
     * @param methodName - Method where exception occurred
     */
    void handleConsumerException(Channel channel, Throwable exception, Consumer consumer, String consumerTag, String methodName);
    
    /**
     * Handle exception during connection recovery
     * @param conn - Connection being recovered
     * @param exception - Exception that occurred
     */
    void handleConnectionRecoveryException(Connection conn, Throwable exception);
    
    /**
     * Handle exception during channel recovery
     * @param ch - Channel being recovered
     * @param exception - Exception that occurred
     */
    void handleChannelRecoveryException(Channel ch, Throwable exception);
    
    /**
     * Handle exception during topology recovery
     * @param conn - Connection being recovered
     * @param ch - Channel being recovered (may be null)
     * @param exception - Exception that occurred
     */
    void handleTopologyRecoveryException(Connection conn, Channel ch, TopologyRecoveryException exception);
}

// Custom exception handler with logging and metrics
public class CustomExceptionHandler implements ExceptionHandler {
    private static final Logger logger = LoggerFactory.getLogger(CustomExceptionHandler.class);
    private final MetricsRegistry metrics;
    
    public CustomExceptionHandler(MetricsRegistry metrics) {
        this.metrics = metrics;
    }
    
    @Override
    public void handleConsumerException(Channel channel, Throwable exception, 
                                       Consumer consumer, String consumerTag, String methodName) {
        logger.error("Consumer exception in {}: {}", methodName, exception.getMessage(), exception);
        metrics.counter("consumer.exceptions").increment();
        
        // Optionally restart consumer
        if (exception instanceof RuntimeException) {
            restartConsumer(channel, consumer, consumerTag);
        }
    }
    
    @Override
    public void handleConnectionRecoveryException(Connection conn, Throwable exception) {
        logger.error("Connection recovery failed: {}", exception.getMessage(), exception);
        metrics.counter("connection.recovery.failures").increment();
        
        // Send alert to monitoring system
        alertingService.sendAlert("RabbitMQ connection recovery failed", exception);
    }
    
    @Override
    public void handleTopologyRecoveryException(Connection conn, Channel ch, TopologyRecoveryException exception) {
        logger.error("Topology recovery failed: {}", exception.getMessage(), exception);
        metrics.counter("topology.recovery.failures").increment();
        
        // Attempt manual topology recreation
        scheduleTopologyRecreation(conn, ch);
    }
    
    // Implement other methods with appropriate logging and handling...
}

// Use custom exception handler
ConnectionFactory factory = new ConnectionFactory();
factory.setExceptionHandler(new CustomExceptionHandler(metricsRegistry));

public class RobustConsumer extends DefaultConsumer {
    private static final Logger logger = LoggerFactory.getLogger(RobustConsumer.class);
    private final int maxRetries;
    
    public RobustConsumer(Channel channel, int maxRetries) {
        super(channel);
        this.maxRetries = maxRetries;
    }
    
    @Override
    public void handleDelivery(String consumerTag, Envelope envelope,
                              AMQP.Properties properties, byte[] body) throws IOException {
        try {
            processMessage(new String(body, "UTF-8"), properties);
            getChannel().basicAck(envelope.getDeliveryTag(), false);
            
        } catch (Exception e) {
            logger.error("Error processing message: {}", e.getMessage(), e);
            handleProcessingError(envelope, properties, body, e);
        }
    }
    
    private void handleProcessingError(Envelope envelope, AMQP.BasicProperties properties, 
                                     byte[] body, Exception error) throws IOException {
        // Get retry count from headers
        Map<String, Object> headers = properties.getHeaders();
        int retryCount = headers != null && headers.containsKey("x-retry-count") ?
            (Integer) headers.get("x-retry-count") : 0;
            
        if (retryCount < maxRetries) {
            // Republish for retry
            republishForRetry(envelope, properties, body, retryCount + 1);
            getChannel().basicAck(envelope.getDeliveryTag(), false);
        } else {
            // Send to dead letter queue or log as failed
            logger.error("Message failed after {} retries, sending to DLQ", maxRetries);
            getChannel().basicNack(envelope.getDeliveryTag(), false, false);
        }
    }
    
    @Override
    public void handleShutdownSignal(String consumerTag, ShutdownSignalException sig) {
        if (!sig.isInitiatedByApplication()) {
            logger.error("Consumer {} received unexpected shutdown: {}", consumerTag, sig.getReason());
            // Implement reconnection logic
            scheduleReconnection();
        }
    }
}

public class ResilientConnectionManager {
    private ConnectionFactory factory;
    private volatile Connection connection;
    private final List<Channel> channels = new CopyOnWriteArrayList<>();
    
    public ResilientConnectionManager() {
        setupConnectionFactory();
    }
    
    private void setupConnectionFactory() {
        factory = new ConnectionFactory();
        factory.setAutomaticRecoveryEnabled(true);
        factory.setNetworkRecoveryInterval(5000);
        
        // Custom recovery listener
        factory.setRecoveryDelayHandler(recoveryAttempts -> {
            long delay = Math.min(1000L * recoveryAttempts, 30000L);
            logger.info("Recovery attempt {}, waiting {}ms", recoveryAttempts, delay);
            return delay;
        });
        
        // Custom exception handler
        factory.setExceptionHandler(new ExceptionHandler() {
            @Override
            public void handleConnectionRecoveryException(Connection conn, Throwable exception) {
                logger.error("Connection recovery failed", exception);
                // Custom recovery logic
                attemptManualRecovery();
            }
            
            // ... implement other methods
        });
    }
    
    public synchronized Connection getConnection() throws IOException, TimeoutException {
        if (connection == null || !connection.isOpen()) {
            connection = factory.newConnection();
            ((RecoverableConnection) connection).addRecoveryListener(new RecoveryListener() {
                @Override
                public void handleRecovery(Recoverable recoverable) {
                    logger.info("Connection recovered successfully");
                    // Recreate channels and consumers
                    recreateChannels();
                }
                
                @Override
                public void handleRecoveryStarted(Recoverable recoverable) {
                    logger.info("Connection recovery started");
                }
            });
        }
        return connection;
    }
}