Tutorial 2 - the ABCs of WCF programming Several communication ...

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Tutorial 2 - the ABCs of WCF programming written by Alex Kogan ([email protected]) winter semester, 2009-2010




Several communication technologies for different needs ◦ ASP.Net Web Services
for platform-independent communication

◦ Web Service Enhancements
advanced Web Services capabilities
reliability, atomic transactions, etc.

◦ .Net Remoting
fast .Net-based communication

◦ Enterprise Services, MSMQ (Message Queuing), …

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Unified communication programming model




Combines all functionality features from the previous technologies




Cross-platform, extendible and secure infrastructure




Designed for service-oriented communication

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Service - a passive piece of code that interacts with clients through messages ◦ clients send messages to request some work/data ◦ services perform the work and respond with a result




Services expose one or more endpoints where messages can be sent Endpoint

Client

Service Endpoint

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Each endpoint is composed of ◦ Address: ddress where is the service? ◦ Binding: inding how do I talk to the service? ◦ Contract ontract: what can the service do?




Writing and configuring a WCF service includes 3 steps (for each endpoint): ◦ define and implement a contract ◦ choose or define a service binding ◦ deploy the contract by binding it to a network address 5

Client code

Service

Proxy

Dispatcher

Channel




invokes a method on the proxy

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Client code

Service

Proxy

Dispatcher

Channel






offers methods as defined by the service contract converts the method call to a message transfers the message to a channel

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Client code

Service

Proxy

Dispatcher

Channel




passes messages between client-side and server-side 8

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Client code

Service

Proxy

Dispatcher

Channel





converts the message to a method call according to message headers invokes the requested service 9

Client code

Service

Proxy

Dispatcher

Channel




executes the requested operation

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Web Services Description Language




Describes the service along with its messages, operations and bindings




Defines service metadata that can be used to create a proxy for the client ◦ manually, by reading the WSDL file ◦ by tools for generating client-side code from WSDL definitions

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Calculator service server side

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Start by defining the interface of the service namespace CalculatorService { public interface ICalculatorService { int Sum(int x, int y); double Sqrt(int x); Rational Sub(Rational r, Rational y); } public class Rational { public int Numerator { get; set; } public int Denumerator { get; set; } } } 13




Add attributes ◦ [ServiceContract] to define the service contract ◦ [OperationContract] to specify the operations of the contract [ServiceContract] public interface ICalculatorService { [OperationContract] int Sum(int x, int y); [OperationContract] double Sqrt(int x); [OperationContract] Rational Sub(Rational x, Rational y); } 14

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Defines the mapping between .Net objects and data transferred in messages WCF provides an implicit mapping for all .Net primitive types ◦ string, int, double, int[] …




In custom types, fields that should be serialized have to be explicitly annotated ◦ also applies to properties [DataContract] public class Rational { [DataMember] public int Numerator { get; set; } [DataMember] public int Denumerator { get; set; } } 15




Add a new class implementing the ICalculatorService interface namespace CalculatorService { public class CalculatorService : ICalculatorService { public int Sum(int x, int y) { return x + y; } public double Sqrt(int x) { return Math.Sqrt(x); } public Rational Sub(Rational x, Rational y) { // implement substraction here } } }

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To use the CalculatorService, it needs to be hosted in a .Net-based application




Several options: ◦ custom service host in a console application ◦ using WCF Service Host application
provided by Visual Studio

◦ using IIS Web Server

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The ServiceHost class provides a direct control over the WCF hosting infrastructure ◦ should be instantiated based on a particular service using System.ServiceModel; namespace CalculatorService { class HostingProgram { static void Main(string[] args) { using (ServiceHost host = new ServiceHost( typeof(CalculatorService), new Uri("http://localhost:8080/Services"))) { …

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Each endpoint consists of an address, a binding and a contract Added to ServiceHost by calling AddServiceEnpoint method using (ServiceHost host = new ServiceHost( typeof(CalculatorService), new Uri("http://localhost:8080/Services"))) { // define the service endpoints host.AddServiceEndpoint(typeof(ICalculatorService), new BasicHttpBinding(), “CalculatorService"); host.AddServiceEndpoint(typeof(ICalculatorService), new NetTcpBinding(), "net.tcp://localhost:8082/Services/CalculatorService");

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The binding controls three aspects of message communication ◦ message encoding
XML, binary, …

◦ transport protocol
HTTP, TCP, MS Message Queuing

◦ suite of Web Services protocols
WS-Security, WS-ReliableMessaging, …


A given binding specifies one encoding, one transport and several WS protocols

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WCF provides a set of predefined bindings The most useful: ◦ BasicHttpBinding : XML encoding + HTTP transport + basic WS functionaliy
for interoperability

