PHP Filters

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Today we will learn about a new and simple topic called filters in this PHP Filters tutorial.

  • What is FILTER?
    • English meaning of filter is removing unwanted things and taking only what is required.
    • In PHP we use filter to validate (check the valid format) and sanitize (remove unwanted data) the input data received from an external source.
    • The external source can be a user input, output of a query evaluation, web service data, server variables, cookies, etc.
    • Till now we used different methods and manual conditions to check, if the user has entered the data or not or if the entered data is valid or not. This requires a lot of code.
    • But PHP has provided us with built in methods to decide the validity of data and filter some unwanted things with the help of different filters.
    • We know that every website gets data from external sources. To make sure that we get correct input data validation is the most important task that is to be performed.
    • This validation process with PHP filters becomes very easy and quick.
  • Details of Validating and Sanitizing:
    • Validating Filter:
      • This is also called as logical Filter.
      • It is used to validate user input i.e. to check if the given input is in correct format.
      • It strictly follows the format rules (I mean the valid format is checked for eg. Email, url, etc.).
      • It returns expected type on success and false on failure.
    • Sanitizing Filter:
      • It is used to allow or disallow specified characters in a string.
      • It does not follow strict format types.
      • It always returns a string.
    • Functions used to filter data are :
      • filter_var(): it filters a single variable with a specified filter.
      • filter_var_array(): it filters number of variables with same or different filters.
      • filter_input(): it gets one input variable and filters it.
      • filter_input_array(): it gets number of input variables and filters them with same or different filters.
    • There is a function called filter_list() which lists all the filters that can be used to filter the input data of different types.
    • Just create a new folder named filters in the htdocs folder in xampp folder. Now open a new notepad++ document and save it as index.php in the newly created filters folder.
    • Write the following code in index.php:
    • Now open a browser and write localhost/filters in the address bar of the browser, you will get the following output:
    • Filter Name Filter ID
      Int 257
      Boolean 258
      Float 259
      validate_regexp 272
      validate_url 273
      validate_email 274
      validate_ip 275
      String 513
      Stripped 513
      Encoded 514
      special_chars 515
      full_special_chars 522
      unsafe_raw 516
      Email 517
      url 518
      number_int 519
      number_float 520
      magic_quotes 521
      Callback 1024
    • These filters are used in the filter_var(), filter_var_array(), etc functions to filter the input data.
    • The filters have their own ids. The string and the stripped filters have same id hence they are treated as same.
    • Let us create a form that accepts some data. Comment the code for table shown above and write the following code in index.php.
    • The form has method post and has value welcome.php in its action attribute.
    • We have fields for name, age, marks, email-id and school URL in the form. The form is shown below:
    • form
      fig 1

