Major Description
Prompted by discussion in: https://forum.xwiki.org/t/nullpointerexception-in-websocket-endpoint-follow-on-from-another-npe-question-i-asked/10687
The NPE is being seen on certain XWiki deployments (a prod environment, compared to a staging and dev environment which don't appear to be having this issue).
- dev is a clean v13 install and it works.
- staging is a v12 upgraded to v13 and it works
- prod is a v12 upgraded to v13 which consistently shows the NPE.
It might not be the upgrade that is the issue but wanted to include as much info as possible.
The v13 being used is 13.10.5 across all instances.
The NPE being thrown is:
2022-07-13 09:56:50,705 [http-nio-8080-exec-3 - https://app.seekingbinary.com/kb/websocket/t725e89b91a72447dab483c204e54e/navmenu] ERROR c.x.x.XWiki - Failed to get URL for provided wiki [t725e89b91a72447dab483c204e54e] java.lang.NullPointerException: null at org.xwiki.wiki.internal.descriptor.document.DefaultWikiDescriptorDocumentHelper.getDocument(DefaultWikiDescriptorDocumentHelper.java:187) at org.xwiki.wiki.internal.descriptor.document.DefaultWikiDescriptorDocumentHelper.getDocumentFromWikiId(DefaultWikiDescriptorDocumentHelper.java:101) at org.xwiki.wiki.internal.descriptor.DefaultWikiDescriptorManager.getById(DefaultWikiDescriptorManager.java:170) at com.xpn.xwiki.XWiki.getServletPath(XWiki.java:5477) at com.xpn.xwiki.web.XWikiServletURLFactory.addServletPath(XWikiServletURLFactory.java:349) at com.xpn.xwiki.web.XWikiServletURLFactory.createURL(XWikiServletURLFactory.java:312) at com.xpn.xwiki.web.XWikiDefaultURLFactory.createURL(XWikiDefaultURLFactory.java:52) at com.xpn.xwiki.web.XWikiDefaultURLFactory.createURL(XWikiDefaultURLFactory.java:46) at com.xpn.xwiki.user.impl.xwiki.XWikiAuthServiceImpl.getAuthenticator(XWikiAuthServiceImpl.java:131) at com.xpn.xwiki.user.impl.xwiki.XWikiAuthServiceImpl.checkAuth(XWikiAuthServiceImpl.java:235) at com.seekingbinary.xwiki.authn.CustomAuthenticationService.checkAuth(CustomAuthenticationService.java:27) at com.xpn.xwiki.XWiki.checkAuth(XWiki.java:4336) at org.xwiki.websocket.internal.DefaultWebSocketContext.createExecutionContext(DefaultWebSocketContext.java:149) at org.xwiki.websocket.internal.DefaultWebSocketContext.initialize(DefaultWebSocketContext.java:78) at org.xwiki.websocket.internal.XWikiEndpointConfigurator.modifyHandshake(XWikiEndpointConfigurator.java:68) at org.apache.tomcat.websocket.server.UpgradeUtil.doUpgrade(UpgradeUtil.java:227) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:78) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) at org.xwiki.container.servlet.filters.internal.SetHTTPHeaderFilter.doFilter(SetHTTPHeaderFilter.java:63) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) at org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) at org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:111) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) at org.xwiki.resource.servlet.RoutingFilter.doFilter(RoutingFilter.java:132) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1743) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.base/java.lang.Thread.run(Thread.java:829)
Looking at the XWiki source, DefaultWebSocketContext#createExecutionContext creates a stub context and calls checkAuth on the Authenticator on line 149. The problem appears to be that the DefaultWikiDescriptorDocumentHelper.getDocument(DefaultWikiDescriptorDocumentHelper.java:187) requires the XWikiContext to have been set/initialised on the Execution; however, that hasn’t happened yet as it’s only on return of the DefaultWebSocketContext#createExecutionContext that the context that is created, is set on the Execution (in DefaultWebSocketContext#initialize on line 105).
To be more specific…
- DefaultWebSocketContext#initialize is called, which calls…
- DefaultWebSocketContext#createExecutionContext, which calls…
- xcontext.getWiki().checkAuth(xcontext);, which eventually calls…
- DefaultWikiDescriptorDocumentHelper#getDocument, which calls…
- XWikiContext context = xcontextProvider.get();. (Line 186), which calls…
- XWikiContextProvider#get, which calls…
- XWikiContextProvider#getXWikiContext, which calls…
- ExecutionContext econtext = this.execution.getContext();, which is returning null, so the xcontextProvider.get(); returns null.
- As the context object is null, Line 187 in DefaultWikiDescriptorDocumentHelper#getDocument fails with an NPE.
- (If it didn’t NPE) The stack unravels back to DefaultWebSocketContext#initialize (step 1), which calls…
- DefaultWebSocketContext#initialize(ExecutionContext context), which calls…
- this.execution.pushContext(context, false); - Which is too late in this process.
What is not clear is why it is happening on one environment compared to others that don't appear to be having this issue. That would suggest that there is maybe a race condition or the opportunity for a different path in the logic. As the environments are set up the same as much as possible, there is nothing obvious that would suggest that the environment/config would be causing a different path in the code to be executed; though that's not to say it isn't possible.