"The difference between a violin and a viola is that a viola burns longer." - Victor Borge
Many developers are familiar with 7-Zip and use it as an alternative to Winzip or Winrar. I use the Windows distribution of 7Zip frequently because of the higher compression ratios it provides, with an excellent balance between speed and high compression with the default settings.
However I would venture to guess that most developers are unaware that Igor Pavlov, the primary developer of SevenZip, provides a full SDK that includes his LZMA source code in several languages, including one in C#.
The C# code in the SDK is designed to be used in an executable with a command - line interface. However, by recompiling this to a class library, removing the command line parser classes, and adding a simple SevenZipHelper class that uses the default property settings, we can get a very handy and powerful class library for in-memory compression tasks.
Some facts on LZMA (7Zip) Compression:
- Average compression ratio of LZMA is about 30% better than that of gzip, and 15% better than that of bzip2.
- Decompression speed is only little slower than that of gzip, being two to five times faster than bzip2.
- In fast mode, 7Zip compresses faster than bzip2 with a comparable compression ratio.
- Achieving the best compression ratios takes four to even twelve times longer than with bzip2. However. this doesn't affect decompressing speed.
To illustrate the usefulness of this approach, I took the code from a previous article on compressing Http Cookies, and added another CompressedCookie class to it in which I use the 7zip library instead of the default System.IO.Compression deflate mode classes. With LZMA compression (the default for 7Zip), we can get a huge increase in the amount of data that can be stored in the 4,000 byte allowable maximum size for a cookie.
The downloadable Visual Studio 2005 Solution below includes the SevenZip C# LZMA classes, my SevenZipHelper "wrapper class", and a reconstructed CompressedCookies Web application illustrating it's use.
Using my "Helper" class is utterly simple:
The static Compress Method:
byte[] SevenZip.Compression.LZMA.SevenZipHelper.Compress( byte[] )
The static Decompress Method:
byte[] SevenZip.Compression.LZMA.SevenZipHelper.Decompress( byte[] )
I don't think it could be made much simpler!
The new LZMA Cookie Compression class:
using System.Text;
using System.Web;
using System.IO.Compression;
using System.Runtime.Serialization.Formatters.Binary;
using System.IO;
using SevenZip.Compression.LZMA;
namespace CompressedCookies
{
public static class CpCookiesLzma
{
public static int Set(string cookieName, object cookieValue, DateTime expirationDate)
{
int siz = 0;
try
{
BinaryFormatter bf = new BinaryFormatter();
MemoryStream ms = new MemoryStream();
bf.Serialize(ms, cookieValue);
byte[] inbyt = ms.ToArray();
byte[] b = SevenZip.Compression.LZMA.SevenZipHelper.Compress(inbyt);
string sCookieVal = Convert.ToBase64String(b);
HttpCookie cook = new HttpCookie(cookieName);
cook.Value = sCookieVal;
siz = sCookieVal.Length;
cook.Expires = expirationDate;
HttpContext.Current.Response.Cookies.Add(cook);
}
catch
{
throw ;
}
return siz;
}
public static object Get(string cookieName)
{
object retval = null;
try
{
byte[] bytCook = Convert.FromBase64String(HttpContext.Current.Request.Cookies[cookieName].Value);
byte[] outByt = SevenZip.Compression.LZMA.SevenZipHelper.Decompress(bytCook);
MemoryStream outMs = new MemoryStream(outByt);
outMs.Seek(0, 0);
BinaryFormatter bf = new BinaryFormatter();
retval = (object)bf.Deserialize(outMs, null);
}
catch(Exception ex)
{
throw ex;
}
return retval;
}
public static bool Delete(string cookieName)
{
bool retval = true;
try
{
HttpContext.Current.Request.Cookies[cookieName].Expires = DateTime.Now.AddDays(-365);
}
catch
{
retval = false;
}
return retval;
}
}
}
The download below includes the LZMA (7Zip) C# class library project, which includes my SevenZipHelper class, the Compressed Cookies class library project with the addition of the CpCookieLzma class with 7Zip, and a web application that illustrates it's use for compressed cookie operation. Of course, the 7Zip library can be used for any general compression need.
NOTE: If you get any "out of memory" errors using this, try reducing the size of the dictionary in the SevenZipHelper class (e.g. <<21 instead of << 23).
Download the Visual Studio 2005 Solution accompanying this article. |