Exist: Null Pointer exception on inspect:inspect-module()

[JonathanRowell]

Following simple query causes a NullPointerException in 3.0RC1 under Windows.

Filename : thisquery.xql

xquery version "3.0";

import module namespace inspect = "http://exist-db.org/xquery/inspection";

let $data := inspect:inspect-module(xs:anyURI("xmldb:exist:///db/apps/JonathanTest/thisquery.xql"))
return
  $data

ie: it is inspecting itself.

java.lang.NullPointerException
    at org.exist.xquery.XQueryContext.compileOrBorrowModule(XQueryContext.java:2835) ~[exist.jar:?]
    at org.exist.xquery.XQueryContext.importModule(XQueryContext.java:2748) ~[exist.jar:?]
    at org.exist.xquery.functions.inspect.InspectModule.eval(InspectModule.java:66) ~[exist.jar:?]
    at org.exist.xquery.BasicFunction.eval(BasicFunction.java:70) ~[exist.jar:?]
    at org.exist.xquery.InternalFunctionCall.eval(InternalFunctionCall.java:56) ~[exist.jar:?]
    at org.exist.xquery.LetExpr.eval(LetExpr.java:142) ~[exist.jar:?]
    at org.exist.xquery.BindingExpression.eval(BindingExpression.java:165) ~[exist.jar:?]
    at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:71) ~[exist.jar:?]
    at org.exist.xquery.PathExpr.eval(PathExpr.java:267) ~[exist.jar:?]
    at org.exist.xquery.AbstractExpression.eval(AbstractExpression.java:71) ~[exist.jar:?]
    at org.exist.xquery.XQuery.execute(XQuery.java:280) ~[exist.jar:?]
    at org.exist.xquery.XQuery.execute(XQuery.java:200) ~[exist.jar:?]
    at org.exist.http.servlets.XQueryServlet.process(XQueryServlet.java:492) [exist-optional.jar:?]
    at org.exist.http.servlets.XQueryServlet.doPost(XQueryServlet.java:198) [exist-optional.jar:?]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:755) [servlet-api-3.0.jar:?]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:848) [servlet-api-3.0.jar:?]
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:684) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:503) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:575) [jetty-security-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:429) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:229) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.Dispatcher.forward(Dispatcher.java:103) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.exist.http.urlrewrite.Forward.doRewrite(Forward.java:50) [exist-optional.jar:?]
    at org.exist.http.urlrewrite.XQueryURLRewrite.doRewrite(XQueryURLRewrite.java:557) [exist-optional.jar:?]
    at org.exist.http.urlrewrite.XQueryURLRewrite.service(XQueryURLRewrite.java:357) [exist-optional.jar:?]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:848) [servlet-api-3.0.jar:?]
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:684) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1496) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at de.betterform.agent.web.filter.XFormsFilter.doFilter(XFormsFilter.java:171) [betterform-exist-5.1-SNAPSHOT-20150603.jar:?]
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1476) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:501) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:533) [jetty-security-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1086) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:429) [jetty-servlet-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1020) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:154) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.Server.handle(Server.java:370) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:494) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.AbstractHttpConnection.content(AbstractHttpConnection.java:982) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.content(AbstractHttpConnection.java:1043) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:865) [jetty-http-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:240) [jetty-http-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82) [jetty-server-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:696) [jetty-io-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:53) [jetty-io-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608) [jetty-util-8.1.17.v20150415.jar:8.1.17.v20150415]
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543) [jetty-util-8.1.17.v20150415.jar:8.1.17.v20150415]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_77]

[joewiz]

Confirmed with current develop branch.

[JonathanRowell]

Confirmed also with version 2017-02-01 Git Hash c1b5b79.

The stack trace is the same except that the crash point is now at line 2822 instead of 2835.

[adamretter]

The issue you have is because you are trying to pass a main module to inspect:inspect-module.

inspect:inspect-module only works with library modules, although that was not clear from the documentation. I just fixed the NPE and updated the documentation here - https://github.com/eXist-db/exist/pull/1372

Calling inspect:inspect-module on a main module now returns an empty sequence.

[JonathanRowell]

If inspect-module only works on library modules, why should it return an empty sequence. I would have though that inspect-module ought to return a something from a library module and nothing otherwise.

There are too many "modules" in the names.
I call XQueries with a module statement a "module" and those without just queries.

[dizzzz]

@JonathanRowell I am not sure if I understand what you suggest? the Java NPE is gone now, that is good. In essence there are two options for returning: an error or a empty sequence. I am not too fond of raising errors (try-catch required), so the empty sequence is a good alternative. For me, this is a good change.

[joewiz]

@JonathanRowell Re: what to call XQuery files, you might find these discussions useful:

• exist-open: http://markmail.org/message/sivbjlyybmwp75gl
• xquery-talk: http://x-query.com/pipermail/talk/2013-January/thread.html#4030

[JonathanRowell]

@dizzz I've read Adam's comment now six times. The last sentence should read "Calling inspect:inspect-module on aN NON- library module now returns an empty sequence."

Yes it is the correct change, since an exception should only be raised if the "thing" being inspected is not well formed.

[adamretter]

@JonathanRowell I chose to return an empty sequence if you try against a main module, because inspect:inspect-module would previously also return an empty sequence if you tried against a URI that did not exist. So keeping the same orthogonality of errors seemed sensible to me.

I note also that in XQuery terms an empty sequence is the equivalent of "nothing".

[JonathanRowell]

@joewiz I don't want to go down that road! But one can get tongue tied now and again.

[adamretter]

@JonathanRowell You are right, there was a mistake in my comment, I have now updated it.