Implementation method of PHP filter Page 1/2_PHP tutorial

PHP filters are used to validate and filter data from non-secure sources, such as user input.
What are PHP filters?
PHP filters are used to validate and filter data from non-secure sources.

Validating and filtering user input or custom data is an important part of any web application.

Filter extensions for PHP are designed to make data filtering easier and faster.
Why use filters?
Nearly all web applications rely on external input. This data usually comes from users or other applications (such as web services). By using filters, you can ensure that your application gets the correct input type.

You should always filter external data!

Input filtering is one of the most important application security topics.

What is external data?
Input data from forms
Cookies
Server variables
Database query results
Functions and filters
To filter variables, use one of the filter functions below:

filter_var() - Filter a single variable by a specified filter
filter_var_array() - Filter multiple variables by the same or different filters
filter_input - Get an input variable and Filter it
filter_input_array - take multiple input variables and filter them through the same or different filters
In the example below, we validate an integer using the filter_var() function:

Copy code The code is as follows:

$int = 123;

if( !filter_var($int, FILTER_VALIDATE_INT))
{
echo("Integer is not valid");
}
else
{
echo("Integer is valid");
}
?>

The above code uses the "FILTER_VALIDATE_INT" filter to filter variables. Since this integer is legal, the output of the code is: "Integer is valid".

If we try to use a non-integer variable, the output is: "Integer is not valid".

For a complete list of functions and filters, visit our PHP Filter Reference Manual.
Validating and Sanitizing
There are two types of filters:

Validating filter:
Used to validate user input
Strict format rules (such as URL or E-Mail validation)
Returns the expected type if successful, otherwise returns FALSE
Sanitizing filter:
Used to allow or disallow specified characters in a string
No data format rules
Always returns a string
Options and Flags
Options and flags are used to add additional filtering options to the specified filter.

Different filters have different options and flags.

In the example below, we validate an integer using filter_var() with the "min_range" and "max_range" options:

Copy code The code is as follows:

$var=300;

$int_options = array(
"options"=>array
(
"min_range"=>0,
"max_range"=>256
)
);

if(!filter_var($var, FILTER_VALIDATE_INT, $int_options))
{
echo("Integer is not valid");
}
else
{
echo("Integer is valid");
}
?> ;

Like the code above, options must be put into a related array called "options". If using flags, they don't need to be in an array.

Since the integer is "300", which is not within the specified atmosphere, the output of the above code will be "Integer is not valid".

For a complete list of functions and filters, please visit the PHP Filter Reference Manual provided by W3School. You can see the available options and flags for each filter.
Validate input
Let’s try validating input from a form.

The first thing we need to do is confirm that the input data we are looking for exists.

Then we use the filter_input() function to filter the input data.

In the following example, the input variable "email" is passed to the PHP page:

Copy the code The code is as follows:

if(!filter_has_var(INPUT_GET, "email"))
{
echo("Input type does not exist");
}
else
{
if (!filter_input(INPUT_GET, "email", FILTER_VALIDATE_EMAIL))
{
echo "E-Mail is not valid";
}
else
{
echo "E-Mail is valid";
}
}
?>

Explanation of the example:
The above example has an input variable (email) transmitted through the "GET" method:

Detect whether there is an "email" input variable of type "GET"
If There is an input variable, check if it is a valid email address
Sanitize input
Let’s try to clean up the URL passed in from the form.

First, we want to confirm that the input data we are looking for exists.

Then, we use the filter_input() function to purify the input data.

In the following example, the input variable "url" is passed to the PHP page:

Copy the code The code is as follows:

if(!filter_has_var(INPUT_POST, "url"))
{
echo("Input type does not exist");
}
else
{
$url = filter_input(INPUT_POST,
"url", FILTER_SANITIZE_URL);
}
?>

Example explanation:
Above The example has an input variable (url) transmitted through the "POST" method:

Detects whether there is a "url" input variable of type "POST"
If this input variable exists, sanitize it ( Delete illegal characters) and store it in the $url variable
If the input variable is similar to this: "http://www.W3#$%S^%$#ool.com.cn/", then after purification The $url variable should look like this:

http://www.W3School.com.cn/ Filter multiple inputs
Forms usually consist of multiple input fields. To avoid repeated calls to filter_var or filter_input, we can use filter_var_array or the filter_input_array function.

In this example, we use the filter_input_array() function to filter three GET variables. The received GET variables are a name, an age and an email address:

Copy code The code is as follows:

$filters = array
(
"name" => array
(
"filter"=>FILTER_SANITIZE_STRING
),
"age" => ; array
(
"filter"=>FILTER_VALIDATE_INT,
"options"=>array
(
"min_range"=>1,
"max_range"=> ;120
)
),
"email"=> FILTER_VALIDATE_EMAIL,
);

$result = filter_input_array(INPUT_GET, $filters);

if (!$result["age"])
{
echo("Age must be a number between 1 and 120.
");
}
elseif(! $result["email"])
{
echo("E-Mail is not valid.
");
}
else
{
echo ("User input is valid");
}
?>

Explanation of the example:
The above example has three input variables (name , age and email)

Set an array that contains the name of the input variable, and the filter for the specified input variable
Call the filter_input_array function, the parameters include the GET input variable and the array just set
Check whether there are illegal inputs in the "age" and "email" variables in the $result variable. (If there is an illegal input,)
The second parameter of the filter_input_array() function can be an array or the ID of a single filter.

If the parameter is the ID of a single filter, then the specified filter will filter all values ​​in the input array.

If the parameter is an array, then the array must follow the following rules:

must be an associative array containing the input variables that are the keys of the array (such as the "age" input variable )
The value of this array must be the ID of the filter, or an array specifying filters, flags and options
Use Filter Callback
By using the FILTER_CALLBACK filter, you can call a custom function to It works as a filter. This way, we have full control over data filtering.

You can create your own custom functions or use existing PHP functions.

Specify the function you want to use for the filter, the same way you specify options.

In the example below, we use a custom function to convert all "_" to spaces:

Copy code Code As follows:

function convertSpace($string)
{
return str_replace("_", " ", $string);
}

$string = "Peter_is_a_great_guy!";

echo filter_var($string, FILTER_CALLBACK,
array("options"=>"convertSpace"));
?>

The result of the above code is like this:

Peter is a great guy! Example explanation:
The above example converts all "_" into spaces:

Create a The function
that replaces "_" with spaces calls the filter_var() function, whose parameters are the FILTER_CALLBACK filter and the array containing our function

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