mysqli connection not working with mysqli_real_escape_string - php

Question

I have a simple demo php scripts am trying out. i have been using the deprecated mysql_ extensions earlier, trying to migrate from that to mysqli_ is being overly buggy. when trying to use mysqli_real_escape_string php throws a variable not defined error cant seem to figure out why.
<?php
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "bridgoo";
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
//do stuff
}
// prepare and bind
$stmt = $conn->prepare("INSERT INTO bridgoo_users (username, email, password) VALUES (?, ?, ?)");
$stmt->bind_param("sss", $username, $password, $email);
//generate password hash using blowfish algorithm
$password_hash = password_hash($_POST['password'], PASSWORD_BCRYPT, ["cost" => 9]);
$username = clean_input($_POST['username']);
$password = clean_input($password_hash);
$email = clean_input($_POST['email']);
function clean_input($input){
$input = htmlentities($input);
$input = htmlspecialchars($input,ENT_QUOTES);
$input = mysqli_real_escape_string($conn,$input);
return $input;
}
$stmt->execute();
$stmt->close();
$conn->close();
?>
php error Notice: Undefined variable: conn in C:\xampp\server1\htdocs\bridgoo\inc\register.php on line 24

Answer 1

The error about undefined variable $conn has to do with PHP variable scope, and other people have answered that.
But your code needs some other suggestions too.
You don't need to clean inputs at all if you use query parameters. That's the point of using query parameters: No need for mysqli_real_escape_string() because parameters are automatically safe.
In fact, you must not use mysqli_real_escape_string(), because your data will be inserted to your database literally with \' escaped apostrophes.
Simply put: SQL parameters and mysqli_real_escape_string() are mutually exclusive. Don't do both.
Also, it makes no sense to use htmlentities() or htmlspecialchars () at all for sanitizing SQL inputs, even if you use mysqli_real_escape_string() instead of parameters.
Those html-related functions are for HTML output only. They're very important for protecting your web app against XSS vulnerabilities, which is another unrelated web security risk you need to know about. But they're not needed for sanitizing SQL input.
Other comments:
It's confusing that you're re-using username and password variables for both the mysqli connection and the application data. There's no reason to re-use variables, they don't cost you anything.
Make sure the order of parameters in your INSERT matches the order of bind variables you pass to bind_param().
Always check the return value of prepare() and execute(). They return FALSE if they fail. If they fail, you must log the error and report to the user that the page didn't work.
I prefer to log the technical error message to the PHP error log
file, and report something more friendly to the user.
Get into the habit of keeping a window open to watch your PHP error log during development, it'll help you a lot.
Here's how I suggest you write your code:
<?php
$mysql_servername = "localhost";
$mysql_username = "root";
$mysql_password = "";
$mysql_dbname = "bridgoo";
$conn = new mysqli($mysql_servername, $mysql_username, $mysql_password, $mysql_dbname);
if ($conn->connect_error) {
error_log($conn->connect_error);
die("Sorry, a database error occurred.");
}
$stmt = $conn->prepare("
INSERT INTO bridgoo_users (username, password, email)
VALUES (?, ?, ?)");
if ($stmt === false) {
error_log($conn->error);
die("Sorry, a database error occurred.");
}
$stmt->bind_param("sss", $username, $password_hash, $email);
//generate password hash using blowfish algorithm
$password_hash = password_hash($_POST['password'], PASSWORD_BCRYPT, ["cost" => 9]);
$username = $_POST['username'];
$email = $_POST['email'];
if ($stmt->execute() === false) {
error_log($conn->error);
die("Sorry, a database error occurred.");
}
if ($stmt->affected_rows == 1) {
echo "Success!"
} else {
echo "Sorry, an unknown problem occurred, and your record was not saved."
}

Answer 2

Your clean_input function does not have access to your $conn variable, it lives in a different scope.
The easy solution would be to add the connection as a parameter to the function. Something like this:
<?php
...
$username = clean_input($_POST['username'], $conn);
$password = clean_input($password_hash, $conn);
$email = clean_input($_POST['email'], $conn);
function clean_input($input, $conn){
...
Wether that is the best or cleanest solution I'll leave in the middle, but it should work just fine.

Answer 3

You should pass $conn as parameter to your function clean_input;
$username = clean_input($conn, $_POST['username']);
$password = clean_input($conn, $password_hash);
$email = clean_input($conn, $_POST['email']);
function clean_input($conn, $input){
$input = htmlentities($input);
$input = htmlspecialchars($input,ENT_QUOTES);
$input = mysqli_real_escape_string($conn,$input);
return $input;
}