Network Programming in .NET

Visitor trackers aren’t new, and even novice HTML coders can place a free tracker in their webpage, but there comes a point when

you outgrow what’s available free, and you really need to get hold of the raw data behind your tracker.

 

Recording data for every visitor to the site may be out of the question, as you end up filling your database with too much archival data. Generally a tracker will keep detailed information about the last day’s traffic, then aggregated information for archival material. For example, it might be of interest to view which websites the last 20 visitors came from, but just a count of how many people came to the site last march might be sufficient.

 

I therefore created two tables in my database, RecentVisitors and AggregatedVisitors. With a trigger set up between the two, to automatically populate the AggregatedVisitors table based on new inserts into the RecentVisitors table, thus:

 

CREATE TRIGGER trigger_RecentVisitors
ON RecentVisitors
FOR INSERT
AS
BEGIN
 — note this will track hits not unique visitors.

 declare @websiteID int

 select top 1 @websiteID = websiteid from inserted  

 declare @VisitorsToday int
 select @VisitorsToday = count(*) from RecentVisitors  
 where dateDiff(day,Date,getdate())=0
 and websiteId=@websiteID
  
 delete from AggregatedVisitors where
 websiteID = @websiteID
 and
 Datediff(day,date,getDate())=0

 insert into AggregatedVisitors (Number,websiteID)
 values (@VisitorsToday,@websiteID)
 
 delete from recentVisitors where dateDiff(day,Date,getdate())>1
 
END

 

 

I then, put together some javascript to load a hidden image, which would execute an insert into RecentVisitors

 

<img name="Tracker" style="display:none">
 <script language="javascript">
 var WebsiteID = 1;
 var Tracker = window.document.images["Tracker"];
 Tracker.src = "default.aspx?WebsiteId=" + WebsiteID + "&Referrer=" + escape(document.referrer);
 </script>

 

To return a 1px x 1px image from asp.net is really easy, and combined with an insert into the database, I came up with:

 

 

 

 

 

 

I had an issue that my ADSL connection kept disconnecting every few hours, which meant that I manually had to go and open

the local web interface to my ADSL modem (Binatone), and press connect.

 

I figured out how to do this from code, by making a GET request to the following URL, my ADSL was reconnected.

 

When setting up a VPN connection on Windows XP Pro, I found the VPN option greyed out.

 

Searching on the net, people said that the Remote Access Connection Manager service wasn’t running, however when you try to start this, you get an Access Denied error, and a "cannot allocate buffers" errror in the event log.

 

This is actually due to a registry corruption,

To fix it, go to HKL:MSystemCurrentControlSetRasmanPPPEAP then delete subkeys EXCEPT 13 & 4. Then reboot the pc.

 

This is one of those horrible asp.net error messages, when for no reason, you update some code with new code and you get an access is denied error.(*)

 

There are some sensible suggestions listed on msdn as to why this happens, and how it’s all down to indexer service – although, when you already have this service disabled, you’d wonder what’s up?

 

Basically, I went through these steps

Kill the asp_wp process

stop w3svc service

delete the bin folder

restart w3svc service, and go to offending page

stop the w3svc service

replace the bin folder with old files

restart the w3svc service.

 

It makes little sense why this works, but it worked for me.

 

 

(*) the specifics of the error (if you do view|Source) are

[FileLoadException]: Access is denied: ‘erc’.
   at System.Reflection.Assembly.nLoad(AssemblyName fileName, String codeBase, Boolean isStringized, Evidence assemblySecurity, Boolean throwOnFileNotFound, Assembly locationHint, StackCrawlMark& stackMark)
   at System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Boolean stringized, Evidence assemblySecurity, StackCrawlMark& stackMark)
   at System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark)
   at System.Reflection.Assembly.Load(String assemblyString)
   at System.Web.UI.CompilationConfiguration.LoadAssemblies(Hashtable original)
[ConfigurationException]: Access is denied: ‘erc’. (c:winntmicrosoft.netframeworkv1.1.4322Configmachine.config line 258)
   at System.Web.UI.CompilationConfiguration.LoadAssemblies(Hashtable original)
   at System.Web.UI.TemplateParser.AppendConfigAssemblies()
   at System.Web.UI.TemplateParser.PrepareParse()
   at System.Web.UI.TemplateParser.Parse()
   at System.Web.UI.TemplateParser.GetParserCacheItemThroughCompilation()
   at System.Web.UI.TemplateParser.GetParserCacheItemInternal(Boolean fCreateIfNotFound)
   at System.Web.UI.TemplateParser.GetParserCacheItemWithNewConfigPath()
   at System.Web.UI.TemplateParser.GetParserCacheItem()
   at System.Web.UI.ApplicationFileParser.GetCompiledApplicationType(String inputFile, HttpContext context, ApplicationFileParser& parser)
   at System.Web.HttpApplicationFactory.CompileApplication(HttpContext context)
   at System.Web.HttpApplicationFactory.Init(HttpContext context)
   at System.Web.HttpApplicationFactory.GetApplicationInstance(HttpContext context)
   at System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr)

When tweaking stored procedures, to make them run faster, we often compare them against a benchmark,

say SP_A vs SP_B.