◦ WSHttpBinding: XML encoding + HTTP transport + advanced WS functionality
for both interoperability and security/reliability

◦ NetTcpBinding: binary encoding + TCP transport + advanced WS functionality
when both server and client use WCF for higher performance

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Hardcoding endpoint information into the host application is not ideal ◦ endpoint details may change over time




Much more flexible approach exists! ◦ application configuration file ◦ can be added to the project (if not there)

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replaces calls to AddServiceEnpoint

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Build the WCF runtime to support the service operation: host.Open();




Now the runtime is ready to receive messages at the addresses specified by each endpoint static void Main(string[] args) { using (ServiceHost host = new ServiceHost( typeof(CalculatorService), new Uri("http://localhost:8080/Services"))) { // define the service endpoints host.Open(); // keep the process alive Console.ReadLine(); } }

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http://localhost:8080 http://localhost:8080/Services 8080/Services

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Visual Studio provides a template for WCF service development ◦ includes interface, implementation and configuration files that have to be customized for the actual service

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When running the library from Visual Studio: ◦ WCF Service Host application is started
no need for a custom service host application

◦ WCF Test Client application is started
can be used for a quick service testing

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3 steps process: ◦ define and implement the interface ◦ configure the endpoints ◦ host the service




Prefer XML-based configuration over coding




Visual Studio provides a useful template to facilitate the development process

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Calculator service client side

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Create ServiceEndpoint instance representing the target endpoint ◦ specify the contact, binding and network address of the service ServiceEndpoint httpEndpoint = new ServiceEndpoint( ContractDescription.GetContract( typeof(ICalculatorService)), new BasicHttpBinding(), new EndpointAddress ("http://localhost:8080/Services/CalculatorService"));




We assume here that the client shares the same ICalculatorService interface 32

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Create a ChannelFactory based on the ServiceEndpoint Use ChannelFactory to create a service proxy Use the service proxy to invoke operations defined by the contract

// create channel factory based on HTTP endpoint using (ChannelFactory httpFactory = new ChannelFactory(httpEndpoint)) { // create channel proxy for endpoint ICalculatorService calc = httpFactory.CreateChannel(); // invoke service operation Console.WriteLine("1 + 2 = {0}", calc.Sum(1, 2); } 33




Similar configuration mechanism for specifying service endpoints at the client

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Use the name of the endpoint to create a ChannelFactory ◦ no need to create ServiceEndpoint

static void Main(string[] args) { // create channel factory based on HTTP endpoint using (ChannelFactory httpFactory = new ChannelFactory("httpEndpoint")) { // create channel proxy for endpoint ICalculatorService calc = httpFactory.CreateChannel(); // invoke service operation Console.WriteLine("1 + 2 = {0}", calc.Sum(1, 2)); } ...

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What if we want to access an external service? ◦ how do we get its interface? ◦ how do we know its endpoints? ◦ what if it is not implemented with the .Net Framework?




Use WSDL metadata provided by the service! ◦ use svcutil.exe tool to extract all the required information from WSDL
the tool can be found in MS SDK installation directory

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$ ./svcutil.exe http://localhost:8080/Services?wsdl Microsoft (R) Service Model Metadata Tool [Microsoft (R) Windows (R) Communication Foundation, Version 3.0.4506.648] Copyright (c) Microsoft Corporation. All rights reserved. Attempting to download metadata from 'http://localhost:8080/Services?wsdl' using WS-Metadata Exchange or DISCO. Generating files... c:\Program Files\Microsoft SDKs\Windows\v6.0A\bin\CalculatorService.cs c:\Program Files\Microsoft SDKs\Windows\v6.0A\bin\output.config

CalculatorService.cs contains an interface definition similar to the one used by the service output.config contains the endpoints configuration information





◦ merge its contents with the application configuration file 37




In addition to ICalculatorService declaration, the generated CalculatorService.cs contains also a proxy public partial class CalculatorServiceClient : System.ServiceModel.ClientBase, ICalculatorService




Can simplify the client code further ◦ instantiate the proxy with the name of the endpoint configuration and make method calls ◦ no ServiceEndpoint and ChannelFactory needed

using (CalculatorServiceClient proxy = new CalculatorServiceClient("NetTcpBinding_ICalculatorService")) { // invoke service operation Console.WriteLine("Invoking TCP endpoint: {0}", proxy.Sqrt(17)); }

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Two ways to define a proxy and configure service endpoints: ◦ manual access to the same interface used by the service + coded or XML-based endpoints configuration ◦ svcutil.exe tool to extract all the required information from WSDL provided by the service

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