Web Services

This introduces basic concepts of web services.

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What are Web Services?

Web services are self-contained and self-describing application functionalities that can be processed through open internet standards.

By offering data that can be consumed without human interaction, web services ...

• act like a block box that may require input and deliver a result.
• work on top of any communication technology stack (TCP).
• can be published, discovered, and invoked base on open technology standards
• work in asynchrounous as well as traditional synchronous scenarios
• facilitate integration within an enterprise as well as across enterprises.

Categories of Web Services

Public web services are exposed by Google, Amazon, Yahoo weather, Microsoft UDDI, and Microsoft Exchange Server 2007 SP2+.

To build web services, two major vendors provide tools and frameworks. IBM's WebSphere product line and Microsoft's .NET framework. This page contrasts these approaches, beginning with Microsoft's approach.

• Creating and Consuming .NET Web Services in 5 Easy Steps by SitePoint
• Using ASP.NET Web Services

Microsoft Web Communication Foundations

With .NET 3.0, Microsoft introduced WCF (Web Communication Foundations) so that web services can be transported not just in HTTP, but other encodings, transports, and security mechanisms. These three concepts define a binding.

1. Basic (HTTP over TCP/IP)
2. TCP
3. Peer networking
4. IPC
5. Web Service (WS)
6. Federated WS
7. Duplex WS
8. MSMQ
9. MSMQ integration

Behind each endpoint address is its binding and contracts:

1. Service contracts describe what operations clients can perform
2. Operation contracts define methods inside Interface of Service
3. Data contracts define what data types are passed.
4. Message contracts define whether a service can interact directly with messages

Microsoft provides a wcfTestClient.exe command-line tool to specify input parameters.

Microsoft .NET Web Service Proxy Architecture

A client.aspx web page contains calculations made by the web service and accesses the listener.asmx request handler file created as a C# or VB.NET language "ASP.NET Web Service Application" project in Visual Studio.

The .asmx file references methods whose structure is defined in a web service proxy.dll library file running in a Virtual Directory within a IIS (Internet Information Service) service (named localhost by default) built into Windows Server. As a binary file, the .dll file is stored in physical folder C:\inetpub\wwwroot\bin so they are picked up automatically by ASP.NET.

A Proxy is a stand-in for the real subject at compile time. A proxy has *the same interface* as the original object. A Remote Proxy provides a reference to an object residing in a separate address space, e.g. EJB, RMI, CORBA, etc. RMI stubs acts as a proxy for the skeleton objects. (By contrast, a facade *changes* the interface - generally to make it more coarse grained.)

SOAP Request Message Structure

The proxy .dll resolves methods defined in an XML file containing WSDL (Web Service Description Language) that describe how to access web services. The code for it is automatically created by the wsdl.exe program that is part of Microsoft's .NET framework 3.5 SDK (in folder C:\Program Files\Microsoft SDKs\Windows\v6.1\Bin) (or \v6.0A for .NET 2.0).

WSDL (Web Services Description Language)

WSDL (Web Services Description Language) are XML files containing descriptions of the methods available.

They are contract between a server and its clients.

Amazon's S3 WSDL http://s3.amazonaws.com/doc/2006-03-01/AmazonS3.wsdl references .xsd file.

Specify this WSDL URL address to a project created in Visual Studio Solution Explorer: right click References, select Add Service Reference, "AmazonS3?" should show in the Services box. Enter a namespace (such as "Amazon.S3").

client.aspx

This sample C# web service client code to invoke the Microsoft's UDDI service returns HTML which begins with this:

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope
    xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <soap:Body>
    <businessList generic="1.0" operator="ms.com" truncated="false" 
	     xmlns="urn:uddi-org:api">
      <businessInfos>
        <businessInfo businessKey="c13cc7b2-642d-41d0-b2dd-7bb531a18997">
          <name>Microsoft DRMS Dev</name>
          <serviceInfos>
            <serviceInfo serviceKey="6166f8b2-436d-4001-9f68-f37ff8b47ea3"
                businessKey="c13cc7b2-642d-41d0-b2dd-7bb531a18997">
              <name>Certification</name>
...
            </serviceInfo>
          </serviceInfos>
        </businessInfo>
      </businessInfos>
    </businessList>
  </soap:Body>
</soap:Envelope>

Only text between <name> tags appear in the web browser.

