CGI Web Programming: what changed

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Title: CGI Web Programming

New		Line
1	+	This article contains some information about basic CGI programs. Note that using one of the frameworks will probably be much more productive.
2	+
3	+	## About CGI
4	+
5	+	[CGI (Common Gateway Interface)](http://en.wikipedia.org/wiki/Common_Gateway_Interface) works simply as follows:
6	+
7	+	We have two computers:
8	+
9	+	- Server Computer - This computer will store the hosted files (web pages, images and CGIs) and serve them using a web server.
10	+	- Client Computer - Generally, this computer has a browser to request the files hosted in server computer.
11	+
12	+	You can use CGI only if your hosting web server has CGI support. After hosting your files, CGI can now be used normally as: http://www.yourserver.com\[.xx\]/yourlogin/cgi-bin/cginame.exe
13	+
14	+	Notes:
15	+
16	+	- The CGI file doesn't need the .exe extension.
17	+	- The CGI should be (obviously) compiled for the platform of the computer server (Linux, Windows...)
18	+
19	+	## About FreePascal CGI and how you can test your CGIs
20	+
21	+	A Free Pascal CGI executable is a normal executable program, like any program on your computer. Unlike the CGIs in Perl or Python, Free Pascal CGI isn't interpreted. It's an independently executable program.
22	+
23	+	To test a CGI, you must have a HTTP Server with support for CGI installed on your PC. A good, and recommended [HTTP Server](http://en.wikipedia.org/wiki/HTTP_Server) is [Apache](http://en.wikipedia.org/wiki/Apache_HTTP_Server), available both for Windows and Linux.
24	+
25	+	## A very basic example
26	+
27	+	Here is an example of a minimal CGI program to demonstrate...
28	+
29	+	1. Setting a cookie
30	+	2. Outputting the content-type (ie make it put out legal text for HTTP)
31	+	3. Reading Cookies
32	+	4. Reading form data via GET
33	+	5. Reading form data via POST
34	+
35	+	``` pascal
36	+	program mini;
37	+
38	+	uses dos;
39	+
40	+	var
41	+	a:string;
42	+	c:char;
43	+	begin
44	+	// set a cookie (must come before content-type line below)
45	+	// don't forget to change the expires date
46	+	writeln('Set-cookie:widget=value; path=/; expires= Mon, 21-Mar-2005 18:37:00 GMT');
47	+
48	+	// output legal http page
49	+	writeln('Content-Type:text/html',#10#13);
50	+
51	+	// demonstrate get cookies
52	+	a:= GetEnv('HTTP_COOKIE');
53	+	writeln('cookies:',a);
54	+
55	+	// demonstrate GET result
56	+	a:='';
57	+	a:= GetEnv('QUERY_STRING');
58	+	writeln('GET: ',a);
59	+
60	+	// demonstrate POST result
61	+	a:='';
62	+	while not eof(input) do
63	+	begin
64	+	read(c);
65	+	a:= a+c;
66	+	end;
67	+	writeln('POST: ',a);
68	+	end.
69	+	```
70	+
71	+	## A simple hitcounter
72	+
73	+	The application hitcounter presents a simple hitcounter for your website. It is possible to enter blocklists in a configfile so robots and perhaps your own computer are excluded from the statistics. There are still a lot of improvements possible ofcourse like setting a cookie so you get only one hit per session, but it gives a good introduction into CGI programming. If you use the code and modify it, please send me a patch so I can update it.
74	+
75	+	You can find the code here: [1](http://sourceforge.net/p/modelbuilder/code/HEAD/tree/html/cgi/)
76	+
77	+	## Debugging CGI
78	+
79	+	Because a CGI application does not write to screen, and is started by another process (the web server), debugging is more difficult than desktop applications.
80	+
