Secure way to write a Code for Username, Email & url or link Input by Users.

There has been many question on internet on how to write a code for secured username, email or url input. So , here is my code which is the best and secured way to take an input from user for Following Field :-

1. Username.
2. Email.
3. Link or URL.

Username

If you would like to take an input as username, here is PHP code, along with HTML form.

PHP Code:

<form metho="post" action="#">
<label>Username</label>
<input type="text" name="username" placeholder="Enter Username.." />
<input type="submit" value"Submit" />
</form>



php// As we know, username can only have "alphabets from a-z or A-Z" and "digits" from '0-9' or '-,_,.'
//So, we will only accept above stuff
// If you see below code in internet anywhere,
// than it has been posted by me only until unless some faggot copies it and says his own.$input = "";$random = mt_rand(5,8);
function validate_username($input)
{
    $allowed = array(".", "-", "_"); // you can add here more value, you want to allow.
    if(ctype_alnum(str_replace($allowed, '', $input ))) {
        return $input;
    } else {
        $input = "Invalid Username ".$random;
        return $input;
    }
}$username = isset($_POST['username']) ? validate_username($_POST['username']) : " ";
if(strpos($username, $random))
{
echo 'Please Enter only alphanumeric or ._- in username':
} else {// Process your code.}?>

Email Validation

Many Developer blindly trust Javascript for validation, this is the world's most stupid stuff you would do since you are developer. I always say, Server Side Validation is Must, Must and Must.

Here is PHP code :-

PHP Code:

<form method="post" action="#">
<label>Email :- </label>

<input type="email" name="myMail" placeholder="Enter Email.." />
<input type="submit" value="Submit" />
</form>


php
$email = isset($_POST['myMail']) ? $_POST['myMail'] : " ";
if(!filter_var($email, FILTER_VALIDATE_EMAIL) )
{
echo "Invalid Email";
} else {
echo "Processing..";//Process your mail..}?>

But Above FILTER_VALIDATE_EMAIL will also validate 'localhost' or other stuff, so not that accurate, I prefer my own Coded php function which i feel is better than FILTER_VALIDATE_EMAIL, though you may combine them and use them, it will be more simple and cool here is mine.

PHP Code:

// In most of the cases, type=email will do, but it only checks if string has "@",
// we will go 1 step beyond than that and will see if such host exists or not.$email = isset($_POST['myMail']) ? $_POST['myMail'] : " ";$fire = explode("@", $email);$present = strpos($fire[1], '.');
if($present !== false) {
    $semifinal = gethostbyname($fire[1]);
    // I am checking only for IPV4 ip address.
    $final = is_numeric(str_replace('.', '', $semifinal));
    $check = strpos($semifinal, '.');
    if($final) {
        echo "Processing..";
        // Process Email
    } else     {
        echo "Invalid Email Address";
    }
} else {
    echo "We dont consider email with domain something like 'localhost' so please input something example.com ";
}?>