Circular dependency between Context and ScriptRuntime leads to a NullPointerException (emptyArgs null)

[egueidao]

Hello,

I think I have a circular dependency problem between the two classes org.mozilla.javascript.Context and org.mozilla.javascript.ScriptRuntime.
The problem is with the initialization of emptyArgs in Context class which is null and leads to a NullpointerExcption in the MemberBox code when the list of parameters is iterated.

Here is the Stacktrace :

java.lang.NullPointerException: Cannot read the array length because "args" is null
	at org.mozilla.javascript.MemberBox.invoke(MemberBox.java:205)
	at org.mozilla.javascript.JavaMembers.get(JavaMembers.java:103)
	at org.mozilla.javascript.NativeJavaObject.get(NativeJavaObject.java:96)
	at org.mozilla.javascript.ScriptableObject.getProperty(ScriptableObject.java:2037)
	at org.mozilla.javascript.ScriptRuntime.getObjectProp(ScriptRuntime.java:1741)
	at org.mozilla.javascript.ScriptRuntime.getObjectProp(ScriptRuntime.java:1736)
	at org.mozilla.javascript.gen.DynamicScript_1._c_main_1(DynamicScript:3)
	at org.mozilla.javascript.gen.DynamicScript_1.call(DynamicScript)
	at org.mozilla.javascript.ContextFactory.doTopCall(ContextFactory.java:383)
	at org.mozilla.javascript.ScriptRuntime.doTopCall(ScriptRuntime.java:3940)
	at org.mozilla.javascript.gen.DynamicScript_1.call(DynamicScript)
	at com.openpricer.common.is.DynamicJavaScriptExecution.javaScriptCodeExecutor(DynamicJavaScriptExecution.java:74)

Here are the different versions used in my application:

Rhino 1.7.15
Spring Framework 6.0.23
Java 17
Tomcat 10.1.6

Here's my problem code :

             Context context = Context.enter();
		try {
			Scriptable scope = context.initStandardObjects(null,true);

			// Inject each class into the JavaScript context
			if (classesToImport != null) {
				for (Class<?> clazz : classesToImport) {
					scope.put(clazz.getSimpleName(), scope, Context.javaToJS(clazz, scope));
				}
			}

			// Inject custom JavaScript imports
			String functionName = "main";
			String fullCode = String.format("""
					%s
					function %s(%s) {
					    %s
					}
					""", imports, functionName, parameters, code);
			
			context.evaluateString(scope, fullCode, "DynamicScript", 1, null);
			// Call the dynamically created function
			Function function = (Function) scope.get(functionName, scope);
			return function.call(context, scope, scope, args);
		} finally {
			Context.exit();
		}

When I try to execute a function by calling Function.call I get a NullPointerException in the MemberBox class on args which is null. The script tries to interpret a simple getter on my object (Script parameter).

I think this is due to the static initialization of emptyArgs in Context class :
public static final Object[] emptyArgs = ScriptRuntime.emptyArgs;

Looking in debug mode, ScriptRuntime.emptyArgs is not yet initialised with the empty array.
I then tried to force the initialization of the ScriptRuntime class first when launching my application but ScriptRuntime also depends on Context (code in ScriptRuntime.class line 102) :

 public static final Class<?> ContextClass = Kit.classOrNull(‘org.mozilla.javascript.Context’),
            ContextFactoryClass = Kit.classOrNull(‘org.mozilla.javascript.ContextFactory’),
            FunctionClass = Kit.classOrNull(‘org.mozilla.javascript.Function’),
            ScriptableObjectClass = Kit.classOrNull(‘org.mozilla.javascript.ScriptableObject’);

Is this a known problem or is something missing from my code ?
How can I ensure that Context.emptyArgs is always initialised with an empty object array ?

Thank you in advance

[rbri]

Our code has only two places where Context.emptyArgs is used - should we deprecate that field and always use ScriptRuntime.emptyArgs?

[egueidao]

It could be a good solution.

[rbri]

PR provided - @gbrail, @andreabergia , @p-bakker what do you think?

[andreabergia]

I am ok with removing the duplication and using only the ScriptRuntime one, but I am puzzled by how it could be null.
ScriptRuntime.emptyArgs is a static final field, it should always be initialized by the JVM's calling <clinit>. Same for Context.emptyArgs. So... what am I missing?

[egueidao]

Maybe the circular dependency. ScriptRuntime needs Context to initialize the static field ContextClass. Maybe moving the initialization emptyArgs before ContextClass is enough.

In my call stack, <clinit> initializes ScriptRuntime first, but tries to initialize Context for the ScriptRuntime.ContextClass field before ScriptRuntime.emptyArgs

[andreabergia]

@egueidao you are right, good point. I think the fix from @rbri is fine.