[jira] [Created] (CAMEL-22705) Camel-Nats: Reuse existing stream for consumers

[Vineet Saurabh (Jira)]

Vineet Saurabh created CAMEL-22705:
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             Summary: Camel-Nats: Reuse existing stream for consumers
                 Key: CAMEL-22705
                 URL: https://issues.apache.org/jira/browse/CAMEL-22705
             Project: Camel
          Issue Type: Bug
          Components: camel-nats
    Affects Versions: 4.16.0
            Reporter: Vineet Saurabh
             Fix For: 4.17.0


The NATS JetStream Consumer setup logic incorrectly attempts to create a stream 
using {{jsm.addStream()}} every time the consumer starts. If a stream with the 
same name exists but has a different configuration (e.g., subject list, storage 
type, or retention policy), this operation fails, preventing the consumer from 
subscribing.
h4. Steps to Reproduce
 # Start the application with a JetStream Consumer configured for stream 
*{{MY_STREAM}}* and subject {*}{{topic.A}}{*}.

 # Stop the application.

 # Modify the consumer configuration (or have an external system create) stream 
*{{MY_STREAM}}* with subjects *{{topic.B}}* (or a different subject set than in 
step 1).

 # Restart the application with the consumer configured for stream 
*{{MY_STREAM}}* and subject {*}{{topic.A}}{*}.

h4. 🔴 Actual Result

The consumer fails to start and shuts down. The application logs the following 
error:
io.nats.client.JetStreamApiException: stream name already in use with a 
different configuration [10058]
h4. 🟢 Expected Result

The consumer should successfully detect that stream *{{MY_STREAM}}* already 
exists and proceed with the subscription setup without attempting to re-add or 
redefine the stream.
h2. Proposed Fix

Modify the stream setup logic in {{setupJetStreamConsumer}} to use the 
*check-then-create* pattern, leveraging the approach from the official NATS 
Java client utilities to gracefully handle the "stream not found" condition.
h3. Implementation Steps
 # *Introduce Stream Existence Check:* Use a helper method (similar to 
{{{}streamExists{}}}) to safely determine if the stream exists.

 # *Conditional Creation:* Only call {{jsm.addStream()}} if the existence check 
returns {{{}false{}}}.

{code:java}
// Method logic (similar to NatsJsUtils) should be available:

public static boolean streamExists(JetStreamManagement jsm, String streamName) 
throws IOException, JetStreamApiException {
    try {
        jsm.getStreamInfo(streamName);
        return true;
    } catch (JetStreamApiException jsae) {
        // NATS uses HTTP status codes for API errors. 404 is Not Found.
        if (jsae.getErrorCode() == 404) {
            return false;
        }
        throw jsae;
    }
} {code}
Note: While this pattern of using {{try-catch}} for resource existence checking 
violates the principle of *Effective Java, Item 69* ("Use exceptions only for 
exceptional conditions"), it is the necessary and idiomatic workaround for 
handling the {{404}} (Not Found) status returned as a {{JetStreamApiException}} 
by the NATS Java Client API.

 

 



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