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Article:
Developing State-enabled Applications With PHP by: John L Installment 1 Developing State-enabled Applications With PHP When a user is browsing through a website and is surfing from one web page to another, sometimes the website needs to remember the actions (e.g. choices) performed by the user. For example, in a website that sells DVDs, the user typically browses through a list of DVDs and selects individual DVDs for check out at the end of the shopping session. The website needs to remember which DVDs the user has selected because the selected items needs to be presented again to the user when the user checks out. In other words, the website needs to remember the State - i.e. the selected items - of the user's browsing activities. However, HTTP is a Stateless protocol and is ill-equipped to handle States. A standard HTML website basically provides information to the user and a series of links that simply directs the user to other related web pages. This Stateless nature of HTTP allows the website to be replicated across many servers for load balancing purposes. A major drawback is that while browsing from one page to another, the website does not remember the State of the browsing session. This make interactivity almost impossible. In order to increase interactivity, the developer can use the session handling features of PHP to augment the features of HTTP in order to remember the State of the browsing session. The are basically 2 ways PHP does this: Using cookies Using Sessions The next installment discusses how to manage sessions using cookies... Installment 2 Cookies Cookies are used to store State-information in the browser. Browsers are allowed to keep up to 20 cookies for each domain and the values stored in the cookie cannot exceed 4 KB. If more than 20 cookies are created by the website, only the latest 20 are stored. Cookies are only suitable in instances that do not require complex session communications and are not favoured by some developers because of privacy issues. Furthermore, some users disable support for cookies at their browsers. The following is a typical server-browser sequence of events that occur when a cookie is used: The server knows that it needs to remember the State of browsing session The server creates a cookie and uses the Set-Cookie header field in the HTTP response to pass the cookie to the browser The browser reads the cookie field in the HTTP response and stores the cookie This cookie information is passed along future browser-server communications and can be used in the PHP scripts as a variable PHP provides a function called setcookie() to allow easy creation of cookies. The syntax for setcookie is: int setcookie(string name, [string val], [int expiration_date], [string path], string domain, [int secure]) The parameters are: name - this is a mandatory parameter and is used subsequently to identify the cookie value - the value of the cookie - e.g. if the cookie is used to store the name of the user, the value parameter will store the actual name - e.g. John expiration_date - the lifetime of the cookie. After this date, the cookie expires and is unusable path - the path refers to the URL from which the cookie is valid and allowed domain - the domain the created the cookie and is allowed to read the contents of the cookie secure - specifies if the cookie can be sent only through a secure connection - e.g. SSL enable sessions The following is an example that displays to the user how many times a specific web page has been displayed to the user. Copy the code below (both the php and the html) into a file with the .php extension and test it out. [?php //check if the $count variable has been associated with the count cookie if (!isset($count)) { $count = 0; } else { $count++; } setcookie('count', $count, time()+'600
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