GZipStream - Compress/Decompress a String

If you want to transform a string into a byte[] and vice versa without involving encoding specifications here you go: https://github.com/garysharp/SmazSharp

I'm losing data on receiving a string of length 5984354 while receiving and unzip , the length is becoming 440798, means I'm losing data. do you have a solution for the same

The posted code can cause resources to not close properly. use this code instead with using clauses

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO.Compression;
using System.IO;

namespace BoomInteractiveInc {
    public class Compression {
        public static string CompressString(string str) {
            var bytes = Encoding.UTF8.GetBytes(str);
            using (var msi = new MemoryStream(bytes)) {
                using (var mso = new MemoryStream()) {
                    using (var gs = new GZipStream(mso, CompressionMode.Compress)) {
                        CopyTo(msi, gs);
                    }
                    return Convert.ToBase64String(mso.ToArray());
                }
            }
        }

        public static string UnCompressString(string str) {
            byte[] bytes = Convert.FromBase64String(str);
            using (var msi = new MemoryStream(bytes))
            using (var mso = new MemoryStream()) {
                using (var gs = new GZipStream(msi, CompressionMode.Decompress)) {
                    CopyTo(gs, mso);
                }
                return Encoding.UTF8.GetString(mso.ToArray());
            }
        }

        private static void CopyTo(Stream src, Stream dest) {
            byte[] bytes = new byte[4096];
            int cnt;
            while ((cnt = src.Read(bytes, 0, bytes.Length)) != 0) {
                dest.Write(bytes, 0, cnt);
            }
        }
    }
}

Hello,

Thanks for sharing your code. I had a small correction actually. The output was actually truncating to the length of compressed text D'Oh! | :doh:

(For Example: If input string is 230 characters, compressed string is 180 characters. While unzipping this code was re-using byteArray so it was causing the output to truncate to 180 characters. What I did is I combined it with this code :-

http://stackoverflow.com/questions/3722192/how-do-i-use-gzipstream-with-system-io-memorystream[^]

So this code was able to DeCompress for me properly:-

C#

using System;
using System.IO.Compression;

public class StringCompressor
    {
        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();
        }

        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
            System.IO.MemoryStream msOut = new System.IO.MemoryStream();

            //decompress
            sr.CopyTo(msOut);
            var rbyte = msOut.ToArray();

            //transform byte[] unzip data to string
            System.Text.StringBuilder sb = new System.Text.StringBuilder(rbyte.Length);
            //read the number of bytes gzipstream red and do not a for each bytes in
            //resultbytearray;
            for (int i = 0; i < rbyte.Length; i++)
            {
                sb.Append((char)rbyte[i]);
            }

            sr.Close();
            ms.Close();
            sr.Dispose();
            ms.Dispose();
            return sb.ToString();
        }

        public static void Main(string[] args)
        {
            string ipstr = @"Lorem ipsum dolor sit amet,
consectetur adipiscing elit, sed do eiusmod tempor incididunt ut 
labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud 
exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum 
dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat
non proident, sunt in culpa qui officia deserunt mollit anim id est laborum";
            string optr = Zip(ipstr);
            Console.WriteLine("Input String Length: "+ ipstr.Length.ToString());
            Console.WriteLine("==============");
            Console.WriteLine("Compressed Output String: \n"+optr);
            Console.WriteLine("==============");
            Console.WriteLine("Compressed Output String Length: " + optr.Length.ToString());
            Console.WriteLine("==============");
            Console.WriteLine("DeCompressed Output String: \n" + UnZip(optr));
            Console.WriteLine("==============");
            Console.WriteLine("Press Enter to Exit!");
            Console.ReadKey();
        }
    }

Hope this helps! Thumbs Up | :thumbsup:

buggy

well idea. but you need to use "System.Text.Encoding.Unicode" or "UTF8" to get bytes / or convert back to string. Other idea is fine.

For a couple of reason I decided to post another piece of code that may be useful for you.

1. This code has some problems that already mentioned in other messages below.
2. My variation is based on Encoding. People who search the web and came to this page may not be concerned about Encoding dropping some letters, or they may even do not believe such a problem exists. So this variation is for those who want to use Encoding for converting text to byte[] and vice versa.

