Adarsh's blog : Net class library

Communicator Web Access AJAX Service SDK Released!!

adarshk — Fri, 07 Apr 2006 03:20:00 GMT

If you are looking for adding cool instant messaging and presence functionality to your web applications or simple C# applications, try out Communicator Web Access AJAX Service SDK, it already includes the sample code to get started. I will also keep posting quick code snippets here.

Quick Info from the SDK:

Communicator Web Access AJAX Service is the application programming interface for Microsoft Office Communicator Web Access. Application developers can use it to create Communicator-compatible clients that allow users to manage and share presence information, to manage contacts and groups, to send and receive instant messages, and to search for users within an enterprise. Such clients can be a browser-based Web application (e.g., an ASP or ASP.NET application) or a standalone network application (e.g., a .NET executable). The client applications can be written in a wide range of programming languages including JavaScript, C#, Perl, C/C++, and the Visual Basic development system. Because the Communicator Web Access AJAX Service is based on the flexible AJAX programming model, the client applications are not limited to running on Microsoft Windows operating systems and can readily be deployed to desktop, laptop, or other devices.

Download Link:

http://www.microsoft.com/downloads/details.aspx?familyid=A839967B-680F-41E6-99B4-F020319BBD88&displaylang=en

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You need to be careful about using event handler for NetworkChange

adarshk — Wed, 30 Nov 2005 05:14:00 GMT

Actually the issue I am discussing here is in general true for any event handler. .net event handler are strong reference. In case of NetworkChange it become more important because both event handler on NetworkChange object are static handlers, so there life time is the lifetime of the process.

For example you may be using code like below for registering an instace method of your object as handler

NetworkAvailabilityChangedEventHandler myHandler = new NetworkAvailabilityChangedEventHandler (myNetworkAvailabilityChangeHandler);
NetworkChange.NetworkAvailabilityChanged += myHandler;

Then you should make sure to unregister event handler once you are done with this object, otherwise your object is not garbage and you will see a memory leak effect on your application

NetworkChange.NetworkAvailabilityChanged -= myHandler

Please note this cleanup code can not be put in finalizer (becuase object is not yet garbage), you need to explicitly call it.

Another option is to go with some sort of weak delegate. .net frameworks still do not have any concept of Weak delegates, but there are some cool solutions developed for simulating weakreference semantics, which will be very useful in this situation. These solution mainly consider using a proxy object standing between your object and final object where you want to register events. Check the Greg's blog Simulating “Weak Delegates” in the CLR for nice explanation and pictorial representation..

There are also some other slight improvement versions of same solution

Simulating Weak Delegates for EventHandler-like Delegates (Ian Grifiths)

Weak Events (Xavier Musy)

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Use object pooling of byte arrays to prevent heap fragmentation in socket applications

adarshk — Sat, 20 Aug 2005 15:25:00 GMT

When you are worrking on managed socket application and your application is very extensively doing send/recieve on the socket, then probably you need to care about understanding the heap management. Socket.Recieve or Socket.Send finally need to call the underlying native winsock API call to recieve the data on user specified buffer. Same is true for NetworkStream.Read and NetworkStream.Write calls, because these methods also finally got translated socket send and recieve.

To make the native API call buffer need to pinned for I/O, these pinned buffer can not be moved when garbage collector is doing the work of cleaning up. If your application is using newly allocated buffer in slow network environment and application is doing multiple I/O call frequently then it is possible that you will hit the problem of heap fragmentation. If fragmentation is small, you probably do not need to worry about it, but if heap fragmentation is reaching more than 10% and you are seeing larger time spend on GC. You need to look into some better techniques to elliminate the unnecessary pressure on GC. One possible solution is create a pool of buffer in the startup and use object pooiling to reuse them as needed.

Check the maoni's blog entry Using GC Efficiently – Part 3 to understand more about pinning and effective usage of GC and other good tips.

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WebException message vs. Response.StatusDescription on FtpWebRequest

adarshk — Wed, 04 May 2005 09:38:00 GMT

Recently one of the reader asked an interesting question, he was using FtpWebRequest with MakeDirectory method, if directory already exist then application received the WebException with message."The remote server returned an error: (550) File unavailable (e.g., file not found, no access).". This exception message appears to be very generic and not helping the user to figure out what causes this request to fail. The reason is exception messages are generally set by framework implementation, because they also need to be localized on different language versions.

