PubSubInboundChannelAdapter does not allow null payload

[michalstefanext]

Hello, I would like to ask, if there is any possibility to receive message with empty payload via PubSubInboundChannelAdapter? It seems to me that this is impossible, however that is perfectly valid scenario in gcp pubsub.

java.lang.IllegalArgumentException: payload must not be null
    at org.springframework.util.Assert.notNull(Assert.java:201)
    at org.springframework.integration.support.MessageBuilder.<init>(MessageBuilder.java:70)
    at org.springframework.integration.support.MessageBuilder.withPayload(MessageBuilder.java:114)
    at org.springframework.integration.support.DefaultMessageBuilderFactory.withPayload(DefaultMessageBuilderFactory.java:72)
    at org.springframework.integration.support.DefaultMessageBuilderFactory.withPayload(DefaultMessageBuilderFactory.java:31)
    at com.google.cloud.spring.pubsub.integration.inbound.PubSubInboundChannelAdapter.consumeMessage(PubSubInboundChannelAdapter.java:146)
    at com.google.cloud.spring.pubsub.core.subscriber.PubSubSubscriberTemplate.lambda$subscribeAndConvert$1(PubSubSubscriberTemplate.java:173)
    at com.google.cloud.pubsub.v1.MessageDispatcher$4.run(MessageDispatcher.java:396)
    at com.google.cloud.pubsub.v1.SequentialExecutorService$AutoExecutor$1.run(SequentialExecutorService.java:134)
    at com.google.cloud.pubsub.v1.SequentialExecutorService$SequentialExecutor$1.run(SequentialExecutorService.java:112)
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
    at java.base/java.lang.Thread.run(Thread.java:833)

[meltsufin]

@michalstefanext This is a validation in Spring Integration itself org.springframework.integration.support.MessageBuilder. I'm not sure why they prevent nulls for the message payload.

cc/ @artembilan

[artembilan]

See here for more info: https://jira.spring.io/projects/INT/issues/INT-997

But generally speaking the null payload was never supported: no data - no message. So, yo need to consider some rework in the PubSubInboundChannelAdapter to prevent such a null to be emitted or some other wrapper object, like we have with KafkaNull as a tombstone signal to send and receive null from Apache Kafka. That's for now until we really introduce an Optional wrapper support in Spring Integration.

[meltsufin]

Thanks @artembilan! It seems that something like a PubSubNull would be the way to go. It will require some changes to PubSubInboundChannelAdapter and our message conversion logic to ensure that PubSubNull is converted to null when needed. We'll accept it as a feature request.

[elefeint]

@emmileaf Take a look at this issue -- it's in the Spring Integration layer of Pub/Sub support.

[emmileaf]

@michalstefanext Do you happen to remember what was the type of the empty payload (string, byte array, etc.) passed to the PubSubInboundChannelAdapter, and whether it went through any custom conversions or transformations?

I am having some difficulty reproducing the exception: directly receiving a pubsub message with empty body seems to be handled as expected (as empty strings and empty byte arrays), and not resulting in null as the Spring message payload.