A cookie is a small amount of information sent by a Web server to a web browser and then sent back unchanged by the browser each time it accesses that server. HTTP cookies are used for authenticating, tracking, and maintaining specific information about users, such as site preferences and the contents of their electronic shopping carts. The term "cookie" is derived from "magic cookie", a well-known concept in computing which inspired both the idea and the name of HTTP cookies.
A cookie consists of a cookie name and cookie value.
How To Send A Cookie To The Browser?
If you want to sent a cookie to the browser when it comes to request your PHP page, you can use the setcookie( ) function. Note that you should call setcookie() function before any output statements. The following script shows you how to set cookies:
<?php
setcookie("LoginName","XYZ");
setcookie("PreferredColor","Blue");
print("2 cookies were delivered.\n");
?>
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How To Receive A Cookie From The Browser?
If you know that a cookie has been sent to the browser when it was visiting the server previously, you can check the built-in $_COOKIE array, which contains all cookies that were sent by the server previously. The script below shows you how to pickup one cookie from the $_COOKIE and loop through all cookies in $_COOKIE:
<?php
if (isset($_COOKIE["LoginName"])) {
$loginName = $_COOKIE["LoginName"];
print("Received a cookie named as LoginName: ".$loginName."\n");
} else {
print("Did not received any cookie named as LoginName.\n");
}
print("All cookies received:\n");
foreach ($_COOKIE as $name => $value) {
print " $name = $value\n";
}
?>
How Cookies Are Transported From Servers To Browsers?
Cookies are transported from a Web server to a Web browser in the header area of the HTTP response message. Each cookie will be included in a separate "Set-Cookie:" header line in the following format:
Set-Cookie: name=value; expires=time; path=pathVal; domain=domainVal.
How Cookies Are Transported From Browsers To Servers?
Cookies are transported from a Web browser to a Web server in the header area of the HTTP request message. Each cookie will be included in a separate "Cookie:" header line in the following format:
GET / HTTP/1.1
Cookie: name1=value1
Cookie: name2=value2
Cookie: name3=value3
......
Accept: */*
Where Are The Persistent Cookies Stored On Your Computer?
The location and file names where persistent cookies are stored on your computer depend on which browser you are using. If you using Microsoft Internet Explorer, persistent cookies are stored in the \Documents and Settings\$user\Cookies directory. Cookies are stored in multiple cookie files with one file per Web server. Check your cookie directory on your local system, you will be surprised to see how many Web servers are setting persistent cookies to your computer.
How To Delete Cookie Files On Your Computer?
A simple way to delete cookie files on your computer is to use the function offered by the IE browser. The following tutorial exercise shows you how to delete cookie files created by IE:
• Open IE (Internet Explorer)
• Go to Options/Internet Options
• Click the Delete Cookies button on the options dialog window.
Check the cookie directory again. All cookie files should be deleted.
How Does Firefox Manage Cookies?
FireFox browser allows you to delete old cookies, and gives you options to keep persistent cookies in cookie files until they reach their expiration time. The following tutorial shows you how to manage cookies in FireFox:
• Run FireFox
• Go to Tools/Options
• Click Privacy and then Cookies
• Click the Clear button to delete all old cookies
• Change the Keep Cookies option to "until they expire" to allow persistent cookies to be store a cookie file.
What Are The Options To Transfer Session Ids?
Once a new session is created, its session ID must be transferred to the client browser and included in the next client request, so that the PHP engine can find the same session created by the same visitor. The PHP engine has two options to transfer the session ID to the client browser:
As URL parameter - The Session ID will be embedded in all URLs in the HTML document delivered to the client browser. When the visitor clicks any of those URLs, the session ID will be returned back to the Web server as part of the requesting URL.
As a cookie - The session ID will be delivered as a cookie to the client browser. When visitor requests any other pages on the Web server, the session ID will be returned back to the Web server also as a cookie.
The PHP engine is configured to use URL parameters for transferring session IDs by default.
Is It More Secure To Use Cookies To Transfer Session Ids?
yes, because attacking your Web site using URL parameters is much easier than using cookies.
So if you are the system administrator of your Web server, you should set session.use_only_cookies=1.
If your Web server is provided by a hosting service provider, ask them to set session.use_only_cookies=1.
How can PHP and Javascript interact?
PHP and Javascript cannot directly interact since PHP is a server side language and Javascript is a client-side language. However, we can exchange variables since PHP can generate Javascript code to be executed by the browser and it is possible to pass specific variables back to PHP via the URL.
What is needed to be able to use image function?
GD library is needed to execute image functions.
What is the use of the function 'imagetypes()'?
imagetypes() gives the image format and types supported by the current version of GD-PHP.
Which function gives us the number of affected entries by a query?
mysqli_affected_rows() return the number of entries affected by an SQL query.
What is the difference between mysqli_fetch_object() and mysqli_fetch_array()?
The mysqli_fetch_object() function collects the first single matching record where mysqli_fetch_array() collects all matching records from the table in an array.
How can we access the data sent through the URL with the GET method?
To access the data sent via the GET method, we use $_GET array like this:
www.url.com?var=value
$variable = $_GET["var"]; this will now contain 'value'
How can we access the data sent through the URL with the POST method?
To access the data sent this way, you use the $_POST array.
Imagine you have a form field called 'var' on the form when the user clicks submit to the post form, you can then access the value like this:
$_POST["var"];
What Is The Timeout Period On Session Values?
The PHP engine has no direct settings on session timeout period. But it has a session garbage collection mechanism that you can set to remove those special files containing session values. There are 3 settings you can use to define the session garbage collection mechanism:
session.gc_probability = 1
session.gc_divisor = 1000
session.gc_maxlifetime = 1440
The first two settings tell the PHP engine to run the garbage collection process once every 1000 requests received by the Web server. The last setting tells the PHP engine to treat session values as garbage 1440 seconds after they have not been used.
Putting all settings together, your session values probably be removed 1440 seconds after the visitor stopping using your Web site. The probability of this removal is one over 1000 requests received after the 1440-second period.
In another word, if visitor John stopped using your site, and there is no other visitors coming to your site, session values created for John will never be removed. However, if you have a busy site, like 1000 requests per minute, John's session values will be removed about one minute plus 1440 seconds after John stopped using the site.