Websocket client UpgradeException: 101 Switching Protocols caused by NullPointerException

[natan-abolafya]

Jetty version
9.4.31.v20200723

Java version
openjdk 11.0.8+10

OS type/version
Ubuntu 18.04.1

Description
Unfortunately I can't give a very clear description but I'm hoping the exception stack trace will help. This feels like a version mismatch but as far as I can see all the jetty jars are 9.4.31.

First, stack trace:

org.eclipse.jetty.websocket.api.UpgradeException: 101 Switching Protocols
	at org.eclipse.jetty.websocket.client.WebSocketUpgradeRequest.onComplete(WebSocketUpgradeRequest.java:529)
	at org.eclipse.jetty.client.ResponseNotifier.notifyComplete(ResponseNotifier.java:218)
	at org.eclipse.jetty.client.ResponseNotifier.notifyComplete(ResponseNotifier.java:210)
	at org.eclipse.jetty.client.HttpSender.terminateRequest(HttpSender.java:411)
	at org.eclipse.jetty.client.HttpSender.someToSuccess(HttpSender.java:331)
	at org.eclipse.jetty.client.HttpSender$CommitCallback.process(HttpSender.java:744)
	at org.eclipse.jetty.client.HttpSender$CommitCallback.succeeded(HttpSender.java:710)
	at org.eclipse.jetty.client.http.HttpSenderOverHTTP$HeadersCallback.onCompleteSuccess(HttpSenderOverHTTP.java:307)
	at org.eclipse.jetty.util.IteratingCallback.processing(IteratingCallback.java:326)
	at org.eclipse.jetty.util.IteratingCallback.iterate(IteratingCallback.java:223)
	at org.eclipse.jetty.client.http.HttpSenderOverHTTP.sendHeaders(HttpSenderOverHTTP.java:65)
	at org.eclipse.jetty.client.HttpSender.send(HttpSender.java:212)
	at org.eclipse.jetty.client.http.HttpChannelOverHTTP.send(HttpChannelOverHTTP.java:85)
	at org.eclipse.jetty.client.HttpChannel.send(HttpChannel.java:128)
	at org.eclipse.jetty.client.HttpConnection.send(HttpConnection.java:225)
	at org.eclipse.jetty.client.http.HttpConnectionOverHTTP$Delegate.send(HttpConnectionOverHTTP.java:247)
	at org.eclipse.jetty.client.http.HttpConnectionOverHTTP.send(HttpConnectionOverHTTP.java:121)
	at org.eclipse.jetty.client.http.HttpDestinationOverHTTP.send(HttpDestinationOverHTTP.java:38)
	at org.eclipse.jetty.client.HttpDestination.process(HttpDestination.java:382)
	at org.eclipse.jetty.client.HttpDestination.process(HttpDestination.java:336)
	at org.eclipse.jetty.client.HttpDestination.send(HttpDestination.java:318)
	at org.eclipse.jetty.client.HttpDestination.succeeded(HttpDestination.java:247)
	at org.eclipse.jetty.client.AbstractConnectionPool.proceed(AbstractConnectionPool.java:206)
	at org.eclipse.jetty.client.AbstractConnectionPool$1.succeeded(AbstractConnectionPool.java:184)
	at org.eclipse.jetty.client.AbstractConnectionPool$1.succeeded(AbstractConnectionPool.java:176)
	at org.eclipse.jetty.util.Promise$Wrapper.succeeded(Promise.java:130)
	at org.eclipse.jetty.client.http.HttpConnectionOverHTTP.onOpen(HttpConnectionOverHTTP.java:129)
	at org.eclipse.jetty.io.SelectorManager.connectionOpened(SelectorManager.java:324)
	at org.eclipse.jetty.io.ManagedSelector.createEndPoint(ManagedSelector.java:368)
	at org.eclipse.jetty.io.ManagedSelector.access$2000(ManagedSelector.java:62)
	at org.eclipse.jetty.io.ManagedSelector$CreateEndPoint.run(ManagedSelector.java:1027)
	at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:806)
	at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:938)
	at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.NullPointerException
	at org.eclipse.jetty.client.http.HttpReceiverOverHTTP.onUpgradeFrom(HttpReceiverOverHTTP.java:118)
	at org.eclipse.jetty.client.http.HttpConnectionOverHTTP.onUpgradeFrom(HttpConnectionOverHTTP.java:163)
	at org.eclipse.jetty.io.AbstractEndPoint.upgrade(AbstractEndPoint.java:432)
	at org.eclipse.jetty.websocket.client.WebSocketUpgradeRequest.upgrade(WebSocketUpgradeRequest.java:659)
	at org.eclipse.jetty.client.http.HttpChannelOverHTTP.exchangeTerminating(HttpChannelOverHTTP.java:118)
	at org.eclipse.jetty.client.HttpSender.terminateRequest(HttpSender.java:403)
	... 30 more

I only use the websocket client for some integration tests for websocket server 9.4.31. And sometimes the connection fails with the exception above.
It started happening, I believe, after upgrading to 9.4.31, from 9.4.30.
It happens on our build environment when it's running tests via gradle, not concurrently.
When I run the tests non-stop on my local environment (Windows 10 + Intellij IDEA + Intellij Runner (not-gradle-runner)), I can never reproduce it. And that kind of strengthens the possibility of library version mismatch caused by gradle. But I can't really find it. Maybe someone familiar with the code can point me to the right direction?

[joakime]

This is a duplicate of #5170
It's been fixed in jetty-9.4.x and is due out in the next release, Jetty 9.4.32

[natan-abolafya]

Ah, should have searched for NullPointerException instead of UpgradeException. Thanks.

[joakime]

No worries. This one was tricky to search for.
The stacktrace you show is one of many that can trigger due to the underlying cause that was identified and fixed in #5170.