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Hello, wondering if anyone has experience using Sp...
# spring
a
Hello, wondering if anyone has experience using Spring Cloud Stream + Spring Cloud Function with Kotlin Coroutines? I had to jump through some hoops for the application to start without error (
@Bean
method that is not suspending that returns a Kotlin function that IS suspending with a method signature that includes 
Flow
) but the kotlin suspending function is not being called when a message is received. Just wondering if maybe I am missing some extra setup/dependencies that will get it working
I'm using a Kafka binder. Here is the exception message I'm getting:
Copy code
2024-04-15 09:10:32.674 ERROR [SNIP,,] 11797 --- [container-0-C-1] o.s.integration.handler.LoggingHandler   : org.springframework.messaging.MessageDeliveryException: Dispatcher has no subscribers for channel 'application-1.SNIP-in-0'.; nested exception is org.springframework.integration.MessageDispatchingException: Dispatcher has no subscribers, failedMessage=SNIP, Source-Name=SNIP, kafka_offset=22, scst_nativeHeadersPresent=true, kafka_consumer=org.apache.kafka.clients.consumer.KafkaConsumer@b1873e8, kafka_receivedPartitionId=0, contentType=application/json, kafka_receivedTimestamp=1713186629650, __TypeId__=[B@6936f77e, kafka_groupId=SNIP}]
	at org.springframework.integration.channel.AbstractSubscribableChannel.doSend(AbstractSubscribableChannel.java:76)
	at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:317)
	at org.springframework.integration.channel.AbstractMessageChannel.send(AbstractMessageChannel.java:272)
	at org.springframework.messaging.core.GenericMessagingTemplate.doSend(GenericMessagingTemplate.java:187)
	at org.springframework.messaging.core.GenericMessagingTemplate.doSend(GenericMessagingTemplate.java:166)
	at org.springframework.messaging.core.GenericMessagingTemplate.doSend(GenericMessagingTemplate.java:47)
	at org.springframework.messaging.core.AbstractMessageSendingTemplate.send(AbstractMessageSendingTemplate.java:109)
	at org.springframework.integration.endpoint.MessageProducerSupport.sendMessage(MessageProducerSupport.java:215)
	at org.springframework.integration.kafka.inbound.KafkaMessageDrivenChannelAdapter.sendMessageIfAny(KafkaMessageDrivenChannelAdapter.java:397)
	at org.springframework.integration.kafka.inbound.KafkaMessageDrivenChannelAdapter.access$300(KafkaMessageDrivenChannelAdapter.java:83)
	at org.springframework.integration.kafka.inbound.KafkaMessageDrivenChannelAdapter$IntegrationRecordMessageListener.onMessage(KafkaMessageDrivenChannelAdapter.java:454)
	at org.springframework.integration.kafka.inbound.KafkaMessageDrivenChannelAdapter$IntegrationRecordMessageListener.onMessage(KafkaMessageDrivenChannelAdapter.java:428)
	at org.springframework.kafka.listener.adapter.RetryingMessageListenerAdapter.lambda$onMessage$0(RetryingMessageListenerAdapter.java:125)
	at org.springframework.retry.support.RetryTemplate.doExecute(RetryTemplate.java:329)
	at org.springframework.retry.support.RetryTemplate.execute(RetryTemplate.java:255)
	at org.springframework.kafka.listener.adapter.RetryingMessageListenerAdapter.onMessage(RetryingMessageListenerAdapter.java:119)
	at org.springframework.kafka.listener.adapter.RetryingMessageListenerAdapter.onMessage(RetryingMessageListenerAdapter.java:42)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeOnMessage(KafkaMessageListenerContainer.java:2670)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeOnMessage(KafkaMessageListenerContainer.java:2650)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeRecordListener(KafkaMessageListenerContainer.java:2577)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeWithRecords(KafkaMessageListenerContainer.java:2457)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeRecordListener(KafkaMessageListenerContainer.java:2335)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeListener(KafkaMessageListenerContainer.java:2006)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeIfHaveRecords(KafkaMessageListenerContainer.java:1375)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.pollAndInvoke(KafkaMessageListenerContainer.java:1366)
	at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.run(KafkaMessageListenerContainer.java:1257)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
	at java.base/java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:264)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java)
	at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: org.springframework.integration.MessageDispatchingException: Dispatcher has no subscribers, failedMessage=SNIP
	at org.springframework.integration.dispatcher.UnicastingDispatcher.doDispatch(UnicastingDispatcher.java:139)
	at org.springframework.integration.dispatcher.UnicastingDispatcher.dispatch(UnicastingDispatcher.java:106)
	at org.springframework.integration.channel.AbstractSubscribableChannel.doSend(AbstractSubscribableChannel.java:72)
	... 29 more
ok I think I resolved my issue. I needed to wrap my coroutine invocation with a coroutine context.
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@Configuration
class ServiceConfig(val handler: Handler) {

    @Bean
    fun consumer(): suspend (Flow<String>) -> Unit = {
        withContext(MDCContext()) {
            it.collect { string ->
                handler.handle(string)
            }
        }
    }
}
One gotcha is that spring-cloud-function expects a Flow rather than POKO, and another is the bean itself must not be a suspend function
s
It’s been awhile but another potential gotcha with this also depends on your failure modes around acknowledging messages. https://stackoverflow.com/questions/60171561/dont-mark-message-as-acknowledged-in-reactive-function-with-spring-cloud-stream If you care about never dropping your messages IIRC our team explored manually acking each message as an option but we ultimately settled around just wrapping the suspended call in 
runBlocking { … }
and returning a normal function.
(not sure if things have changed btw, it’s been a couple of years now)
a
@Saharath Kleips thanks for the info!
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