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GZipStream - Compress/Decompress a string

, 23 Jun 2008
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An article on how use GZipStream with string as input parameter.

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 where 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!

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Frankidoze
Systems Engineer
United States United States
No Biography provided

Comments and Discussions

 
GeneralMy vote of 1 PinmemberYclkvnc8-May-13 6:28 
GeneralMy vote of 4 PinmemberNasenbaaer12-Apr-13 6:24 
SuggestionSharing my code PinmemberSamNaseri16-Nov-11 18:38 
GeneralRe: Sharing my code PinmemberThymine20-Mar-12 11:40 
GeneralRe: Sharing my code PinmemberSamNaseri20-Mar-12 12:53 
GeneralRe: Sharing my code PinmemberFrankidoze21-Mar-12 6:00 
GeneralThis code will work properly if PinmemberMember 28508507-Jun-11 19:16 
GeneralThis article is full of bugs, don't use it! Pinmemberxxbbcc28-May-11 16:51 
GeneralMy vote of 1 Pinmemberxxbbcc28-May-11 16:42 
GeneralMy vote of 1 Pinmemberdjpitagora27-Sep-10 7:04 
GeneralRe: My vote of 1 PinmemberFrankidoze21-Mar-12 5:50 
GeneralDecompress bug fix Pinmemberfiloteanuadrian9-Apr-10 4:10 
GeneralRe: Decompress bug fix PinmemberTEST ME26-Apr-11 16:37 
GeneralDoesn't work at all PinmemberVikcia26-Mar-10 7:49 
GeneralPublic Class CZip .... PinmemberErfan2-Feb-10 19:45 
GeneralRe: Public Class CZip .... PinmemberNasenbaaer12-Apr-13 6:23 
GeneralobjCompressedStream.Length not supported Pinmemberoops.uvj26-Aug-09 20:17 
GeneralPerformance Improvement/Cleanup Pinmembermatthias Weiser10-Dec-08 3:34 
GeneralRe: Performance Improvement/Cleanup Pinmembermatthias Weiser10-Dec-08 3:48 
GeneralIn the decompression to string the buffer size is wrong. A decompressed string may be larger than the original data. Pinmemberelinder91225-Sep-08 10:59 
GeneralFlush doesn't flush PinmemberRichard Birkby8-Sep-08 3:16 
Generalzipping don't work PinmemberMSaty9-Aug-08 3:32 
Questiondecompressing binary concatenated files PinmemberRobin Debnath25-Jul-08 3:27 
AnswerRe: decompressing binary concatenated files PinmemberFrankidoze2-Sep-08 5:11 
GeneralCompress persian or arabic string Pinmemberelahe babaee22-Jul-08 21:37 

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