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Zipping with C#

In order to save on bandwidth and improve the user experience, by making the route files faster to download, I needed a way to compress files. This was one of the goals for Mapze Beta 1 but considering future improvement, I wanted to be able to uncompress uploaded route files too. Allowing users to upload GPX, ITN, CSV or multiple route files by zipping them. would than unzip the route files on server and process each file like normal route files.

The soution : the GZipStream class

The .Net Framework comes with the System.IO.Compression namespace which has an interesting class called GZipStream. At first I though job done. The namespace and class name clearly indicated a class that can handle compressing and uncompressing streams. Plus, using a class in the .Net Framework has the advantage of knowing it will be supported in future releases, if not, an alternative will be provided. It will be installed with the Framework, so one less assembly to be concerned with at deployment time and if there are any bugs or issues, Microsoft will take care of it.

Turns out the GZipStream class can only handle .gz files, well known formats like zip and tar are not support. Another important point was it did not support hierarchical or directory level compression, or at least did not make the task easy. I needed the ability to read and create zip files that could contain multiple files or at least files at one directory level deep. Considering the above two points, it was time to search for other solutions. A quick google brought up sharpziplib library. It supported Zip, BZip2 and GZip format and was written in C# for the .Net Framework. Bliss.

The solution: the SharpZipLib

The final zipping code snippet looks like:

bool GetZippedITNFile (string SaveToFilePath, int ITNFileCount)
//Create a Zip file
ZipOutputStream zipstream = new ZipOutputStream(File.Create(SaveToFilePath));
//Set the compression level

//Temporary variable to indicate a new zip file entry
ZipEntry tempZipEntry;
//Temporary variable to store the file contents
string tempITNFileContents;
//Temporary variable to encode the contents before adding it to the zip stream
UTF8Encoding enc = new UTF8Encoding();

for(int currentFileNo = 1 ; currentFileNo <= ITNFileCount; currentFileNo++)
//Create a zip entry and set its filename, i.e. Route-1.itn, Route-2.itn, etc
tempZipEntry = new ZipEntry(string.Format("Route-{0}.itn", currentFileNo));
//Set other file properties
tempZipEntry.DateTime = DateTime.Now;
tempZipEntry.Comment = string.Format("Route file {0}", currentFileNo);

//Add the zip entry to the stream. Indicates that any
// characters / bytes written to the stream are now a part of a new zip file
//Get the file contents to zip
tempITNFileContents = GetITNFileContents(currentFileNo);
//UTF8 encode the contents and add it to the zip stream
zipstream.Write(enc.getBytes(tempITNFileContents), 0, tempITNFileContents.Length);

//Flush any buffered contents to the file
//Close the file

The out come will be a .ZIP file that can be opened with well known zipping softwares like WinRAR, WinZip, 7Zip, etc. The .Zip file will containing .ITN files and the ITN file will be named Route-1.itn, Route-2.itn, Route-3.itn, etc

By Schubert on 03 January 2010 22:52

Categories: Development | Tags: , , , ,

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