Setting a custom GlobalObject of sorts

[luttje]

With the new TypeResolver we can filter members. I use attributes to decide which methods can and can't be accessed. I'm looking for a way to use the same system to filter, compare (and provide) members in the global scope.

Normally this is done using Engine.SetValue, but I'd prefer to also use attributes to decide which members of a "Global Object" should be exposed using the same TypeResolver.

Playing around it seemed like IReferenceResolver may be able to help me. Though I run into this problem like #947 where I can't return a method so it can be called.

This is a "short" version of what I'm trying:

1. Setup TypeResolver to filter and change compare type. Also setup IReferenceResolver (implemented in step 3)

engine = new Engine(options =>
{
    options.SetTypeResolver(TypeResolver); // Has a MemberFilter (checks [ScriptAllowed] IsDefined) and MemberNameComparer (case insensitive)
    options.SetReferencesResolver(new GlobalScopeReferenceResolver(global));
});

2. global given to the reference resolver above is an instance of this class which contains all my custom global variables and functions amongst functions I do not wish to share

public class GlobalScope : MonoBehaviour
{
    [ScriptAllowed]
    public UserInterface UI => userInterface;

    [ScriptAllowed]
    public GameInput Input;

    [ScriptAllowed]
    public TypeReference Log { get; private set; }

    [ScriptAllowed]
    public TypeReference KeyCode { get; private set; }

    public UserInterface userInterface;

    void Awake()
    {
        Input = new GameInput();
    }

    void Update()
    {
        Input?.DoUpdate();
    }

    internal void SetEngine(Engine engine)
    {
        this.engine = engine;

        Log = TypeReference.CreateTypeReference(engine, typeof(Log));
        KeyCode = TypeReference.CreateTypeReference(engine, typeof(KeyCode));
    }

    [ScriptAllowed]
    public void Require(string filePath)
    {
        var script = File.ReadAllText(Path.Combine(Application.dataPath, filePath));
        engine.Evaluate(script);
    }

    // ... etc
}

3. My attempt with IReferenceResolver but there may be a better way

public class GlobalScopeReferenceResolver : IReferenceResolver
{
    private GlobalScope global;
    private Type globalType;

    public GlobalScopeReferenceResolver(GlobalScope global)
    {
        this.global = global;
        globalType = global.GetType();
    }

    // Source: https://github.com/sebastienros/jint/blob/2548f0681b295123f590bccd4a2e22b7b4541b25/Jint/Runtime/Interop/TypeResolver.cs#L170
    public bool TryUnresolvableReference(Engine engine, Reference reference, out JsValue value)
    {
        var referenceName = reference.GetReferencedName();

        if (!referenceName.IsString())
        {
            value = JsValue.Undefined;
            return false;
        }

        var memberName = referenceName.AsString();
        const BindingFlags bindingFlags = BindingFlags.Public | BindingFlags.Instance;
        var typeResolver = ScriptManager.Instance.TypeResolver;

        // look for a property, bit be wary of indexers, we don't want indexers which have name "Item" to take precedence
        PropertyInfo property = null;
        foreach (var p in globalType.GetProperties(bindingFlags))
        {
            if (!typeResolver.MemberFilter(p))
            {
                continue;
            }

            // only if it's not an indexer, we can do case-ignoring matches
            var isStandardIndexer = p.GetIndexParameters().Length == 1 && p.Name == "Item";
            if (!isStandardIndexer && typeResolver.MemberNameComparer.Equals(p.Name, memberName))
            {
                property = p;
                break;
            }
        }

        if (property != null)
        {
            value = JsValue.FromObject(engine, property.GetValue(global));
            return true;
        }

        // look for a field
        FieldInfo field = null;
        foreach (var f in globalType.GetFields(bindingFlags))
        {
            if (!typeResolver.MemberFilter(f))
            {
                continue;
            }

            if (typeResolver.MemberNameComparer.Equals(f.Name, memberName))
            {
                field = f;
                break;
            }
        }

        if (field != null)
        {
            value = JsValue.FromObject(engine, field.GetValue(global));
            return true;
        }

        // if no properties were found then look for a method
        List<MethodInfo> methods = null;
        foreach (var m in globalType.GetMethods(bindingFlags))
        {
            if (!typeResolver.MemberFilter(m))
            {
                continue;
            }

            if (typeResolver.MemberNameComparer.Equals(m.Name, memberName))
            {
                methods ??= new List<MethodInfo>();
                methods.Add(m);
            }
        }

        if (methods?.Count > 0)
        {
            value = ;// Same issue as #947, how to return callable method
            return true;
        }

        value = JsValue.Undefined;
        return false;
    }

    // ... etc
}

4. Then from JavaScript I can access methods, properties and fields as if they are members of the globalThis:

Log.debug(Input.getLastKey()); // Would access Log in the GlobalScope instance from step 2
require("somefilepath.js"); // Would access Require from that same GlobalScope object

This works somewhat for properties and fields, but for members it seems more challenging since I can't return a method (like #947).

Is there a way to do what I want? I had a look at Jint/GlobalObject.cs, but it's sealed. Furthermore it seems that if I want to override Host.CreateGlobalObject I have to specify a HostFactory that provides my own host, but that feels like overkill (so I haven't tried).

Which direction would be preferred? Or is what I want not possible/desired?

If anythings unclear let me know. I had trouble keeping the question short.

[luttje]

Now that I think about it, I could perhaps SetValue that object normally and then set it as the prototype to the global object

I'll try that first thing tomorrow

[luttje]

I think this is a bug due to my perhaps unorthodox usage: I believe Jint should pass the object reference to that function somehow. Am I right or am I missing something?

I believe this this snippet is functionally similar to the above test-case and shows that regardless if a reference is provided, it should be known inside the method:

const CORRECT_TEST_VALUE = 1234;
let log = console.log;

let global = function(){
	this.test = CORRECT_TEST_VALUE;
	this.BoundLog = function(x){
		console.log(this.test); // to demonstrate this is in this scope
		console.log(x);
	}
}

//Object.setPrototypeOf(globalThis, global); // protected in browser
globalThis.prototype = global();

log(test === CORRECT_TEST_VALUE);
BoundLog(CORRECT_TEST_VALUE);

I realize JavaScript's this behaves very differently from C#'s this, so I can imagine if this is quite a hassle to work around.

Would love to hear someone's thoughts on this :)

[luttje]

I see now that I'm confusing the prototype instance for the global object instance. So the above is mostly false.

I'll consider my original question unanswered. I'm still open for ideas on how to create a custom global object that lives mostly in C#

[luttje]

I guess the easiest way forward is to just make my GlobalScope class mostly static or a Singleton so no reference is needed.

[lahma]

I probably haven't fully understood the need here, but I would just manually register items (functions and objects) manually to global scope (SetValue) and then let object wrapping handle CLR object creation and filtering. Unless you really want to hide default global things like JSON and friends.

[luttje]

I think you're right. There's no real need and the path I was going down brought a whole can of worms with it.
I'm making this more complicated than it needs to be (which I enjoy from time to time 😜)

I'll try another way soon or fallback to simply using SetValue as intended.