    • To validate and sanitize the data entered in the form, the following code is written above the html form code:
    • We have validated the form using the above code. In it we have used the function filter_input() to filter the information entered by user.
    • The filter_input() function returns false on failure and the expected value on success.
    • It has 3 parameters:
      • First is the method by which the data will be accepted and transferred to another page say INPUT_POST for post method and INPUT_GET for get method.
      • Next is the value entered by user.
      • Next is the filter applied for that particular input.
    • Here we are using the filter_input() function because we are accepting input from user through a form.
    • The filter FILTER_SANITIZE_STRING is used to filter the strings to allow us to use input data safely.
    • The FILTER_SANITIZE_STRIPPED filter is same as FILTER_SANITIZE_STRING so you can use either of it to filter strings.
    • The filter FILTER_VALIDATE_INT is used to filter integer values, we have used it for age in the form.
    • Here, if user doesn’t enter his age, an error message will be shown and an error message of invalid value will also be displayed if the filter_input() function returns false.
    • The FILTER_VALIDATE_FLOAT filter is used to filter float values, we have used it for percentage in the form.
    • The email input is first sanitized with FILTER_SANITIZE_EMAIL and then validated using FILTER_VALIDATE_EMAIL.
    • Next the school website URL is sanitized using FILTER_SANITIZE_URL and then validated using FILTER_VALIDATE_URL.
    • Then the $errors variable is checked to see if it has any errors. If it is empty, it means the data is validated and so the user is redirected to welcome.php page using the following statement:
  • Options and Flags:
    • Options and flags are the additional options to add additional filters to the specified filters.
    • Different filters have different options and flags.
    • Options and flags are specified in an array.
    • We can provide additional validation to an input value entered by the user by giving a minimum and maximum range for an integer number, sanitizing special characters from a string etc.
    • Let us see different options and flags for different types of values one by one:
      1. Validating Integer values:
        • Setting a range for integer input:
          • See the following code:
          • Here, we have the integer number in a variable $no. The minimum range limit is 10 and maximum range limit is 100 which is stored in variables $min and $max.
          • Here we have used filter_var() function because we are filtering a value stored in a variable. It has parameters as the variables to be filtered, the filter used to validate/sanitize the variable, options/flags.
          • In this above statement
            we have validated the number to be an integer using FILTER_VALIDATED_INT. And the options min_range and max_range validation is added to it in an array. These options allow only those numbers which are within the given minimum and maximum range values.
          • If the number fails to fit in the conditions given in filter_var() function, the filter_var() function returns false and nothing will be displayed and if it satisfies the conditions the number will be displayed.
          • If you want to give only minimum range value and if you want no limit for maximum range value, then you can give only min_range in the options array and vice –a versa.
        • Allowing octal or hex values using flags:
          • Write the following code:
          • Here we have used flag FILTER_FLAG_ALLOW_OCTAL in the array as shown in the statement
          • If the function filter_var() returns true, it will display the statement The given number is octal. And if it returns false, it will display the statement The given number is not an octal number.
          • In the same way we can use FILTER_FLAG_ALLOW_HEX for hexadecimal numbers.
      2. Validating Regular Expression:
        • Using options for regular expression :
          • See the code below:
          • In the above code, we have a string “Ashok Patil” in the variable $name.
          • The $pattern is a variable which contains the regular expression to which we want to match the string in variable $name.
          • The regular expression starts with a forward slash followed by an ex-or sign and ends with forward slash. Then the formula for the expression is written between it.
          • The variable $pattern contains formula [a-z]*. This means only a to z characters are allowed and the asterisk (*) means there is no restriction on the number of characters.
          • The function filter_var() is used to validate the string. FILTER_VALIDATE_REGEXP is the filter used to filter the string and the key-value pair regexp=>$pattern in the options array is used to check the string according to the regular expression given in the $pattern variable.
            If it returns true then the value in $name variable is displayed otherwise the statement echo $name.”is not in proper format.”; will be executed.
          • You can use regular expressions for anything like for email, for some specific format number etc.
      3. Validating URL:
        • We can validate a URL with FILTER_VALIDATE_URL filter as shown in the form validation code.
        • But a URL can be in different forms and all these forms cannot be validated using the same format of URL used by FILTER_VALIDATE_URL.
        • To validate all the forms of URL 4 flags have been provided as shown below:
          • FILTER_FLAG_SCHEME_REQUIRED,
          • FILTER_FLAG_HOST_REQUIRED,
          • FILTER_FLAG_PATH_REQUIRED,
          • FILTER_FLAG_QUERY_REQUIRED
        • See the code given below:
        • In the above code we have a url address www.school.com in the variable $url.
        • We check it in the filter_var() function using the filter FILTER_VALIDATE_URL and the flag FILTER_FLAG_SCHEME_REQUIRED. This flag allows the url containing http://.
