Publisher Confirms and Returns

/**
 * Enable publisher confirms on this channel
 * All subsequently published messages will be confirmed
 */
void confirmSelect() throws IOException;

/**
 * Wait for all outstanding confirms to be received
 * @return true if all confirms received, false if timeout
 */
boolean waitForConfirms() throws InterruptedException;

/**
 * Wait for confirms with timeout
 * @param timeout - Maximum time to wait in milliseconds
 * @return true if all confirms received within timeout
 */
boolean waitForConfirms(long timeout) throws InterruptedException, TimeoutException;

/**
 * Wait for at least one confirm to be received
 * Throws exception if any message is nacked
 */
void waitForConfirmsOrDie() throws IOException, InterruptedException;

/**
 * Wait for confirms with timeout, throw exception on nack
 * @param timeout - Maximum time to wait in milliseconds
 */
void waitForConfirmsOrDie(long timeout) throws IOException, InterruptedException, TimeoutException;

/**
 * Get the next publish sequence number
 * @return Sequence number for next published message
 */
long getNextPublishSeqNo();

/**
 * Add a confirm listener for asynchronous confirm handling
 * @param listener - Listener to receive confirm/nack notifications
 */
void addConfirmListener(ConfirmListener listener);

/**
 * Remove a confirm listener
 * @param listener - Listener to remove
 * @return true if listener was removed
 */
boolean removeConfirmListener(ConfirmListener listener);

/**
 * Clear all confirm listeners
 */
void clearConfirmListeners();

// Synchronous confirms - wait for each message
Channel channel = connection.createChannel();
channel.confirmSelect();

for (int i = 0; i < 1000; i++) {
    String message = "Message " + i;
    channel.basicPublish("exchange", "routing.key", null, message.getBytes());
    
    // Wait for this message to be confirmed
    if (channel.waitForConfirms(5000)) {
        System.out.println("Message " + i + " confirmed");
    } else {
        System.out.println("Message " + i + " not confirmed within timeout");
    }
}

// Batch confirms - publish multiple messages then wait
channel.confirmSelect();
int batchSize = 100;

for (int i = 0; i < 1000; i++) {
    String message = "Message " + i;
    channel.basicPublish("exchange", "routing.key", null, message.getBytes());
    
    if ((i + 1) % batchSize == 0) {
        // Wait for batch to be confirmed
        try {
            channel.waitForConfirmsOrDie(10000);
            System.out.println("Batch " + ((i + 1) / batchSize) + " confirmed");
        } catch (IOException e) {
            System.out.println("Batch failed: " + e.getMessage());
        }
    }
}

/**
 * Listener interface for publisher confirms
 */
public interface ConfirmListener {
    /**
     * Called when message(s) are acknowledged by broker
     * @param deliveryTag - Delivery tag of confirmed message
     * @param multiple - True if multiple messages confirmed (up to and including deliveryTag)
     */
    void handleAck(long deliveryTag, boolean multiple) throws IOException;
    
    /**
     * Called when message(s) are rejected by broker
     * @param deliveryTag - Delivery tag of rejected message
     * @param multiple - True if multiple messages rejected (up to and including deliveryTag)  
     */
    void handleNack(long deliveryTag, boolean multiple) throws IOException;
}

/**
 * Functional interface for confirm acknowledgments
 */
@FunctionalInterface
public interface ConfirmCallback {
    /**
     * Handle confirm acknowledgment
     * @param deliveryTag - Delivery tag of confirmed message
     * @param multiple - True if multiple messages confirmed
     */
    void handle(long deliveryTag, boolean multiple) throws IOException;
}

// Asynchronous confirms with listener
channel.confirmSelect();

channel.addConfirmListener(new ConfirmListener() {
    @Override
    public void handleAck(long deliveryTag, boolean multiple) throws IOException {
        if (multiple) {
            System.out.println("Messages up to " + deliveryTag + " confirmed");
            // Remove confirmed messages from tracking
            removeConfirmedMessages(deliveryTag);
        } else {
            System.out.println("Message " + deliveryTag + " confirmed");
            removeConfirmedMessage(deliveryTag);
        }
    }
    
    @Override
    public void handleNack(long deliveryTag, boolean multiple) throws IOException {
        if (multiple) {
            System.out.println("Messages up to " + deliveryTag + " rejected");
            // Handle rejected messages
            handleRejectedMessages(deliveryTag);
        } else {
            System.out.println("Message " + deliveryTag + " rejected");
            handleRejectedMessage(deliveryTag);
        }
    }
});

