Discover ISAPI. Feed provider for graphical applets

• Download ISAPI source files - 107 Kb
• Download WEB project files - 328 Kb
• Download DB backup files - 319 Kb

Introduction

Some time ago I implemented a data feed system from SQL database to some graphical applets. At the beginning we decided a normal ASP script which read data and gave it to that applets would be useful. Unfortunately it wasn't! The web server was crashed every time the number of simultaneous users on the site was more than 80-100 users and when an user tried to get larger data in an applet. For those reasons we decided to move the feed to ISAPI dll.

Advantages

• the ASP server is freed  by the calls from clients applets. In that way the asp will respond only to the normal site calls; the asp will not produce any timeouts caused by applets calls.
• keeping the connection to the DB in the ISAPI cache, in that way all requests against DB don't loose time opening a connection, and will use the public open connection variable (CAdoDatabase m_AdoDB).
• The ISAPI extension dll are the best choice if you want to obtain the maximum number of simultaneous connections to the IIS web server or to provide huge quantities of HTML data.

Functionality

The ASP script loads the applet class and gives it some parameters, like colors, time interval of http's requests, web application URL, etc. 

<applet codebase="../AspDemoFeed/Tools/OnlineScroll/CLASSES/JavaScroller/" 
archive="../AspDemoFeed/Tools/OnlineScroll/Scroller.jar" code="ScrollerStartUp.class" width="600"
height="20" VIEWASTEXT id="Scroller">
  param name="speed" value="3"
  param name="bgcolor" value="696969"
  param name="Font" value="Arial|1|16"
  param name="changeFontSize" value="11"
  param name="feedURL" value="<%=Application("WebURL")%>cgi-bin/IsapiDemoFeed.dll?GetOnlineScrollerData?"
  param name="updateInterval" value="20000"</applet>

The java applet will make requests from the client's side to the web server HTTP using the received web URL parameter. The requests are madedat equal intervals of time given in milliseconds by the updateInterval parameter. If you open the java console on the client you will see some messages like:

    Loading data from 
http://localhost/projects/Articles/AspDemoFeed/cgi-bin/IsapiDemoFeed.dll?GetOnlineScrollerData?0&4

The ISAPI module responds to the HTTP hit with a format known by the applet, html stream:

0|2232160|453.4|2|14:19:06
1|576920|139.1|1|14:19:06
2|4006410|796.8|4|14:19:06
3|2511860|-31.5|2|14:19:06
4|2478810|529.2|0|14:19:06 

For each HTTP hit, the ISAPI module makes a request again to the SQL database, using the CAdoDatabase and CAdoRecordset classes from CodeProject site :). A minor modification was to keep the database connection as public variable. In each method the record sets needed are opened and closed. An optimization is the use of GetString method of the AdoRecordset class, which returns formatted data text. Because the ISAPI dll is harder to debug, more attention must be given to capturing errors, handled with try/catch macros.

try
{
  CAdoRecordset* AdoRS = new CAdoRecordset;  //create a recordset variable 
  if ( DBConnectionOpen( m_bstrConnectionString ) )  //look at db connection to be online
  { 						//open the recordset
    if ( AdoRS->Open(m_AdoDB.GetActiveConnection(), bstrSTMT, adOpenForwardOnly, 
		adLockReadOnly, adUseClient ) ) //here the disc params
    {
      if (!AdoRS->IsEof())  //look if we have records
        varOutput = AdoRS->GetString("|", "\n", 0 );			
      else
        varOutput = "0 0 0 0 0 ";
      AdoRS->Close(); //close the recordset 
      if (AdoRS)
        delete AdoRS;
    }
    else              //set the custom error
    {
      wsprintf(wcOut,"Encountered Error:<br>%s<br>%s<br>%s<br>%s<br>","MyFunction" 
         (LPCTSTR)m_AdoDB.GetLastError(), "RS isnt open", bstrSTMT );
      *pCtxt << wcOut ;
      return;
    } 
  }
  else                //set the custom error
  {
    wsprintf(wcOut, "Encountered Error:<br>%s<br>%s<br>%s<br>%s<br>","GetMarketMapData", 
    (LPCTSTR)m_AdoDB.GetLastError(), "DB isn't open", bstrSTMT );
    *pCtxt << wcOut ;	
    return;
  }
}
catch(_com_error err)
{ 	
  wsprintf(wcOut, "Encountered Error :<br>%s<br>%d<br>%s<br>", (LPSTR)err.Description(), 
     err.Error(), (LPSTR)err.ErrorMessage() );
  *pCtxt << wcOut ;
  return;
}
*pCtxt << varOutput;  //here the output

IMPORTANT:  To test the feed, you must make updates on the values of the tblOnline* tables. The updates will be reflectied online instantaneously in the Online tables and scrolling applets. To see how it works with Intraday charts applets make inserts in tblIntraday* tables. Those applets look permanently at those tables and updates the values in cells and points on the charts.

Install

• The ASP connection string are located in the Includes\_incConnectionOn.asp file.
  cnx.Provider = "sqloledb"
cnx.Open "Data Source=andi;Initial Catalog=ArticlesIsapiFeed;", "sa", ""
• The ISAPI connection string are located in IsapiDemoFeed.cpp file, on the constructor:
  m_bstrConnectionString="Provider=SQLOLEDB;Data Source=andi;Initial Catalog=ArticlesIsapiFeed;
User ID=sa;Password=;";
• Copy the folder "AspDemoFeed" under your web site and make it ASP application, to work the session and
  application ASP objects.
• Give "Scripts and Executables" Execute Permision to "cgi-bin" directory of "AspDemoFeed" web application.
  In that way the ISS web server will be able to execute the IsapiDemoFeed.dll.
• To install the database on your SQL server select restore database option on SQL Server Enterprise Manager and choose
   the "DB/ArticlesIsapiFeed.bak" file backup. The name of database is ArticlesIsapiFeed.