Databases - Delphi CGI Web Server

The purpose of a Web Server is to generate a web page (html) that is displayed in a regular web browser.

A CGI Web Server is an *.exe file - ISAPI and NSAPI Web Servers are *.dll files.

*.dll Web Servers are better (faster and more efficient) for high volume sites, but they are very difficult to debug because the main Web Server (IIS, Netscape, Apache, and the like) must be shut down each time a new *.dll is compiled. As a result, it is always easier to create a CGI server first and convert it to an *.dll latter. (Only the project (*.dpr) file is different.)

See C:\Program Files\BORLAND\Delphi5\Demos\Webserv for a demo where the CGI (*.exe) and ISAPI (*.dll) applications use a common module (*.pas file).

For an overview, see Creating Internet server applications in the Delphi help. (In the help contents, it is under Writing Distributed Applications. You can also launch it via Start / Programs / Delphi / Help / Developing Distributed Applications, but then many of the links won't work.)

Creating the Application | Producing html | TDataSetTableProducer | Reading Parameters

Running your program under IIS | Version Issues | Testing

Creating the Application

From the menu, select

File / New... / Web Server Application

File / New / Other... / Web Server Application

Then, from the wizard, you select CGI stand-alone executable.

Web servers do not have a "form" as such (it actually runs as a console application), instead they produce html which is sent back to a browser.

This example will access the Interbase/Firebird database employee.gdb (it ships with Delphi).

Add a WebActionItem
- Double click in the white part of the WebModule's "Components" tab
- Click the first icon to add a new WebAction
- Close the window

On the WebModule's Components tab, place

 Tab           Component
InterBase     TIBDatabase
InterBase     TIBTransaction
InterBase     TIBTable
Internet      TDataSetTableProducer
Internet      TDataSetPageProducer

Set the following properties in the order shown

Component Property Value Comments
IBDatabase1 DatabaseName Set this to the *.gdb or *.fdb file
Params
user_name=sysdba password=masterkey
These are used to connect to the database. In a "real" application, these should be read from an *.ini file or some other location - Never hardcode this type of data.
LoginPrompt false This program MUST connect automatically without user intervention
DefaultTransaction IBTransaction1
Connected True This connects the database
IBTransaction1 DefaultDatabase IBDatabase1
Active True
IBTable1 Database IBDatabase1
Transaction IBTransaction1 Automatically selected
TableName Pick one from the list
Active True
DataSetTableProducer1 DataSet IBTable1
Header Optional
Footer Optional
DataSetPageProducer1 DataSet IBTable1
Header Optional
Footer Optional

Component	Property	Value	Comments
IBDatabase1	DatabaseName		Set this to the .gdb or .fdb file
Params	user_name=sysdba password=masterkey	These are used to connect to the database. In a "real" application, these should be read from an *.ini file or some other location - Never hardcode this type of data.
LoginPrompt	false	This program MUST connect automatically without user intervention
DefaultTransaction	IBTransaction1
Connected	True	This connects the database
IBTransaction1	DefaultDatabase	IBDatabase1
Active	True
IBTable1	Database	IBDatabase1
Transaction	IBTransaction1	Automatically selected
TableName		Pick one from the list
Active	True
DataSetTableProducer1	DataSet	IBTable1
Header		Optional
Footer		Optional
DataSetPageProducer1	DataSet	IBTable1
Header		Optional
Footer		Optional

If you edit some parameter and no data is displayed, check IBDatabase1.Connected, IBTransaction1.Active, and IBTable1.Active, in that order. (Actually, just setting IBTable1.Active to True will automatically set the others.)

To connect to the Interbase example database distributed with Delphi, set IBDatabase1.DatabaseName to

MachineID:C:\Program Files\Common Files\Borland Shared\Data\employee.gdb

This is only one of many ways to produce a Web Server. For an advanced application, you will probably want many WebActionItem's - each one associated with a separate function - and a default WebActionItem to handle 404 (page not found) type errors.

