Welcome to the 11th article in the series. Updated: Nov 23, 2008
In this article, I will take a broad detour from the abstract into the concrete with WCF. The title of this article is "Introduction to WCF: Architecture and the "ABCs" of Indigo." BTW, I have been in the Indigo SDR program for over 4 years and the term Indigo has stuck in my mind, so I will use the terms interchangeably. Plus, as I think Don Box said in a presentation," It's spelled W-C-F and pronounced Indigo. The WCF is silent." :)
What is WCF in Simple Terms?
The focus of this post is to show "Hello Indigo" code in a step-by-step manner. We will dive deep into the Indigo Architecture in the next installment of this series. Simply put, WCF is Microsoft's SDK and platform for creating and deploying Services in both a Service-Oriented Architecture (SOA see Articles 1-10) in the series as well as absorbing and subsuming the feature sets of legacy distributed technologies such as COM, COM+, Enterprise Services, .NET Remoting, WSE, ASMX and MSMQ.
WCF provides a runtime environment for your services, and deals with exposing CLR types as services, as well as consuming other services as CLR types. I will get into much more detail in future installments, but WCF was also built with Interoperability as a major goal, and as such, is built on top of an implementation of a set of industry standards. The WCF Architecture was also built to be fully extensible. There is no better example of this than the product group itself as full REST and Web programming was rather easily added to WCF 3.5 and 3.5 SP1 with no changes to the programming model. The skills that are learnt in constructing a basic WCF service are very applicable to creating a "REST service."
Let's see how easy it is to get started.
Hello Indigo Step by Step
I am going to show you WCF step by step and make it as easy as possible. To that end, I am put both the Sender and Receiver in the same console application and I am not going to use either generated proxies or config files. You would never do this in the real world, but it makes it easy to describe the "ABCs" of WCF.
So, let's start with a shell console application that should be totally familiar to you. Run VS2008 and Create a new C# Console application and replace the code with the following.
using System;
using System.ServiceModel;
namespace HelloIndigo
{
class Program
{
static void Main()
{
}
}
}
A Service is a Set of Endpoints
A WCF service is a set of endpoints that provide something of value to the client. Every service must expose at least one endpoint to be of any use, and each endpoint has exactly one contract. An endpoint is simply a resource on the network to which messages can be sent. Specifically, that endpoint is a fusion of an address, a binding, and a contract; such that it has become known as the "ABCs" of WCF.
The ABC's of WCF
A is For Address, the "Where"
The first concept is that of the Address. The Address is where our application will hang its hat, waiting and listening for incoming messages. It's unique and a combination of the location of the service and the transport protocol or schema. For now, we will keep it simple and stick with the HTTP transport and URIs. We need to use the System.Uri type to do this:
Uri address = new Uri("http://localhost:8000/HelloIndigo");
B is For Binding, the "How"
The next thing we need is a Binding. Bindings can get complicated with their shaping of channel stacks but for now, lets leave it as a binding defines the channel used to communicate with an endpoint. A channel is combined of a series of binding elements which are a combination of a transport, Message Exchange Pattern, and a message encoder. We will use bacicHttpBinding which directs WCF to implement the WS-I Basic Profile 1.1, the lowest common denominator of interoperability.
BasicHttpBinding binding = new BasicHttpBinding();
C is For Contract, the "What"
The Contract is the heart and soul of WCF, and I would say Service-Orientation. It is a syntactic description of what operations the service responds to and what shape the messages take going in and out. [ServiceContract]
public interface IHelloIndigo
{
[OperationContract]
void SaySomething(string message);
}
Here I have defined a contract, IHelloIndigo, and the [ServiceContract] attribute marks the interface as a contract. Be assured, however, that [ServiceContract] generates an underlying WSDL PortType and the [OperationContract] defines WSDL Operations and messages.
So our code looks like this so far:
[ServiceContract]
public interface IHelloIndigo
{
[OperationContract]
void SaySomething(string message);
}
sealed class HelloIndigo : IHelloIndigo
{
private static void Main()
{
// We got an "A" and a "B"
Uri address = new Uri("http://localhost:8000/IHelloIndigo");
BasicHttpBinding binding = new BasicHttpBinding();
Can You Hear Me Now?
