GZipStream - Compress/Decompress a String

Introduction

This article presents two methods to compress and decompress strings using System.IO.Compression.GZipStream.

Context/Problem

After converting code from VB.NET 1.1 to C#.NET 3.5, I needed to change some code using a third party zip class to GZipStream. Code samples found on the web or on VS help were presenting solutions dealing with FileStream but in this case, a string is given as an input parameter.

So the little challenge was to go from a string to a byte array (byte[]) and vice versa without losing a char nor changing its encoding because I ended up finding that System.Text.Encoding.Unicode.GetBytes()/GetString() previously used in the VB code was not acting properly, resulting in a loss of characters. Plus the Flush() method on GZipStream with the compression option doesn't flush everything...

Tips

So as I found no method transforming a string into a byte[] and vice versa without involving encoding specifications, I ended up with a loop and a cast. If you have a better idea, please tell me so.

And I found out, if you only flush a GZipStream instance and retrieve the data from the underlying stream without closing this GZipStream instance, you miss part of the data.

The Code

Compress/zip a string:

public static string Zip(string value)
{
    //Transform string into byte[]
    byte[] byteArray = new byte[value.Length];
    int indexBA = 0;
    foreach (char item in value.ToCharArray())
    {
        byteArray[indexBA++] = (byte)item;
    }

    //Prepare for compress
    System.IO.MemoryStream ms = new System.IO.MemoryStream();
    System.IO.Compression.GZipStream sw = new System.IO.Compression.GZipStream(ms,
        System.IO.Compression.CompressionMode.Compress);

    //Compress
    sw.Write(byteArray, 0, byteArray.Length);
    //Close, DO NOT FLUSH cause bytes will go missing...
    sw.Close();

    //Transform byte[] zip data to string
    byteArray = ms.ToArray();
    System.Text.StringBuilder sB = new System.Text.StringBuilder(byteArray.Length);
    foreach (byte item in byteArray)
    {
        sB.Append((char)item);
    }
    ms.Close();
    sw.Dispose();
    ms.Dispose();
    return sB.ToString();
}

Decompress/Unzip a string: input value has been previously compressed with GZipStream.

public static string UnZip(string value)
{
    //Transform string into byte[]
    byte[] byteArray = new byte[value.Length];
    int indexBA = 0;
    foreach (char item in value.ToCharArray())
    {
        byteArray[indexBA++] = (byte)item;
    }

    //Prepare for decompress
    System.IO.MemoryStream ms = new System.IO.MemoryStream(byteArray);
    System.IO.Compression.GZipStream sr = new System.IO.Compression.GZipStream(ms,
        System.IO.Compression.CompressionMode.Decompress);

    //Reset variable to collect uncompressed result
    byteArray = new byte[byteArray.Length];

    //Decompress
    int rByte = sr.Read(byteArray, 0, byteArray.Length);

    //Transform byte[] unzip data to string
    System.Text.StringBuilder sB = new System.Text.StringBuilder(rByte);
    //Read the number of bytes GZipStream red and do not a for each bytes in
    //resultByteArray;
    for (int i = 0; i < rByte; i++)
    {
        sB.Append((char)byteArray[i]);
    }
    sr.Close();
    ms.Close();
    sr.Dispose();
    ms.Dispose();
    return sB.ToString();
}

Points of Interest

Well, if you haven't dealt with a lot of streams like me, hopefully this will avoid loss of time!