Producing html

Web Servers automatically create a TWebResponse object. When data is requested from a page (server), a WebActionItem is called (your application may have several of them) with the TWebResponse object passed to the OnAction event handler as a parameter named Response. html can be returned by setting Response.Content to an html string. If WebActionItem.Producer is set, whatever html the producer generates will also be sent.

This will manually return the html from a "Producer"

Response.Content := SomeProducer.Content;

These are the main producers

TDataSetTableProducer: This produces just the html table (populated with data from the specified database table), no header or other code. Optional Header and Footer properties may be included.
TQueryTableProducer: Use this when parameters are returned with the http request.
TPageProducer: This stores html header and footer information, an entire html page, or points to an *.html file - your choice. You must write the code that interprets and replaces HTML-transparent tags.
TDataSetPageProducer: This is similar to the TPageProducer, except that it replaces those HTML-transparent tags that match fields in a dataset with the current value of those fields.

TDataSetTableProducer

The TDataSetTableProducer formats a table into an html table.

However, several properties have problems - they don't work at all UNLESS you replace the default fields with one you have "manually" entered.

At design time, it is possible to set properties for the individual columns and their headers. The changes take effect immediately in the provided dialog box, but do not appear in the final output.

Formating Individual Cells

This TDataSetTableProducer code (attached to the OnFormatCell event) converts a field stored as Single to a Date/Time. Notice that the Row must be greater than zero to avoid the column headers.

procedure TWebModule1.DataSetTableProducer1FormatCell(Sender: TObject; CellRow, CellColumn: Integer; var BgColor: THTMLBgColor; var Align: THTMLAlign; var VAlign: THTMLVAlign; var CustomAttrs, CellData: String); begin if (CellColumn = 2) and (CellRow > 0) then begin // date/Time field CellData := DateTimeToStr(StrToFloat(CellData)); CellData := '<font color=green>' + CellData + '</font>'; end; end;

Reading Parameters

Web Servers automatically create a TWebRequest object that is passed to a WebActionItem OnAction event handler as a parameter named Request.

Various http headers can be read as TWebRequest properties, many more can be read via

tempStr := Request.GetFieldByName('parameterName');

Query parameters should be read via the QueryFields name/value pair String List

tempStr := Request.QueryFields['parameterName'];

Running your program under IIS

To run your code under IIS, you must place it in a directory that has permission to execute programs.

Your files are stored as

c:\Inetpub\wwwroot\xyz\WebCGI.exe

and accessed as

http://localhost/xyz/WebCGI.exe

The Apache configuration is slightly different.

Version Issues

HTTPProd is used in Delphi 6, but not present in Delphi 5.

{$IFDEF VER130}       // Delphi 5
  {$DEFINE mc_LE_D5}  // Less than or equal to Delphi 5
                      // I use "mc" to help avoid conflicts
{$ENDIF}


interface

uses
  SysUtils, Classes, HTTPApp,

{$IFNDEF mc_LE_D5}
  HTTPProd, // Delphi 6 and above only
{$ENDIF}

   DSProd, DBWeb, mcCommon;

Testing

The Delphi help says that CGI files are more difficult to test than *.dll's - I don't agree at all.

There are several ways to test your CGI programs

As a DOS application

Open a DOS window (command prompt) and run the program from there. Since the output is written to stdout, the generated html is displayed in the window. If you just double click your program (or use the Delphi Run button), the DOS window closes automatically before you can read the output.

This can be simplified by making the following registry modification

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\exefile\shell\shell]
@="Run in command shell"

[HKEY_CLASSES_ROOT\exefile\shell\shell\command]
@="C:\\WINDOWS\\system32\\cmd.exe /k  %1"

Notice that the default action is called (I don't know how to select a specific page). To get another page, just select another action as the default.

Add instrumentation

"Instrumentation" means extra code to make testing easier. In this case, add code to write the generated html code to a file.

Use a web server (I use IIS)

I have a dummy web page that calls the program. This way, the program is called with all the "correct" parameters (assuming that your web page produces the correct parameters). I do most of my testing this way.

Author: Robert Clemenzi - clemenzi@cpcug.org