Writing callback function pointers leads to unexpected object creation

[lwahonen]

lwahonen@35acd04

See above commit for a minimal unit test.

It fails with

java.lang.IllegalArgumentException: Structure field "callback" was declared as interface com.sun.jna.CallbacksTest$vTable$functionpointer, which is not supported within a Structure

at com.sun.jna.Structure.writeField(Structure.java:864)
at com.sun.jna.Structure.write(Structure.java:768)
at com.sun.jna.CallbacksTest.testWriteCallback(CallbacksTest.java:1577)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at junit.framework.TestCase.runTest(TestCase.java:154)
at junit.framework.TestCase.runBare(TestCase.java:127)
at junit.framework.TestResult$1.protect(TestResult.java:106)
at junit.framework.TestResult.runProtected(TestResult.java:124)
at junit.framework.TestResult.run(TestResult.java:109)
at junit.framework.TestCase.run(TestCase.java:118)
at junit.framework.TestSuite.runTest(TestSuite.java:208)
at junit.framework.TestSuite.run(TestSuite.java:203)
at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:84)
at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

Caused by: java.lang.IllegalArgumentException: Exception thrown while instantiating an instance of class com.sun.jna.platform.win32.OaIdl$SAFEARRAY
at com.sun.jna.Structure.newInstance(Structure.java:1790)
at com.sun.jna.Structure.validate(Structure.java:2128)
at com.sun.jna.CallbackReference.getNativeType(CallbackReference.java:275)
at com.sun.jna.CallbackReference.(CallbackReference.java:248)
at com.sun.jna.CallbackReference.getFunctionPointer(CallbackReference.java:449)
at com.sun.jna.CallbackReference.getFunctionPointer(CallbackReference.java:426)
at com.sun.jna.Pointer.setValue(Pointer.java:885)
at com.sun.jna.Structure.writeField(Structure.java:856)
... 20 more
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
at com.sun.jna.Structure.newInstance(Structure.java:1771)
... 27 more
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
at com.sun.jna.Structure.toArray(Structure.java:1551)
at com.sun.jna.Structure.toArray(Structure.java:1576)
at com.sun.jna.platform.win32.OaIdl$SAFEARRAY.read(OaIdl.java:610)
at com.sun.jna.platform.win32.OaIdl$SAFEARRAY.(OaIdl.java:604)
... 32 more

If you change the parameter type for runtimeId to int, the test passes successfully.

Not sure why writing a function pointer ends up trying to create a SAFEARRAY object. I can patch this by getting the SAFEARRAY as Pointer to the callback, and constructing the SAFEARRAY manually in the callback.

[matthiasblaesing]

This sounds like a bug in the override SAFEARRAY#read. Could you please check if this helps:

# This patch file was generated by NetBeans IDE
# It uses platform neutral UTF-8 encoding and \n newlines.
--- a/contrib/platform/src/com/sun/jna/platform/win32/OaIdl.java
+++ b/contrib/platform/src/com/sun/jna/platform/win32/OaIdl.java
@@ -607,8 +607,12 @@
         @Override
         public void read() {
             super.read();
+            if(cDims.intValue() > 0) {
             rgsabound = (SAFEARRAYBOUND[]) rgsabound[0].toArray(cDims.intValue());
+            } else {
+                rgsabound = new SAFEARRAYBOUND[]{ new SAFEARRAYBOUND() };
         }
+        }
         
         @Override
         protected List<String> getFieldOrder() {

This is a degenerated case - it is a SAFEARRAY without dimensions. Structure#validate checks the type by trying to instantiate the structure, and this runs into this issue.

[lwahonen]

Hi,

I think it's leading towards Structure.java [185]:

protected Structure(Pointer p, int alignType, TypeMapper mapper) {
    setAlignType(alignType);
    setStringEncoding(Native.getStringEncoding(getClass()));
    initializeTypeMapper(mapper);
    validateFields();
    **if (p != null) {**
        useMemory(p, 0, true);
    }
    else {
        allocateMemory(CALCULATE_SIZE);
    }
    initializeFields();
}

As P is not null here, it's native@0x0. Should a zero valued pointer be treated as a null pointer here?

[lwahonen]

For the record, your fix solves this problem. I'm just sleuthing to see if this is a more systemic problem in JNA

[matthiasblaesing]

@lwahonen could could you please have a look at PR #926? This holds the necessary changeset.

For your question and reference in Structure.java, you are in prinicipal right, that for the PLACEHOLDER_MEMORY case p is a C null pointer. The code in Structure#read and Structure#write handles this case by preventing writes and reads if the backing memory of the structure is the PLACEHOLDER_MEMORY.

[lwahonen]

The safearray fix fixes things, but honestly I'm not familiar enough with the inner workings of Structure.newInstance to comment on that part. Looks good to me, and I think the worst thing that can happen is moving an error from validation time to actual call time.

[matthiasblaesing]

Thanks for your input - I merged the changeset to master and the 4.5.X branch.