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WCF Extensibility Guidance - Introduction

Jesus Rodriguez
Pablo Cibraro
Tellago, Inc

Published: October 2009

Articles in this series

Introduction

Extensibility is an essential element of any programming technology or framework. By leveraging extensibility mechanisms, developers can enhance the basic set of capabilities provided by a technology and adapt it to specific scenarios. Rich extensibility models are particularly relevant in distributed systems such as service oriented solutions given the heterogeneity and complexity of the scenarios addressed by these types of technologies. The lack of extensibility has traditionally been a challenge for most Web Services technologies in the market. To give an example without getting into a market analysis, most of the J2EE Web Services technologies faced tremendous difficulties adopting the Representational State Transfer (REST) model given that their messaging engine was completely based on the SOAP messaging model.

Windows Communication Foundation (WCF) provides a versatile extensibility model that allows developers to customize a large variety of the WCF client and service runtime capabilities. The flexibility of incorporating extensions in  different subsystems has made it possible for WCF to adopt emerging architecture styles such as REST or syndication formats without requiring major redesigns in its core infrastructure.  Similarly, other Microsoft technologies such as BizTalk Server or ADO.NET Data Services have been able to seamessly incoporate WCF into their infrastructure by leveraging various WCF extensibility points. In its current version, WCF includes several dozen extensibility points that encompass diverse functional areas such as security, message processing, hosting, instancing or metadata.

The richness of WCF’s extensibility model enables developers to adopt WCF in diverse service-oriented scenarios while maintaining a seamless developer experience. However, learning how and when to use different WCF extensions can be a difficult and often challenging endeavor.

This paper provides a pragmatic view of the fundamental components of the WCF programming model. The paper intends to provide developers with the guidance they need to quickly and effectively apply the different extensions available in WCF. We have structured this paper into a series of chapters that cover the different extensibility points available in the different WCF’s subsystems:

  • Extending the WCF Channel Model This chapter illustrates the fundamentals of the WCF channel programming model emphasizing the development techniques that developers can use to build custom WCF channels. In that sense, this chapter showcases the implementation of custom elements of the WCF channel model such as factories, listeners and , of course, custom channels.
  • Extending the WCF Client-Dispatcher Runtimes: This chapter illustrates the extensibility points of WCF’s client and dispatcher runtimes. The chapter covers the patterns and techniques that can help developers to customize different capabilities of WCF such as message interception, message filtering, operation selection, error handling among many others.
  • Extending the WCF Security Model: This chapter covers the fundamental extensibility points of WCF’s security runtime. The chapter provides a series of practical recipes that developers can use to customize the different elements of the WCF security model such as credentials, tokens, authentication, authorization, or identity representation.
  • Extending the WCF Hosting Model: This chapter explores the different extensions that developers can use to customize WCF’s hosting model. The chapter emphasizes the techniques used to create custom service hosts and host factories in order to extend the hosting capabilities of the WCF runtime.
  • Extending the WCF Metadata Model: This chapter illustrates the extensions available in the WCF metadata model. The chapter covers the fundamental techniques that allow developers to customize the WSDLs and policies associated with WCF services.
  • Extending the WCF Web Programming Model: This chapter explores the fundamental extensibility points that developers can leverage in their REST-based solutions. The chapter illustrates the different extensions that can be used to customize capabilities such as content type processing or syndication extensions.
  • Extending Dublin Application Server: This chapter provides an overview of how the WCF’s extensibility model enables some of the capabilities of the upcoming Windows Application Server. The chapter illustrates the extensions available to customize Dublin’s forwarding and tracking runtime services.
  • Building Custom Binding Elements and Behaviors: This section illustrates the use of binding elements and behaviors as the fundamental mechanisms for initializing the different extensions of the WCF programming model .

As explained previously, one of the objectives of this paper is to provide a real world and pragmatic view of the WCF extensibility model. In that spirit, the paper explores each WCF extensibility point within the context of real world scenarios. Additionally, we provide practical code examples that demonstrate the techniques developers should use in order to effectively implement WCF’s different extensions. In order to keep things practical, we have provided a set of code samples that provide complete implementation of the extensibility points illustrated in this paper.

About the Authors

Jesus Rodriguez: Jesus Rodriguez is the Chief Architect of Tellago, Inc. He is also a Microsoft BizTalk Server MVP, an Oracle ACE and one of a few Architects worldwide to be a member of the Microsoft Connected Systems Advisor team. As a member, Jesus has been selected to participate in a variety of Software Design Reviews with Microsoft's Product Teams including Windows Communication Foundation, Windows Workflow Foundation and BizTalk Server.

Jesus derived his extensive experience with business process integration and messaging through numerous implementations of disparate systems founded on the principles of SOA and BPM. Jesus is an active contributor to the .NET and J2EE communities and an internationally recognized speaker and author with contributions that include several articles for various publications including MSDN Magazine, Microsoft Architecture Journal, SOAWorld and Web Services Journal as well as speaking engagements at top industry conferences such as Microsoft TechEd, SOAWorld, Microsoft SOA and BPM Conference, Oracle Open World, software Architect Conference, Web Services Security Conference and the Microsoft MVP Summit. Additionally, Jesus has conducted a number of Web Casts on varying SOA technologies.

Jesus is a prolific blogger on all subjects related to integration and has a true passion for technology. You can gain valuable insight on leading edge technologies through his blog at http://weblogs.asp.net/gsusx.

Pablo Cibraro: Pablo is a senior architect in Tellago Inc, and an internationally reconigzed expert with over 10 years of experience in architecting and implementing large distributed systems with Microsoft Technnologies.

He has spent the past few years working directly with the Microsoft Patterns & Practices team on sample applications, patterns and guidance for building service-oriented applications with Web Services, Web Services Enhacements (WSE) and Windows Communication Foundation (WCF). The biggest contributions with this team were the Web Services Security patterns, and the implementation of a Secure Token Service quickstart for WSE 3.0 and WCF.

He now focuses on technologies that enable developers to build large scale systems such as WCF, WF, Dublin, OSLO and Windows Azure.

The community knows Pablo mainly for his weblog and active participation in conferences and forums.

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