Commands in the Page_Load function are performed upon invocation.

In Visual Studio, click on "Add Web Reference" to specify the URL and Name of the WebService.

Setting the WebServiceBinding attribute's ConformsTo property to WsiProfiles.BasicProfile1_1 instructs Visual Studio to generate WSDL and ASMX files and other "behind-the-scenes" work, in accordance with the Basic Profile 1.1 (BP 1.1) best practices developed by the Web Services Interoperability Organization (WS-I), a group dedicated to promoting interoperability among Web services developed on different platforms with different programming languages.

By default, each new Web service class created in Visual Studio inherits from class System.Web.Services.WebService.

Yahoo weather XML feed.

WSDL Program

C:\>wsdl /language:C# /out:MyProxyClass.cs  http://localhost/ASP.NET/MyWebService.asmx

/protocol:SOAP specifies the payload protocol to be used (SOAP, HttpGet, HttpPost).

/namespace:mynamespace specifies the namespace of the generated Proxy class.

ASP.NET automatically creates WSDL and SOAP documents from .asmx code such as this VB.NET sample:

<%@ WebService Language="VBScript" Class="TempConvert" %>
Imports System
Imports System.Web.Services
Public Class TempConvert :Inherits WebService

	<WebMethod()> Public Function FahrenheitToCelsius
		(ByVal Fahrenheit As String) As String
		dim fahr
		fahr=trim(replace(Fahrenheit,",","."))
		if fahr="" or IsNumeric(fahr)=false then return "Error"
		return ((((fahr) - 32) / 9) * 5)
	end function

	<WebMethod()> Public Function CelsiusToFahrenheit
		(ByVal Celsius As String) As String
		dim cel
		cel=trim(replace(Celsius,",","."))
		if cel="" or IsNumeric(cel)=false then return "Error"
		return ((((cel) * 9) / 5) + 32)
	end function

end class 'TempConvert

SOAP Headers

[SoapHeader("timeStamp", Direction=SoapHeaderDirection.InOut)]

C# code such as this sample and this sample:

<%@ WebService language="C#" class="TempConvert" %>
using System;
using System.Web.Services;
using System.Xml.Serialization;

[WebService(Namespace="http://localhost/MyWebServices/")]
public class FirstService : WebService
{
      [WebMethod(Description="Add integers")]
      public int Add(int a, int b)
      {
          return a + b;
      }

      [WebMethod(Description="Say Hello")]
      public String SayHello()
      {
          return "Hello World";
      }
}

In order for a client to access a Web method, it must be marked with [WebMethod] or [WebMethod()] compiler declarative attribute No method with this WebMethod attribute can be declared static because an instance of that Web service must exist for access by clients.

Web Service Consuming Amazon Web Service

This and this C# client code issues SOAP to the Amazon S3 web service. This creates a object defined in the library specified by a using statement.

using System;
using System.IO; // for Console.WriteLine()
using Amazon.com.amazon.soap;

namespace SvcConsumer{
class SvcEater{
    public static void Main(String[] args){ // for console program.
        
