Managing State in the Client Tier
Data sent with the GET or POST methods can include the application state with each HTTP request. An illustration of this approach can be seen in the previous and next browsing features developed in Chapter 5. In this example, there are two pieces, or states, that need to be considered when a page is browsed: the query parameters the user provided and which page should be displayed.
The solution developed in Chapter 5 encodes the query and an offset as an embedded link. An example URL that displays the fourth page of results may be as follows:
http://localhost/example.5-10.php?regionName=All&offset=40
This solution allows navigation through large search result sets. Similar solutions are used in the URLs generated to jump between the results pages of web search engines such as Google or Altavista. Cookies can be used for the same purpose.
Encoding the variables that hold state with each HTTP request increases the amount of data that has to be transmitted over the Web, and when data is encoded using the GET method, applications can generate long URLs. While HTTP doesn't restrict the length of URLs, some older browsers and proxy servers do enforce limits.
When state variables are encoded as part of the URL, or even when they are included as cookies, it is possible for the user to change the values that are sent with the request. For example, a user can enter the following URL manually if she wants to see the records starting from row #7 in the result set:
http://localhost/example.5-10.php?regionName=All&offset=7
Changing the offset in a results page is harmless, but changing the item price of a bottle of wine is more serious. As discussed in Chapter 6 and Chapter 7, an application can't rely on data that is sent from the browser.