Message Retry Handler

Build a message processing system that handles transient failures by retrying messages that fail processing.

Overview

You need to implement a message processor that receives messages from a queue, attempts to process them, and handles failures appropriately. When a message fails processing due to a transient error (e.g., temporary network issue), the system should return the message to the queue for retry. Messages should only be permanently removed after successful processing.

Requirements

Message Processing

Implement a function process_messages(connection_string, queue_name, max_messages, processor_callback) that:

1. Connects to a Service Bus queue using the provided connection string
2. Receives up to max_messages from the queue
3. For each message:
   • Invokes the processor_callback function with the message body
   • If the callback succeeds (returns True), confirms successful processing
   • If the callback fails (returns False or raises an exception), returns the message to the queue for redelivery
4. Closes all connections properly when done

The processor_callback is a function that takes a single argument (the message body as a string) and returns a boolean indicating success (True) or failure (False).

Error Handling

• Handle processing failures gracefully by returning failed messages to the queue
• Ensure successful messages are properly completed and removed from the queue
• Do not let exceptions in the callback crash the entire processor

Implementation

@generates

API

def process_messages(connection_string: str, queue_name: str, max_messages: int, processor_callback) -> dict:
    """
    Process messages from a Service Bus queue with retry handling.

    Args:
        connection_string: Azure Service Bus connection string
        queue_name: Name of the queue to receive messages from
        max_messages: Maximum number of messages to process
        processor_callback: Function that processes message body and returns True for success, False for failure

    Returns:
        Dictionary with keys:
        - 'processed': count of successfully processed messages
        - 'failed': count of messages that failed processing and were returned to queue
    """
    pass

Tests

• When all messages process successfully, all are completed and removed from queue @test
• When a message fails processing, it is abandoned and remains in queue for redelivery @test
• When callback raises an exception, message is abandoned and processing continues @test
• Mixed success and failure messages are handled correctly @test

Dependencies { .dependencies }

azure-servicebus { .dependency }

Provides Azure Service Bus messaging capabilities.

@satisfied-by