		KeywordRequest kr = new KeywordRequest();
		kr.devtag=getAmazonToken();
		kr.keyword=this.txtSearch.Text;
		kr.mode="books";
		kr.sort="+titlerank";
		kr.tag="webservices-20";
		kr.type="lite";
		
		kr.page="1";
		
			ProductInfo pi = srch.KeywordSearchRequest(kr);
			Details[] allDetails = pi.Details;

			// showAmazonResult();
		
		// Did the request fail?
		
		if (pi.TotalResults > 10){ // get the second page of results
			kr.page="2";
		}
			ProductInfo pi = srch.KeywordSearchRequest(kr);
			Details[] allDetails = pi.Details;

	} // Main
} // class SvcEater

getAmazonToken(){
	return "1234567890";
}

showAmazonResult(){
// Replace this code with application event coding:
	//    Console.WriteLine("Calling Hello World Service: " +
	//                        mySvc.SayHello());
	//    Console.WriteLine("Calling Add(2, 3) Service: " +
	//                        mySvc.Add(2, 3).ToString());
}

} // SvcConsumer

Before invoking, change the number in function getAmazonToken() with what Amazona provided.

For this application to parse XML content using XMLHTTP and DOM COM object xmlObj.loadXML(), the client machine is dependent on Microsoft XML Parser 3.0 being already installed.

This sample SOAP client can also include SOAP Headers with Extensions shows a solution that passes authentication information out-of-band (that is, outside the Web methods' parameter lists) and that "front-ends" each method call with an authentication module that operates independently of the Web methods themselves.

UDDI WSDL Discovery

Microsoft provides a utility to discover

disco http://localhost:33973/Service1.asmx?DISCO

If the .asmx file does not contain a namespace specification, Microsoft automatically defaults to the http://tempuri.org/ namespace.

Microsoft's UDDI Services (Universal Description, Discovery and Integration) Business Registry (UBR).

Calling Google Web Service

Visual Studio.NET Default Web Service

Within Visual Studio 2008, create a new C# or VB.NET language project (solution) "ASP.NET Web Service Application" with default name WebService1 in default location C:\Users\W\Documents\Visual Studio 2008\Projects.

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;

namespace WebService1
{
    /// 

    /// Summary description for Service1
    /// 
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class Service1 : System.Web.Services.WebService
    {
        [WebMethod]
        public string HelloWorld()
        {
            return "Hello World";
        }
    }
}

This sample web service has a "HelloWorld" operation using the default namespace at http://tempuri.org/.

Press F5 to run it in a Development Server such as at http://localhost:33973/Service1.asmx.

The HelloWorld operation is invoked upon page load by a client running IE and specifying the Service1.aspx file.

<%@ import Namespace = "NameSp" %>
<script language = "c#" runat = "server">
public void Page_Load(object o, EventArgs e){
	int x = 10;
	int y = 5;
	int sum;

	AddNumbers AN = new AddNumbers();
	sum = AN.Add(x,y);
	string str = sum.ToString();
	response.writeline(str);
}
</script>

Proxy Generation from Assembly

Either way, the proxy assembly is compiled into a .dll file using cs.exe.

C:\>CSC  /t:library  /out:bin/MyWebServiceImpl.dll  MyWebServiceImpl.cs 

Add /optimize to produce a smaller, faster, and more efficient dll.

IIS Web Service Publishing

To publish a Web Service, configure IIS running on a local machine.

1. Open Internet Information Services (IIS) Manager from Start > Settings > Control Panel > Administrative Tools
2. Expand Sites and right-click on [Default Web Site]
3. Select Add (New) > Virtual Directory
4. The Virtual Directory Creation Wizard opens. Click Next.
5. The "Virtual Directory Alias" screen opens. Type the virtual directory name [MyWebServices] Click Next.
6. The "Web Site Content Directory" screen opens. Enter the directory path name for the virtual directory. Click Next.
7. The "Access Permission" screen opens. Change the settings as per your requirements. Click Next. Click Finish to complete the configuration.

Ths sample creates a .NET Webservice in C# that screen scrapes the Microsoft Search Site for any search term. The results are parsed into a SOAP return call containing all the URLs and associated link titles for display.

