Resource leak when Controller returns a ResponseEntity<InputStreamResource>

Affects: 5.1.5

I return a stream with BodyBuilder.body(new InputStreamResource(stream)) from a @Controller:

@SpringBootApplication
@Controller
public class Issue22626 {

	@Autowired(required = false)
	private Supplier<InputStream> source = () -> new NullInputStream(10000);

	@GetMapping("/")
	public ResponseEntity<InputStreamResource> download() {
		var resource = new InputStreamResource(source.get());
		return ok().eTag("Issue22626").lastModified(22626).body(resource);
	}

	public static void main(String[] args) {
		run(Issue22626.class, args);
	}
}

That stream is a proxy which helps me to detect resource leaks. The proxy contains the stack trace of the last read operation and a scheduled task to close the resource and log an error after 10 minutes of inactivity.

In the region 5 out of 10000 streams, I see a resource leak. That is, the log shows the “Returning resource” message, then shows that the thread is already serving others requests and then after 10 minutes I see a message from my stream proxy that the resource is leaking. There was no read operation at all called on that stream. Which means the framework left the resource untouched and never reaches ResourceHttpMessageConverter.writeContent() (which would then close the stream). I tried to dig into the framework, but it is for me not possible to understand what is going on at all.

~Note, this is an production issue which happens in the region 5 out of 10000, I cannot provide something to reproduce this memory leak. I will however try my best to give some more follow up information.~ I will provide a minimal application to reproduce the issue.

All I can see is that the framework assumes that ResourceHttpMessageConverter.writeContent() would close the resource. I think that is too late. Obviously many things could happen before reaching that place (and something silently does… ~my suspicion goes into a unfortunately timed client sided connection closing~) which leaves the resource unclosed. Could you please revise the framework code in regard of serving a Controller which returns an InputStream and make sure that the very first thing into which this Controller returns wraps the stream into a try-with-resource block?