I can’t get the ack=’client’ to behave as expected. I think that a message consumed by the code below should nack it and send it to the DLQ. But no! The message just disappears. I guess that it is considered processed.If, on the other hand, I just throw an error, it does end up in the DLQ.

I want to ack it if all is well, and nack it if it does not work as expected.

Producer.py

import stomp

# STOMP server configuration
server = 'localhost'
port = 61613
username = 'artemis'
password = 'artemis'
destination = 'your.queue.name'
message = 'hello :-)'

# Create a connection to the STOMP server
conn = stomp.Connection([(server, port)])
conn.set_listener('', stomp.PrintingListener())

# Connect to the server
conn.connect(username, password, wait=True)

# Send a durable message to the specified destination
conn.send(destination=destination, body=message, headers={'persistent': 'true'})

# Disconnect from the server
conn.disconnect()

Consumer.py

import stomp
import time

class MyListener(stomp.ConnectionListener):
    def __init__(self, conn):
        self.conn = conn

    def on_error(self, frame):
        print('Received an error:')
        print(f'Headers: {frame.headers}')
        print(f'Body: {frame.body}')

    def on_message(self, frame):
        print('Received a message:')
        print(f'Headers: {frame.headers}')
        print(f'Body: {frame.body}')
        
        time.sleep(1)
        
        #self.conn.ack(frame.headers['message-id'], frame.headers['subscription'])
        
        # This line ha no effect 4 what I can tell.
        self.conn.nack(frame.headers['message-id'], frame.headers['subscription'])
        
        #error will send it DLQ!
        #raise Exception("I will send this message to DLQ!")
        print('Done!!!')

def main():
    server = 'localhost'
    port = 61613
    username = 'artemis'
    password = 'artemis'
    destination = 'your.queue.name'

    conn = stomp.Connection([(server, port)], heartbeats=(4000, 4000))
    conn.set_listener('', MyListener(conn))

    try:
        conn.connect(username, password, wait=True)
    except Exception as e:
        print(f'Failed to connect to STOMP server: {e}')
        return

    try:
        # Ack modes:
        # stuff I tried:
        # client-individual
        # https://jasonrbriggs.github.io/stomp.py/api.html
        # client
        # https://activemq.apache.org/components/artemis/documentation/1.4.0/pre-acknowledge.html
        # CLIENT_ACKNOWLEDGE

        conn.subscribe(destination=destination, id='1', ack='client', headers={'subscription-type': 'ANYCAST'})
    except Exception as e:
        print(f'Failed to subscribe to queue: {e}')
        conn.disconnect()
        return

    print('Waiting for messages...')
    
    # Keep the main thread alive to receive messages
    try:
        while True:
            time.sleep(1)
    except KeyboardInterrupt:
        print('Disconnecting...')
        conn.disconnect()
    except Exception as e:
        print(f'An unexpected error occurred: {e}')
        conn.disconnect()

if __name__ == '__main__':
    main()

broker.xml

<addresses>
    <address name="your.queue.name">
        <anycast>
            <queue name="your.queue.name" />
        </anycast>
        <dead-letter-address>DLQ.your.queue.name</dead-letter-address>
        <expiry-address>ExpiryQueue</expiry-address>
        <redelivery-delay>5000</redelivery-delay> <!-- 5 seconds delay before redelivery -->
        <max-delivery-attempts>1</max-delivery-attempts> <!-- Max attempts before moving to DLQ -->
        <redelivery-delay-multiplier>2.0</redelivery-delay-multiplier> <!-- Exponential backoff -->
        <max-redelivery-delay>60000</max-redelivery-delay> <!-- Max delay of 1 minute -->
    </address>
    
    <address name="DLQ.your.queue.name">
        <anycast>
            <queue name="DLQ.your.queue.name" />
        </anycast>
    </address>
</addresses>