        • Since the $url does not contain http:// it is treated as invalid and the statement The www.school.com is not valid. Is displayed.
        • Similarly, the flag FILTER_FLAG_HOST_REQUIRED allows the URL containing the host name. For example http://boaston.
        • The flag FILTER_FLAG_PATH_REQUIRED allows the URL containing the path. For example http://boaston/computer/index.php.
        • The flag FILTER_FLAG_QUERY_REQUIRED allows the URL containing query. For example http://boaston/computer/index.php?name=Ashok&age=12.
      4. Sanitizing a string:
        • We know sanitizing means removing unwanted data. To sanitize a string we use FILTER_SANITIZE_STRING or FILTER_SANITIZE_STRIPPED filters.
        • Along with it we use flags such as
          • FILTER_FLAG_NO_ENCODE_QUOTES,
          • FILTER_FLAG_STRIP_LOW,
          • FILTER_FLAG_STRIP_HIGH,
          • FILTER_FLAG_ENCODE_LOW,
          • FILTER_FLAG_ENCODE_HIGH,
          • FILTER_FLAG_ENCODE_AMP.
        • When we use quotes in the string, sometimes these quotes are converted to their html equivalent codes, in such situation we can use the flag FILTER_FLAG_NO_ENCODE_QUOTES and keep them from converting to html codes.
        • See the following code:
        • The FILTER_SANITIZE_STRING filter removes the script tags and the FILTER_FLAG_NO_ENCODE_QUOTES flag keeps the quotes from converting to html code.
        • Similarly the flag FILTER_FLAG_STRIP_LOW allows stripping of characters having ASCII values less than 32.
        • The flag FILTER_FLAG_STRIP_HIGH allows stripping of characters having ASCII values higher than 32.
        • The flag FILTER_FLAG_ENCODE_LOW allows encoding of characters having ASCII values less than 32.
        • The flag FILTER_FLAG_ENCODE_HIGH allows encoding of characters having ASCII values higher than 32.
        • The flag FILTER_FLAG_ENCODE_AMP allows encoding of character & in a string to
      5. Encoding a URL:
        • We use the filter FILTER_SANITIZE_ENCODED to sanitize the filter.
        • Along with that we can use the flags
          • FILTER_FLAG_STRIP_LOW,
          • FILTER_FLAG_STRIP_HIGH,
          • FILTER_FLAG_ENCODE_LOW,
          • FILTER_FLAG_ENCODE_HIGH
        • These are used same as for the string above.
      6. Sanitizing Special Characters:
        • We can sanitize special characters using FILTER_SANITIZE_SPECIAL_CHARS filter.
        • Let us see the code below:
        • The special characters in the string are encoded.
        • The flags used with this are
          • FILTER_FLAG_STRIP_LOW,
          • FILTER_FLAG_STRIP_HIGH,
          • FILTER_FLAG_ENCODE_HIGH
      7. Sanitizing a URL:
        • We use filter FILTER_SANITIZE_URL to sanitize a URL.
      8. Sanitize an integer number:
        • To sanitize an integer a filter FILTER_SANITIZE_NUMBER_INT is used.
        • It allows numbers + and – signs.
        • See the code below:
        • In the above code we have a variable $int with a string containing numbers and some other characters such as period, semi-colon, addition sign.
        • After sanitizing this string with FILTER_SANITIZE_NUMBER_INT we get 12345+6789 as the output. It has removed the period and semicolon from the string.
        • This shows us that it allows only +,- and integers in the number.
      9. Sanitizing a float number:
        • The filter FILTER_SANITIZE_NUMBER_FLOAT is used to sanitize a float number.
        • This filter removes all characters except numbers, + and – from the string.
        • See the code below:
        • Here, you can see that the output has the numbers and the + sign. Even though it is a float number no decimal point is kept.
        • So to avoid removal of a period (.) we use a flag FILTER_FLAG_ALLOW_FRACTION.
        • Let’s see the following code and its output:
        • Here, you can when we use flag FILTER_FLAG_ALLOW_FRACTION along with the filter FILTER_SANITIZE_NUMBER_FLOAT, the decimal point is retained from the string as shown in the output.
        • We can also use the flag FILTER_FLAG_ALLOW_THOUSAND with the filter FILTER_SANITIZE_NUMBER_FLOAT to allow the use of number of separators.
        • Another flag FILTER_FLAG_ALLOW_SCIENTIFIC is used to allow the use of scientific notations like e, E etc.
      10. Callback Filter:
        • Callback filter is a functionality provided for us to have full control on the filtering of data, because it allows us to use our user-defined functions for filtering.
        • Let us see an example. The code is given below:
        • Here, we have defined a function uppercase() which will allow us to return the string given to it in a uppercase format.
        • To allow the use of uppercase() function for filtering, we have used FILTER_CALLBACK. The function name is provided in an associative array with options as a key and function name uppercase as its value.
        • The output of the string is shown above; all the letters have been converted to uppercase letters.
        • You cannot use more than one function in callback filter.
        • We can write the above code even in another way, as shown below:
  • Using array for validating and sanitizing all the input fields:
    • As we used the functions filter_var() and filter_input() for a single variable or input, we can use filter _var_array () and filter_input_array () functions for number of variables and inputs.
    • Let us see an example, the code is given below:
    • We will validate the form shown in fig 1 using the filter_input_array() function.
    • Here we have applied filters to input values in an array and this array is passed as a parameter to filter_input_array() function.
    • The INPUT_POST is used because the form has POST method.
    • You can have the input type according to the way the input is accepted such as INPUT_GET, INPUT_POST, INPUT_COOKIE, INPUT_SESSION, INPUT_SERVER, INPUT_ENV, INPUT_REQUEST.
    • The filter_var_array() function is also used in the same way.

Thus we studied how to validate and sanitize input accepted from the user to simplify the further functions that work on the input in this PHP Filters tutorial.

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