WebsocketReader.cs

private static async ValueTask<ReadOnlyMemory<byte>> ReceiveStringAsync(WebSocket socket, CancellationToken ct = default)
{
    var buffer = ArrayPool<byte>.Shared.Rent(128); //use shared?
    using var ms = new MemoryStream(); //is there a better way here, w/o memstream?
    WebSocketReceiveResult result;
    do
    {
        ct.ThrowIfCancellationRequested();

        result = await socket.ReceiveAsync(buffer, ct);
        ms.Write(buffer, 0, result.Count);
    } while (!result.EndOfMessage);

    ms.Seek(0, SeekOrigin.Begin);
    if (result.MessageType != WebSocketMessageType.Text || result.Count.Equals(0))
    {
        throw new Exception("Unexpected message");
    }

    return ms.ToArray(); //this is not great
}

see: https://gist.github.com/MiloszKrajewski/75a8c8dca999ba1bae5f81c6b8b5ff44