2. Provide finer cache control to both sender and recipient
A new general Cache-Control directive that must be
obeyed!
Cache Proxy, Client browser and server are obligated to
obey
Some of the directives in requests:
Cache-control: no-cache Client forces up-to-date
check with origin server.
3. Cache-control: max-age=1000 Client (user
or intermediate cache) is prepared to accept
object without up-to-date check if age is < 1000
seconds.
Overrides expires: If document has not expired but
document age is > max-age, then cache performs an up-
to-date check.
4. Cache-control : public The object is
cacheable by client and network
caches…basically anywhere!
Cache-control: private The object can be
cached only by the client.
Cache-control: max-age =1000 Server
imposes up-to-date check after 1000 seconds.
Similar to Expires header.
5. Server control:
If origin server doesn’t want the object cached, it can
put in response cache-control:private .
If origin server wants an up-to-date check for each
request, it can put in response cache-control: proxy-
revalidate .
If origin server wants up-to-date check once the object
age > 1000, it can put in response: cache-control: max-
age=1000
6. Browser control:
If client wants an up-to-date check even if the object
has not expired, it puts in request: Cache-control: no-
cache .
In client is willing to accept the object that is less than
1000 seconds old without an up-to-date check, it can put
in request: Cache-control: max-age=1000 .
7.
8. CGI stands for Common Gateway Interface.
CGI is a standard programming interface to Web
servers that gives us a way to make our sites
dynamic and interactive.
CGI is not a programming language. It is just a
set of standards (protocols.)
CGI can be implemented in an interpreted
language such as PERL or in a compiled language
such as C.
9. CGI programs work as follows:
STEP 1 (On the client side): Get Information from
the user (using HTML forms, SSI, Java Applet,
…,etc).
STEP 2 (On the server side): Process the data,
connect to DATABASE, search for PATTERNS,
…,etc.
STEP 3 (On the server side): Send the result of
computation back to the client.
10.
11. The steps involved in preparing a CGI
program for work.
1. Contact your Web host to find out where
you should put your CGI programs on the
server. Usually it will be a directory on
the server named “cgi-bin”.
2. Set up the access permission of directory
“cgi-bin”
12. 3- Set up the access permission of the CGI
program
4- Test your CGI program from the server
command line to make sure it works
perfectly before publishing it.
13. <form action=“cgi-prog.cgi”
method=“POST”>
. . .
</form>
Two HTTP methods are available:
GET
POST
The CGI program will be invoked every
time you the button SUBMIT is clicked.
14. GET Method the data passed within the
query string of URL : for example:
http://std.edu/info/program?querystring
the data sent after the “?”
POST Method :
The data sent via entity body
15. CGI Script Output Format :
In whatever language a CGI script is
programmed it MUST send information back
in the following format:
The Output Header
A Blank Line
The Output Data
16. Content-Types
The following are common formats/content-
types :
Format Content-Type
HTML text/html
Gif image/gif
JPEG image/jpeg
17. Depending on the Content-Type defined the data that follows
the header declaration :
• If it is HTML that follows then the CGI script must output
standard HTML syntax.
Example: To produce aWeb page that the server sends to a
browser with a simple line of text ”HelloWorld!” . A CGI script
must output:
Content-Type: text/html
<html>
<head>
<title>Hello, world!</title>
</head>
<body>
<h1>Hello, world!</h1>
</body>
</html>