So, we have our ABCs of WCF but our Service is lacking an Endpoint to listen on and it's lacking a host. Remember, that a Service has one or more Endpoints that listen for messages. Each Endpoint is made up of an Address, Binding, and Contract. We will use the AddServiceEndpoint method on the ServiceHost class to do this. Say what? We haven't talked about ServiceHost. The System.ServiceModel.ServiceHost type builds and hosts endpoints, along with the rest of the receiving architecture. We'll have a lot more to say about this class later.
ServiceHost serviceHost = new ServiceHost(typeof (HelloIndigo));
serviceHost.AddServiceEndpoint(typeof (IHelloIndigo), binding, address);
serviceHost.Open();
Console.WriteLine("We is ready to receieve");
Console.ReadLine();
serviceHost.Close();
We have one aspect that I neglected. Up above, you will see that class HelloIndigo implements IHelloIndigo, so that there is a mapping in the messaging infrastructure to the programming type HelloIndigo.
We will implement the method so that received messages are dispatched to this instance:
Public void SaySomething(String message)
{
Console.WriteLine("We got the message, And the body contains: {0}", message);
}
Now we are 1/2 way down. We have a Service Endpoint just hanging out at some address patiently waiting for some kind soul to send messages to it. If we now run and do a netstat -a -b, we can see that it is indeed the case.
TCP [::]:8000 Sam-PC:0 LISTENING
Send Me!
At this point, you would normally create the separate client project, would generate the proxy with svcutil.exe or Add Service Reference. But since we are after simplicity, as I mentioned, we will put the sender in the same application. It is the sender's responsibility to use an address, binding, contract that is compataible with the receiver/service.
However, the types are a bit different on the sender side. Instead of a URI type, we have a System.ServiceModel.EndpointAddress which is a WCF abstraction for a WS-Addressing endpoint. Also, instead of ServiceHost, we are the client and we use the ChannelFactory<T> type. Now, normally one would put the address, binding and contract in a config file and use a proxy, but what I am showing you here avoids the need to generate a proxy altogether. So we have:
// Sender time
ChannelFactory<IHelloIndigo> channelFactory =
new ChannelFactory<IHelloIndigo>(binding, new EndpointAddress(address));
IHelloIndigo proxy = channelFactory.CreateChannel();
proxy.SaySomething("Hello Capital City");
Console.ReadLine();
serviceHost.Close();
If we now run the complete program we get our desired result:
We is ready to receieve
HelloIndigo Object Created
We got the message, and the body contains: Hello Capital City
The whole program is as follows:
using System;
using System.ServiceModel;
namespace Gentile.Demos.HelloIndigo
{
[ServiceContract]
public interface IHelloIndigo
{
[OperationContract]
void SaySomething(string message);
}
sealed class HelloIndigo : IHelloIndigo
{
public HelloIndigo()
{
Console.WriteLine("HelloIndigo Object Created");
}
private static void Main()
{
// We got an "A" and a "B"
Uri address = new Uri("http://localhost:8000/IHelloIndigo");
BasicHttpBinding binding = new BasicHttpBinding();
ServiceHost serviceHost = new ServiceHost(typeof (HelloIndigo));
serviceHost.AddServiceEndpoint(typeof (IHelloIndigo), binding, address);
serviceHost.Open();
Console.WriteLine("We is ready to receieve");
// Sender time
ChannelFactory<IHelloIndigo> channelFactory =
new ChannelFactory<IHelloIndigo>(binding, new EndpointAddress(address));
IHelloIndigo proxy = channelFactory.CreateChannel();
proxy.SaySomething("Hello Capital City");
Console.ReadLine();
serviceHost.Close();
}
#region IHelloIndigo Members
public void SaySomething(string message)
{
Console.WriteLine("We got the message, and the body contains: {0}", message);
}
#endregion
}
}
Where the Heck are the Messages?