In such case if FtpWebRequest user want to diagnose and figure out why request actually failed, he could access the actual response message from server using ((FtpWebResponse)e.Response).StatusDescription property. Your actual code would look like as below

try
{
   . . . . . . . .
   WebResponse response = request.GetResponse();
. . . . . . . . . .
}
catch(WebException e)
{
        String status = ((FtpWebResponse)e.Response).StatusDescription;
}

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Using FtpWebRequest to do FTP over SSL

adarshk — Fri, 22 Apr 2005 23:27:00 GMT

Last few weeks we were busy to get Whidbey Beta-2 bits ready for release.

If you are looking for some API where your application could talk to a FTP server, which supports SSL. FtpWebRequest under System.Net namespace is your solution. Here I will just point to SSL specific features of the class

Enabling FtpWebrequest to use Ssl is pretty simple, you just need to set EnableSsl flag before calling GetResponse() or GetRequestStream() on the FtpWebRequest object.

FtpWebRequest request = WebRequest.Create(ftp://myftpserver/dir/filename);
request.Method = WebRequestMethods.Ftp.DownloadFile;
request.EnableSsl = true; // Here you enabled request to use ssl instead of clear text
WebResponse response = request.GetResponse();

Some people asked me why FtpWebRequest support "ftps:" protocol based uri similar to "https:", the reason is there is no standard "ftps" scheme specified (yet) and ftp-over-ssl mechanism actually does not demand dedicated port for ssl, you could do it on the same server port on which you are doing regular clear text ftp. It depends on server configuration choice to force the SSL or allow both.

Once you start doing Ftp over SSL there are two important things you will need to know

Validating Server Certificate

If you were old WebRequest user, you might already know about using ServicePointManager.CertificatePolicy for https server certificate validation. In whidbey you will notice the compiler warning saying ServicePointManager.CertificatePolicy is obsolete and replaced with ServicePointManager.ServerCertificateValidationCallback which is delegate of type RemoteCertificateValidationDelegate. New delegate provide better programming model with all certificate errors reported in a single callback and you will also get instance of X509Chain object, which allow you to make decision on certificate chain.

ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(myCertificateValidation);

Actual method will look as below
  public bool myCertificateValidation(Object sender,
      X509Certificate cert,
      X509Chain chain,
      SslPolicyErrors Errors)
{ return (certificate.GetName() == "my_trusted_name"); }; //Just an example, not real world scenaio

:) Another additional advantage you can take with delegate is from anonymous method support of C# 2.0, especially if you have very simple 1-2 line certificateplicy to implement, see follwing example.

ServicePointManager.ServerCertificateValidationCallback = delegate(Object obj, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
{ return (certificate.GetName() == "my_trusted_name"); }; //Just an example, not real world scenaio

Using Client Certificate

Using Client certificate based authentication when connecting to FTP-SSL is no different then existing HttpWebRequest. You just need to assign appropriate X509Certificate instance to the request object before making GetResponse() or GetRequestStream() call.

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Use NetworkInformation classes to get the list of listening ports on your machine

adarshk — Mon, 14 Mar 2005 19:01:00 GMT

.Net frameworks 2.0 have new addition of Namespace, System.Net.NetworkInformation, it provide a number of interesting classes to extract the network related statistics and state of the machine, it pretty much provide most of the functionality which is exposed by native IPHelper APIs.

Earlier I had shown a simple example for getting network availbility event notification. Here is another simple 4 line example, where your application could check all the listening ports on the machine.

using System;
using System.Net;
using System.Net.NetworkInformation;
public class Test
{
      public static void Main()
      {
            IPGlobalProperties ipGlobal = IPGlobalProperties.GetIPGlobalProperties();
            IPEndPoint[] connections = ipGlobal.GetActiveTcpListeners ( ) ;
            foreach(IPEndPoint ipe in connections)
           Console.WriteLine("Listening IPEndPoint = "+ipe.Port);
      }

}

Client side certificate with strong key protection and WebServices

adarshk — Thu, 17 Feb 2005 21:46:00 GMT

When you are writing application to run as service or middle tier, which is using client certificates. You should not enable strong key protection during certificate installation.