Here is the code:

C#

public class Zip
{
    //public static Encoding Encoding = System.Text.Encoding.Unicode;
    public static byte[] Compress(string text, Encoding Encoding = null)
    {
        if (text == null) return null;
        Encoding = Encoding ?? System.Text.Encoding.Unicode;            // If the encoding is not specified use the Unicode
        var textBytes = Encoding.GetBytes(text);                        // Get the bytes according to the encoding
        var textStream = new MemoryStream();                            // Make a stream of to be feeded by zip stream
        var zip = new GZipStream(textStream, CompressionMode.Compress); // Create a zip stream to receive zipped content in textStream
        zip.Write(textBytes, 0, textBytes.Length);                      // Write textBytes into zip stream, then zip will populate textStream
        zip.Close();
        return textStream.ToArray();                                    // Get the bytes from the text stream
    }

    public static string Decompress(byte[] value, Encoding Encoding = null)
    {
        if (value == null) return null;
        Encoding = Encoding ?? System.Text.Encoding.Unicode;                // If the encoding is not specified use the Uncide
        var inputStream = new MemoryStream(value);                          // Create a stream based on input value
        var outputStream = new MemoryStream();                              // Create a stream to recieve output
        var zip = new GZipStream(inputStream, CompressionMode.Decompress);  // Create a stream to decompress inputStream into outputStream
        byte[] bytes = new byte[4096];
        int n;
        while ((n = zip.Read(bytes, 0, bytes.Length)) != 0)                 // While zip results output bytes from input stream
        {
            outputStream.Write(bytes, 0, n);                                // Write the unzipped bytes into output stream
        }
        zip.Close();
        return Encoding.GetString(outputStream.ToArray());                  // Get the string from unzipped bytes
    }
}

Sam Naseri
Software Developer
Blog : http://samondotnet.blgospot.com

Great code Sam, I modified it slightly to use using statements to make sure everything is disposed:

In my tests (on long UTF8 encoded strings) this is working great.

C#

public class Zip
{
    //public static Encoding Encoding = System.Text.Encoding.Unicode;
    public static byte[] Compress(string text, Encoding Encoding = null)
    {
        if (text == null) return null;
        Encoding = Encoding ?? System.Text.Encoding.Unicode;            // If the encoding is not specified use the Unicode
        var textBytes = Encoding.GetBytes(text);                        // Get the bytes according to the encoding
        using (var textStream = new MemoryStream())                            // Make a stream of to be feeded by zip stream
        {
            using (var zip = new GZipStream(textStream, CompressionMode.Compress)) // Create a zip stream to receive zipped content in textStream
            {
                zip.Write(textBytes, 0, textBytes.Length);                      // Write textBytes into zip stream, then zip will populate textStream
                zip.Close();
            }
            return textStream.ToArray();                                    // Get the bytes from the text stream
        }
    }

    public static string Decompress(byte[] value, Encoding Encoding = null)
    {
        if (value == null) return null;
        Encoding = Encoding ?? System.Text.Encoding.Unicode;                // If the encoding is not specified use the Uncide
        using (var inputStream = new MemoryStream(value))                          // Create a stream based on input value
        using (var outputStream = new MemoryStream())                              // Create a stream to recieve output
        {
            using (var zip = new GZipStream(inputStream, CompressionMode.Decompress))  // Create a stream to decompress inputStream into outputStream
            {
                byte[] bytes = new byte[4096];
                int n;
                while ((n = zip.Read(bytes, 0, bytes.Length)) != 0)                 // While zip results output bytes from input stream
                {
                    outputStream.Write(bytes, 0, n);                                // Write the unzipped bytes into output stream
                }
                zip.Close();
            }
            return Encoding.GetString(outputStream.ToArray());                  // Get the string from unzipped bytes
        }
    }
}

Thanks for the improvement, now its much better.

Thanks for this contructive help.

"Nothing is lost, Nothing is created, Everything is transformed" Lavoisier

http://wlwilliamsiv.com

You have to set max length of array equals to original string length in UnZip function.
I mean to say see the first line of function UnZip()

//Transform string into byte[]
byte[] byteArray = new byte[value.Length];
will be replace with

//Transform string into byte[]
byte[] byteArray = new byte[orginal text length];

The string "encoding" used by this article is all wrong - it assumes that all characters are single bytes which is not true even for English text. Internally .NET stores all characters as UTF16 but even then, some symbols may need 2 characters to describe them. (Chinese text, for example.) Encoding.UTF8.GetBytes() should've been used instead.

There are other errors as others pointed out, too.

Avoid this garbage.

