Cookies

What is a Cookie?

Cookies are small files which are stored on a user's computer. They are designed to hold a small amount of data specific to a particular client and website, and that can be accessed by the web server and the client browser.

Why cookies are necessary? 

Even before jumping into the details of cookies, let’s see why cookies are required and why has it become an essential piece in the web world.

1.      Provides information about the user

a. How many users are visiting the website?

b. How many of them are new?

c. how often does the users visit?

2.      User Preferences

a. User customization will be stored so that the same preferences will be restored when the same user logins again.

3.      Tracks the session

a. When online shopping, database adds the shopping carts based on the items we choose. By the end, it will be able to tell how many items did the user select. Database saves the shopped carts tagged with unique id generated by Cookie.

Cookies are a convenient way to carry information from one session on a website to another, or between sessions on related websites, without having to burden a server machine with massive amounts of data storage. Storing the data on the server without using cookies would also be problematic because it would be difficult to retrieve a particular user's information without requiring a login on each visit to the website.

If there is a large amount of information to store, then a cookie can simply be used as a means to identify a given user so that further related information can be looked up on a server-side database. For example the first time a user visits a site they may choose a username which is stored in the cookie, and then provide data such as password, name, address, preferred font size, page layout, etc. - this information would all be stored on the database using the username as a key. Subsequently when the site is revisited the server will read the cookie to find the username, and then retrieve all the user's information from the database without it having to be re-entered.

What's in a Cookie? 

Each text file has name value pairs and information about the website. So each website has

got its own Cookie files. So your cookie file looks something like this: 

              UserID    A9A3BECE0563982D    www.goto.com/

 Website has unique ID given by the web server for each user.

When are Cookies created?

Writing data to a cookie is usually done when a new webpage is loaded - for example after a 'submit' button is pressed the data handling page would be responsible for storing the values in a cookie. If the user has elected to disable cookies then the write operation will fail, and subsequent sites which rely on the cookie will either have to take a default action, or prompt the user to re-enter the information that would have been stored in the cookie.

How it works? 

When you click “www. Amazon.com” in browser, it will look into your hard disk and searches for cookie file. If it finds, Cookies will send that name-value pair information to Webserver along with URL. If it doesn’t find, it will not send cookie data. So webserver will understand that you are a new user and allocate a unique id that will send in the subsequent response. Browser will place this cookie information in hard disk.

How Long Does a Cookie Last?

The time of expiry of a cookie can be set when the cookie is created. By default the cookie is destroyed when the current browser window is closed, but it can be made to persist for an arbitrary length of time after that.

Types of Cookies

1.  Session Cookies/Transient Cookies
These cookies get erased when you close the Web browser. The session cookie is stored in temporary memory and is not retained after the browser is closed. Session cookies do not collect information from your computer. They typically will store information in the form of a session identification that does not personally identify the user.
2.  Persistent Cookies 
This is also called as permanent cookie/stored cookie. This cookies are stored on your hard drive until it expires (persistent cookies are set with expiration dates) or until you delete the cookie. Persistent cookies are used to collect identifying information about the user, such as Web surfing behavior or user preferences for a specific Web site.