1UCN 2012

Why use distributed (client / server) applications?

• To connect tiers within the same application...– client & server is both .NET assemblies

• Example:– A typical business app has Business and Data Access tiers– GUI calls into the business tier to get data, calculation &

validation– Business tier makes calls to the data tier for writing / reading data

DBDTBT

Client (.NET)Server (.NET)

Business

Tier

Data AccessTier

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Distributed app seen from the client and the server

• The client sees the server as an assembly .DLL– sets a reference to a object as normally

• The server makes .DLL available in one of two ways:

1. Runs as a service on the server, that responds on remote calls

2. Runs in the web server & trigger remote calls via URL

– advances?

• #1 can use proprietary protocols & formats (more efficient)

• #2 is firewall-friendly, easy use of Windows security

Client.exeClient.exe .DLL

Server

3UCN 2012

Windows Communication Foundation

• Introduction– .Net foundations– Communication Protocols– SOA tenets (principles)

• WCF– Basics– Contracts– Bindings

• Build a WCF application– Build the service– Build the client– Host the service

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.NET At The Core

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Distributed applications• Many protocols and api’s for communication

Web services

MSMQ

COM+DCOM

.NET Remoting

SocketsCORBA

P2PRMI

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WCF

• WCF provides a single extendable programming object model that can be used to interact with number of distributed technologies

• It makes it possible to offer multiple ways of communications, e.g. Web Services or .Net Remoting

• It is possible to extend the application with a new protocol without adding or refactoring code. It is done in the config file

• WCF is based on the design principles of SOA -Service-Oriented Architecture

• Supports strongly typed (.Net remoting) and loosely typed messages (XML)

• Supports multiple web service specs (WS*) e.g. SOAP and JSON

• Fully integrated security models (both windows models and independent models)

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Service-Oriented Architecture

• Many definitions exists.• The simple definition:

SOA is a way to design distributed systems where several autonomous services works in conjunction by passing messages across boundaries using interfaces

• WCF is based on 4 tenets of SOA:

1. Boundaries are explicit

2. Services are autonomous

3. Services communicates via contract, not implementation

4. Service compatibility is based on policy

8UCN 2012

The ABC of WCF

• Three things are needed to build a WCF application:

A. AddressThe location of the service. Normally stored in the config file

B. BindingHow to bind to the service. Should it be xml, binary etc.

C. ContractNormally implemented as an interface in c#. But it is possible to add [ServiceContract] attributes to a normal class.

• Note: You don’t have to do it in the order of A, B and C.Actually in most cases you do it the opposite order

• Together ABC forms an endpoint.

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Contract

• Make an interface as usual. The interface methods will be the operations of the service.

• Use [ServiceContract] to define the interface as a (uhm..) service contract.

• Use [OperationContract] to define the method as an operation

• Let’s look at the WCFHelloWorld.

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Contract

Contract:

Uses and references the backend:

Implementing the service acting as a proxy for the backend:

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Binding

• The binding specifies how to use the service• There may be specified more than one binding, meaning

that there may be more than one way to access the service.• The binding can specify:

– The contracts implemented by the service– The transport layer (http, tcp, named pipes, msmq)– The channel for the transport (request-reply, one-way,

duplex)– The encoding method (xml, binary, etc)– If a WS: Any supported web service protocols

(WS-Transaction, WS-Security etc.)

Don't confuse the terms tcp and http with OSI.Tcp and http are on different layers in OSI, and as you know

http is on top of tcp

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Binding – App.config in the WcfService Project

Binding and Contract(The “mex” endpoint is used by VS or other EDI)

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Binding – app.config in the Client Project

Binding and Contract

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Exercises

• Exercise 1 (from GettingStartedWCF.pdf):

1. HelloWorld

2. Add another client:Create a WinForm application that says ´”Hello World” using the same WCF service. Go through the same steps as when the console application was created.

3. Make your own distributed application:Make a back-end (Calculator) with methods for adding, subtracting and multiplying two numbers in same way as the HelloServer. Add a WCF service that uses the back-end. And finally, add a client.

15UCN 2012

Http Binding – Open to the world

• The binding can be specified in the code by declaring an object, or (the easiest way) in the config file (using xml)

• Use http if the service should be reached by non .Net platforms or through Nat’s and firewalls

• There are by default 4 types of http binding: • Element < basicHttpBinding> or the class BasicHttpBinding

Basic web service functionality based on http and xml.• Element <wsHttpBinding>, class WSHttpBinding

Like BasicHttpBinding, but with support for transactions and reliable messaging

• Element <wsDualHttpBinding>, class WSDualHttpBindingLike WSHttpBinding, but makes possible for the service and the client to send message back and forth.

• Element <wsFederationHttpBinding>, WSFederationHttpBindingExtended security. Supports ws-federation.

16UCN 2012

Tcp binding – In-house• Use tcp binding in-house on .Net based platforms• Based on binary streams. Less bytes are transferred and no

need for parsing• Element <netTcpBinding>, NetTcpBinding

A secure and optimized method.• Element <netNamedPipeBinding>, NetNamedPipeBinding

Used for communication between applications on the same machine.

• Element <netPeerTcpBinding>, NetPeerTcpBindingUsed for peer-to-peer

• <netMsmqBinding>, NetMsmqBindingUses messages for cross-machine .Net platform communication

• <msmqIntegrationBinding>, MsmqIntegrationBindingUsed for communication with COM and native C++

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Which binding methods should I know for a start?

