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Domain Walker

, 22 Jan 2006
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An object that allows you to explore the topology of the internet.

What is it?

DomainWalker in action DomainWalker is an object that discovers domains reachable from a URL.  Unlike traditional crawlers and site downloaders that identify all reachable URLs on a page, DomainWalker explores a subset of the world wide web's topology by targeting root URLs only.  DomainWalker guarantees that its walk will complete in a finite amount of time by ensuring that duplicate domains are never crawled.

DomainWalker is an example of a WebResourceProvider and uses my StringParser utility class, both of which are published elsewhere at this site.  As an aside, the demo application shows how to spin off a worker thread from a GUI and have it update the GUI in a safe manner.  This is done by having the app respond to events fired by the worker thread.

How do I use it?

You use DomainWalker by initializing it, calling its Walk() method, and getting its results.

  1. Initialize the DomainWalker instance
    // Initialize the DomainWalker
    DomainWalker dw = new DomainWalker();
    dw.StartUrl = "www.ravib.com";
    dw.MaxDepth = 3;
  2. Do the walk
    // Do walk
    dw.walk();
  3. Get the results
    // Get results
    HashTable domainTree = dw.DomainTree;
    printHashTableAsTree (domainTree);   // left as an exercise to the reader

Getting DomainWalker's results

You retrieve DomainWalker's results by accessing its DomainTree property at the end of the walk and/or responding to the OnNotifyUrlBeingTraversed event.

DomainTree property

DomainWalker's result is a tree of discovered domains obtained from the object's DomainTree property. The tree is actually a nested Hashtable, where each collection of child nodes is stored in a new Hashtable.

Domain tree retrieved by DomainWalker

OnNotifyUrlBeingTraversed event

It may be more convenient to get at DomainWalker's results by being notified every time a new URL is discovered. This is done by subscribing to the object's OnNotifyUrlBeingTraversed event and is the approach taken by the demo app. Domain discovery notifications are received by registering a OnNotifyUrlBeingTraversed delegate which has the following signature:

  /// <summary>
  /// Notifies an observer when a url is about to be traversed.
  /// </summary>
  /// <param name="strParentUrl">The parent url (may be null).</param>
  /// <param name="strUrlBeingTraversed">The url being traversed.</param>
  /// <param name="nCurrentDepth">Current traversal depth.</param>
  /// <param name="nDomains">Number of domains discovered so far.</param>
  /// <param name="tsElapsed">Time elapsed since start of crawl.</param>
  public delegate void OnNotifyUrlBeingTraversed
    (string strParentUrl,
     string strUrlBeingTraversed,
     int nCurrentDepth,
     int nDomains,
     TimeSpan tsElapsed);

The demo app responds to the OnNotifyUrlBeingTraversed event by adding strUrlBeingTraversed to a list box. The string is indented by an appropriate number of spaces proportional to nCurrentDepth. Other useful information such as the elapsed walk time (tsElapsed) is displayed in a label control.

OnNotifyWalkCompleted event

DomainWalker also fires the OnNotifyWalkCompleted event at the end of a walk. The OnNotifyWalkCompleted delegate has the following signature:

  /// <summary>
  /// Notifies an observer when the walk has completed.
  /// </summary>
  /// <param name="nDomains">Number of domains discovered.</param>
  /// <param name="tsElapsed">Time taken to complete crawl.</param>
  public delegate void OnNotifyWalkCompleted
    (int nDomains,
     TimeSpan tsElapsed);

Revision History

  • 22 Jan 2006
    • Corrected DomainWalkerForm delegates to ensure controls are accessed from the GUI thread. (Thanks, Birgir K!)
    • Added missing .resx file to project.
    • Upgraded project to VS2005.
  • 15 Jan 2006
    Initial version.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Ravi Bhavnani
Technical Lead
Canada Canada
Ravi Bhavnani is an ardent fan of Microsoft technologies who loves building Windows apps, especially PIMs, system utilities, and things that go bump on the Internet. During his career, Ravi has developed expert systems, desktop imaging apps, marketing automation software, EDA tools, a platform to help people find, analyze and understand information, trading software for institutional investors and advanced data visualization solutions. He currently works for a company that provides enterprise workforce management solutions to large clients.
 
His interests include the .NET framework, reasoning systems, financial analysis and algorithmic trading, NLP, HCI and UI design. Ravi holds a BS in Physics and Math and an MS in Computer Science and was a Microsoft MVP (C++ and C# in 2006 and 2007). He is also the co-inventor of 2 patents on software security and generating data visualization dashboards. His claim to fame is that he crafted CodeProject's "joke" forum post icon.
 
Ravi's biggest fear is that one day he might actually get a life, although the chances of that happening seem extremely remote.
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Comments and Discussions

 
GeneralMy vote of 5 Pinmembercmptr_kemist16-Aug-11 17:32 
GeneralThank you and Found a bug PinmemberPhebous3-Apr-08 10:59 
GeneralRe: Thank you and Found a bug PinmemberRavi Bhavnani30-Aug-08 11:57 
GeneralRe: Thank you and Found a bug PinmemberPhebous30-Aug-08 15:02 
QuestionWhat about robots.txt Pinmembermariusco20-Dec-06 5:55 
Does it handles robots.txt
AnswerRe: What about robots.txt PinmemberRavi Bhavnani20-Dec-06 6:03 
Generalneed your help! Pinmemberbeyondwm200411-Apr-06 4:38 
GeneralRe: need your help! PinmemberRavi Bhavnani12-Apr-06 4:52 
GeneralStill the Same Problems PinmemberDavid7778-Apr-06 9:47 
GeneralRe: Still the Same Problems PinmemberRavi Bhavnani9-Apr-06 5:01 

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