nats message queue – ack a message from jetstream consumer in a separate request – Node.js

The Problem:

In NATS, a consumer can receive and acknowledge messages in a single request. However, I want to build an API where I need to handle message acknowledgement in a separate request. Specifically, I have a GET endpoint for retrieving messages and a POST endpoint for acknowledging them. However, when I try to acknowledge a message in the POST endpoint after receiving it in the GET endpoint, the message object doesn’t have an ‘ack’ method anymore. How can I manually acknowledge a message sequence in a separate request?

The Solutions:

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Solution 1: Leverage Consumer handles for acknowledgement

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Instead of using streams.get() to retrieve a message directly from a stream, utilize a consumer handle to receive messages. This consumer handle will enable you to acknowledge messages explicitly, even after the initial context of the message is lost. Here’s the approach:

1. Create a JetStream Consumer:

   const consumer = await jetstream.consumers.create({
        stream: 'mystream',
        name: 'myconsumer'
    });
   

2. Pull Messages from the Stream:
   Use the consume() method to start pulling messages from the stream:

   const messages = await consumer.consume({ max_messages: maxMessages });
   

3. Process and Acknowledge Messages:
   Process the messages as required, and acknowledge them individually:

   for await (const m of messages) {
        // Some processing logic
        await m.ack();
    }
   

4. Handle Acknowledgments Separately:
   Create a separate API endpoint to handle acknowledgment requests. When a message acknowledgment request is received, use the consumer handle to acknowledge the specified sequence ID:

   // Inside the implementation of POST /events/ack endpoint
   const s = await jetstream.streams.get('mystream');
   await s.ack(lastReceivedEventSeqId);
   

By using a consumer handle, you can acknowledge messages explicitly, even if the context of the original message is lost, ensuring reliable message processing and acknowledgment.

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