// Publish with tracking
Map<Long, String> outstandingConfirms = new ConcurrentHashMap<>();

for (int i = 0; i < 1000; i++) {
    String message = "Message " + i;
    long deliveryTag = channel.getNextPublishSeqNo();
    outstandingConfirms.put(deliveryTag, message);
    
    channel.basicPublish("exchange", "routing.key", null, message.getBytes());
}

// Using functional confirm callbacks
ConfirmCallback ackCallback = (deliveryTag, multiple) -> {
    System.out.println("Acked: " + deliveryTag + " (multiple: " + multiple + ")");
    confirmTracker.handleAck(deliveryTag, multiple);
};

ConfirmCallback nackCallback = (deliveryTag, multiple) -> {
    System.out.println("Nacked: " + deliveryTag + " (multiple: " + multiple + ")");
    confirmTracker.handleNack(deliveryTag, multiple);
    // Retry logic here
};

channel.addConfirmListener(ackCallback, nackCallback);

/**
 * Add a return listener to handle returned messages
 * @param listener - Listener to receive returned messages
 */
void addReturnListener(ReturnListener listener);

/**
 * Remove a return listener
 * @param listener - Listener to remove
 * @return true if listener was removed
 */
boolean removeReturnListener(ReturnListener listener);

/**
 * Clear all return listeners
 */
void clearReturnListeners();

/**
 * Listener interface for returned messages
 */
public interface ReturnListener {
    /**
     * Called when a message is returned by the broker
     * @param replyCode - Reply code indicating why message was returned
     * @param replyText - Human-readable reply text
     * @param exchange - Exchange the message was published to
     * @param routingKey - Routing key used for publishing
     * @param properties - Message properties
     * @param body - Message body
     */
    void handleReturn(int replyCode, String replyText, String exchange, String routingKey, 
                      AMQP.BasicProperties properties, byte[] body) throws IOException;
}

/**
 * Functional interface for handling returned messages  
 */
@FunctionalInterface
public interface ReturnCallback {
    /**
     * Handle returned message
     * @param returnMessage - Return information
     */
    void handle(Return returnMessage) throws IOException;
}

/**
 * Class representing a returned message
 */
public class Return {
    public int getReplyCode();
    public String getReplyText();
    public String getExchange();
    public String getRoutingKey();
    public AMQP.BasicProperties getProperties();
    public byte[] getBody();
}

// Handle returned messages with listener
channel.addReturnListener(new ReturnListener() {
    @Override
    public void handleReturn(int replyCode, String replyText, String exchange, String routingKey,
                           AMQP.BasicProperties properties, byte[] body) throws IOException {
        
        String message = new String(body, "UTF-8");
        System.out.printf("Message returned: %d - %s%n", replyCode, replyText);
        System.out.printf("Exchange: %s, Routing Key: %s%n", exchange, routingKey);
        System.out.printf("Message: %s%n", message);
        
        // Handle based on reason
        switch (replyCode) {
            case 312: // NO_ROUTE
                System.out.println("No route found for message");
                // Try alternative routing or store for retry
                handleUnroutableMessage(exchange, routingKey, properties, body);
                break;
            case 313: // NO_CONSUMERS  
                System.out.println("No consumers available");
                // Queue exists but no consumers
                handleNoConsumers(exchange, routingKey, properties, body);
                break;
            default:
                System.out.println("Unknown return reason: " + replyCode);
                handleUnknownReturn(replyCode, replyText, properties, body);
        }
    }
});

// Publish with mandatory flag
String message = "Important message";
boolean mandatory = true; // Return if unroutable
channel.basicPublish("my.exchange", "nonexistent.key", mandatory, null, message.getBytes());

// Using functional return callback
ReturnCallback returnCallback = returnMessage -> {
    System.out.println("Returned: " + returnMessage.getReplyText());
    System.out.println("Exchange: " + returnMessage.getExchange());  
    System.out.println("Routing Key: " + returnMessage.getRoutingKey());
    
    String messageBody = new String(returnMessage.getBody(), "UTF-8");
    System.out.println("Message: " + messageBody);
    
