Web Services with .Net

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Web Services with .Net

• Presented by
• Paul Turner
• pturner_at_eds.com

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Overview

• What is a Web Service
• Web Service Design Principals
• Exploring the Façade pattern
• Creating a Web Service
• Attributes
• Returning simple and complex objects
• Soap Headers and Extensions
• Consuming a Web Service
• IAsyncResult
• Security
• Deploying Web Services

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What is a Web Service

• Hype, mainly generated by marketing people

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What is a Web Service Really!!

• The execution of code on a remote machine
• The idea has been around for a long time!!!
• Remote Procedure Call (RPC)
• Distributed Component Object Model (DCOM)
• Enterprise Java Bean (EJB)
• WinSock (create your own protocol)

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What is a Web Service cont

• XML is the primary means of communication, called
  SOAP
• Usually over port 80 (HTTP), but can use any TCP
  port
• Serializes all method calls into SOAP
• Returns serialized objects in a SOAP format

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What is a Web Service cont

• Pros
• Portable across platforms
• IBM, Microsoft, BEA, Sun and the WC3 support it
• Cons
• Slower than most traditional RPC methods because
  SOAP is VERY longwinded
• Still immature and undergoing change (BE WARNED)

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Web Service Design Principals

• Different to most popular RPC
• Everything is SingleCall
• Not Object Orientated (OO)
• Stateless
• No properties (you can butdont)
• Limited OO, the more OO the slower it will be
• One common pattern is the Façade

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Exploring the Façade pattern

• Think of an a Car steering wheel
• Hides complexity behind a well defined interface
• Ideal for Web Services

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Creating a Web Service

• Create a new ASP.Net Web Service project
• You get an .asmx and an .asmx.cs
• using System.Web.Services
• Derive your class from WebService
• Add methods to your class and mark them with
  WebMethod()

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Creating a Web Service

• DEMO
• basicws.asmx

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WebService Attribuites

• Description Provides a nice description
• Name Used for Aliasing
• Namespace Effects the WSDL output
• Defaults to http//tempuri.org/
• You should change this when developing your
  WebService and DEFINITELY before deploying it

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WebMethod Attribuites

• Description Provides a nice description
• MessageName Used for Aliasing methods with
  same name but different signatures
• BufferResponse Speeds up responses
• CacheDuration Less load on resources
• TransactionOption Enterprise transactions
• EnableSession Allow you to read the IIS Session
  object from the Web Service

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WebMethod Attributes

• DEMO
• Basicws.asmx

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Returning Simple Types

• Simple to return simple types
• WebMethod()
• public int DoSomething() return 1
• Returns a simple Xml response
• lt?xml version"1.0" encoding"utf-8" ?gt
• ltint xmlns"http//tempuri.org/"gt1lt/intgt

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Sidebar

• Compatibility
• using System.Web.Services.Protocols
• SoapRpcMethod()
• WebMethod()
• public int DoSomething() return 1
• Returns a different style of Xml

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Simple Types and SoapRpcMethod

• DEMO
• Basicws.asmx

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Returning Simple Objects

• Same as simple types
• Properties
• Need to be read/write
• Constructors
• Need to have constructor with NO parameters
• Methods cannot be serialized

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Returning Complex Objects

• using System.Web.Services.Protocols
• To return a proxy of a custom type
• XmlIncude(type)
• To customise the Body
• XmlAttribute()
• XmlElement(elementname)

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Returning Simple and Complex objects

• DEMO
• Complex.asmx

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Soap Headers

• Allows you to pass extra information/class to
  WebMethods
• using System.Web.Services.Protocols
• Derive a class from SoapHeader
• Create a public object of the class you want to
  pass within the WebService

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Soap Headers

• Add the SoapHeader(ClassInstance) attribute
  to the WebMethod
• Create an instance of the class
• Set the InstanceClassValue property of the
  WebService
• Call the WebMethod and get a handle on the
  SoapHeader

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Soap Headers

• DEMO
• Headers.asmx

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Soap Extensions

• Allows you to inspect Soap and different stages
• You can modify the Soap
• Encryption
• Compression
• Logging
• Derive from SoapExtension
• Use ChainStream to get a writable stream
• Use SoapMessageStage in the ProcessMessage method
  to process the message
• Implement the other required methods

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Soap Extensions

• ProcessMessage has several SoapMessageStages
• BeforeSerialize intercept before serialized
• BeforeDeserialize intercept messages before
  they are deserialized
• AfterSerialize intercept messages after they
  are serialized
• AfterDeserialize intercept before processed

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Soap Extension

• DEMO

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Consuming Web Services

• Add Web Reference to your project
• ASP.Net, Windows Forms, Console, Windows Service,
  COM
• Any .NET project
• Using WSDL.exe
• Wsdl /outproxyclassfilename.cs mywsdlfile.wsdl
• Add generated proxy file to project then call
  methods
• Creating Proxy objects

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Consuming Web Services

• Call WebMethods just like ordinary methods
• Update Web References when you add new stuff
• Regenerate proxy with WSDL.exe when you add new
  stuff, re-add the proxy class file

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Consuming and WSDL

• DEMO

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IAsyncResult (Callback method)

• Create an AsyncCallback
• Create a method that takes an IAsyncResult
  parameter
• Call the Begin method and pass in any
  parameters, the AsyncCallback and the proxy

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IAsyncResult (WaitOne method)

• Call the Begin method and pass in any
  parameters, null as the Callback and null as the
  proxy
• Call WaitOne until IsCompleted is true

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Async Calls

• DEMO

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Security

• Often security is an afterthought
• It IS IMPORTANT !!
• Credentials are NOT passed to WebServices even
  when you use impersonation
• Web.Config file is STILL important to WebServices
• You must Enable it

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Security

• Credentials (Point-To-Point)
• Set the Credentials property
• You can also create credentials at run-time
• Based on Windows accounts
• Tickets (Application)
• Needs to be passed with every method call
• Custom, roll your own
• Soap Header based

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Security

• WS-Security (End-To-End)
• Emerging standard
• Can use Custom, Binary, Kerberos Tokens
• X.509 digital certificates
• Soap Header based
• Need WS Enhancements V1.0 (V2.0 in preview)
• Soap Extensions
• Can provide some basic message level encryption

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Security

• Passing Credentials
• Proxy.Credentials System.Net.CredentialCache.Def
  aultCredentials
• You can also create your own credentials and
  attach them to the request
• Watch out for WS-Security. things are changing

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Security

• DEMO

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Deployment

• When you Add a Web Reference the URL property
  is HARD CODED
• WSDL contains the URL from the site it was
  generated
• To the rescue
• the proxy has a URL property that you can set to
  point to the WebService
• You can implement Load Balancing
• Remember the MSI
• Create Web Setup projects to deploy your
  WebService

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Deployment

• DEMO

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Summary

• Beware of the HYPE!!
• Remember to design differently
• Use Attributes to customise your Xml
• As a minimum, set the Description and the
  Namespace
• Think (consider) Async
• Be secure!!
• Use the deployment tools you have in the box

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References

• Patterns and Practices
• Building Secure ASP.NET Applications
  Authentication, Authorization, and Secure
  Communication
• MSDN
• Search for Web Services
• MCAD/MCSD Self Paced Training
• Developing XML Web Services and Server Components
  with Visual Basic.NET and Visual C.NET,
  Microsoft Press