Customer requests come in waves, as if fashion was driving the development industry. Lately, many customers were trying to compress log files. I've deviced it was time for a little sample.
The idea was to encode each string message in unicode and compress it in a plain file, one after the other. I could have used a zip file with each file entry representing a message, but for small messages, the zip headers would take too much space for nothing, wasting the need for compression in the first place.
The deflate compression method has one nice feature: it can detect the end of the compressed data while decompressing, without knowing the total compressed size. That's why the CompressedStream class exposes a GetRemainingStream method for retrieving a Stream reference on the rest of the data in the inner stream.
I've kept the sample real simple, so you get the general idea:
using System;
using System.IO;
using Xceed.Compression;
namespace CompressedLogExample
{ public class CompressedLog
{ public CompressedLog( string filename )
{ if( filename == null )
throw new ArgumentNullException( "filename" );
if( filename.Length == 0 )
throw new ArgumentException( "The filename cannot be empty.", "filename" );
Xceed.Compression.Licenser.LicenseKey = "SAMPLE-APPLICATION-KEY";
m_filename = filename;
}
public void AddMessage( string message )
{ if( message == null )
throw new ArgumentNullException( "message" );
lock( m_lock )
{ using( Stream fileStream = new FileStream( m_filename, FileMode.Append ) )
{ using( CompressedStream compStream = new CompressedStream( fileStream ) )
{ byte[] encodedMessage = System.Text.Encoding.Unicode.GetBytes(
DateTime.Now.ToString() + Environment.NewLine + message );
compStream.Write( encodedMessage, 0, encodedMessage.Length );
}
}
}
}
public void DisplayMessages( TextWriter writer )
{ if( writer == null )
throw new ArgumentNullException( "writer" );
lock( m_lock )
{ try
{ using( Stream originalStream = new FileStream( m_filename, FileMode.Open ) )
{ Stream workStream = originalStream;
do
{ using( CompressedStream compStream = new CompressedStream( workStream ) )
{ // We don't want compStream to close sourceStream!
compStream.Transient = true;
using( StreamReader reader = new StreamReader(
compStream, System.Text.Encoding.Unicode ) )
{ writer.WriteLine( reader.ReadToEnd() );
writer.WriteLine( "---" );
// Before closing the reader (thus compStream), acquire a stream on
// the rest of the data if present.
workStream = compStream.GetRemainingStream();
// We must do this AFTER calling GetRemainingStream since compStream
// may have read more from its inner stream than necessary.
if( workStream.Position == workStream.Length )
{ workStream = null;
}
}
}
}
while( workStream != null );
}
}
catch( FileNotFoundException )
{ writer.WriteLine( "The log is empty." );
}
}
}
private string m_filename = string.Empty;
private object m_lock = new object();
}
}
Unfortunately, you can't replace the CompressedStream with a formatted stream like GZipCompressedStream, because they do not expose a GetRemainingStream method yet. Too bad, since the GZipCompressedStream can store a few minimal informations in its header. I'll have to open a feature request about that!
Here is some sample code for using this CompressedLog class:
static void Main(string[] args)
{ CompressedLog log = new CompressedLog( @"d:\temp\log.cmp" );
while( true )
{ Console.WriteLine( "Write your next message below (empty message to quit):" );
string line = Console.ReadLine();
if( line.Length == 0 )
break;
log.AddMessage( line );
}
Console.WriteLine();
Console.WriteLine( "Your messages were:" );
log.DisplayMessages( Console.Out );
Console.WriteLine( "Press <Enter> to quit." );
Console.ReadLine();
}