Starting Services on LinuxJuly 24, 2010
Exposing WCF Services using xfNetLink .NETJuly 1, 2011
At the recent SPC’s in Chicago and Oxford several of the sessions that I presented were focused on networking, and in particular on the various tools and technologies that are available to Synergy developers to allow them to build and deploy distributed software applications. In particular I spent quite a bit of time talking about a technology called Windows Communication Foundation.
This is the first in a series of posts relating to the various ways in which Synergy developers can use of Windows Communication Foundation (WCF) when building their applications. The posts in the series are:
- Building Distributed Apps with Synergy/DE and WCF (this post)
- Exposing WCF Services using xfNetLink .NET
- Hosting WCF Services in an ASP.NET Web Application
- Exposing WCF Services using Synergy .NET Interop
- Self-Hosting WCF Services
- Exposing WCF services using Synergy .NET
What is WCF
WCF is a part of the .NET framework that provides a powerful and flexible way to implement network communication between the various parts of a distributed software application. For many years Synergy developers have been able to build distributed applications using xfServerPlus and xfNetLink. Many have done so, and have deployed a wide variety of applications based on these technologies. When developing a new .NET client application developers would use xfNetLink .NET to gain access to their Synergy business logic and data.
This approach has served us well over the years, will continue to do so, and is still the most appropriate solution in some scenarios. But in some other scenarios using WCF might now be more appropriate, and could help developers to broaden the capabilities of their applications in several key areas, some of which are:
Because the communication between xfServerPlus and xfNetLink uses a custom protocol which operates on a “non-standard” port, it may not be appropriate for use over wide area networks and the Internet. The primary problem here is that there is a high chance that this communication would be blocked by firewalls, some of which may be outside of your control. WCF supports multiple network transport protocols, the most basic of which is HTTP. This means that it is designed with the Internet in mind, and is very suitable for implementing applications which communicate over the Internet.
Another advantage of WCF is that the same WCF service can be exposed via multiple “endpoints”, and each of these endpoints can be configured to use different communication protocols and mechanisms. For example a single service could be exposed via one endpoint which uses HTTP and SOAP which would be suitable for a wide variety of client applications to be able to access from anywhere (including via the Internet), while at the same time being exposed by a second endpoint which uses low-level TCP/IP communications and binary messaging protocols suitable for use by applications running on the same local network as the service, at much higher performance. A single client application could even be configured to dynamically switch between these endpoints based on the current location of the user.
More Client Options
When using xfServerPlus and xfNetLink, client applications must be written in a programming language which is able to use one of the supported xfNetLink clients (COM, Java or .NET), but because WCF services can be interacted with via “standard” protocols such as HTTP and SOAP there are many more client application possibilities, because almost all development environments and programming languages are able to use these basic protocols.
WCF also provides the ability to easily support asynchronous communication between clients and servers. When a client application calls an xfServerPlus method the client must wait for the execution of the method to complete, and for any resulting data to be returned, before performing any other processing. Using WCF it’s easy to support asynchronous method support, where the client application can call a method and then continue with other processing, later receiving an event when the remote method has completed its operation and when any resulting data is ready for use. This approach can make client applications appear to be much more dynamic and responsive.
In many distributed software applications interaction between the client and the server is initiated by some event in the client application which requires some subsequent processing in the server application. But in some situations it is necessary for the server application to be able to, at will, initiate some processing in the client application. Unfortunately xfServerPlus and xfNetLink don’t really address this use case, but it can be addressed with WCF, because WCF service endpoints can be “self-hosted” within any type of .NET application. This means that as well as a client application having the ability to interact with a WCF service on some server somewhere, the client can also expose a WCF service, which the server application (or in fact any other application) could interact with.
WCF is an extensive subject area, and in this BLOG I’m not even going to attempt to teach you about the specifics of using WCF. Instead I’m simply going to try to make you aware of some of the reasons that you might want to explore the subject further, and make sure that you know about the various ways that you can get started.
There are several ways that Synergy developers can utilize WCF in their applications, and I’ll briefly describe each of these mechanisms below.
WCF via xfNetLink .NET
In xfNetLink .NET 9.5.1 a new feature was introduced which gives developers a lot of additional flexibility in the way that they build their applications, or rather the way that they communicate between the various parts of the application. This new feature is enabled through a new command line parameter to the gencs utility (-w). When you use this new option, two things change.
