WEB PROGRAMMING

1. WEB PROGRAMMING COOKIES, SESSION andObject Oriented Programming With PHP

2. INTRODUCTION • Cookies are a technology which can be easily and simply used by a Webmaster to achieve a great many very useful tasks when creating websites. • Although cookies are well known to users, many people are not really sure what they are used for, and a large amount of webmasters don't realise the possibilities open to them when they use cookies. • Cookies can be set and used by a simple command in most scripting languages.

3. What Is A Cookie? • Apart from being a type of biscuit, a cookie is also a very useful piece of technology for use on the web. • One of the problems which many websites need to overcome is that there is no way of directly finding out who is on a website. • They basically give the website owner the opportunity to store a little piece of information on a user's computer which they can then retrieve at a later date. • Cookies are just tiny text files (only up to 4Kb in size) and a website can write them to the user's computer via the web browser.

4. What Use Is A Cookie? • So why would anyone want to store 4000 characters of text on a user's computer? • It isn't enough to put anything really worthwhile on there! The power of the cookie, though, is to recognise a site visitor over and over again.

5. Using Cookies • A cookie is a very basic data file. • It has a name and a value and also stores the address of websites which are allowed to access it and an expiry time. • Basically, a website will set a cookie and give it a name and value. • This name is used by the website to refer to it, and no other website can access the cookie, even if they know it's name. • The name should be unique to the website, but it doesn't matter if it clashes with the name of a cookie from another website.

6. Using Cookies • To retrieve data, the website simply has to request if the user has a cookie with a particular name. • If the user does, the value is returned to the script and it can be dealt with however the website owner chooses (for example a name stored in a cookie could be returned, a user ID could be loaded from a database, or a record could be made of a user visiting a site).

7. Using Cookies • Every cookie is assigned an expiry date and time. • It is up to the website owner to decide how long the cookie should exist for. • Many owners may just choose to set the cookie for an hour, meaning it is only available for the user's single session. • This is common in visitor tracking.

8. Cookie Security • Despite much worrying in the news a few years ago, cookies pose no real danger to users. • Unless they are really worried about themselves being recognised by a website, they are harmless. • The browser actually writes and reads cookies from the computer when requested to by a website, so a malicious website cannot damage the computer.

9. Cookie Security • For webmasters, there are some security concerns. • When the cookie is set, the domain(s) which can access it are set. • Usually this is just the website who set the cookie. • This makes them relatively secure, as you can be sure that your competitor cannot load your cookie from one of your visitors' computers (they cannot even find out if it exisits).

10. Cookie Security • One major security problem with cookies, though, is that they can easily be read by anyone using the computer. • They are just a simple text file, so you should not under any circumstances store passwords in cookies. • A common way to log people in automatically is to store an encrypted version of their password, which can then be matched with an encrypted version on the server.

11. Cookie Security • Another method is to store a unique ID and a unique validation number on the user's system. • This is then referenced in a database to the user's account. • This way, no actual details are stored and a malicious user cannot simply guess users' IDs (as there is the validation number).

12. Setting a Basic Cookie • The PHP function for setting cookies is called:setcookie() • It is a PHP function which can be used without returning a value (for example you can simply execute a setcookie()) command, or you can take the return value and use it.

13. Setting a Basic Cookie • The setcookie() function returns a boolean (true or false) value depending on whether it is successful. So you could execute:if(setcookie()){echo "Cookie set";}else{echo "Cookie not set";}

14. Setting a Basic Cookie • The most basic information for a cookie is it's name and it's value. • The name of the cookie must be something which you can refer to it later as. • You don't need to worry about it clashing with other sites as cookie names are site specific but you should try and use a descriptive and unique name for your cookies.

15. Setting a Basic Cookie • For this first example, assume that you have used PHP to load the user's name into the variable $name and want to greet the user in the future by their name. • You would need to create a cookie which stores their name as follows:setcookie("UsersName",$name);

16. Reading Cookie Values • PHP makes it extremely simple to read the value of a cookie. In PHP, reading form values are achieved using $_GET and $_POST. PHP has a similar global variable for cookies:$_COOKIE['CookieName']; • This variable contains the value of the cookie with name 'CookieName'.

17. Reading Cookie Values • So on your website, if you wanted to display the name of the user, you could simply use the following:echo "Hello, ".$_COOKIE['UsersName']."! Welcome back!";

18. Reading Cookie Values • Of course, the user may not already have the cookie, so you should use the PHP function isset. This returns true if a variable has been set and false if not. Using this, your site could do the following:if(isset($_COOKIE['UsersName']){echo "Hello, ".$_COOKIE['UsersName']."! Welcome back!";}else{setcookie("UsersName",$name);}

19. Cookie Settings • One of the most powerful features of cookies is the ability to set and expiry date for the cookie. The cookie will remain on the users computer until the expiry date, then will automatically delete itself. • To set a cookie with an expiry date, use: setcookie("UsersName", $name, time()+3600); • This code takes the current time (using time()) and then adds 3600 seconds to it, and uses this value to set as the expiry time for the cookie.

20. Cookie Settings • Basically this means that the cookie will remain on the user's computer for an hour (it expires 3600 seconds (1 hour) from the current time). For one week (for example) you would set the cookie as:setcookie("UsersName", $name, time()+604800);

21. Cookie Settings • There are three other options which can be used when setting cookies. • Firstly, the path • This refers to where in the domain you are able to access the cookie in future. • A second setting you can change is the domain. • a cookie is only available in the domain you set it in, • Finally, a cookie has the option to be set as a secure cookie. • If this is turned on, the cookie will only ever be surrendered to the site over a secure connection, not an insecure one.

