Remotely/Shared/Utilities/RewritableStream.cs

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

namespace Remotely.Shared.Utilities
{
    public class RewritableStream : Stream
    {
        private readonly Stream _underlyingStream;
        private readonly Dictionary<long, byte> _rewriteMap;

        public RewritableStream(Stream underlyingStream, Dictionary<long, byte> rewriteMap)
        {
            _underlyingStream = underlyingStream;
            _rewriteMap = rewriteMap;
        }

        public override bool CanRead => _underlyingStream.CanRead;

        public override bool CanSeek => _underlyingStream.CanSeek;

        public override bool CanTimeout => _underlyingStream.CanTimeout;

        public override bool CanWrite => _underlyingStream.CanWrite;

        public override long Length => _underlyingStream.Length;

        public override long Position
        {
            get => _underlyingStream.Position;
            set => _underlyingStream.Position = value;
        }

        public override int ReadTimeout
        {
            get => _underlyingStream.ReadTimeout;
            set => _underlyingStream.ReadTimeout = value;
        }

        public override int WriteTimeout
        {
            get => _underlyingStream.WriteTimeout;
            set => _underlyingStream.WriteTimeout = value;
        }

        public override void Close()
        {
            _underlyingStream.Close();
            base.Close();
        }


        public override ValueTask DisposeAsync()
        {
            GC.SuppressFinalize(this);
            return _underlyingStream.DisposeAsync();
        }

        public override void Flush()
        {
            _underlyingStream.Flush();
        }

        
        public override int Read(byte[] buffer, int offset, int count)
        {
            var i = 0;
            for (; i < count; i++)
            {
                if (_rewriteMap.TryGetValue(Position, out var newValue))
                {
                    buffer[offset + i] = newValue;
                    Seek(1, SeekOrigin.Current);
                }
                else
                {
                    var current = _underlyingStream.ReadByte();
                    if (current == -1)
                    {
                        break;
                    }
                    buffer[offset + i] = current == -1 ? (byte)0 : (byte)current;
                }
            }
            return i;
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            return _underlyingStream.Seek(offset, origin);
        }

        public override void SetLength(long value)
        {
            _underlyingStream.SetLength(value);
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            _underlyingStream.Write(buffer, offset, count);
        }

        protected override void Dispose(bool disposing)
        {
            _underlyingStream.Dispose();
            base.Dispose(disposing);
        }
    }
}