Accessing bytes of ArrayBuffer

[viceice]

I'm trying to create TextEncoder and TextDecoder API.

The TextDecoder.decode function should support TypedArray, ArrayBuffer and DataView.

Jint is currently automatically converting Uint8Array to byte[] which is good.
But how do i get the bytes from an ArrayBuffer in an performant way?

[viceice]

btw JsDataView is also internal 😕

[lahma]

But how do i get the bytes from an ArrayBuffer in an performant way?

Can you show example code and what you would like use as API?

btw JsDataView is also internal

For now, anything can be made public after there's a need and this is the first time anyone asks...

[viceice]

/// <summary>
/// https://encoding.spec.whatwg.org/#textdecoder
/// https://developer.mozilla.org/en-US/docs/Web/API/TextDecoder
/// </summary>
public sealed class TextDecoder
{
    public string Decode() => string.Empty;

    //public string Decode(JsTypedArray buffer) => Decode(buffer.???);

    public string Decode(JsArrayBuffer buffer) => Decode(ArrayBufferData(buffer));

    //public string Decode(JsDataView buffer) => Decode(buffer.GetBytes());

    public string Decode(byte[] buffer)
    {
        return Util.UTF8NoBom.GetString(buffer);
    }

        /// <summary>
        /// Workaround to access internal bytes from <c>ArrayBuffer</c>
        /// https://github.com/sebastienros/jint/discussions/1785
        /// </summary>
        internal static readonly Func<JsArrayBuffer, byte[]> ArrayBufferData = InitArrayBufferData();

        private static Func<JsArrayBuffer, byte[]> InitArrayBufferData()
        {
            var pi = typeof(JsArrayBuffer).GetProperty("ArrayBufferData", BindingFlags.NonPublic | BindingFlags.Instance);
            if (pi == null)
            {
                LogManager.GetLogger<TextDecoder>().Error("Missing property ArrayBufferData on JsArrayBuffer.");
                return null;
            }

            var pThis = Expression.Parameter(typeof(JsArrayBuffer), "@this");
            var pCall = Expression.Property(pThis, pi);

            return Expression.Lambda<Func<JsArrayBuffer, byte[]>>(pCall, pThis).Compile();
        }
}

• ArrayBufferData is a Func<JsArrayBuffer, byte[]> to access the internal ArrayBufferData data.

(()=> { const buff = new TextDecoder().decode(); return buff === ''; })() // true
(()=> { const buff = new TextDecoder().decode(Uint8Array.from([102,111,111])); return buff === 'foo'; })() // true
(()=> { const buff = new TextDecoder().decode(Uint8Array.from([102,111,111]).buffer); return buff === 'foo'; })() // true with workaround
(()=> { const buff = new TextDecoder().decode(new DataView(Uint8Array.from([102,111,111]).buffer)); return buff === 'foo'; })() // error `Object of type 'Jint.Native.JsDataView' cannot be converted to type 'Jint.Native.JsArrayBuffer'.`

[lahma]

Cool thanks, maybe you could do a PR which would contain test coverage for the public interface test project and proposed unsealing of types?

[viceice]

sure, thanks

[viceice]

it seems an implicit conversion make most sense 🤗

• feat: implicit convert DataView and ArrayBuffer to byte array #1786