StringBuilderStream.cs

using System;
using System.IO;
using System.Text;

namespace StringBuilderStream
{
    public class StringBuilderStream : Stream
    {
        public StringBuilder stringBuilder { get; private set; }
        public Encoding Encoding { get; private set; }

        public StringBuilderStream(Encoding encoding, StringBuilder stringBuilder)
        {
            this.stringBuilder = stringBuilder;
            this.Encoding = encoding;
        }
        public StringBuilderStream(Encoding encoding)
            :this(encoding, new StringBuilder())
        {
        }
        public StringBuilderStream()
            : this(Encoding.Default)
        {
        }

        public override string ToString()
        {
            return stringBuilder.ToString();
        }

        public override bool CanRead
        {
            get { return true; }
        }

        public override bool CanSeek
        {
            get { return true; }
        }

        public override bool CanWrite
        {
            get { return true; }
        }

        public override void Flush()
        {
            
        }

        public override long Length
        {
            get { return stringBuilder.Length; }
        }

        public override long Position { get; set; }

        public override int Read(byte[] buffer, int offset, int count)
        {
            int remainingLength = stringBuilder.Length - (int)Position;
            int actualCount = count < remainingLength ? count : remainingLength;

            var chars = new char[actualCount];
            stringBuilder.CopyTo((int)Position, chars, 0, actualCount);
            
            var bytes = Encoding.GetBytes(chars);
            bytes.CopyTo(buffer, offset);

            return actualCount;
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            if (origin == SeekOrigin.Begin)
            {
                Position = offset;
            }
            else if (origin == SeekOrigin.Current)
            {
                Position += offset;
            }
            else if (origin == SeekOrigin.End)
            {
                Position = stringBuilder.Length - Position;
            }
            return Position;
        }

        public override void SetLength(long value)
        {
            if (stringBuilder.Length > value)
            {
                stringBuilder.Length = (int)value;
            }
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            if (stringBuilder.Length > Position)
            {
                stringBuilder.Length = (int)Position;
            }
            stringBuilder.Append(Encoding.GetString(buffer, offset, count));
            Position = stringBuilder.ToString().Length;

        }
        //You don't need to override BeginWrite/EndWrite, etc., unless you can call subsequent async methods:
        //http://blogs.msdn.com/b/pfxteam/archive/2012/04/06/10291582.aspx
    }
}