Looking forward to the coroutine support in Spring...

# spring

[Jonas Bark]

Looking forward to the coroutine support in Spring MVC - We can then finally get rid of our runBlocking "workaround" - thanks @sdeleuze !

Less Kotlin, probably more about Spring itself:
We're also using functional routing for a year now and we're very happy with it. The only thing I miss is support for server side events for Spring MVC projects.
The functional routing receives a ServerRequest and expects a ServerResponse in return but I don't see a way to incorporate to respond with the SseEmitter object that is used for SSE on Spring MVC.
Am I missing something or should I open a ticket?

[sdeleuze]

For Coroutines support in Spring MVC, that will be much better than runBlocking because it will not block Tomcat thread, it will use Spring MVC async support.

[sdeleuze]

For SSE in WebMvc.fn, indeed I think it is missing but I think we could add it, see https://github.com/spring-projects/spring-framework/issues/25920.

[Jonas Bark]

thank you!

[Jonas Bark]

Regarding the Coroutine support: could WebMvc.fn be adjusted to support the suspending functions as well?

With a little bit of guidance I could work on a PR to add it
e.g.
• if it's possible at all
• if a coRouter for servlet environments would be better than adjusting the router DSL to accept suspending functions as well

[sdeleuze]

For WebMvc.fn I don't think a coRouter would make sense but maybe a ServerResponse.async extension taking a suspending function as parameter? That would be the Coroutines variant for static ServerResponse async(Object asyncResponse).

[Jonas Bark]

I'll try 👍

[Jonas Bark]

could you point me to where suspended functions are handled? I'm wondering if they get 'converted' to CompleteableFuture to use with ServerResponse.async

EDIT: seems to be https://github.com/spring-projects/spring-framework/blob/master/spring-core/kotlin-coroutines/src/main/kotlin/org/springframework/core/CoroutinesUtils.kt

[sdeleuze]

Yep

[Jonas Bark]

I'm currently testing this:

fun test(request: ServerRequest): ServerResponse {

        return ServerResponse.async(mono(Dispatchers.Unconfined) {
            throw ResponseStatusException(HttpStatus.BAD_GATEWAY)
        })
    }

the exception is swallowed, resulting in a HTTP 200 while the logs show
javax.servlet.ServletException: javax.servlet.ServletException: org.springframework.web.server.ResponseStatusException

will I have to invoke Springs internal exception handling system (that renders ResponseStatusException to their HTTP codes) manually?

[Jonas Bark]

if I solve this, the proof of concept (and PR) for handling suspending functions in WebMvc.fn can easily be made 🙂

[Jonas Bark]

issue: https://github.com/spring-projects/spring-framework/issues/25931