Give better errors for non public Websocket Endpoints

[fredbar]

based on org.eclipse.jetty.websocket:javax-websocket-server-impl:jar:9.4.28.v20200408

If an Endpoint is a private inner class, jetty fails silently, responding with a 503. This is due to the fact that the ContainerDefaultConfigurator looks for a static initializer and the fact that inner classes can not have them.

Following is a stack trace for the call, gotten when enabling debug log traces.

java.lang.InstantiationException: java.lang.NoSuchMethodException: com.xxx$MyServer.<init>()
	at org.eclipse.jetty.websocket.jsr356.server.ContainerDefaultConfigurator.getEndpointInstance(ContainerDefaultConfigurator.java:75)
	at org.eclipse.jetty.websocket.jsr356.server.JsrCreator.createWebSocket(JsrCreator.java:155)
	at org.eclipse.jetty.websocket.server.WebSocketServerFactory.acceptWebSocket(WebSocketServerFactory.java:230)
	at org.eclipse.jetty.websocket.server.WebSocketUpgradeFilter.doFilter(WebSocketUpgradeFilter.java:258)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1618)
	at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:549)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)
	at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1610)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233)
	at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1363)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:188)
	at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:489)
	at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1580)
	at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:186)
	at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1278)
	at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
	at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127)
	at org.eclipse.jetty.server.Server.handle(Server.java:500)
	at org.eclipse.jetty.server.HttpChannel.lambda$handle$1(HttpChannel.java:383)
	at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:547)
	at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:375)
	at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:273)
	at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
	at org.eclipse.jetty.io.ssl.SslConnection$DecryptedEndPoint.onFillable(SslConnection.java:543)
	at org.eclipse.jetty.io.ssl.SslConnection.onFillable(SslConnection.java:398)
	at org.eclipse.jetty.io.ssl.SslConnection$2.succeeded(SslConnection.java:161)
	at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
	at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:117)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:336)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:313)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:171)
	at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:129)
	at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:375)
	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)

There are two points, i might have incorrect assumptions but here they are:

• i would have expected the exception to be thrown or at least printed so that problem can be found rapidly
• i would have expected a type 500 error for such a problem, which would have put me in the right direction much faster.

[lachlan-roberts]

@fredbar You must declare your inner class as public static for this to work.
But I agree that we could do a better job at reporting these errors. I think in this case jetty should throw DeploymentException when the endpoint is added to the ServerContainer, this way you get an error at deployment time and not just when the first request comes in.

[fredbar]

Oh, sure, having a deployment exception is even better.
Thanks for your work on this.

[gregw]

@lachlan-roberts Also that thrown exception is losing the root cause. It does echo the class and message, but the stack is lost. Can we set the cause on that exception as well.

[lachlan-roberts]

Fixed with PR #4906, will be released with 9.4.30.

[joakime]

This change has broken endpoints that extend from javax.websocket.Endpoint and do not have public default constructors. (not a requirement of the spec)