Safari doesn't receive chunked data using WebFlux's SSE [SPR-16691]

[spring-projects-issues]

Adrian Marszałek opened SPR-16691 and commented

Complete source code:

@Configuration
class Routing {

    @Bean
    fun booksRouter(handler: BooksHandler) = router {
        ("/books" and accept(MediaType.APPLICATION_JSON)).nest {
            GET("/", handler::getAll)
        }
    }
}


data class Book(val title: String,
                val author: String)

@Component
class BooksHandler(private val repository: BookRepository) {

    fun getAll(request: ServerRequest): Mono<ServerResponse> {
        val interval = Flux.interval(Duration.ofSeconds(1))

        val books = listOf(Book("title", "author"),
                Book("title", "author"),
                Book("title", "author"),
                Book("title", "author")).toFlux()
        return ok().bodyToServerSentEvents(Flux.zip(interval, books).map({ it.t2 }))
    }
}

The whole project generated from Intializr: Spring Boot 2.0.0 with Kotlin 1.2.31.
Run the application and access the resource directly through Safari: http://localhost:8080/books
Instead of receiving a book every second, Safari waits for as long as the Flux.zip() takes and then it receives the whole list of books.

---

No further details from SPR-16691

[spring-projects-issues]

Brian Clozel commented

Thanks for the report, but Safari does properly support SSE with WebFlux.

The issue seems to be with your RouterFunction only accepting MediaType.APPLICATION_JSON for this endpoint. This might work with some browsers, if they send an Accept header that's flexible (maybe accepting "\*/\*"?).

Safari seems to be more restrictive and sends an "Accept: text/event-stream" request header for SSE requests done with EventSource. In this case, the server responds with an HTTP 404...

Changing that part in your sample with the following works:

@Bean
fun booksRouter(handler: BooksHandler) = router {
    GET("/", handler::home)
    ("/books" and accept(MediaType.TEXT_EVENT_STREAM)).nest {
        GET("/", handler::getAll)
    }
}

Thanks,