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Revision as of 09:36, 16 July 2010 by Michael (talk | contribs) (Using Actions)

Template:Web and Networking Programming

Using fpWeb together with Lazarus

Installing the fpWeb Lazarus Package

The first step to do is installing the package which comes in the path lazarus/components/fpweb/weblaz.lpg

Creating a cgi application

After the weblaz package is installed, a very simple cgi web application which displays an html page can be created by going to the Lazarus menu "File->New...". From the list of possible applications select "CGI Application" as in the image bellow, which will create a main cgi project file and a fpweb web module.

New cgi.PNG

To add code to show the page a request handler should be added, by double clicking the OnRequest property in the object inspector, as in the image bellow:


In the event handler one should write the html code which will be displayed by the browser. To avoid mixing Pascal and HTML, this page can be loaded from the same directory of the cgi executable by using AResponse.Contents.LoadFromFile(). The type of the response should be set in AResponse.ContentType and for html pages it will have the value 'text/html;charset=utf-8'. In the end Handled should be set to True to indicate that the request was successfully handled. After adding this code, the web module should look like this:

<delphi> unit mainpage;

{$mode objfpc}{$H+}



 Classes, SysUtils, FileUtil, HTTPDefs, websession, fpHTTP, fpWeb; 


 { TFPWebModule1 }
 TFPWebModule1 = class(TFPWebModule)
   procedure DataModuleRequest(Sender: TObject; ARequest: TRequest;
     AResponse: TResponse; var Handled: Boolean);
   { private declarations }
   { public declarations }


 FPWebModule1: TFPWebModule1; 


{$R *.lfm}

{ TFPWebModule1 }

procedure TFPWebModule1.DataModuleRequest(Sender: TObject; ARequest: TRequest;

 AResponse: TResponse; var Handled: Boolean);


 AResponse.ContentType := 'text/html;charset=utf-8';
 AResponse.Contents.LoadFromFile(ExtractFilePath(ParamStr(0)) + 'mainpage.html');
 Handled := True;



 RegisterHTTPModule('TFPWebModule1', TFPWebModule1);

end. </delphi>

Deploying this very simple application

Apache, the most popular web server, can be downloaded here: [1]

The default installation of Apache will treat all files located in it's cgi-bin directory as CGI Programs, so the user won't be able to access plain html files placed there. This directory can be set in the file httpd.conf in the following section:

   # ScriptAlias: This controls which directories contain server scripts.
   # ScriptAliases are essentially the same as Aliases, except that
   # documents in the target directory are treated as applications and
   # run by the server when requested rather than as documents sent to the
   # client.  The same rules about trailing "/" apply to ScriptAlias
   # directives as to Alias.
   ScriptAlias /cgi-bin/ "C:/Program Files/Apache Software Foundation/Apache2.2/cgi-bin/"

If you place an executable called "mywebpage.cgi" in this directory, then the page can be accessed as http://localhost/cgi-bin/mywebpage.cgi or with the corresponding domain name if accessed remotely.

Formating the HTML and Reading GET fields

To extend the previous example which just shows a plain HTML page without modification, one might wish to change the HTML page and to read the variables passed to the webpage by GET or POST fields. A simple solution for the first problem is simply using the standard Pascal routine Format and add %s or %d in the HTML file in the appropriate places which will receive a custom value.

To read the GET variables one can use ARequest.QueryFields, which is a TStrings descendent. Each variable will be in a separate line in the TStrings in the format variablename=value, similarly to how they are shown in the browser page address. To search for a specific variable one can use ARequest.QueryFields.Values[], passing the variable name in the brackets to receive it's value back, instead of parsing the string manually. This can be seen in the example bellow:

<delphi> procedure TFPWebModule1.DataModuleRequest(Sender: TObject; ARequest: TRequest;

 AResponse: TResponse; var Handled: Boolean);


 HexText, AsciiText: string;


 HexText := ARequest.QueryFields.Values['hex'];
 AsciiText := HexToAnsii(HexText);
 AResponse.ContentType := 'text/html;charset=utf-8';
 AResponse.Contents.LoadFromFile(ExtractFilePath(ParamStr(0)) + 'mainpage.html');
 AResponse.Contents.Text := Format(AResponse.Contents.Text,
   [HexText, AsciiText]);
 Handled := True;

end; </delphi>

Using multiple modules

If there is only one module in the web application, all requests will be directed to this module.