22. Cookie Settings • The following code shows the imiplementation of a cookie with all settings specified:setcookie("UsersName", $name, time()+3600, "/", ".mysite.com", 1);

23. Cookie Settings • The cookie set here, is called 'UsersName' and again stores the value $name. • It will expire an hour from the current time. It is available in all directories of the site (/ is the root directory). • It is available across any subdomain of the site mysite.com as '.mysite.com' has been given as the domain. • The final 1 means that this is a secure cookie, and can only be transmitted over a secure connection. This would be 0 for a standard (non-secure) cookie.

24. Deleting Cookies • There are occasions on which you may wish to delete a cookie from a user's computer. • This could be if, for example, you want to log the user out of a system (perhaps they are on a public computer). • Deleting a cookie is quite simple to do because all you have to do is to set the expiry time in the past. • By doing this, the cookie will be automatically deleted as soon as it is created, and will remove any data that already exists there.

25. Deleting Cookies • The simplest way is using:setcookie("UsersName", "", time()-3600); • This sets the expiry time in the past so it should be deleted immediately. • There is also no information stored in the cookie.

26. Deleting Cookies • There is a known problem with this, though. Although it works in most cases, there can be problems if a user's timezone is set wrongly. The safest way to completely delete a cookie is to use the following:setcookie("UsersName", "", mktime(12,0,0,1, 1, 1990)); • The mktime() function is a PHP function for setting up a time specified. The time specified here is in the year 1990, so even a badly configured computer should still delete the cookie immediately.

27. WEB PROGRAMMING Sessions

28. Introduction • Session is an alternative and effective solution to cookies in PHP which might actually be better for your website and security • A session is defined in PHP and throughout the Internet as a unique visit to a particular website and it's subsidiaries

29. Introduction • How can sessions in PHP help you out? • Let's say you have a dynamic website where you want to have a person sign in with a username and password. • Once he's in, you want him to be able to access all parts of your website using that name and password.

30. Introduction • There are several ways to "remember" his username and password while he's at your site. • One way is to use cookies. • The advantage of using cookies is that once he logs in, the cookie stores the visitors information on that computer for as long as the duration of the cookie, even if the session is over.

31. Introduction • The obvious disadvantage of cookies is that it's a security hazard. • Also, some people have cookies disabled so it may not be a viable solution. • PHP Sessions are a safer, always working method of storing variables in PHP throughout the duration of the visitors stay.

32. How to start a session? • The first thing you have to place in your php page is: <? session_start(); header("Cache-control: private"); ?>

33. How to start a session? • Explanation • The session_start() and the header has to be placed on the TOP (before any output) of every page you want these variables to follow along with the user • Once you have started the session, to add variables to the session, all you have to do is use the _session varible

34. How to start a session? • For example, if you want to have a username variable with a value of “Popo", you write: <? $_SESSION["username"] = “Popo"; ?>

35. How to destroy/kill a session? • Now, just think of $_SESSION["username"] as any other variable like $username • You can do anything you want with it, and it'll follow around your website from one page to another

36. How to destroy/kill a session? • A session is ended whenever the visitor leaves your site, if you ever want to destroy/kill a variable inside the session, just use this command: <? unset($_SESSION["variable"]); ?> • and replace variable, with the name of the variable you want to delete.

37. How to destroy/kill a session? • If you want to end the session all together while still keeping the visitor on your site, use: <? session_destroy(); ?>

38. WEB PROGRAMMING Object Oriented Programming With PHP

39. Introduction • What is object-oriented programming? • Object-oriented programming consists of three main vocabulary words: classes, methods, and objects

40. Introduction • First off, an object (also know as a class) is a very simple section of code that has a section of its own variables and functions. • An object is basically a data structure (also known as an abstract data type), which are encapsulated in a set of routines known as methods

41. Introduction • In a simple way an object is kind of like a program itself. • Objects can be used for many different things as they are very expandable • What an object is capable of doing is entirely up to the developer. • A class can be used for things as simple as creating a link and or to store data loaded from a file and or SQL query.

42. Introduction • A class is a collection of methods and objects. • What's the purpose of classes in PHP? • It's the same reason as any other programming language: for large projects, classes provide superior organization and less repetitive code • A class can be used for things as simple as creating a link and or to store data loaded from a file and or SQL query.

43. Basic Syntax • The basic syntax of an object is quite simple. As you can see in the example bellow the syntax is much different from that of a function. class className { <? code ?> } • In the above code we have created a simple object that is named "className".

44. Object Variables • An Object can have variables declared inside the object. • While it is not necessary for an object to have any variables it is most likely that they will. • Most, if not all, objects use variables to store information that can be accessed at any time by any function within ,and outside of, the object. • To create an object variable you must use the 'var' command when creating the variable.

45. Object Variables • An example of variable declaration is listed bellow. class className { var $variable1; var $variable2; <? code ?> }

46. Accessing Object Variables • The method of accessing object variables is different depending on if you are accessing the variables from within or outside of the object.

47. Accessing Object Variables • Accessing From Within The Object: • To access a variable from within an objects own function you must use the '$this' reference. An example of this would be: $localvar = $this->variable1; • Notice how we didn't not use the '.' (period) operator but instead we used the '->' (reference/arrow) operator. This is because we are pointing to the variable within the object.

48. Accessing Object Variables • Accessing From Outside of The Object: • Accessing a variable from out side of an object isn't that dissimilar from accessing one within the object. • Instead of using the '$this' reference you use the name of the object you wish to access. An example of this would be: $localvar = $object->variable1;

49. Object Functions • Creating an object function is not that dissimilar from creating a normal function. • To create an object function all you have to do is create a function inside of the objects brackets as shown on next slide.

50. Object Functions Class className { var $variable1; var $variable2; function classFunction($arg1, $arg2) { <? function code ?> } }