Building a Web Service Client using C# and .NET by Gopalan Suresh Raj

Web Services and the .NET Framework
Building a Web Service Client using C# and .NET

Clients communicate with Web Services using standard web protocols, using XML-encoded messages to send and receive messages between themselves. This makes it possible for client applications running on any platform to access web services as long as they use standard web protocols, and understand the XML-encoded messages. There are three protocols that web clients can use to communicate with web services namely, HTTP GET, HTTP POST, and SOAP.

The various steps that are involved in creating a Web Service Client using C# and the .NET Framework are as follows:

The .NET SDK simplifies the process of creating Web Service clients by providing the Web Services Description Language (wsdl.exe) utility. This utility generates proxy source code for an existing Web Service, just as IDL compilers generate DCOM proxies for DCOM components. The only difference between IDL and WSDL is that, WSDL is a language that describes the interface of a software component that is XML-based.

Let us generate source code for the proxies to the actual web service as shown below:

The above command creates a proxy for the OIDServer web service from the WSDL document obtained from the URL http://localhost/OIDServer/OIDServer.asmx?WSDL. The proxy uses SOAP as its protocol to talk to the web service and is generated as a C# source file which is shown below for your perusal.

The wsdl.exe utility can also take a WSDL file as input instead of a URL pointing to the location where the WSDL can be obtained. This C# proxy source file represents the proxy class for the OIDServer web service that clients can compile against. If you examine the above class, you will notice that it contains an OIDServer proxy class that derives from the System.Web.Services.Protocols.SoapHttpClientProtocol class. If you use the /protocol:HttpGet or /protocol:HttpPost parameters, the OIDServer derives from either the System.Web.Services.Protocols.HttpGetClientProtocol class or the System.Web.Services.Protocols.HttpPostClientProtocol class.

We can compile the C# source file into a dynamic link library (DLL) and then add a reference to this DLL to any project you want to create. Compile the proxy class as a DLL as shown below:

Create a new Visual C# ASP.NET Web Service project. Create a Reference to the OIDServer.dll library.

On Line 40, we create an instance of the proxy to the web service OIDServer. Line 43 invokes the generateOID() web method to get a string as the result.

Client.cs

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//////////////////////////////////////////////////////
/// The following example illustrates a Client to a
/// WebService developed using C# and the .NET Framework.
///
/// author: Gopalan Suresh Raj
/// Copyright (c), 2002. All Rights Reserved.
/// URL: https://gsraj.tripod.com/
/// email: gopalan@gmx.net
///
/// <generate>
/// wsdl /l:CS /protocol:SOAP http://localhost/OIDServer/OIDServer.asmx?WSDL
/// wsdl /l:CS /protocol:HttpGet http://localhost/OIDServer/OIDServer.asmx?WSDL
/// wsdl /l:CS /protocol:HttpPost http://localhost/OIDServer/OIDServer.asmx?WSDL
/// </generate>
/// <compile>
/// csc /t:library /r:System.Web.Services.dll /r:System.Xml.dll OIDServer.cs
/// </compile>
/// <compile>
/// csc Client.cs /r:OIDServer.dll
/// </compile>
//////////////////////////////////////////////////////
using System;

namespace TestOIDServer {
  /// <summary>
  /// Summary description for Client.
  /// </summary>
  public class Client {
    /// <summary>
    /// Default No argument constructor
    /// </summary>
    public Client() {
    }

    /// <summary>
    /// Entry Point to this Application
    /// </summary>
    public static void Main () {
      // Create a proxy
      OIDServer server = new OIDServer();

      // Invoke generateOID() over SOAP and get the new OID
      string oid = server.generateOID ();

      // Print out the value
      Console.WriteLine ("The new OID is :"+oid);
    }
  }
}

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