Saturday, May 24, 2008

.NET Framework Client Profile

The .NET framwork keeps on growing and so does the size, so it has become apparent that a lighter version of the .NET Framework is needed.
Last week, Microsoft released the Visual Studio 2008 and .NET Framework 3.5 SP1 Beta. This includes the .NET Framework Client Profile,a smaller, optimized verson of the .NET framework needed for clients applications to run.The size of this framework is approximatley 27 MB (not that small), some of the assemblies that still lies in the beta but will be removed in the RTM version are

System.Management,

System.Messaging,
System.ServiceProcess,
System.Web,
System.Web.RegularExpressions

Visula Studio 2008 also has an option where you can make sure that an application targeted for the Client Profile Framework does not reference assemblies that are not included in the Client Profile Framework.You can have a look at the list of assemblies that are inluded in the client profile here

Monday, May 12, 2008

WS-* and REST, Which Is Better and Why?

I have been hooked up to REST these days after having some times to go through the WCF Web Programming Model (I know I am lagging behind in technologies !).
While looking at the pros and cons of REST and WS-*, I could see more then few web pages, blogs, on the debate of what’s the best solution for SOA.
REST is easy to use, no SOAP-client tool kits needed to generate web service proxies, as the fundamental concept behind REST being every operation is accessed by its unique URI, it's just a matter of typing it in your web browser, this also makes testing easier for developers (as all they need to do to see if the service is working, is to type the url in the browser !)
Further more if your are practicing an asynchronous pattern such as using AJAX, it might be very easy to call a REST service, get the response in JSON and do the processing on the client side, this is much easier then using the typical DOM method to parse XML.
When it comes to coupling, REST is more loosely coupled then WS-* services, because with WS-* web services, the client needs to know a great deal about the service and if the web service changes, your client need to update for it to continue working, but with REST, your only need to know the URL of the resource and nothing more, this makes REST more loosely coupled then WS-* web services.
From the non-functional requirement point of view, simplicity of architecture, performance due to no or less XML overhead and caching of result set (page) which is
built into the back bones of HTTP and the ability to server a huge number of clients due caching and clustering support built into REST (HTTP), stand out.
This does not mean WS-* or SOAP web services are going away...WS-* web services from my opinion are the best choice for enterprise applications (although there is a debate to this), with it's reliability, security and transactional capabilities.
REST does not support distributed transaction directly, and when it comes to security, REST has to entirely depend on the best it has, SSL.
REST would always be a better choice when it comes to developing services when you don’t know your clients, in other words the type of clients. As a final point, it’s is very clear that when it comes to WS-* web services, there are more alternatives when it comes to making architectural decisions and if advanced functionality delivered by WS-* is needed, it is no easy thing to extend RESTful services to deliver this
So finally to say, I am not saying REST is better then SOAP or vice versa, but what I am saying it's a matter of
pure architectural decision.
This is not a compressive comparison between REST and WS-* but instead a snap shot.



Tuesday, May 6, 2008

RESTful Example

Here is an example on how you would create a RESTful webservice with the WCF Web programming model. I assume that you know how to write a WCF service and host it in IIS.
In this example I am going to create a service that will say "Hello" plus a string that is passed into the service, further more the service is going to be hosted in IIS.
the following is a WCF service class,
[ServiceContract]

public interface ITest
{
[OperationContract]
[WebGet(UriTemplate="/SayHello/{str}",ResponseFormat= ebMessageFormat.Xml)]
string SayHello(string str);
}
public class TestImpl : ITest

{
public string SayHello(string str) { return "Hello " + str; }
}

SayHello is our service operation. Note that this is a general WCF service with addittion of a [WebGet] attribute on top of our service operation. by using the [WebGet] attribute we mean that the operation is to be invoked with the HTTP GET verb.The next step is to define our .svc file for our service, the content of the .svc file would look like this.
< @ ServiceHost language=c# Debug="true" Service="RestService.TestImpl" Factory="System.ServiceModel.Activation.WebServiceHostFactory" % >

Again this a general .svc file with the exception of having a WebServiceHostFactory specifed as a factory class to create the appopriate webHttpbinding endpoint.
Now all we have to do is host the service in IIS. The binding used to create RESTfull services, the webHttpbinding does not support multiple authentication, therefor make sure to select only one type of authentication for the directory security in IIS.
We are done...you can access you service like this (assuming that your IIS is running local):
http://localhost/RestService/RstSvc.svc/SayHello/ Iron Man
your response would look something like this...