81	+	One solution is to let the CGI application start a debugger: When used in a program this unit will as part of the initialization launch a new process which opens a terminal (windows:cmd, linux:xterm) and starts the gdb debugger attaching to the calling proces.
82	+
83	+	A short "sleep" makes sure gdb breaks the program while still initializing.
84	+
85	+	It has been tested on
86	+
87	+	- Windows XP32 with apache 2.2 running as an application or as a service (does not work anymore is higher versions of Windows, see <http://forum.lazarus.freepascal.org/index.php/topic,21931.msg128849.html#msg128849>)
88	+	- on ubuntu 10.04 x64 with Apache 2.2
89	+	- on Debian unstable x64 with Apache 2 (Feb 2013)
90	+
91	+	Further instructions are in the unit.
92	+
93	+	``` pascal
94	+	unit SelfDebug;
95	+
96	+	{
97	+	Instructions:
98	+	-Include unit anywhere in the program.
99	+	-Change DEBUGGER constant to match your debugger (gdb, ddd,gdbtui...)
100	+	-For Windows, if the program to debug is running as a service (e.g. CGI application
101	+	from Apache running as a service), make sure the service is configured with
102	+	"Interact with desktop" checked. Failing to do so, the debugger will be started
103	+	without a console, break the program and hang waiting for input. Killing the debugger
104	+	is your only option.
105	+	-For Linux, if the program to debug is running as a different user (e.g. CGI application),
106	+	run "xhost +" in a terminal to enable all users to connect to xserver.
107	+	If needed, change DISPLAY to match your DISPLAY environment variable
108	+	}
109	+
110	+	{$mode objfpc}{$H+}
111	+
112	+	interface
113	+
114	+	uses
115	+	Classes, SysUtils,Process;
116	+
117	+	implementation
118	+
119	+	const
120	+	{$ifdef windows}
121	+	DEBUGGER='C:\lazarus\mingw\bin\7.3\gdb.exe';
122	+	{$endif}
123	+	{$ifdef linux}
124	+	DEBUGGER='gdb';
125	+	DISPLAY=':0.0';
126	+	{$endif}
127	+	MSWAIT=2000;
128	+
129	+	var
130	+	AProcess: TProcess;
131	+
132	+	initialization
133	+	AProcess := TProcess.Create(nil);
134	+	{$ifdef windows}
135	+	AProcess.CommandLine := format('cmd /C START "Debugging %s" /WAIT "%s" "%s" %d"',[paramstr(0),debugger,paramstr(0),GetProcessID]);
136	+	{$endif}
137	+	{$ifdef linux}
138	+	AProcess.CommandLine := format('xterm -display %s -T "Debugging %s" -e "%s" "%s" %d',[DISPLAY,paramstr(0),DEBUGGER,paramstr(0),GetProcessID]);
139	+	{$endif}
140	+	AProcess.Execute;
141	+	sleep(MSWAIT);
142	+	finalization
143	+	AProcess.Free;
144	+	end.
145	+	```
146	+
147	+	Source: <http://www.hu.freepascal.org/lists/fpc-pascal/2011-October/030752.html>
148	+
149	+	Other solutions are writing to a file or event log/syslog.
150	+
151	+	## Existing CGI Frameworks
152	+
153	+	There are existing CGI units and frameworks that make working with CGI trivial (and allow one to set cookies, sessions, retrieve POST and GET).
154	+
155	+	- See [[Brook for Free Pascal]], the perfect Free Pascal framework for your web applications.
156	+	- See [FastPlaz](http://www.fastplaz.com/), Free Pascal framework for your web applications with MVC Style.
157	+	- See [[fcl-web]], an FPC and Lazarus (weblaz) framework
158	+	- See [Powtils](http://z505.com/powtils/idx.shtml)
159	+	- [ExtPascal](http://extpascal.googlecode.com) an Ext JS wrapper.
160	+	- See [Fano Framework](https://fanoframework.github.io/), Web application framework for modern Pascal programming language. It is written in Free Pascal.
161	+
162	+	---
163	+	From the Free Pascal wiki, page "CGI Web Programming", as it stood on 2020-06-26 after a change by Almuhandis, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).

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