Good ole SOAP

Application Concept	Web Standard	Programs
Data	XML Universal data format	Objects
Schema	XSD Universal type system	Classes
Directory	UDDI Directory of Services
Listing	DISCO Service discovery
Services	WSDL Service descriptions	Methods
Services Invocation	SOAP	Calls
Services Invocation	REST	Calls

• Visual Studio SOAP toolkit for Microsoft Windows® 2000 (not Win 9x) can be download from
  • Versions:
    • Version 1 released July 2000 interoperates with Visual Studio.NET Beta 1 uses older Service Description Language (SDL) and scalar atomic data types using UTF-8 encoding based on Windows code page 1252.
    • Version 2 Beta 1 released January 2, 2001 based on SOAP Specification version 1.1, adds support for new Web Services Description Language (WSDL) 1.0 contracts to define the SOAP messages and service call formats; Universal Description, Discovery and Integration (UDDI), and the Version 2.0 will pass strings to BSTR parameters encoded as UTF-16.
    • The final release of SOAP Toolkit version 2.0 will be fully supported by Microsoft product support.
  • This requires Visual Studio SP 4.
  • The Listener provided is ASP, not ISAPI.
  • MSXML Parser 3.0 is included in the SOAP toolkit.
• All this work done by developers will be hadled automatically by Microsoft's Visual Studio.NET which was distributed as Beta 1 on January 2001.

  Although VisualBasic.NET (also known as Visual Basic 7.0) features new Web Forms which are HTML pages with Visual Basic events (such as native support for accessibility). Microsoft recommends using it for business objects and use ASP.NET, an enhanced version of ASP, which uses Web Forms for interfacing with Web Services hosted by ASP.NET, which targets disconnected data. The Mobile Internet Toolkit is part of ASP.NET.

  The NET Framework SDK TDG (Tool Developer Guide) is included in the ASP.NET CD to manipulate new & old registry classes.

Chris Dengler's July 2000 SDL wrapper code to returing ADO Recordtypes and arrays with SOAP messaging.

Understanding SOAP: The Authoritative Solution by Kennard Scribner

Client ROPE Proxy

A ROPE proxy serves a similiar function as WinSock, through which client software issue and receive communications to web services on a web server.

If a SOAP client is on a different computer than the SOAP server, you will need to copy ROPE.dll from the Visual Studio SOAP Toolkit and register it on the client computer (tunning command regsvr32 rope.dll).

The ROPE Proxy uses methods in COM objects written to SOAP standard which defines the "handshaking" between client and server.

A client first sends a Services Description method ROPE.SDMethodInfo and other methods to discover what web services a particular server provides

The ROPE.SoapPackager object creates a SOAP envelope and calls

It then calls ROPE.WireTransfer to execute HTTP GET and POST requests by calling methods AddStdSOAPHeaders and PostDataToURI using parameters DataSent and DataReceived.

Web Serices Discovery

methods in the ROPE.SDServiceDescriptors collection: <> ROPE.SDEndPointInfo describes the URI location of web services.

ROPE.SDMethodInfo provides information about methods exposed by a Web Service.

ROPE.SDParameterInfo then provides requirements for calling those methods.

SDL = Service Description Language

Here is a sample request.

<SERVICE>
   <ADDRESSES>
   <ADDRESS URL='http://x.com/soap/Products.asp'>
   <IMPLEMENTS name='Products/'>
</SERVICE>

The SDL wizard can generate this.

ASP

XML references COM methods.

<%@ language=VB Script %>
<%Option Explicit

ADO

<element name='GetProductsResponse'>
 <type>
  <element name='ProductStruct'/>
  <element name='ProductID' type='dt:string'/>
  <element name='ProductName' type='dt:string'/>
 </type>
<element>

For XML Schema

WS (Web Services) Stack

Microsoft's WSE (Web Services Enhancements) v2.0 download has been available since 6/2004. Installing for "VS Developer" provides additional configuration help.

A lot of behavior is defined in the config.xml.

Custom code obtains a reference to RequestSoapContext and/or ResponseSoapContext

BooK: Understaing Web Services Specifications in the WSE pub. by Microsoft Press by Genine galey