IArrayBuffer.WriteBytes taking a span/memory?

[oconnor0]

I have a situation where I have some data sitting in a class that exposes access to a ReadOnlyMemory<bytes>. I'd like to be able to move the bytes directly from this into V8 via IArrayBuffer.WriteBytes, but I have to convert the ReadOnlyMemory to a byte[] and then copy that in. Would it be feasible to add a method like the following to IArrayBuffer?

ulong WriteBytes(
	ReadOnlySpan<byte> source,
	ulong offset
)

I believe the conversion from ReadOnlyMemory to ReadOnlySpan is fast and should avoid one copy of the byte array.

I guess this is somewhat dependent on WriteBytes immediately writing the bytes from C# to V8 vs keeping a reference to the source around.

This is not a high priority for me, just something I noticed today.

[ClearScriptLib]

Hi @oconnor0,

Yes, fast data transfer from spans to array buffers and vice versa makes perfect sense.

Thanks for suggesting it!

[ClearScriptLib]

Hi @oconnor0,

By the way, it's already possible to do the copy without creating a byte array.

First, let's set up a ReadOnlyMemory<byte> and an ArrayBuffer:

const int size = 16;
var array = Enumerable.Range(0, size).Select(Convert.ToByte).ToArray();
var memory = new ReadOnlyMemory<byte>(array);
using var buffer = (IArrayBuffer)engine.Evaluate($"new ArrayBuffer({size})");

In this example, the ReadOnlyMemory<byte> is backed by a managed array, but it could just as well refer to unmanaged memory. Here's how to copy data from the ReadOnlyMemory<byte> to the ArrayBuffer without creating an intermediate array:

buffer.InvokeWithDirectAccess(pBuffer => {
    unsafe {
        using var hMemory = memory.Pin();
        Buffer.MemoryCopy(hMemory.Pointer, pBuffer.ToPointer(), size, size);
    }
});

The only allocation here is of the delegate passed to InvokeWithDirectAccess, but ClearScript 7.5 will provide a way to avoid that too.

Good luck!