Zend_Filter_Input provides a declarative interface to associate
multiple filters and validators, apply them to collections of data, and
to retrieve input values after they have been processed by the filters
and validators. Values are returned in escaped format by default for
safe HTML output.
Consider the metaphor that this class is a cage for external data. Data enter the application from external sources, such as HTTP request parameters, HTTP headers, a web service, or even read from a database or another file. Data are first put into the cage, and subsequently the application can access data only by telling the cage what the data should be and how they plan to use it. The cage inspects the data for validity. It might apply escaping to the data values for the appropriate context. The cage releases data only if it can fulfill these responsibilities. With a simple and convenient interface, it encourages good programming habits and makes developers think about how data are used.
Filters transform input values, by removing or changing characters within the value. The goal is to "normalize" input values until they match an expected format. For example, if a string of numeric digits is needed, and the input value is "abc123", then it might be a reasonable transformation to change the value to the string "123".
Validators check input values against criteria and report whether they passed the test or not. The value is not changed, but the check may fail. For example, if a string must look like an email address, and the input value is "abc123", then the value is not considered valid.
Escapers transform a value by removing magic behavior of certain characters. In some output contexts, special characters have meaning. For example, the characters '<' and '>' delimit HTML tags, and if a string containing those characters is output in an HTML context, the content between them might affect the output or functionality of the HTML presentation. Escaping the characters removes the special meaning, so they are output as literal characters.
Zend_Filter_Input, perform the following steps:
Declare filter and validator rules
Create the filter and validator processor
Provide input data
Retrieve validated fields and other reports
The following sections describe the steps for using this class.