How To Write Pluggable Protocol to Support FTP in Managed Classes by Using Visual C# .NET

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For a Microsoft Visual Basic .NET version of this article, see 812404 (http://support.microsoft.com/kb/812404/EN-US/ ) .

SUMMARY

This step-by-step article describes how to write pluggable protocol by using classes from the System.Net namespace.

Microsoft .NET Framework provides a layered, extensible, and managed implementation of Internet services that can be integrated quickly and easily into your applications. The internet application that uses the request-response model can request data from the Internet in a protocol-agnostic manner.

The .NET Framework uses specific classes to provide the three pieces of information that are required to access Internet resources through a request-response model: the URI class, the WebResponse class, and the WebRequest class.

This article details how to use System.Net to write a pluggable protocol to support FTP in managed classes. Pluggable protocols can communicate in both synchronous and asynchronous modes. However, this article discusses only synchronous FTP communication. Asynchronous FTP is out of the scope of this article.

The following file is available for download from the Microsoft Download Center:

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Download the FtpClient.exe package now. (http://download.microsoft.com/download/3/c/f/3cf0a7eb-d99f-4fee-bec3-cb1bf48afa81/ftpclient.exe)

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 (http://support.microsoft.com/kb/119591/ ) How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

Note This sample will not work with CERN proxies. For additional information about CERN proxies, click the following article number 166961 to view the article 166961 in the Microsoft Knowledge Base:

166961 (http://support.microsoft.com/kb/166961/ ) How To FTP with CERN-Based Proxy Using WinInet API

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Create the FtpWebResponse and FtpWebRequest Classes

The WebRequest and WebResponse classes are the basis of pluggable protocols. The descendant classes of WebRequest are registered with the WebRequest class to manage the details of making the actual connections to Internet resources.

In the earlier example of FtpClient, the FtpWebResponse class inherits from the WebResponse class. You have to override ContentType and GetResponseStream methods. The ContentType property provides special information that the client requires to identify the type of content that is delivered by the server. The GetResponseStream method returns a data stream from the internet resource.

In the earlier example, the FtpStream class is used to handle the data stream that is delivered to the server together with the request. The following sample code describes how this is done:

	public class FtpWebResponse : WebResponse
	{
		public override String ContentType 
		{
			get	{/* override */} 
			set { /* override */ }
		}
		public override Stream GetResponseStream()
		{
			/* override */
		}	
	}

Similarly, using WebRequest you can manage the details of a request to an Internet resource. The sample uses the FtpWebRequest class that inherits from the WebRequest class. The WebRequest.Create method creates FTP WebRequest instance based on the URI that is passed. The instance that is returned is a typecast to the FtpWebRequest class to access protocol-specific properties. In most cases, the WebRequest instance provides all the necessary information to formulate a request.

The following example demonstrates the methods that are implemented or overridden in FtpWebRequest class. For more information and implementation, visit the Download Center for the FtpClient.exe file that is mentioned earlier in this article.

	public class FtpWebRequest : WebRequest
	{
		public override String Method
		{/* override */ }
	
		public override ICredentials Credentials 
		{
			/* override */  get {}
			/* override */ set {}
		}

		public override string ConnectionGroupName 
		{
			/* override */ get {}
			/* override */ set {}
		}

		public  override long ContentLength 
		{
			/* override */ get {}
			/* override */ set {}
		}

		public  override string ContentType 
		{
			/* override */ get {}
			/* override */ set {}
		}
		public override IWebProxy Proxy 
		{
			/* override */ get {}
			/* override */ set {}
		}
     
		public override Stream GetRequestStream()
		{/*override*/}
	
		public override WebResponse GetResponse() 
		{/*override*/}
	}

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Create FtpClient

The FtpClient application accesses the information from the Internet using a request-response model. You can retrieve protocol-specific information by using the WebRequest and WebResponse classes. To retrieve protocol-specific information, register the descendants of WebRequest by using the WebRequest.RegisterPrefix static method. The IWebRequestCreate interface defines the method that WebRequest descendants will use to register with the WebRequest.Create method.

The following sample code demonstrates how to use IWebRequestCreate:

public class FtpRequestCreator : IWebRequestCreate
{
    public FtpRequestCreator()
    {
    }
    
    public WebRequest Create(Uri  Url)

    {
        return new FtpWebRequest(Url);
    }
}

The following sample code demonstrates how the RegisterPrefix method is used and how to create a WebRequest instance:

		// FtpRequestCreator class implements IWebRequestCreate class, which implement Create method
 FtpRequestCreator Creator = new FtpRequestCreator();
	WebRequest.RegisterPrefix("ftp:", Creator);

	String szUri= new String("ftp://localhost");

	// Create WebRequest
	WebRequest w = WebRequest.Create(szUri);

The WebRequest.RegisterPrefix method registers the class and notifies the descendants to use FTP protocol for retrieving the data. After registration, descendants of WebRequest are created by using the WebRequest.Create method with an argument passed as URI. The WebRequest instance exposes properties, such as GetResponse, that control the request to the server and access to the data stream that is sent to the server. The GetResponse method of the WebRequest instance sends the request from the client application to the server that is identified in the URI.

	WebResponse r = w.GetResponse();
	Stream respstream = r.GetResponseStream();
	if(respstream.CanRead) 
	{
		StreamReader rdr = new StreamReader(respstream);
		String resp = rdr.ReadToEnd();
		rdr.Close();
		Console.WriteLine(resp);		
	}

The GetResponse method returns a WebResponse instance. The WebResponse provides access to the data that is returned by the server in the form of a stream returned by the GetResponseStream method. This stream can be used and modified in an application. You can derive a class from the stream class and override the method, based on application requirements.

For more information, visit the Download Center for the FtpClient.exe file that is mentioned earlier in this article.

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Steps to Run the FtpClient Executable

Download the FtpClient.exe file that is mentioned earlier in this article.
Extract the file.
Open the Readme.htm file in the browser.
To read the steps to build the application, click Building the sample.
To read the steps to run the application, click Running the sample.

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REFERENCES

For more information, see the Microsoft .NET Framework SDK documentation or visit the following MSDN Web site:

Programming Pluggable Protocols
http://msdn.microsoft.com/en-us/library/1f6c88af(vs.71).aspx (http://msdn.microsoft.com/en-us/library/1f6c88af(vs.71).aspx)

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