<string xmlns="http://schemas.microsoft.com/2003/10/Serialization/%22>Hello Iron Man</string >
If you notice carefully, you would see that the way we sent the request is mapped to our [WebGet] attribute's UriTemplate : [WebGet(UriTemplate="/SayHello/{str})]" where {str} is a place holder for the parameter of the operation. You would also see that the response format is set to xml. ResponseFormat= WebMessageFormat.Xml, so the response will be sent to us in xml.


Saturday, May 3, 2008

RESTful Web Services and the WCF Web Programming Model

REST (Representational State Transfer) is not a new thing to the web service world; you can find a lot about what it is on the net, but for formality...REST is an architectural style (not a standard) it simply means web services are identified as resources and each operation as a unique URI assigned to it.You invoke the object's operation using the HTTP verbs like GET, POST etc...
Most web services are being shifted to using this style, for an example yahoo web services use REST. But some companies continue to have a REST service in addition to the SOAP based service.
One of the advantages of using REST over SOAP based services is that REST is light weight, as there is not much XML markup; for an example, REST does not use the SOAP header which is chunky.
Another benefit of REST is that the client accessing the service does not need special SOAP tool kit to use the service, as the service operation is identified as a URI, it is just a matter of accessing it like a web page in a browser.
REST responses can also be of variety, currently XML, raw binary data and JSON responses are supported.
.NET provides a way to create RESTful web service through the WCF web programming model. This basically allows you to build your RESTful services on top of WCF; this also means that you can expose your current WCF service as a RESTful service by adding certain attributes to you operation contracts and exposing it on a different endpoint.
WCF 3.5 supports a webHttpBinding for this purpose and also a WebServiceHost class to host your RESTful service.So how is this done?.. look at the code sample below.

[ServiceContract]
public interface ICalculator
{
[OperationContract]
[WebGet]
int Add(int num1, int num2);
}

In addition to the general {OperationContract}, a [WebGet] attribute is added, this just signals the frame work that the Add method is exposed as a RESTful operation as well.On the next post I will show you how we can create a RESTful service in WCF.


Friday, May 2, 2008

Finalization, Know What it Costs

This is a post about object finalization in .NET.
Finalization is not as inexpensive as we think, it increases the pressure put on GC.All objects that need finalization are moved into a finalizable queue and the actual finalization happens in a separate thread. Because the objects full state may be needed, the object itself and all the object it points to are promoted to the next generation (this is needed so that GC does not clean these objects off in the current round), and these objects are cleaned up only after the following GC.
Due to this reason, resources that need to be released should be wrapped in as small a finalizable object as possible, for instance if your class needs a reference to an unmanaged resource, then you should wrap the unmanaged resource in a separate finalizable class and make that a member of your class and furthermore the parent should be a non-finalizable
class. This approach will assure that only the wrapped class (class that contains the unmanaged resource) will be promoted.And as mentioned earlier the finalization occurs in a separate thread and furthermore there is only one finalization thread hence if a finalizer causes this thread to block, all the other objects needing finalization in the queue will not be called and your application will
leak !!!.

Therefore, when implementing finalizers, keep it as simple as possible.A good practice to follow when the lifetime of an object is explicitly know, is to implement the dispose pattern, by implementing the IDisposable interface and calling it explicitly; or use the using statment to wrap you created instance, so that once the scope of the object is no longer valid the dispose method of the object is called.
A time may arise when you may at some places know the lifetime of the object but at some point you may not; in this case put your clean up code in a separate function, call that function in the finalizer and also in your dispose method, additioanlly call the GC.SupressFinalization() in your dispose method after the clean up method; this will inform GC not to run the finalizer.