4.x Intermittent pipeline test failure in `SseClientTest.testSseJson1`

[tjquinno]

Environment Details

• Helidon Version: 4.x
• Helidon SE or Helidon MP
• JDK version:
• OS:

---

Problem Description

Intermittent pipeline test failure:

https://github.com/helidon-io/helidon/actions/runs/16668098611/job/47178543193?pr=10470#step:3:6321

Error:  Errors: 
Error:    SseClientTest.testSseJson1:146 » InsufficientDataAvailable
[INFO] 
Error:  Tests run: 24, Failures: 0, Errors: 1, Skipped: 0

[jbescos]

I cannot reproduce it locally after 189 tries.

[tjquinno]

That might be, but it is still happening in the pipelines. From a few hours ago: https://github.com/helidon-io/helidon/actions/runs/16739471713/job/47385035288

[tjquinno]

Happening very frequently.

[jbescos]

I guess the server socket wrote in the stream and closed it, but maybe the stream was buffered and it was not flushed. In this way the client could get that error. I am going to investigate it.

[jbescos]

This is the stack when data is written by the SseSink:

System Thread [[0x6cff6fb4 0x0481208b] WebServer socket] (Suspended)	
	GrowingBufferData.writeTo(OutputStream) line: 66	
	PlainSocket.write(BufferData) line: 136	
	SocketWriterDirect(SocketWriter).writeNow(BufferData) line: 81	
	DataWriterSseSink.emit(SseEvent) line: 124	
	DataWriterSseSink.emit(SseEvent) line: 49	
	SseBaseTest.sseJson1(ServerRequest, ServerResponse) line: 69	
	0x00007f56941b8478.handle(ServerRequest, ServerResponse) line: not available	
	HttpRoutingImpl$RoutingExecutor.doRoute(ConnectionContext, RoutingRequest, RoutingResponse) line: 174	
	HttpRoutingImpl$RoutingExecutor.call() line: 132	
	HttpRoutingImpl$RoutingExecutor.call() line: 110	
	ErrorHandlers.runWithErrorHandling(ConnectionContext, RoutingRequest, RoutingResponse, Callable<Void>) line: 76	
	Filters.filter(ConnectionContext, RoutingRequest, RoutingResponse, Callable<Void>) line: 83	
	HttpRoutingImpl.route(ConnectionContext, RoutingRequest, RoutingResponse) line: 74	
	Http1Connection.route(HttpPrologue, WritableHeaders<?>) line: 544	
	Http1Connection.handle(Limit) line: 224	
	ConnectionHandler.run() line: 176	
	ConnectionHandler(InterruptableTask<T>).call() line: 47	
	ThreadPerTaskExecutor$ThreadBoundFuture<T>.run() line: 240	
	VirtualThread(Thread).runWith(Object, Runnable) line: 1596	
	VirtualThread.run(Runnable) line: 309	
	VirtualThread$VThreadContinuation$1.run() line: 190	
	VirtualThread$VThreadContinuation(Continuation).enter0() line: 320	
	Continuation.enter(Continuation, boolean) line: 312	

Although it is going through SocketWriterDirect(SocketWriter).writeNow(BufferData) line: 81 that the name suggests that it is going to flush it immediately, I don't see that the outputstream is flushed in GrowingBufferData.writeTo(OutputStream) line: 66.

And later, when DataWriterSseSink.close(), I don't see the flush either.

System Thread [[0x6cff6fb4 0x0481208b] WebServer socket] (Suspended (breakpoint at line 130 in DataWriterSseSink))	
	DataWriterSseSink.close() line: 130	
	SseBaseTest.sseJson1(ServerRequest, ServerResponse) line: 70	
	0x00007f56941b8478.handle(ServerRequest, ServerResponse) line: not available	
	HttpRoutingImpl$RoutingExecutor.doRoute(ConnectionContext, RoutingRequest, RoutingResponse) line: 174	
	HttpRoutingImpl$RoutingExecutor.call() line: 132	
	HttpRoutingImpl$RoutingExecutor.call() line: 110	
	ErrorHandlers.runWithErrorHandling(ConnectionContext, RoutingRequest, RoutingResponse, Callable<Void>) line: 76	
	Filters.filter(ConnectionContext, RoutingRequest, RoutingResponse, Callable<Void>) line: 83	
	HttpRoutingImpl.route(ConnectionContext, RoutingRequest, RoutingResponse) line: 74	
	Http1Connection.route(HttpPrologue, WritableHeaders<?>) line: 544	
	Http1Connection.handle(Limit) line: 224	
	ConnectionHandler.run() line: 176	
	ConnectionHandler(InterruptableTask<T>).call() line: 47	
	ThreadPerTaskExecutor$ThreadBoundFuture<T>.run() line: 240	
	VirtualThread(Thread).runWith(Object, Runnable) line: 1596	
	VirtualThread.run(Runnable) line: 309	
	VirtualThread$VThreadContinuation$1.run() line: 190	
	VirtualThread$VThreadContinuation(Continuation).enter0() line: 320	
	Continuation.enter(Continuation, boolean) line: 312	

If what I said is correct, the best fix is to flush it when #close is invoked, for performance reasons.

@tomas-langer to check this.

Suggested fix. I will rerun actions to see whether it is fixed or not: #10493