As your web application grows, multiple modules can be used. A new module can be added by choosing 'File - New' and then one of 'Web module' or 'HTML Web Module'.

FCL-web uses the URL to determine how a HTTP request should be handled. It must therefor know which web-modules exist in the application, and for this, each module must be registered.

Each module is registered with fcl-web in the initialization section of the unit it is defined in: <delphi> RegisterHTTPModule('location',TMyModule); </delphi> The module will then be invoked if an URL is used of the form




Note that if multiple modules are present, the name of the module must appear in the URL, or an error will be raised.

This behaviour can also be forced for applications that have only a single module by setting the Application's property AllowDefaultModule to false: <delphi> Application.AllowDefaultModule:=False; </delphi> In that case, the fcl-web application will always require the name of the module in the URL.

The name of the request variable that determines the module name (by default, this is 'module') can be set in the Application.ModuleVariable property. The following code <delphi> Application.ModuleVariable:='m'; </delphi> ensures that the following URL is directed to TMyModule:


If all this is not enough to determine the module to which the request should be passed, the Application.OnGetModule event can be used. It is of type TGetModuleEvent: <delphi> Type

 TGetModuleEvent = Procedure (Sender : TObject; ARequest : TRequest;
                              Var ModuleClass : TCustomHTTPModuleClass) of object;

</delphi> Creating an event handler for this event allows fine control over the module that is created to handle the request: the request (passed in ARequest) can be examined, and the 'ModuleClass' variable must be set to the class of the module that should handle the request.

If 'ModuleClass' is 'Nil' on return, an error will be sent to the browser.

Using Actions

A module can be used to group certain kinds of actions that logically belong together. Imagine a module TUserModule that is used to handle user management in the webpages. There can be multiple actions associated with a user:

  • Creating
  • Deleting
  • Editing
  • Displaying

These different actions can be handled by the same module. One can determine the action from the URL manually, as in:


This can be automated.

In order to make it easier to distinguish between various actions, the module has a property actions: this is a collection, in which each item is associated with a different response to the request. The actions have various properties:

Name The name of the action. The URL will be examined to determine the name of the action.
A string. If set, this is sent to the browser.
A stringlist. If set, this is sent to the browser.
If set, the contentproducer will handle the request.
if set to 'True', then this action is the default action. That means that if FCL-Web cannot determine the action name, this action will be executed instead.
If set, this template will be processed, and the results sent to the browser.

There are also some events:

executed before the request is processed. CAn be used to set the 'Content' or other properties.
executed after the request is processed.
an event handler to handle the request. If set, the handler is used to handle the request.

Again, as in the case of multiple modules, the URL is used to determine which action to execute. The part right after the module part is used:


would execute the action named 'delete'. This is equivalent to the URL


The 'ActionVar' property of the module can be used to set the name of the request variable to use. Setting <delphi> UserModule.ActionVar:='a'; </delphi> Reduces the above URL to


If there is only one module in the application, the URL can be shortened to



The cgiapp unit is deprecated, please use fpcgi as much as possible.

The fastcgi, custfcgi, and fpfcgi units are not supported on Darwin at this time, because it uses a different mechanism than the MSG_NOSIGNAL option for recv() to indicate that no SIGPIPE should be raised in case the connection breaks. See http://lists.apple.com/archives/macnetworkprog/2002/Dec/msg00091.html for how this should be fixed.