Anuken/Mindustry · error · RuntimeException

Nested arrays are not allowed

Error message

Nested arrays are not allowed

What it means

TypeIO.readObject throws a plain RuntimeException when it encounters type tag 6 (IntSeq) and allowArrays is false. allowArrays is passed false by the recursive readObject call inside case 22 (Object[]), so an IntSeq nested inside an Object[] is rejected to prevent unbounded nested allocation. The guard is a structural check, not a data-integrity check.

Source

Thrown at core/src/mindustry/io/TypeIO.java:201

        byte type = read.b();
        return switch(type){
            case 0 -> null;
            case 1 -> read.i();
            case 2 -> read.l();
            case 3 -> read.f();
            case 4 -> {
                byte exists = read.b();
                if(exists != 0){
                    //in a safe context, strings can only be 1200 chars
                    yield read.str(safe ? 1200 : 0);
                }else{
                    yield null;
                }
            }
            case 5 -> mapper == null ? content.getByID(ContentType.all[read.b()], read.s()) : mapper.get(ContentType.all[read.b()], read.s());
            case 6 -> {
                if(!allowArrays) throw new RuntimeException("Nested arrays are not allowed");
                short len = read.s();
                if(len > maxArraySize) throw new RuntimeException("Invalid array size: " + len);
                IntSeq arr = new IntSeq(len);
                for(int i = 0; i < len; i ++) arr.add(read.i());
                yield arr;
            }
            case 7 -> new Point2(read.i(), read.i());
            case 8 -> {
                if(!allowArrays) throw new RuntimeException("Nested arrays are not allowed");
                int len = read.ub();
                Point2[] out = new Point2[len];
                for(int i = 0; i < len; i ++) out[i] = Point2.unpack(read.i());
                yield out;
            }
            case 9 -> content.<UnlockableContent>getByID(ContentType.all[read.b()], read.s()).techNode;
            case 10 -> read.bool();
            case 11 -> read.d();
            case 12 -> !box ? world.build(read.i()) : new BuildingBox(read.i());

View on GitHub (pinned to f695ad7e60)

Solutions

1. Do not nest array configs: ensure Object[] elements are scalar types (Integer, String, Content, etc.).
2. If array data is legitimate, send it as a top-level config (allowArrays=true path), not inside an Object[].
3. Validate on the write side that Object[] elements are non-array before calling writeObject.

Example fix

// before
Object[] nested = {new int[]{1,2,3}, "x"};
TypeIO.writeObject(write, nested); // read-back throws 'Nested arrays are not allowed'

// after
Object[] flat = {1, 2, 3, "x"}; // scalars only
TypeIO.writeObject(write, flat);

// Enforce no nested arrays in Object[] before writing
static void assertFlat(Object[] objs) {
    for (Object o : objs) if (o != null && o.getClass().isArray())
        throw new IllegalArgumentException("Nested array in Object[] config: " + o.getClass());
}

static boolean isFlatObjectArray(Object[] objs) {
    if (objs == null) return true;
    for (Object o : objs) if (o != null && o.getClass().isArray()) return false;
    return true;
}

try {
    Object o = TypeIO.readObject(read);
} catch (RuntimeException e) {
    if ("Nested arrays are not allowed".equals(e.getMessage())) {
        // reject the packet/config
    }
}

When it happens

Trigger: A serialized Object[] (tag 22) whose elements recurse via readObject(..., allowArrays=false); if any element is itself an array type (tag 6/8/14/16/18/22), this fires. Can also occur if a caller manually invokes readObject with allowArrays=false on a stream containing an array tag.

Common situations: A client sending a crafted or buggy packet that nests arrays inside an Object[] config; mod code reading configs in a restricted (safe) context.

Related errors

• Invalid array size: {}
• Player cannot configure a tile.
• Player cannot control a building.
• Player cannot control a unit.
• Player attempted to control invalid unit.

AI-assisted analysis of Anuken/Mindustry@f695ad7e60 (2026-08-14). Data as JSON: /api/errors/e5fe52634054031e. Report an issue: GitHub.