Converting a string to a byte array assuming a character is a single byte is wrong.

did you even test the code before posting or did you just copy it from somewhere? When decompressiong you are using a buffer of the same size with the compressed data. Since compression is supposed to make the file smaller this code will always fail to decompress corectly

Dah!
Did that for a special need...this code is not meant to satisfy everybody...adapt it to your needs or move on to what you need...
DA

"Nothing is lost, Nothing is created, Everything is transformed" Lavoisier

http://wlwilliamsiv.com

public static string DecompressData(string sData)
{
byte[] byteArray = new byte[sData.Length];

int indexBa = 0;
foreach (char item in sData)
byteArray[indexBa++] = (byte)item;

MemoryStream memoryStream = new MemoryStream(byteArray);
GZipStream gZipStream = new GZipStream(memoryStream, CompressionMode.Decompress);

byteArray = new byte[1024];

StringBuilder stringBuilder = new StringBuilder();

int readBytes;
while ( (readBytes = gZipStream.Read(byteArray, 0, byteArray.Length)) != 0)
{
for (int i = 0; i < readBytes; i++)
stringBuilder.Append((char)byteArray[i]);
}

gZipStream.Close();
memoryStream.Close();

gZipStream.Dispose();
memoryStream.Dispose();

return stringBuilder.ToString();
}

what is this, please explain this fixed.

Tryed to compress html page. Sourcelength = 1764, compressed = 1764. Something wrong.

hi there .
this code work fine . Rose | [Rose]

Imports System.IO
Imports System.IO.Compression
Public Class CZip

    Public Shared Function Compress(ByVal Buff() As Byte) As Byte()
        Dim MS As New MemoryStream()
        Dim ZipStream As New GZipStream(MS, CompressionMode.Compress)
        ZipStream.Write(Buff, 0, Buff.Length)
        ZipStream.Close()
        Compress = MS.ToArray
        MS.Close()
        ZipStream.Dispose()
        MS.Dispose()
        GC.Collect()
    End Function

    Public Shared Function DeCompress(ByVal Buff() As Byte) As Byte()
        Dim MS As New MemoryStream(Buff)
        Dim ResultMS As New MemoryStream
        Dim ZipStream As New GZipStream(MS, CompressionMode.Decompress)
        Dim br As New BinaryReader(ZipStream)
        Dim BW As New BinaryWriter(ResultMS)
        While True
            Dim arr() As Byte = br.ReadBytes(1000000)
            If arr Is Nothing OrElse arr.Length = 0 Then
                Exit While
            End If
            BW.Write(arr)
        End While
        BW.Flush()
        ResultMS.Flush()
        DeCompress = ResultMS.ToArray
        ZipStream.Close()
        MS.Close()
        ResultMS.Close()
        ZipStream.Dispose()
        MS.Dispose()
        ResultMS.Dispose()
        GC.Collect()
    End Function

End Class

I wonder. GC Collect is not needed. The intention of the main thread is the using of any string, not Byte array. And what should br.Readbytes(1000000) should stand for??? Sorry but this code is horrible!

Hi,
I am doing like this:
GZipStream objCompressedStream = new GZipStream(objmod, CompressionMode.Compress, true);
objCompressedStream.Write(btReadArray, 0, aiNo_of_bytes_read);

Now when I am trying to get length of objCompressedStream using objCompressedStream.Length property it throws exception that operation is not supported.

Can anyone suggest the alternatives or some way to get the length of compressed stream

Thanks

From my point of view the code gets a lot faster and cleaner if you use the right encoding from System.Text to create the byte array and also to change the byte array back into a string.

Sorry - I missed before what you read in the text. I guess that there is somewhere else a bug or you are not 100 % sure about the right decoding - at least the second part should be used encoidng anyway.

//Reset variable to collect uncompressed result
//There was a mistake here in the original code.
//A buffer that is the same size may not hold the
//result of what is decompressed. The decompressed
//version may be larger.
byteArray = new byte[byteArray.Length*5];

This worked for me. The buffer size is probably overkill. Some of you guys can probably figure out what the difference in a gzip compresses and uncompressed character can have on the result of decompression size.

You are correct that GZipStream Flush() doesn't work. In fact, this problem can be traced to the underlying DeflateStream.Flush() implementation.

As you say, a workaround is to call GZipStream.Close() - however, this will also close the underlying stream. Luckily, GZipStream has a 3rd parameter on it's constructor which tells GZipStream/DeflateStream not to close the underlying stream when disposing.

GZipStream - Compress/Decompress a String

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