Websockets don't work when using WebFlux with Jetty

[mhalbritter]

I'm using a WebFlux app and switched from Netty to Jetty. When using websockets, this fails when trying to connect to the websocket.

You'll see this in the logs

ERROR 57214 --- [ttp@61d01788-21] o.s.w.s.adapter.HttpWebHandlerAdapter    : [66bc796c] Error [java.lang.NullPointerException: Cannot invoke "org.eclipse.jetty.websocket.server.JettyWebSocketServerContainer.upgrade(org.eclipse.jetty.websocket.server.JettyWebSocketCreator, jakarta.servlet.http.HttpServletRequest, jakarta.servlet.http.HttpServletResponse)" because "container" is null] for HTTP GET "/ws", but ServerHttpResponse already committed (200 OK)

The whole stacktrace is this:

java.lang.NullPointerException: Cannot invoke "org.eclipse.jetty.websocket.server.JettyWebSocketServerContainer.upgrade(org.eclipse.jetty.websocket.server.JettyWebSocketCreator, jakarta.servlet.http.HttpServletRequest, jakarta.servlet.http.HttpServletResponse)" because "container" is null
	at org.springframework.web.reactive.socket.server.upgrade.JettyRequestUpgradeStrategy.lambda$upgrade$2(JettyRequestUpgradeStrategy.java:82)
	at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:47)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:240)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:203)
	at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onComplete(MonoIgnoreElements.java:89)
	at reactor.core.publisher.FluxConcatArray$ConcatArraySubscriber.onComplete(FluxConcatArray.java:230)
	at reactor.core.publisher.FluxConcatArray.subscribe(FluxConcatArray.java:78)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.FluxFlatMap.trySubscribeScalarMap(FluxFlatMap.java:203)
	at reactor.core.publisher.MonoFlatMap.subscribeOrReturn(MonoFlatMap.java:53)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4429)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:165)
	at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:79)
	at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:74)
	at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:82)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.innerNext(FluxConcatMapNoPrefetch.java:258)
	at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:863)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:129)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2508)
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:171)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.request(Operators.java:2268)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.request(FluxConcatMapNoPrefetch.java:338)
	at reactor.core.publisher.MonoNext$NextSubscriber.request(MonoNext.java:108)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2304)
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:2178)
	at reactor.core.publisher.MonoNext$NextSubscriber.onSubscribe(MonoNext.java:70)
	at reactor.core.publisher.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.onSubscribe(FluxConcatMapNoPrefetch.java:164)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:165)
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:87)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263)
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4444)
	at org.springframework.http.server.reactive.ServletHttpHandlerAdapter.service(ServletHttpHandlerAdapter.java:197)
	at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:764)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:529)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:221)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1380)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:176)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:484)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:174)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1302)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:129)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:122)
	at org.eclipse.jetty.server.Server.handle(Server.java:563)
	at org.eclipse.jetty.server.HttpChannel.lambda$handle$0(HttpChannel.java:505)
	at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:762)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:497)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:282)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:314)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:100)
	at org.eclipse.jetty.io.SelectableChannelEndPoint$1.run(SelectableChannelEndPoint.java:53)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.runTask(AdaptiveExecutionStrategy.java:421)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.consumeTask(AdaptiveExecutionStrategy.java:390)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.tryProduce(AdaptiveExecutionStrategy.java:277)
	at org.eclipse.jetty.util.thread.strategy.AdaptiveExecutionStrategy.produce(AdaptiveExecutionStrategy.java:199)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:933)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1077)
	at java.base/java.lang.Thread.run(Thread.java:833)

That's because in org.springframework.web.reactive.socket.server.upgrade.JettyRequestUpgradeStrategy#upgrade there's this code:

JettyWebSocketServerContainer container = JettyWebSocketServerContainer.getContainer(servletContext);

try {
	container.upgrade(webSocketCreator, servletRequest, servletResponse);
}
catch (Exception ex) {
	return Mono.error(ex);
}

and container is null. The container is usually set by calling org.eclipse.jetty.websocket.server.JettyWebSocketServerContainer#ensureContainer, which is not done for WebFlux. This is done for WebMVC in JettyWebSocketServletWebServerCustomizer, but a reactive pendant is missing.

A reproducer can be found here: https://github.com/mhalbritter/jetty-webflux-websockets

Btw, it's working for Netty, Tomcat and Undertow.

I've used SB 3.0.0-SNAPSHOT. I'll test this with 2.7.x too and report back.

[mhalbritter]

It's working with Spring Boot 2.7.5.