ln.tools.mailpdfextract/ln.tools.mailpdfextract/HashingStream.cs

using System.Security.Cryptography;

namespace ln.tools.mailpdfextract;

public class HashingStream : Stream, IDisposable
{
    public Stream BaseStream { get; }
 
    SHA256 _sha256 = SHA256.Create();

    public byte[] Hash
    {
        get
        {
            Dispose();
            return _sha256.Hash;
        }
    }
        
    public HashingStream(Stream baseStream)
    {
        BaseStream = baseStream;
    }

    public override void Flush() => BaseStream.Flush();
    public override int Read(byte[] buffer, int offset, int count) => throw new NotSupportedException();
    public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
    public override void SetLength(long value) => throw new NotSupportedException();

    public override void Write(byte[] buffer, int offset, int count)
    {
        _sha256.TransformBlock(buffer, offset, count, null, 0);
        BaseStream.Write(buffer, offset, count);
    }

    public override bool CanRead => false;
    public override bool CanSeek => false;
    public override bool CanWrite => true;
    public override long Length => BaseStream.Length;

    public override long Position
    {
        get => BaseStream.Position;
        set => throw new NotSupportedException();
    }

    public void Dispose()
    {
        if (BaseStream is Stream)
        {
            _sha256.TransformFinalBlock(null, 0, 0);
            BaseStream?.Dispose();
            base.Dispose();
        }
    }

}