DAP4 in TDS dap4.core.util.DapException: Resource root not found

[rkouznetsov]

Hi,
I use THREDDS Data Server [Version 4.6.15 - 2020-06-16T13:36:16-0600]
hosted at http://silam.fmi.fi/thredds/catalog.html.

I have found out that when downloading large subsets over lousy connections DAP requests result sometimes in corrupt output. If I got it right, DAP does not support any checksum or other verification mechanisms, therefore I have tried to switch to DAP4 that seems to have a checksum mechanism. However DAP4 seems to be broken in the server: a request to e.g.
http://silam.fmi.fi/thredds/dap4/silam_china_v5_5_1/silam_china_v5_5_1_best.ncd.dmr.xml
results 500 error code. Corresponding error appears in the tomcat logs as:

Feb 09, 2021 1:27:11 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [root] in context with path [/thredds] threw exception
dap4.core.util.DapException: dap4.core.util.DapException: Resource root not found
        at dap4.servlet.DapRequest.<init>(DapRequest.java:78)
        at dap4.servlet.DapController.getRequestState(DapController.java:415)
        at dap4.servlet.DapController.handleRequest(DapController.java:185)
        at thredds.server.dap4.Dap4Controller.handleRequest(Dap4Controller.java:65)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:90)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55)
        at java.lang.reflect.Method.invoke(Method.java:508)
        at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:849)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:760)
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
        at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
        at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at thredds.servlet.filter.RequestQueryFilter.doFilter(RequestQueryFilter.java:118)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.logging.log4j.web.Log4jServletFilter.doFilter(Log4jServletFilter.java:71)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at thredds.servlet.filter.RequestCORSFilter.doFilterInternal(RequestCORSFilter.java:49)
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
        at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:347)
        at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:263)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at thredds.servlet.filter.RequestPathFilter.doFilter(RequestPathFilter.java:94)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at thredds.server.RequestBracketingLogMessageFilter.doFilter(RequestBracketingLogMessageFilter.java:81)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:498)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
        at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.valves.RemoteIpValve.invoke(RemoteIpValve.java:683)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
        at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:318)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1160)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:820)
Caused by: dap4.core.util.DapException: Resource root not found
        at dap4.servlet.DapRequest.parse(DapRequest.java:134)
        at dap4.servlet.DapRequest.<init>(DapRequest.java:76)
        ... 59 more

Any idea?
Thank you!

[DennisHeimbigner]

It is going to be tough for me to debug a foreign server. Have you contacted the
server's owner to see how they have configured the DAP4; specifically, what is
in /WEB-INF?

[rkouznetsov]

Hi Dennis! Thank you for the prompt reply. I am the owner :).
WEB-INF (in webapps/thredds/) has a lot of stuff that came from the official .war and has not been changed since then.
The only reference to dap4 is in catalog.xml:

  <service name="all" base="" serviceType="compound">
    <service name="odap" serviceType="OpenDAP" base="/thredds/dodsC/" />
    <service name="dap4" serviceType="DAP4" base="/thredds/dap4/" />
    <service name="http" serviceType="HTTPServer" base="/thredds/fileServer/" />
    <service name="wms" serviceType="WMS" base="/thredds/wms/" />
    <service name="ncss" serviceType="NetcdfSubset" base="/thredds/ncss/grid/" />
  </service>

Other services (odap, http, wms, and ncss) work fine.

[rkouznetsov]

Hi,
Just an update. The latest THREDDS Data Server [Version 4.6.16.1 - 2021-02-23T15:50:43-0700] still has the same issue.
Thank you!