Nesting ifs to catch errors

Question

You probably know this image:

Lets say I want to validate a single user input through various methods, and each ones depends on the success of the previous one. How can I avoid this enourmus and ugly if nesting?

I can't think of other way, which validates correctly and in the event of an error, returns the correct message, but it does look ugly and could probably a pain in the ass to mantain.

Any ideas?

Answer 1

My experiece so far says if you have more than 4-5 validations for the same goal, you are most probably doing something wrong. For validating user input, you might need certain pattern of chars, which you could achieve with regex, you might need all fields to be populated, some exotic things like the user to be from certain country IP or to have checked at least 18 years old in a dropdown. All other things, either beolng to the group of these, or chances are - they are redundant.

As the others stated, you, also, should not nest the blocks, but return the execution if the conditions are not met.

For example:

function isFormPopulated() {
    $requiredFields = array('user', 'pass', 'age', 'sex');
    foreach ($requiredFields as $field) {
        if (empty($_POST[$field])) { 
            $_SESSION['msg'] = $field . ' field should be populated'; // here better throw exception, instead of session saving the message
            return false;
        }
    }
    return true;
}

function isPatternValid() {
     $fieldPatterns = array('user' => '/w+/', 'pass' => 'someOtherRegex')
     foreach ($fieldPatterns as $field => $pattern) {
         if (!preg_match($pattern, $_POST[$field])) {
             return false;
         }
     }
     return true;
}

function isUserAllowed() {
    if (in_array($_SERVER['REMOTE_ADDR']......) {
        return false;
    }
    return true;
}

function isUserLegal() {
    if ($_POST['age'] < self::MIN_ALLOWED_AGE) {
        return false;
    }
    return true;
}

function isValid() {
     // here you can check with && the evaluation of the previous functions
     // or you can check one by one and return false aswell
     // return true at the end
}


function register() {
     if (!isValid()) {
         return false;
     }
     // continue execution of the registration process
}

Validating a user input is in most of the cases not coupled on each condition. E.g. a regex condition is not coupled to the legal condition. However, if by design (which I assume wrong) you have coupling. you can chain validation like

function validationFour() {
    if (!validationThree() || !current_validation) {
        return false;
    }
    return true;
}

function validationThree() {
    if (!validationTwo() || !current_validation) {
        return false;
    }
    return true;
}

Answer 2

A good practice is to prevent deeply nested statements. So better to find the negative condition, and deal with it straight away. For instance:

if(!$_POST['user_name']){
    // exit
}

if(!$_POST['password']){
    // exit
}

// if we get to here, we assume all previous checks passed

This creates clean code because deeply nested code is harder to maintain, and deals with conditions as soon as it finds them.

Answer 3

You could use a try/catch block and throw an exception when validation fails. For example:

try {
  if (!$_POST['user_name']) {
    throw new Exception('Invalid username');
  }

  if (!$_POST['user_password_new']) {
    throw new Exception('Invalid password');
  }

} catch (Exception $e) {
  echo 'Caught exception: ',  $e->getMessage(), "\n";
}

Answer 4

if (!$_POST['user_name']) {
    $_SESSION['msg'] = 'Empty Username';
    return register_form();
}

if (!$_POST['user_password_new']) {
    $_SESSION['msg'] = 'Empty Password';
    return register_form();
}

...

create_user();
...

Answer 5

Based on the following statement, it seems that you can just stack them up, and return immediately if the previous one failed. If the previous one succeeded, then it is safe to perform the next check.

each ones depends on the success of the previous one