Multiple Kotlin functions are not registered

[iamceph]

Describe the bug
When using multiple Kotlin function beans in a Spring Cloud Function setup, only one function gets registered. However, if the same logic is implemented using the Java Function interface, all functions are correctly registered.
Explicitly defining the return type in Kotlin does not resolve the issue.

Observed behavior

• Kotlin definition → Only one function is registered:

  Registered Spring Cloud Functions: [routeConsentChanges, streamBridge, functionRouter]
  

• Java definition → Both functions are registered correctly:

  Registered Spring Cloud Functions: [routeConsentRepair, routeConsentChanges, streamBridge, functionRouter]
  

To Reproduce
The issue occurs when defining multiple functions using Kotlin lambda syntax.

Kotlin function definition (only one function is registered):

@Bean
fun routeConsentChanges(): (Message<ByteArray>) -> Message<Any>? = (
    { message -> messageMapper.remapMessage(message, log) })

@Bean
fun routeConsentRepair(): (Message<ByteArray>) -> Message<Any>? = (
    { message -> messageMapper.remapMessage(message, log) })

Java function definition (both functions are correctly registered):

@Bean
fun routeConsentChanges(): Function<Message<ByteArray>, Message<Any>?> = Function { message ->
    messageMapper.remapMessage(message, log)
}

@Bean
fun routeConsentRepair(): Function<Message<ByteArray>, Message<Any>?> = Function { message ->
    messageMapper.remapMessage(message, log)
}

Configuration (YAML) used in both cases:

function:
  definition: routeConsentChanges;routeConsentRepair

Expected behavior
Both Kotlin and Java function definitions should behave consistently, ensuring that all declared beans are properly registered.

Environment

• Spring Boot version: 3.4.3
• Spring Cloud version: 2024.0.0
• Spring Cloud Azure Starter version: 5.20.1
• Kotlin version: 2.1.10

Additional context

It appears that Spring Cloud Function does not correctly recognize multiple Kotlin function beans when using lambda syntax. Using the explicit Java Function interface resolves the issue, but this behavior is unexpected.

Let me know if you need additional details or a minimal reproducible example. 🚀

[olegz]

I am not sure what do you mean by "registered". Functions are accessible on the first request and registered at that time.
I just tested it with the latest and everything works as expected.

@SpringBootApplication
class DemoKotlinFunctionApplication {

	@Bean
	fun echoA(): (Message<ByteArray>) -> Message<ByteArray>? = (
			{ message -> message })

	@Bean
	fun echoB(): (Message<ByteArray>) -> Message<ByteArray	>? = (
			{ message -> message })
}

fun main(args: Array<String>) {
	runApplication<DemoKotlinFunctionApplication>(*args)
}

and relevat POM dependencies

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
	<groupId>org.springframework.cloud</groupId>
	<artifactId>spring-cloud-function-web</artifactId>
	<version>4.3.0-SNAPSHOT</version>
</dependency>

You can do a simple GET from the browser http://localhost:8080/echoA/bob or http://localhost:8080/echoB/bob and see the output.

Please let me know if I am missing something

[rozagerardo]

I am facing a similar issue.

My app is binding functions to receive and process RabbitMQ messages.

This was working with older versions. After I upgraded my Spring Boot version (from 3.1 to 3.4 and my Spring Cloud libraries from 2022.0 to 2024.0), my application started showing an error like the following:

Dispatcher has no subscribers for channel '<...>'

The function is never invoked.

However, if I leave just one function, or put the definition in the first place of the list, the function is executed as expected.

I see the function beans are being discovered OK, but they are not correctly configured with the AMQP setup.

And as with @iamceph , if I use Java functions, it works correctly regardless of the order of the definitions.

[olegz]

Can someone please provide a reproducible sample?

[iamceph]

Sorry for the delay, I will look into creating reproducible sample.

@rozagerardo Looks like you have exactly the same issue as us.

[iamceph]

I've created minimal sample here: https://github.com/iamceph/spring-function-sample

When you launch the app, you can see in the log that only registered functions are: Registered functions: [funcB, streamBridge, functionRouter]

When you change the function definition in the yaml to let's say funcB;funcC;funcD, you'll see that only registered function will now be funcB. Let me know if you need anything else.

[olegz]

So, there seem to be a bug in functionCatalog.getNames(..). That said, it doesn't affect function registration as you can see form the image below . . . sorry I had to switch to Rabbit as I don't know much about azure bus and we are not the maintainers of it.

However, now I am thinking that if Azure bus is relying on functionCatalog.getNames(..) to do the actual binding of functions to destinations, then it could be a problem. So let me fix that as it is not right regardless