    // Store for retry or send to dead letter
    storeForRetry(returnMessage);
};

channel.addReturnListener(returnCallback);

public class RobustPublisher {
    private final Channel channel;
    private final Map<Long, PendingMessage> pendingConfirms = new ConcurrentHashMap<>();
    private final AtomicLong publishSeqNo = new AtomicLong(0);
    
    public RobustPublisher(Channel channel) throws IOException {
        this.channel = channel;
        channel.confirmSelect();
        setupListeners();
    }
    
    private void setupListeners() {
        // Handle confirms
        channel.addConfirmListener(new ConfirmListener() {
            @Override
            public void handleAck(long deliveryTag, boolean multiple) throws IOException {
                if (multiple) {
                    // Remove all confirmed messages up to deliveryTag
                    pendingConfirms.entrySet().removeIf(entry -> entry.getKey() <= deliveryTag);
                } else {
                    pendingConfirms.remove(deliveryTag);
                }
                System.out.println("Confirmed: " + deliveryTag + " (multiple: " + multiple + ")");
            }
            
            @Override
            public void handleNack(long deliveryTag, boolean multiple) throws IOException {
                if (multiple) {
                    // Handle all nacked messages up to deliveryTag
                    pendingConfirms.entrySet().stream()
                        .filter(entry -> entry.getKey() <= deliveryTag)
                        .forEach(entry -> handleNackedMessage(entry.getValue()));
                    pendingConfirms.entrySet().removeIf(entry -> entry.getKey() <= deliveryTag);
                } else {
                    PendingMessage message = pendingConfirms.remove(deliveryTag);
                    if (message != null) {
                        handleNackedMessage(message);
                    }
                }
                System.out.println("Nacked: " + deliveryTag + " (multiple: " + multiple + ")");
            }
        });
        
        // Handle returns
        channel.addReturnListener(returnMessage -> {
            System.out.println("Message returned: " + returnMessage.getReplyText());
            
            // Find the corresponding pending message and mark as returned
            String correlationId = returnMessage.getProperties().getCorrelationId();
            if (correlationId != null) {
                handleReturnedMessage(correlationId, returnMessage);
            }
        });
    }
    
    public void publishReliably(String exchange, String routingKey, AMQP.BasicProperties props, 
                               byte[] body) throws IOException {
        
        // Generate correlation ID for tracking
        String correlationId = UUID.randomUUID().toString();
        AMQP.BasicProperties propsWithCorrelation = new AMQP.BasicProperties.Builder()
            .correlationId(correlationId)
            .contentType(props != null ? props.getContentType() : null)
            .deliveryMode(props != null ? props.getDeliveryMode() : null)
            .headers(props != null ? props.getHeaders() : null)
            .build();
        
        // Track the message
        long seqNo = channel.getNextPublishSeqNo();
        PendingMessage pending = new PendingMessage(correlationId, exchange, routingKey, 
                                                   propsWithCorrelation, body, System.currentTimeMillis());
        pendingConfirms.put(seqNo, pending);
        
        // Publish with mandatory flag
        channel.basicPublish(exchange, routingKey, true, propsWithCorrelation, body);
        
        System.out.println("Published message " + seqNo + " with correlation ID: " + correlationId);
    }
    
    private void handleNackedMessage(PendingMessage message) {
        System.out.println("Message nacked: " + message.getCorrelationId());
        // Implement retry logic or dead letter handling
        scheduleRetry(message);
    }
    
    private void handleReturnedMessage(String correlationId, Return returnMessage) {
        System.out.println("Message returned: " + correlationId);
        // Handle unroutable message
        storeInDeadLetter(correlationId, returnMessage);
    }
    
    // Helper class for tracking pending messages
    private static class PendingMessage {
        private final String correlationId;
        private final String exchange;
        private final String routingKey;
        private final AMQP.BasicProperties properties; 
        private final byte[] body;
        private final long timestamp;
        
        // Constructor and getters...
    }
}

Channel channel = connection.createChannel();
RobustPublisher publisher = new RobustPublisher(channel);

// Publish messages reliably
for (int i = 0; i < 100; i++) {
    String message = "Message " + i;
    AMQP.BasicProperties props = MessageProperties.PERSISTENT_TEXT_PLAIN;
    
    publisher.publishReliably("my.exchange", "routing.key", props, message.getBytes());
}

// Monitor pending confirms
Thread.sleep(5000);
System.out.println("Pending confirms: " + publisher.getPendingConfirmCount());

// Return message information
public class Return {
    public int getReplyCode();        // AMQP reply code (312=NO_ROUTE, 313=NO_CONSUMERS)
    public String getReplyText();     // Human-readable explanation
    public String getExchange();      // Exchange message was published to
    public String getRoutingKey();    // Routing key used
    public AMQP.BasicProperties getProperties(); // Message properties
    public byte[] getBody();          // Message body
}

// Common AMQP reply codes for returns
public static final int REPLY_SUCCESS = 200;
public static final int NO_ROUTE = 312;        // No route found for message
public static final int NO_CONSUMERS = 313;    // Queue exists but no consumers