Strong key protection is the way you are informing the system that whenever someone want to use this protected resource (client certifcate) then prompt me for the permission. In middle tier environment you really do not want this prompt, you really want to run your application unattended. In fact with .Net frameworks 1.1, SP1 you won't be able to use the certificate with strong key protection.

Check the posting from Kevin W. Hammond about his experience on this issue

http://blogs.msdn.com/kevinha/archive/2005/02/15/373254.aspx

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You could help us on application compatibilty verification

adarshk — Fri, 04 Feb 2005 20:11:00 GMT

Hi,

If you have an application build on .net frameworks 1.0 or .net frameworks 1.1, which is using System.Net classes. If you want to make sure that your app works behaves as expected on 2.0 we could help.This would also enable you to contribute on our effort for application compatibility verification and make sure application works perfectly with 2.0 version of frameworks.

Here are some basic requirements

a) You are willing to share the app with us under NDA, application should be small to medium size that can be set up in less than a day on one or two machine

c) Please note this effort should not be considered as any official guarantee for compatibility, we will do best effort to verify and tell, if there is any breaking changes

This posting is provided "AS IS" with no warranties, and confers no rights

Must watch MSDNTV shows on network programming

adarshk — Fri, 21 Jan 2005 21:09:00 GMT

If you love working on network programming and curious to see the demo of upcoming network programming features in .Net frameworks 2.0, you will love these MSDN TV shows from our team.

Write Connected Applications Using System.Net

Learn how to write better connected apps with System.Net in Visual Studio 2005. Since VS 2003, we've significantly enhanced the System.Net class libraries to make writing connected apps easier with added support for FTP, SMTP protocols, and the ability to listen and respond to HTTP requests

http://msdn.microsoft.com/msdntv/episode.aspx?xml=episodes/en/20050113NETDG/manifest.xml

What's New in .NET Remoting for .NET Framework 2.0

Matt Tavis shows some new features and code examples in .NET Remoting in .NET Framework 2.0, including the new IpcChannel, the secure TcpChannel, and Version Tolerant Serialization (VTS) to allow authors to version their types without breaking serialization.

http://msdn.microsoft.com/msdntv/episode.aspx?xml=episodes/en/20050120NETMT/manifest.xml

Understanding HttpWebRequest Connection Management and ServicepointManager

adarshk — Sun, 02 Jan 2005 10:34:00 GMT

If you are looking for some information on understanding the basics of HttpWebRequest connection management and servicepointmanager, I just posted an article which could be useful for you.

http://blogs.msdn.com/adarshk/articles/345411.aspx

This is first in the series, in future posting I promise to provide more details about specific scenarios which include Http with authentication and proxy server and also for other protocols like FtpWebRequest and SmtpClient, which were added in .net frameworks 2.0.

Update Windows Form UI with Network Available Change Event

adarshk — Fri, 17 Dec 2004 03:06:00 GMT

.Net frameworks 2.0 has a new namespace System.Net.NetworkInformation, which you could use to gather various network statistics on the machine, it also provide two interesting events NetworkAddressChanged and NetworkAvailabilityChanged. If you are writing winform application and want to update some UI information based on network availability status, then Network availibility changed event is very handy for you. Look at following few lines of handy code as demo to change a text label in windows form.

First Step is to hook up an event handler on NetworkChange.NetworkAvailabilityChanged event

public myMainForm()
{

                        ///        Do all your applicatio stuff here
                        updateNetworkStatus(NetworkInterface.GetIsNetworkAvailable());
                       NetworkChange.NetworkAvailabilityChanged +=
                             new NetworkAvailabilityChangedEventHandler (myNetworkAvailabilityChangeHandler);
       }

Implement the event handler

          public void myNetworkAvailabilityChangeHandler(object sender,
            NetworkAvailabilityEventArgs args)
        {// you can't update UI here because because windows form UI could be only updated on main UI thread
            this.Invoke(new WaitCallback(updateNetworkStatus), args.IsAvailable);
        }

Implement the method to update the UI information, in this example a label on form will be updated to show the availability of network, but you can do more cool stuff here

        private void updateNetworkStatus(object state)
        {
            if ((bool)state)
            {
                lblNetworkStatus.ForeColor = Color.Green;
                lblNetworkStatus.Text = "NetworkStatus: Online";
            }
            else
            {
                lblNetworkStatus.ForeColor = Color.Red;
                lblNetworkStatus.Text = "NetworkStatus: Offline";
            }

}

NetworkAvailability changed is available in post Beta1 bits, check http://lab.msdn.microsoft.com/vs2005/ for latest bits.