• BasicHttpBinding (or wsHttpBinding)• NetTcpBinding

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The EightBall exampleThe steps

1. Define the contract == define the interface and add contract attributes

2. Implement the service class (that implements the interface)

3. Do the ABC in the App.config file (on the server)

4. Implement the server

5. Implement the client– Generate proxy– Use the service

Recommended: In VS2010 start by using the WCF Service project template

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Step 1: Define the contract

• Just make an interface as usual, and add the attributes

[ ServiceContract(Namespace="noea.dk")] public interface IEightBall { [OperationContract] string ObtainAnswerToQuestion(string userQuestion); }

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Step 2: Implement the service

• Just a class

public class MagicEightBallService:IEightBall { public MagicEightBallService() { Console.WriteLine("The 8-ball awaits your question...."); }

public string ObtainAnswerToQuestion(string userQuestion) { string[] answers =

{ "Future uncertain", "Yes", "No", "Hazy", "Ask again later", "Definitely" }; Random r = new Random(); return string.Format("{0}? {1}",userQuestion,answers[r.Next(answers.Length)]);

} }

21UCN 2012

The .config file

• Configuration files are widely used in .Net• A configuration file provides an easy way of changing

different kind of setting.• For example:

– Database connection strings– Authorization settings– Remoting settings– Application specific properties

• In Visual Studio: Add a new item using the “Application Configuration File” template

• Leave the name as app.config. It will be renamed to <assemply filename>.config.

• E.g.: MyProgram.exe.config

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Step 3: The config file (basic)

<?xml version="1.0" encoding="utf-8" ?><configuration> <system.serviceModel> <services> <service name="MagicEightBallServiceLib.MagicEightBallService”/> <endpoint address="" binding="basicHttpBinding" contract="MagicEightBallServiceLib.IEightBall"/> <host> <baseAddresses> <add baseAddress="http://localhost:8080/MagicEightBallService"/> </baseAddresses> </host> </service> </services> </system.serviceModel></configuration>

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Step 3: The config file (enable wsdl)

…………<service name="MagicEightBallServiceLib.MagicEightBallService" behaviorConfiguration="EightBallServiceMEXBehavior"> <endpoint address="" binding="basicHttpBinding" contract="MagicEightBallServiceLib.IEightBall"/>

<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" /> <host>………….. </host> </service> </services> <behaviors> <serviceBehaviors> <behavior name="EightBallServiceMEXBehavior"> <serviceMetadata httpGetEnabled="true"/> </behavior> </serviceBehaviors>……………….

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Step 4: The Server

using System;using System.ServiceModel;using MagicEightBallServiceLib;

namespace MagicEightBallServiceHost{ class Program { static void Main(string[] args) { Console.WriteLine("Console Based WCF Host"); using (ServiceHost serviceHost = new

ServiceHost(typeof(MagicEightBallService))) { serviceHost.Open(); Console.WriteLine("The service is ready."); Console.WriteLine("Press the Enter key to terminate service."); Console.ReadLine(); } } }}

25UCN 2012

The using statement(not the using declaration)

• The using statement ensures that the object is disposed, when it goes out of scope.

• Is similar to this code:

{ ServiceHost serviceHost = new ServiceHost(typeof(MagicEightBallService))) try { serviceHost.Open();….. } finally { if (serviceHost != null) ((IDisposable) serviceHost).Dispose(); }}

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The Client

• Basically create the proxy class• It can be done in VisualStudio by adding a Service

Reference• If you have the server and the client in the same solution,

you have start the server from outside of VS before adding the reference

• Another way is to use svcutil.exe from the command promptThis will create a config file and a cs file containing the proxy class

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Step 5: The ClientAutogenerated config file

<?xml version="1.0" encoding="utf-8" ?><configuration> <system.serviceModel> <bindings> <basicHttpBinding> <binding name="BasicHttpBinding_IEightBall" closeTimeout="00:01:00" openTimeout="00:01:00" receiveTimeout="00:10:00" sendTimeout="00:01:00" allowCookies="false" bypassProxyOnLocal="false" hostNameComparisonMode="StrongWildcard" maxBufferSize="65536" maxBufferPoolSize="524288" maxReceivedMessageSize="65536" messageEncoding="Text" textEncoding="utf-8" transferMode="Buffered" useDefaultWebProxy="true"> <readerQuotas maxDepth="32" maxStringContentLength="8192" maxArrayLength="16384" maxBytesPerRead="4096" maxNameTableCharCount="16384" /> <security mode="None"> <transport clientCredentialType="None" proxyCredentialType="None" realm="" /> <message clientCredentialType="UserName" algorithmSuite="Default" /> </security> </binding> </basicHttpBinding> </bindings> <client> <endpoint address="http://localhost:8080/MagicEightBallService" binding="basicHttpBinding" bindingConfiguration="BasicHttpBinding_IEightBall" contract="test.IEightBall" name="BasicHttpBinding_IEightBall" /> </client> </system.serviceModel></configuration>

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Step 5: The ClientStripped config file

<?xml version="1.0" encoding="utf-8" ?><configuration> <system.serviceModel> <client> <endpoint address="http://localhost:8080/MagicEightBallService" binding="basicHttpBinding" contract="test.IEightBall" name="BasicHttpBinding_IEightBall" /> </client> </system.serviceModel></configuration>

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Step 5: The ClientThe exe file

using MagicEightBallClient.test;

namespace MagicEightBallClient{ class Program { static void Main(string[] args) { using (test.EightBallClient ball = new EightBallClient()) { Console.Write("Your question: "); string question = Console.ReadLine(); string answer = ball.ObtainAnswerToQuestion(question); Console.WriteLine("8-ball says: {0}",answer); } Console.ReadLine(); } }}

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Run the example

• The server must run in administrator mode on Vista and Windows 7

• Either start Visual Studio or the server in administrator mode: right click-> run as administrator

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Exercises

• Exercise 2:– Change the EightBall server so it also supports .netTcp– Change the client (or make a new) to use the .netTcp