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Desktop Search Application: Part 1

, 6 Jul 2006
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Building an application that searches your Office documents in tenths of a second.

Sample Image - screenshot1.gif


Let's take the following exercise: Build a C# application that instantly searches your Documents folder. We need the application to:

  • Search the contents of Office documents (Word, Excel, PowerPoint). I.e., XLS, DOC, PPT files.
  • Search the contents of HTML documents.
  • Search the contents of text documents.
  • Search quickly (i.e., give results in less than a second).
  • Allow to open the documents directly from the results list.

Update: This Desktop Search application is now part of the Seekafile Server 1.0 - Open-Source Indexing Server. The server provides automatic indexing on the background, and you can search the index through a Windows Forms client search application. See also the Seekafile Server roadmap.

Task 1: Full-Text Indexing

For the indexing and searching, we will use an excellent search engine called DotLucene. It's a C# port of Java Lucene, maintained by George Aroush. It has many great features:

  • Very good performance.
  • Ranked search results.
  • Search query highlighting in results.
  • Searches structured and unstructured data.
  • Metadata searching (query by date, search custom fields...).
  • Index size approximately 30% of the indexed text.
  • Can also store fully indexed documents.
  • Pure managed .NET in a single assembly.
  • Very friendly licensing (Apache Software License 2.0).
  • Localizable (support for Brazilian, Czech, Chinese, Dutch, English, French, German, Japanese, Korean, and Russian included in the DotLucene National Language Support Pack).
  • Extensible (source code included).

For more details on creating the index and searching, see my previous article: DotLucene: Full-Text Search for Your Intranet or Website using 37 Lines of Code.

Task 2: Parsing Office Documents

As DotLucene can index only plain text, we need to parse the Office documents and extract text from them. Reading their binary structure isn't an easy job. However, on Windows 2000+, we can use the IFilter interface which is a part of the Windows Indexing Service. This is installed by default on all Windows 2000+ systems (no Office installation is required).

The IFilter API is also being used by the Windows Desktop Search (MSN Search Toolbar) and Lookout, so you don't have to be afraid that we will use something obscure to parse the documents. It can also parse other file types if you install the appropriate filter.

Working with the IFilter interface requires a lot of COM interop which is a bit tricky. After tweaking the samples available on the web, I finally had a code that worked correctly in most cases:

public static string Parse(string filename)
  IFilter filter = null;
  try {
    StringBuilder plainTextResult = new StringBuilder();
    filter = loadIFilter(filename); 
    STAT_CHUNK ps = new STAT_CHUNK();
    IFILTER_INIT mFlags = 0;
    uint i = 0;
    filter.Init( mFlags, 0, null, ref i);
    int resultChunk = 0;
    resultChunk = filter.GetChunk(out ps);
    while (resultChunk == 0)
      if (ps.flags == CHUNKSTATE.CHUNK_TEXT)
        uint sizeBuffer = 60000;
        int resultText = 0;
        while (resultText == Constants.FILTER_S_LAST_TEXT || resultText == 0)
          sizeBuffer = 60000;
          System.Text.StringBuilder sbBuffer = 
             new System.Text.StringBuilder((int)sizeBuffer);
          resultText = filter.GetText(ref sizeBuffer, sbBuffer);
          if (sizeBuffer > 0 && sbBuffer.Length > 0)
            string chunk = sbBuffer.ToString(0, (int)sizeBuffer);
      resultChunk = filter.GetChunk(out ps);
    return plainTextResult.ToString();
    if (filter != null)

Assembling the Application

In short:

  • The index can only be built from scratch.
  • We are not returning the sample of the found document.
  • We are skipping the files that can't be parsed successfully.
  • We are loading the associated explorer icon for each document in the results.
  • You can choose the folder to be indexed; by default, it's your Documents folder.
  • The indexed file types are hard-coded (txt, htm/html, doc, xls, ppt).
  • The index is stored in your profile in the Local Settings/Application Data/DesktopSearch folder.
  • Remember that it is possible to search while the indexing is in progress.