 

However, if SP_A has been used actively, as part of a running system (i.e. website). it will be optimized by SQL server and will be placed in the procedural cache. This then results in Biased tests between SP_A and SP_B.

 

Therefore I would recommend using

DBCC FREEPROCCACHE

and

DBCC DROPCLEANBUFFERS

 

before timing the execution of SP_A against SP_B. Although, the affect of clearing the cache will cause them both to run slower, it will highlight performance gains of one against the other fairly.

 

 

 

I had a problem with a full text catalog stopping at a particular point, and not populating further,

 

To diagnose, problems like this, open C:Program FilesMicrosoft SQL ServerMSSQL.1MSSQLLOG

 

where I saw, Could not allocate space for object ‘sys.fulltext_index_map_1813581499’.’i2′ in database ‘CFGlobal’ because the ‘PRIMARY’ filegroup is full. Create disk space by deleting unneeded files, dropping objects in the filegroup, adding additional files to the filegroup, or setting autogrowth on for existing files in the filegroup.

Therefore I just increased the space allocated to the primary filegroup, and it kicked off again.

 

If you have an Iframe on a page, and you press the back button, then oftentimes, only the Iframe goes back in it’s history, not the containing page.

 

There are a few workarounds for this, this is just a proposal, if it helps…

 

firstly, if you have a pre-loader on the iframe, such as…

 

graph.contentWindow.document.write(‘Please wait…’);
graph.src = ‘someurl’

 

when you can poll the Iframe for a change in the "Please wait message". (Note, that the url that you are redirecting to must be on the same domain as the parent page, or else you get a security exception)

 

// 951 – back button fix. 
 var wasGraphLoaded = false;
 setTimeout(‘checkGraph()’,500);
 function checkGraph()
 {
  if (imgGraph.document.body.innerHTML.indexOf("…")==-1)
  {
   // Graph must be loaded…
   wasGraphLoaded = true;  
   
  }
  else
  {
   // Graph isn’t loaded.
   if (wasGraphLoaded)
   {
    // The back button bust have been pressed
    window.history.go(-1);
   }
  }
  setTimeout(‘checkGraph()’,500);
 }

After finding out that my WISE installer had passed it’s 30 day limit, and my Installshield CD scratched beyond repair, I looked on the web for a free way to redistribute a VB6 application.

 

My first attempt, was Advanced Installer 4, which looked promising. However, it also, is a 30 day trial, if you want go beyond the absolute basics. For instance, my app required the Soap Toolkit,(a COM object), so that was beyond the basic version. Also, it couldn’t properly self-register the COM DLL’s in the Advanced mode either. – Waste of time.

 

I then came accross a Microsoft tool, Visual Studio Installer, which looked well. With a bit of fiddling, I got it to create an MSI. However, an MSI may not work first time on pre-XP machines, since the Windows Installer is not guaranteed to be on the machine, So I looked for a generic MSI to EXE converter

 

The best I found was this: http://www.tmgdevelopment.co.uk/setuputility.htm Which you place in the same folder as the MSI.

 

I zipped them both together, and placed them on the website.

 

 

I am almost cerain this is a bug in the .NET bitmap Codec, that you cannot change the color Depth… It always saves in its native format for Bitmap.

 

However, if you convert the image to a TIFF first, then it works.

 

 

 

 

 

(for reference:)

I was looking for some high performance code to convert a bitmap into a 2D byte array, this is what I came up with.

 

first I have a class called pixel.

{

  public byte red;

  public byte green;

  public byte blue;

}

 

then I read it using some Unsafe code thus:

public pixel[,] BitmapToArray(Bitmap b)

{

pixel[,] bmpData=new pixel[b.Width,b.Height];

// GDI+ still lies to us – the return format is BGR, NOT RGB.

BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

int stride = bmData.Stride;

System.IntPtr Scan0 = bmData.Scan0;

unsafe

{

byte * p = (byte *)(void *)Scan0;

int nOffset = stride – b.Width*3;

int nWidth = b.Width * 3;

for(int y=0;y<b.Height;++y)

{

for(int x=0; x < nWidth; ++x )

{

switch(x%3)

{

case 0:

bmpData[x/3,y] =

new pixel();

bmpData[x/3,y].blue = (

byte)(p[0]);

break;

case 1:

bmpData[x/3,y].green = (

byte)(p[0]);

break;

case 2:

bmpData[x/3,y].red = (byte)(p[0]);

break;

}

++p;

}

p += nOffset;

}

}

b.UnlockBits(bmData);

return bmpData;

}