Set engine in WrapObjectHandler

[loonwong]

Hello!

I'm porting my code from Jurassic to jint. Ported classes are actually wrappers for CLR objects, but in some places can convert values to JsValue. I would like to avoid manually declaring JS properties and methods with FastSetProperty, so I don't inherit from ObjectInstance, but use the following code:

public class ClrUnderlyingObject
{
     [CanBeNull] public byte[] Bytes { get; set; }
}

public class JintObjectWrapper
{
    private Engine _engine;

    // js side
    public JsValue bytes
    {
        get { return Underlying.Bytes != null ? _engine.Realm.Intrinsics.Uint8Array.Construct(Underlying.Bytes) : JsValue.Null; }
        set { Underlying.Bytes = value?.AsUint8Array(); }
    }

    // clr side
    internal ClrUnderlyingObject Underlying { get; } = new ClrUnderlyingObject();

    // clr side
    internal void SetEngine([NotNull] Engine engine)
    {
        _engine = engine ?? throw new ArgumentNullException(nameof(engine));
    }
}

[TestMethod]
public void GithubJintHandler()
{
    var engine = new Engine(options =>
    {
        options.SetWrapObjectHandler((e, target) =>
        {
            if (target is JintObjectWrapper jow)
                jow.SetEngine(e); // intercept the instance and set the engine

            return new ObjectWrapper(e, target);
        });
    });

    var result = (JintObjectWrapper) engine
        .SetValue("JintObjectWrapper", TypeReference.CreateTypeReference<JintObjectWrapper>(engine))
        .Evaluate(@"
var bytes = new Uint8Array(6);
bytes[0] = 1;
bytes[1] = 2;
bytes[2] = 4;
bytes[3] = 8;
bytes[4] = 16;
bytes[5] = 32;

var res = new JintObjectWrapper();
res.bytes = bytes;
return res;")
        .ToObject();

    var expected = new byte[] { 1, 2, 4, 8, 16, 32 };
    CollectionAssert.AreEqual(expected, result.Underlying.Bytes);
}

Am I doing things wrong?
Thank you in advance.

[lahma]

I think ideally everything would just work without you manually creating wrappers. Jint tries hard to get the interop right and automatically convert between suitable types + allows you to create the converters needed. So I would just use ClrUnderlyingObject directly as type injected to engine and ensure proper conversions when/if needed via type converters.

[loonwong]

Ok, when I change the code to this:

public class ClrUnderlyingObject
{
    [CanBeNull] public object Bytes { get; set; } // NOW IT IS AN OBJECT
}

public class JsToClrConverter : DefaultTypeConverter
{
    public JsToClrConverter([NotNull] Engine engine) : base(engine)
    {
    }

    public override object Convert(object value, Type type, IFormatProvider formatProvider)
    {
        // here value comes as an empty ExpandoObject
        return base.Convert(value, type, formatProvider);
    }
}

[TestMethod]
public void GithubJintHandler()
{
    var engine = new Engine(options =>
    {
        options.SetTypeConverter(e => new JsToClrConverter(e));
    });

    var result = (ClrUnderlyingObject) engine
        .SetValue("ClrUnderlyingObject", TypeReference.CreateTypeReference<ClrUnderlyingObject>(engine))
        .Evaluate(@"
var bytes = new Uint8Array(6);
bytes[0] = 1;
bytes[1] = 2;
bytes[2] = 4;
bytes[3] = 8;
bytes[4] = 16;
bytes[5] = 32;

var res = new ClrUnderlyingObject();
res.Bytes = bytes;
return res;")
        .ToObject();

    Assert.AreNotEqual(result.Bytes?.GetType(), typeof(ExpandoObject));
}

then I face the following issue, Uint8Array is converted to an empty ExpandoObject and I can't convert to byte[] in any way.

[loonwong]

Apparently, the point is that TypedArrayInstance is incorrectly converted to a clr array. Therefore, for example, this code does not work:

public class ClrUnderlyingObject
{
    public bool checkBytes(byte[] bytes)
    {
        // this method will not be involved as expected
        return bytes != null;
    }
}

[TestMethod]
public void GithubJintHandler()
{
    var engine = new Engine();

    var result = (bool) engine
        .SetValue("ClrUnderlyingObject", TypeReference.CreateTypeReference<ClrUnderlyingObject>(engine))
        .Evaluate(@"
var bytes = new Uint8Array(6);
bytes[0] = 1;
bytes[1] = 2;
bytes[2] = 4;
bytes[3] = 8;
bytes[4] = 16;
bytes[5] = 32;

var res = new ClrUnderlyingObject();
return res.checkBytes(bytes);")
        .ToObject();

    Assert.AreEqual(true, result);
}

As a workaround, I added an overload for checkBytes(TypedArrayInstance array) and it works.

[lahma]

A PR for better internal conversions (with test case(s)) is always appreciated!

[loonwong]

Thank you so much for support! But there is no need for PR, everything I needed was implemented using the built-in SetTypeConverter, AddObjectConverter and Interop.CreateClrObject.