{"record":{"id":"ae325b5b511ee594","repo":"java-native-access/jna","slug":"maximum-argument-count-is-max-nargs","errorCode":null,"errorMessage":"Maximum argument count is <MAX_NARGS>","messagePattern":"Maximum argument count is <MAX_NARGS>","errorType":"validation","errorClass":"UnsupportedOperationException","httpStatus":null,"severity":"error","filePath":"src/com/sun/jna/Function.java","lineNumber":332,"sourceCode":"     */\n    public Object invoke(Class<?> returnType, Object[] inArgs, Map<String, ?> options) {\n        Method invokingMethod = (Method)options.get(OPTION_INVOKING_METHOD);\n        Class<?>[] paramTypes = invokingMethod != null ? invokingMethod.getParameterTypes() : null;\n        return invoke(invokingMethod, paramTypes, returnType, inArgs, options);\n    }\n\n    /** Invoke the native function with the given arguments, returning the\n     * native result as an Object. This method can be called if invoking method and parameter\n     * types are already at hand. When calling {@link Function#invoke(Class, Object[], Map)},\n     * the method has to be in the options under key {@link Function#OPTION_INVOKING_METHOD}.\n     */\n    Object invoke(Method invokingMethod, Class<?>[] paramTypes, Class<?> returnType, Object[] inArgs, Map<String, ?> options) {\n        // Clone the argument array to obtain a scratch space for modified\n        // types/values\n        Object[] args = { };\n        if (inArgs != null) {\n            if (inArgs.length > MAX_NARGS) {\n                throw new UnsupportedOperationException(\"Maximum argument count is \" + MAX_NARGS);\n            }\n            args = new Object[inArgs.length];\n            System.arraycopy(inArgs, 0, args, 0, args.length);\n        }\n\n        TypeMapper mapper = (TypeMapper)options.get(Library.OPTION_TYPE_MAPPER);\n        boolean allowObjects = Boolean.TRUE.equals(options.get(Library.OPTION_ALLOW_OBJECTS));\n        boolean isVarArgs = args.length > 0 && invokingMethod != null ? isVarArgs(invokingMethod) : false;\n        int fixedArgs = args.length > 0 && invokingMethod != null ? fixedArgs(invokingMethod) : 0;\n        for (int i=0; i < args.length; i++) {\n            Class<?> paramType = invokingMethod != null\n                ? (isVarArgs && i >= paramTypes.length-1\n                   ? paramTypes[paramTypes.length-1].getComponentType()\n                   : paramTypes[i])\n                : null;\n            args[i] = convertArgument(args, i, invokingMethod, mapper, allowObjects, paramType);\n        }\n","sourceCodeStart":314,"sourceCodeEnd":350,"githubUrl":"https://github.com/java-native-access/jna/blob/d036ad9781adad4b66693e8fa7098e4ac665e0a3/src/com/sun/jna/Function.java#L314-L350","documentation":"The native invocation path has a hard limit MAX_NARGS on the number of arguments a function call may have. Java arrays larger than this cannot be marshaled, so JNA throws UnsupportedOperationException before any native code runs.","triggerScenarios":"Invoking a native function whose mapped interface method declares more parameters than MAX_NARGS (typically 256), e.g. a generated binding with a huge parameter list or a variadic-style misuse.","commonSituations":"Code-generating large argument-pass-through functions; attempting to pass a big batch of scalars one-by-one instead of via a struct or array.","solutions":["Reduce the parameter count by bundling arguments into a JNA Structure passed by reference","Use a Pointer/pointer-array argument to pass bulk data instead of individual parameters","Change the native signature to take a struct or array if you control the native code"],"exampleFix":"// before\nint f(int a1,int a2,...,int a300);\n// after\nclass Args extends Structure { public int[] a = new int[300]; }\nint f(Args args);","handlingStrategy":"validation","validationCode":"if (inArgs != null && inArgs.length > Function.MAX_NARGS) {\n    throw new IllegalArgumentException(\"too many args: \" + inArgs.length);\n}","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Keep mapped native signatures under MAX_NARGS parameters","Bundle large parameter sets into a Structure passed by pointer","Review generated bindings for pathological parameter counts"],"tags":["jna","argument-count","unsupported-operation"],"backgroundTag":"value-out-of-range","analyzedSha":"d036ad9781adad4b66693e8fa7098e4ac665e0a3","analyzedAt":"2026-09-12T06:50:59.239Z","contentChangedAt":"2026-09-12T06:50:59.239Z","schemaVersion":2},"datasetVersion":"2026-09-19T12:17:13.211Z"}