springboot2 actuator endpoint not supporting Server Sent Event(SSE)

Question

I am trying to expose few metrics as a stream using SSE. I am able to consume the SSE event from the restController but when I added custom actuator endpoint , it just closes the connection right way.

@Component
@Endpoint(id = "test")
public class StreamMetrics {

  
    @ReadOperation
    public Flux<ServerSentEvent<String>> streamEvents() {
        return Flux.interval(Duration.ofSeconds(1))
                .map(sequence -> ServerSentEvent.<String> builder()
                        .id(String.valueOf(sequence))
                        .event("pingpong")
                        .data("ping")
                        .build());
    }

}

Result

curl  -n -v http://localhost:9080/actuator/test
*   Trying ::1:9080...
* TCP_NODELAY set
* Connected to localhost (::1) port 9080 (#0)
> GET /actuator/test HTTP/1.1
> Host: localhost:9080
> User-Agent: curl/7.68.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< transfer-encoding: chunked
< Content-Type: text/event-stream;charset=UTF-8
< 
id:0
event:pingpong
data:ping

* Connection #0 to host localhost left intact

this is terminated right after the fist event

where as

@RestController
 @RequestMapping(value = "/test")
 public class SSETest {


    @GetMapping("/stream-sse")
    public Flux<ServerSentEvent<String>> streamEvents() {
        return Flux.interval(Duration.ofSeconds(1))
                .map(sequence -> ServerSentEvent.<String> builder()
                        .id(String.valueOf(sequence))
                        .event("pingpong")
                        .data("ping")
                        .build());
    }

}

Result

curl -v -n http://localhost:9080/test/stream-sse
*   Trying ::1:9080...
* TCP_NODELAY set
* Connected to localhost (::1) port 9080 (#0)
> GET /test/stream-sse HTTP/1.1
> Host: localhost:9080
> User-Agent: curl/7.68.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< transfer-encoding: chunked
< Content-Type: text/event-stream;charset=UTF-8
< 
id:0
event:pingpong
data:ping

id:1
event:pingpong
data:ping

id:2
event:pingpong
data:ping

this goes on without getting terminated.

What is special about endpoint annotation that is terminating the event (continuous flow)?

I tested this in '2.2.4 ' and '2.3.0'

Answer 1

I found an answer. @ReadOperation(produces = "text/event-stream") will alter the default content type application/vnd.spring-boot.actuator.v3+json in actuator endpoints. There was not a document so I looked at the code.

@Component
@Endpoint(id = "test")
public class StreamMetrics {

@ReadOperation(produces = "text/event-stream")
public Flux<ServerSentEvent<String>> streamEvents() {
    return Flux.interval(Duration.ofSeconds(1))
            .map(sequence -> ServerSentEvent.<String> builder()
                    .id(String.valueOf(sequence))
                    .event("pingpong")
                    .data("ping")
                    .build());
}

}