So, this doesn't look at all like a messaging system! To the WCF developer, looks, feels, smells like any other OO or component object program. Be assured, that at run time, however, that the Indigo architecture is configuring channel stacks and dealing with messages. How can I show that? If I change the implementation of the of the SaySomething method to the following, we can see the messages:
public void SaySomething(string message)
{
Console.WriteLine("We got the message, and the body contains: {0}", message);
// This looks like RPC! Where's the Messages???
Console.WriteLine(OperationContext.Current.RequestContext.RequestMessage.ToString());
}
We
is ready to receieve
HelloIndigo Object Created
We got the message, and the body contains: Hello Capital City
<s:Envelope xmlns:s=
"http://schemas.xmlsoap.org/soap/envelope/">
<s:Header>
<To s:mustUnderstand=
"1" xmlns=
"http://schemas.microsoft.com/ws/2005/05/addr
essing/none">http://localhost:4000/IHelloIndigo</To>
<Action s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/
addressing/none">http://tempuri.org/IHelloIndigo/SaySomething</Action>
</s:Header>
<s:Body>
<SaySomething xmlns="http://tempuri.org/">
<message>Hello Capital City</message>
</SaySomething>
</s:Body>
</s:Envelope> What About WS-* Messages?
If we comment out one line and change the binding, we see the WS-* messages:
We is ready to receive
HelloIndigo Object Created
We got the message, and the body contains: Hello Capital City
<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope" xmlns:a="http://ww
w.w3.org/2005/08/addressing" xmlns:u="http://docs.oasis-open.org/wss/2004/01/oas
is-200401-wss-wssecurity-utility-1.0.xsd">
<s:Header>
<a:Action s:mustUnderstand="1" u:Id="_2">http://tempuri.org/IHelloIndigo/Say
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<a:MessageID u:Id="_3">urn:uuid:5d7c73b2-ad24-4839-881f-f01e035d7cdf</a:Mess
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<a:ReplyTo u:Id="_4">
<a:Address>http://www.w3.org/2005/08/addressing/anonymous</a:Address>
</a:ReplyTo>
<a:To s:mustUnderstand="1" u:Id="_5">http://localhost:4000/IHelloIndigo</a:T
o>
<o:Security s:mustUnderstand="1" xmlns:o="http://docs.oasis-open.org/wss/200
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</u:Timestamp>
<c:SecurityContextToken u:Id="uuid-07366b5a-18e1-46bc-9df7-bb5fc5cf842d-9"
xmlns:c="http://schemas.xmlsoap.org/ws/2005/02/sc">
<c:Identifier>urn:uuid:be58d427-4e04-45d5-8e9d-2b9a5c304a53</c:Identifie
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</c:SecurityContextToken>
<c:DerivedKeyToken u:Id="uuid-07366b5a-18e1-46bc-9df7-bb5fc5cf842d-15" xml
ns:c="http://schemas.xmlsoap.org/ws/2005/02/sc">
<o:SecurityTokenReference>
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</o:SecurityTokenReference>
<c:Offset>0</c:Offset>
<c:Length>24</c:Length>
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</c:DerivedKeyToken>
<c:DerivedKeyToken u:Id="uuid-07366b5a-18e1-46bc-9df7-bb5fc5cf842d-16" xml
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<o:SecurityTokenReference>
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</o:SecurityTokenReference>
<c:Nonce>fBMvI6q1DGWhXk4w9zr7tQ==</c:Nonce>
</c:DerivedKeyToken>
<e:ReferenceList xmlns:e="http://www.w3.org/2001/04/xmlenc#">
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</e:ReferenceList>
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<e:EncryptionMethod Algorithm="http://www.w3.org/2001/04/xmlenc#aes256-c
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<KeyInfo xmlns="http://www.w3.org/2000/09/xmldsig#">
<o:SecurityTokenReference>
<o:Reference ValueType="http://schemas.xmlsoap.org/ws/2005/02/sc/dk"
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</o:SecurityTokenReference>
</KeyInfo>
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</o:Security>
</s:Header>
<s:Body u:Id="_0">
<SaySomething xmlns="http://tempuri.org/">
<message>Hello Capital City</message>
</SaySomething>
</s:Body>
</s:Envelope>