Passing Special Characters to PHP via AJAX - php

Question

I'm collecting form data, sending that to PHP validation script through AJAX call. The issue is on special characters the php validation script is not working as expected.
HTML:
<input type="text" name="firstName" class="firstName"
placeholder="[first name]" required autofocus maxlength="25" size="25" />
JS:
$(".button").click(function () {
var firstName = encodeURIComponent($("input.firstName").val());
var datastring = "firstName=" + firstName;
$.ajax({
type: "POST",
url: "/scripts/validateSignup.php",
data: datastring,
cache: false,
success: function (errorMessage) {
//print to screen
}
});
});
PHP Validation
$postData = $_POST;
if (Filter::validateString($postData['firstName']) == false) {
echo "Oops! Some characters used in your first name are not valid.";
}
PHP Filter
//Returns true if string is good, false otherwise
public static function validateString($string) {
$string = trim($string);
if ($string == null || $string == "") {
return false;
} else {
if (preg_match("/[^\.\,\-\_\'\"\#\?\!\:\;\$\#\%\&\+\= a-zA-Z0-9()]/", $string) == true) {
return false;
} else {
return true;
}
}
}
On an empty string it prints error to screen just fine. But if I do something like "~!##$%^&*()", then it accepts the string as good and doesnt throw and error, even though the result of preg_match == false.

Answer 1

$string = trim($string);
if ($string == null || $string == "") {
return false;
} else {
if (preg_match("/[^\.,\-_'\"#?!:;\$#&\+=\sa-zA-Z0-9\(\)]/", $string) == true) {
return false;
} else {
return true;
}
}
That is more valid regex, but not the result you want: you're checking for pretty much all input, so it'll match "abcd" and return false as well. There are 11 characters with special meanings to regular expressions, only those and the " need to be escaped: ^$[]()|.*+-

Answer 2

Try this:-
<?php
$string = "tes$%tname"; // invalid string
//$string = "testname"; // valid string
if(test($string) == false)
{
echo "String is invalid";
}
function test($string){
$string = trim($string);
if ($string == null || $string == "") {
return false;
} else {
if (preg_match("/[^\.,\-_'\"#?!:;\$#&\+=\sa-zA-Z0-9\(\)]/",$string) == true) {
return false;
} else {
return true;
}
}
}
?>
PHPFiddle is here:- http://phpfiddle.org/main/code/cdu-xg2