inspect data (url variable) before inserting to mysql - php

Question

My php script is posting bad urls that ajax send to it. When I try to filter the url and cancel the insert into mysql, it doesn't work. What I want to do is verify the $link variable if it a link. If not, don't post data to mysql. Can i know what I did wrong and how to fix it? Thank you :)
Here is my code
$con = mysql_connect("localhost","root","");
if (!$con) {
die('Could not connect: ' . mysql_error());
}
mysql_select_db("database", $con);
$link = $_POST['new'];
$name = $_POST['name'];
$size = $_POST['size'];
$cat = $_POST['cat'];
// PHP 5.3.5-1ubuntu7.2
$link = mysql_real_escape_string($link);
$name = mysql_real_escape_string($name);
$size = mysql_real_escape_string($size);
$cat = mysql_real_escape_string($cat);
if (filter_var($link, FILTER_VALIDATE_URL)) {} else {
echo "URL is NOT valid";
mysql_close($con);
exit();
}
$check = mysql_query("SELECT link FROM links WHERE link = '{$link}';");
if (mysql_num_rows($check) == 0) {
// insert
$sql="INSERT INTO links (link, name, size, category) VALUES ('$link','$name','$size','$cat')";
if (!mysql_query($sql,$con))
{
die('Error: ' . mysql_error());
}
echo "1 record added. Redirecting!";
mysql_close($con);
}

Answer 1

try this one:
if(filter_var($link, FILTER_VALIDATE_URL, FILTER_FLAG_SCHEME_REQUIRED) === false){
echo "URL is NOT valid";
mysql_close($con);
exit();
}
Your are right xxxhxtxtp://example.com will pass as valid url.
Try it with preg_match instead.
if (!preg_match("#^http(s)?://[a-z0-9-_.]+\.[a-z]{2,4}#i", $link)) {
echo "URL is NOT valid";
mysql_close($con);
exit();
}
With this regex you need to have http(s) scheme. So you can search for another regex if that don't work for you.

Answer 2

Is this what you're trying to do? Perhaps you need a regex solution.
if (filter_var($link, FILTER_VALIDATE_URL)) {
$check = mysql_query("SELECT link FROM links WHERE link = '{$link}';");
if (mysql_num_rows($check) == 0) {
// insert
$sql="INSERT INTO links (link, name, size, category) VALUES ('$link','$name','$size','$cat')";
if (!mysql_query($sql,$con))
{
die('Error: ' . mysql_error());
}
echo "1 record added. Redirecting!";
mysql_close($con);
}
} else {
echo "URL is NOT valid";
mysql_close($con);
exit();
}