PositionStream.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace Blazor.FileReader.Demo.Common
{
    /// <summary>
    /// Writable test Stream that does nothing other than setting it's Position property
    /// </summary>
    public class PositionStream : Stream
    {

        public override bool CanRead => false;

        public override bool CanSeek => false;

        public override bool CanWrite => true;

        public override long Length => throw new NotImplementedException();

        public override long Position { get; set;}

        public override void Flush()
        {
            // No-op
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            throw new NotImplementedException();
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            throw new NotImplementedException();
        }

        public override void SetLength(long value)
        {
            throw new NotImplementedException();
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            throw new NotImplementedException();
        }

        public override async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            Position += count;
        }
    }
}