#include <stdio.h>
int main(void){
// http header
printf("Content-Type: text/html\r\n");
// a blank line ends the header
printf("\r\n");
// http body
printf("<html><head></head>\r\n");
printf("<body>\r\n");
printf("Hello world.\r\n");
printf("<br />\r\n");
printf("Bye Bye\r\n");
printf("</body></html>\r\n");
return 0;
}
CGI Example: Compile
> ~# cd /var/www/html/IE/cgi-enabled
> /var/www/html/IE/cgi-enabled# gcc -Wall -o hello_c.cgi hello_c.c
> /var/www/html/IE/cgi-enabled# ./hello_c.cgi
Content-Type: text/html
<html><head></head>
<body>
Hello world.
<br />
Bye Bye
</body></html>
> /var/www/html/IE/cgi-enabled# ./hello_c.cgi | od -c | head -3
0000000 C o n t e n t - T y p e : t e
0000020 x t / h t m l \r \n \r \n < h t m l
0000040 > < h e a d > < / h e a d > \r \n
CGI script will receive the parameters from the web server in an
environment variable $QUERY_STRING
In C: You can access it by
getenv("QUERY_STRING")
Parameters can be passed through the
POST method (in the body of the HTTP
Request)
The CGI script will receive the parameters from the web server in the
standard input (stdin)
CGI Environment Variables
CONTENT_TYPE
The data type of the content. Used when the client is sending attached
content to the server. For example, file upload.
CONTENT_LENGTH
The length of the query information. It is available only for POST
requests.
HTTP_COOKIE
Returns the set cookies in the form of key & value pair.
HTTP_USER_AGENT
The User-Agent request-header field contains information about the
user agent originating the request. It is name of the web browser.
PATH_INFO
The extra path in the URL after the script name. Requesting
/cgi-bin/hello.cgi/a/b runs hello.cgi with
PATH_INFO=/a/b — this is how one script serves many
paths.
QUERY_STRING
The URL-encoded information that is sent with GET method request.
REMOTE_ADDR
The IP address of the remote host making the request. This is useful
logging or for authentication.
REMOTE_HOST
The fully qualified name of the host making the request. If this
information is not available, then REMOTE_ADDR can be used to get the
IP address.
REQUEST_METHOD
The method used to make the request. The most common methods are GET
and POST.
SCRIPT_FILENAME
The full path to the CGI script.
SCRIPT_NAME
The name of the CGI script.
CGI Pros & Cons
What is the main advantage(s) of CGI?
Any programming language can be used
What the main drawback(s) of CGI?
We should generate whole HTML document in CGI
For each request, a new process is created
Process creation & termination & Inter-process communication
overhead
Security is another major issue
Any other way to run code in server side?
Solving CGI Problems
CGI pays process start-up on every request: fork,
exec, load the interpreter, open the database, answer, exit. Every fix keeps
the program running between requests:
Approach
Where the code runs
Examples
Server module
inside the web server's own workers
mod_php, mod_perl
FastCGI
long-lived worker processes; the server talks to them over a socket
PHP-FPM
Application server
the app is its own HTTP server, behind a reverse proxy
Gunicorn, Node.js, Go net/http
Server-side scripting (next) also lets you mix code into the HTML instead of
printing the whole page.
Overview of Server-Side Scripting
Embed vs. External Server Side Code
External code
A separated program: C, C++, …
Server runs it and sends its output back to client
Embed code
Scripting inside the HTML
Embed programming interface within server
Which is called when server see the scripting directions
Examples
Perl: Apache mod_perl module to embed
Java Server Pages (JSP): Compiled and served by a JSP server
Python
PHP (the most common language)
Server Side Scripting Benefits
How does server side scripting solve CGI problems?
We don’t need to generate whole HTML by code
Only dynamic parts are coded
A process is not created per request
All requests are processed by the interpreter
Which is implemented as a library for web server process
Each request is served by an existing worker (process or thread)
![Five steps. 1: the browser sends GET /hello.php?name=ali. 2: the web server picks a handler by the file name: .html and .png files are read from disk and sent as they are, .php files go to the PHP runtime (mod_php inside the server or PHP-FPM beside it). 3: the runtime parses the request into $_GET, $_POST, cookies and the session. 4: it runs the code inside the HTML of hello.php, so <p>Hello, <?= htmlspecialchars($_GET["name"]) ?></p> becomes <p>Hello, ali</p>. 5: only that output goes back to the browser as 200 OK.](./img/sss.svg)
