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Bug #6091

closed

NPE in ContextStackIterator.getMajorCaller with Saxon 12

Added by Radu Coravu 10 months ago. Updated 10 months ago.

Status:
Closed
Priority:
Low
Assignee:
Michael Kay
Category:
Internals
Sprint/Milestone:
-
Start date:
2023-06-23
Due date:
% Done:

100%

Estimated time:
Legacy ID:
Applies to branch:
12, trunk
Fix Committed on Branch:
12, trunk
Fixed in Maintenance Release:
12.3
Platforms:
.NET, Java

Description

We have some code like this:

protected void attachXSLTStackTrace(TransformerException e, XSLTransformerValidationDPI errorDpi) {
    if (e instanceof XPathException) {
      XPathException xPathException = (XPathException) e;
      XPathContext context = xPathException.getXPathContext();
      if (context != null) {
        Iterator<ContextStackFrame> iterator = new ContextStackIterator(context);
        final StringWriter sw = new StringWriter();
        while (iterator.hasNext()) {
            ContextStackFrame frame = iterator.next();
            frame.print(new net.sf.saxon.lib.Logger() {
              @Override
              public void println(String message, int severity) {
                sw.write(message + "\n");
              }
              @Override
              public StreamResult asStreamResult() {
                return new StreamResult(sw);
              }
            });
        }
        
        String entireStackTrace = sw.toString();
        if(entireStackTrace.length() > 0){
          errorDpi.setDetailedExceptionInfo(new DetailedExceptionInfo("XSLT Stack Trace:\n" + entireStackTrace, null, e.getMessage()));
        }
      }
    }
  }

called when we get a falal error from Saxon and now we have a nullpointerexception here with Saxon 12:

java.lang.NullPointerException: null
	at net.sf.saxon.trace.ContextStackIterator.getMajorCaller(ContextStackIterator.java:147)
	at net.sf.saxon.trace.ContextStackIterator.next(ContextStackIterator.java:79)
	at net.sf.saxon.trace.ContextStackIterator.next(ContextStackIterator.java:24)
	at ro.sync.xml.transformer.DPIErrorListener.attachXSLTStackTrace(DPIErrorListener.java:438)
	at ro.sync.xml.transformer.DPIErrorListener.addError(DPIErrorListener.java:399)
	at ro.sync.dxsl.debugger.TrAXErrorListener.addError(TrAXErrorListener.java:78)
	at ro.sync.xml.transformer.DPIErrorListener.fatalError(DPIErrorListener.java:358)
	at net.sf.saxon.lib.ErrorReporterToListener.report(ErrorReporterToListener.java:68)
	at net.sf.saxon.Controller.reportFatalError(Controller.java:444)
	at net.sf.saxon.trans.XsltController.applyTemplates(XsltController.java:700)

Can we prohibit this in some way?

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 #1

Updated by Michael Kay 10 months ago

The class ContextStackIterator has a comment

    // TODO: this class is no longer used by StandardErrorListener.printStackTrace(). It's potentially
    // still useful to have a programmatic way of obtaining the stack trace, but this class is rather
    // clumsy and probably isn't used.

which almost certainly means there are no unit tests.

But the failing method in Saxon 11 reads:

private static XPathContextMajor getMajorCaller(XPathContext context) {
        XPathContext caller = context.getCaller();
        while (!(caller == null || caller instanceof XPathContextMajor)) {
            caller = caller.getCaller();
        }
        return (XPathContextMajor) caller;
    }

and in Saxon 12 it reads:

private static XPathContextMajor getMajorCaller(XPathContext context) {
        XPathContext caller = context.getCaller();
        return caller.getMajorContext();
    }

The change was made on the 12 branch on 2022-06-24 supposedly "to allow old XPathContextMajor objects to be garbage collected".

It seems unlikely that we would have made this change unless we actually encountered a problem that showed it to be necessary. However, the change to this method was made as part of a larger change that removed duplication in code that navigates the context stack, so I suspect that this was an incorrectly-implemented refactoring to simplify duplicated code, done in the course of solving a performance problem.

I'll change it to:

        XPathContext caller = context.getCaller();
        return caller == null ? null : caller.getMajorContext();
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 #2

Updated by Michael Kay 10 months ago

  • Tracker changed from Support to Bug
  • Category set to Internals
  • Status changed from New to Resolved
  • Assignee set to Michael Kay
  • Applies to branch 12, trunk added
  • Fix Committed on Branch 12, trunk added
  • Platforms .NET, Java added
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 #3

Updated by Radu Coravu 10 months ago

Thanks Michael! I will attempt the same patch on my side.

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 #4

Updated by O'Neil Delpratt 10 months ago

  • Status changed from Resolved to Closed
  • % Done changed from 0 to 100
  • Fixed in Maintenance Release 12.3 added

Bug fix applied in the Saxon 12.3 maintenance release.

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