This posting is provided "AS IS" with no warranties, and confers no rights

Does your application require customizing System.Net.WebPermission, SocketPermission or DnsPermission settings?

adarshk — Mon, 06 Dec 2004 09:43:00 GMT

.Net frameworks comes with deefault security settings where components running under Intranet, Internet Zone can only have WebPermission to connect back to the server, from where they are downloaded. Also the component from Intranet zone and Internet zone don't have any SocketPermission and DnsPermission by default.

I am trying to find out some real world usage scenarios, where people are customizing these security settings for there application or components in either intranet or internet zone deployment. Special interest is WebPermission, SocketPermission, DnsPermission or NetworkInformationPermission (NetowrkInformationPermission is only in .net frameworks 2.0).

If you are one of them, please drop your comment about scenario and your experience with it.

Resuming broken file download with FtpWebRequest class

adarshk — Wed, 01 Dec 2004 23:04:00 GMT

This post is valid for .Netframeworks 2.0

When we are downloading a large file from ftp site and connection got broken in between, on next attempt you would be interested in downloading the rest of the file content instead of full file. FtpWebRequest class have a nice way to meet this requirement. You could use the FtpWebRequest.ContentOffset property to specify the starting position for file to download. See code example below

Following is the code for downloading the file

public static void ResumeFtpFileDownload(Uri sourceUri, string destinationFile)
{
        FileInfo file = new FileInfo(destinationFile);
        FileStream localfileStream ;
        FtpWebRequest request = WebRequest.Create(sourceUri) as FtpWebRequest;
        request.Method = WebRequestMethods.Ftp.DownloadFile;
        if (file.Exists)
        {
            request.ContentOffset = file.Length;
            localfileStream = new FileStream(destinationFile, FileMode.Append, FileAccess.Write);
        }
        else
        {
               localfileStream = new FileStream(destinationFile, FileMode.Create, FileAccess.Write);
        }
        WebResponse response = request.GetResponse();
        Stream responseStream = response.GetResponseStream();
        byte[] buffer = new byte[1024];
        int bytesRead = responseStream.Read(buffer, 0, 1024);
        while (bytesRead != 0)
        {
               localfileStream.Write(buffer, 0, bytesRead);
               bytesRead = responseStream.Read(buffer, 0, 1024);
        }
        localfileStream.Close();
        responseStream .Close();
}

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Create your own asp.net hosting server with System.Net.HttpListener

adarshk — Mon, 22 Nov 2004 02:24:00 GMT

.Net frameworks 2.0 contain HttpListener class under System.Net namespace and a number of ASP.Net hosting classes under System.Web.Hosting namespace.

HttpListener class is implemented on top of low level protocol stack http.sys, probably you also know that IIS 6.0 is also architected on top of http.sys. So user of HttpListener class could get advantage of many of the http.sys. System.Web.Hosting namespace is providing the classes to create and handle the ASP.Net hosting envoronment. In combination of both these features you could create your own hosting environment to handle aspx, asmx pages without using the IIS.

I was initially planning to put here some real code sample for simple host application. But looking at recent MSDN magazine, I found Aaron Skonnard has already done a great job in the article Run ASMX Without IIS with complete source code. So for code samples and more details I would recommend to read this MSDN article.

This posting is provided "AS IS" with no warranties, and confers no rights

HttpWebRequest.GetResponse() gives "HTTP protocol violation" error after .net frameworks service packs

adarshk — Mon, 08 Nov 2004 20:44:00 GMT

This blog is valid for users of .Net frameworks 1.0 SP3 and .Net frameworks 1.1 SP1

The error is really because server is sending response with bad header format, which violates the http protocol specifications. These changes had been made to disallow bad headers. Bad http header could cause security vulnerability based on response-splitting and other attacks based on misinterpreting HTTP streams.

However if your application still need to deal with such responses, you could roll back to old bahavior of relaxed header parsing. You need to use following app.config file.

This posting is provided "AS IS" with no warranties, and confers no rights