Archive for April 2008

String Stream for .NET

9th April 2008, 01:11 am

I was working with C++ Standard Template Library (STL) library and when using the StringStream class I felt like we need this for .NET :) Yes we have a great class StringBuilder but we can’t use it as a Stream (because it is not).

Most of the cryptographic classes works with the stream object. I wanted to save the encrypted information as text. Ideally we could use memoryStream but it is not really efficient, because it is bits and we need to build a model for serializing/deserializing as text.

String Stream class (as I call it) is just an ugly but functional wrapper around StringBuilder class as shown some snippets below. I just wanted it to use with encryption and decryption a string. So only the functions needed is there which is enough to use. But I doubt it leaks a little, so use with care if needed.

public class StringStream : Stream
{
        private StringBuilder strBuilder;
        public StringStream()
        {            strBuilder = new StringBuilder();        }
 
        public StringStream(string str)
        {            strBuilder = new StringBuilder(str);        }
 
        public override int Read(byte[] buffer, int offset, int count)
        {
            int howMuchRead = 0;
            for (int i = offset; i < count; i++)
            {
                var actualIndex = i * 2;                
                howMuchRead = i+1;
                if (actualIndex >= strBuilder.Length) 
                {
                    howMuchRead = count;
                    break;
                }                                   
                string s = strBuilder[actualIndex].ToString() + strBuilder[actualIndex + 1].ToString();
                buffer[i] = Convert.ToByte(s,16);
            }
            return howMuchRead;
        }
      public override void Write(byte[] buffer, int offset, int count)
        {            
            for (int i = offset; i < count; i++)
            {
                strBuilder.Append(buffer[i].ToString("x2"));
            }
        }
}

Download

StringStream

Downloads: 334 File Name: StringStream.cs

The main magic is happening on reading and writing. each byte is represented as 2 characters in the string. It is using the helper function Convert.ToByte to make it happen.
In the next post I will use it with a symmetric encryption helper class.

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Category: C#  |  Comment