When you use gencs –w, the first thing that changes is that various attributes are added to the wrapper classes that are created by gencs. These attributes in turn allow those generated classes (and the assembly that they are compiled into) to be directly exposed as a WCF service. Previously, if a Synergy developer wanted to expose a WCF service which in turn exposed their Synergy business logic and data, they have to manually “wrap” their xfNetLink .NET procedural and data classes in other classes which in turn exposed a web or WCF service.
The second change when using gencs -w is that any collections which are exposed by the application API are transformed from un-typed “ArrayList” collections, to more useful and flexible “Generic List” collections. This change will require a small amount of re-coding in any existing client applications, but results in a significantly enhanced development experience.
This mechanism is likely to be of interest to developers who already have an existing solution using xfNetLink .NET and xfServerPlus, and want to take advantage of some of the additional capabilities of WCF, or to developers who wish to expose a new WCF service where the server application exposes code running on a UNIX, Linux or OpenVMS server.
WCF via Synergy .NET Interop
Another way that Synergy developers can expose WCF services is via Synergy .NET’s “Interop” project. The primary purpose of an Interop project is to allow developers with existing xfServerPlus applications to migrate their existing Synergy methods to a native .NET environment. By adding their method source code to an interop project they are able to execute those methods directly in the .NET environment, instead of using xfNetLink .NET and xfServerPlus to execute the methods with traditional Synergy on a remote server.
The Interop project works by generating Synergy .NET “wrapper classes” for your traditional Synergy methods (subroutines and functions) and data structures (records). The external interface of these wrapper classes is very similar to that of the C# wrapper classes produced by xfNetLink .NET’s gencs utility. The primary goal of the Interop project is to allow developers to migrate existing applications from a mixed .NET / traditional Synergy environment to a 100% .NET environment, with only minor changes to the code of existing client applications.
When you create an Interop project in Visual Studio, one of the options that you have (via the project properties dialogs) is to “Generate WCF contracts”, and as discussed earlier in this article, the effect of this is to add various attributes to the generated wrapper classes so that they can be directly exposed as a WCF service.
So again, for Synergy developers, this approach can provide a quick-and-easy way to expose a WCF service based on existing code. Again, this approach is likely to be primarily of interest to those who already have xfServerPlus based applications running on the Windows platform.
WCF via Synergy .NET
Both of the previous approaches were primarily focused on those who already use xfServerPlus, and both provide an easy way to get started with WCF. However in both of the previous scenarios, the external interface of your WCF service is directly defined by the interface to your underlying traditional Synergy methods (subroutines and functions), and the WCF data contracts that are exposed are defined by the repository structures exposed by the parameters of those methods. So, while the WCF capabilities provided by xfNetLink .NET and by the Synergy .NET Interop project are easy to use, you don’t get full control over the exposed interface and data. If you want that finer level of control, or if you’re just getting started with server application development and don’t have existing xfServerPlus methods, there is a better way to go.
The third way that Synergy developers can leverage WCF is by using Synergy .NET to create an all-new WCF service with native .NET code. This task was possible in 9.5.1 when Synergy .NET was first introduced, but has been made much easier through the introduction of a new “WCF Service Library” project template in 9.5.1a.
Creating a new WCF service via a WCF Service Library is the way to go for developers who want to write an all-new service application, or who don’t mind a little extra effort to re-work some existing code in order to factor out some of the “wrapper” layers involved with the previous two approaches. As a result you will have full control of the resulting WCF service, and the contracts that it exposes.
Wrapping Up – For Now
So, as you can see, Synergy/DE is now providing you will all kinds of new and exciting things that you can do in your Synergy applications, and I firmly believe that WCF is one of the most important, and powerful. In the near future I will be writing several additional BLOG posts which will explain these three ways of exposing WCF services in more detail, and I’ll also try to provide more detail about WCF generally. So for now, be thinking about how your existing distributed applications are built, and what things you might wish to improve about them. Or be thinking about that all-new distributed application that you’ve wanted to get started on. If you’re thinking of enhancing or implementing a distributed application, then using WCF is almost certainly the way to go.