Some statistics (Athlon XP 2000+, 1GB RAM, Seagate SATA drive 7200 RPM):

  • Documents indexed: 1185
  • Total size of indexed documents: 120,690,622 bytes
  • Rebuilding the index took: 5 minutes 55 seconds
  • Index size: 4,339,950 bytes
  • Search time (including the rendering on display): from 0.0937 seconds (25 found items) to 0.3125 seconds (213 found items)

To Be Continued...

In the next part of the article, we will extend this simple application with the following features:

  • The indexing will be handled by a separate application which will update the index continuously on the background.
  • The results will contain a sample of the document with highlighted query words.
  • We will index and search the file name and the last modified date.

Resources and Acknowledgements

Search Engine:

Seekafile Server - Open-Source Indexing Server

Office Documents Parsing:



This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Dan Letecky

Czech Republic Czech Republic
My open-source event calendar/scheduling AJAX controls:

DayPilot for JavaScript/HTML5/jQuery
DayPilot for ASP.NET
DayPilot for MVC
DayPilot for Java

Comments and Discussions

QuestionUnable to filter Msoffice Documents PinmemberMember 974777518-Mar-13 3:05 
QuestionUnble to filter office Documents PinmemberMember 974777518-Mar-13 1:09 
Questionis it possible to use IFilters to extract multilanguage text content? PinmemberSweetdin18-Mar-10 21:19 
GeneralThe IFilter doesn't parse Word docs correctly in office 2003 but work perfectly in office2007 Pinmember8482977mn16-Mar-10 0:39 
Generalfinding just the filename Pinmemberemmmatty116-Aug-09 23:36 
GeneralRe: finding just the filename Pinmember8482977mn16-Mar-10 1:22 
GeneralQuestion Please Pinmemberhom_rcp25-Feb-09 5:30 
Generalwaoh! Pinmemberchenli051324-Nov-08 21:28 
GeneralHighlighter or fragmenter Pinmembermbowles2019-Oct-07 5:31 
GeneralRe: Highlighter or fragmenter PinmemberDan Letecky9-Oct-07 22:48 
GeneralRe: Highlighter or fragmenter Pinmembermbowles20110-Oct-07 4:15 
GeneralRe: Highlighter or fragmenter PinmemberDan Letecky10-Oct-07 4:32 
GeneralI look forward to Part 2 PinmemberDrTom21-Jan-07 12:00 
GeneralRe: I look forward to Part 2 PinmemberDan Letecky2-May-07 5:59 
GeneralRe: I look forward to Part 2 Pinmembermbowles20125-Sep-07 17:43 
QuestionHow to search in pdf files? PinmemberAjayarora14-Oct-06 1:56 
AnswerRe: How to search in pdf files? PinmemberDan Letecky2-May-07 6:02 
GeneralVB.Net Version PinmemberJonathan M Patrick8-Sep-06 19:10 
QuestionPart 2? Pinmemberjames_carter18-Jul-06 3:45 
Hi there,
have you any plans to write Part2 of this excellent article?
I am particularly interested in the possibilty of a preview with the search terms highlighted.

Obviously I accept that you are busy but if you could give me a couple of pointers on how to achieve this myself I would be very grateful

cheers and thanks for your time

AnswerRe: Part 2? PinmemberDan Letecky2-May-07 5:55 
GeneralRe: Part 2? Pinmemberjames_carter2-May-07 6:01 
QuestionIS Dotlucene Free? Pinmembervisva6-Apr-06 18:45 
AnswerRe: IS Dotlucene Free? PinmemberDan Letecky6-Apr-06 22:57 
GeneralTitle and score questions Pinmembermbowles20120-Mar-06 7:22 
GeneralNeed Information PinmemberVijay Kumar Raja Grandhi3-Mar-06 4:15 

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