Issue with PHP Script with MySQL - php

Question

My code was working and I don't see issues with it. I tested all the MySQL statements in SQL and everything is fine there.
Everytime it fetches the password variable now it only returns Bad Password as if m_Pass is empty.
Anyone see anything wrong with those statements I don't?
I am using this as a one time password file transfer tool that you have to specify the filename and the password for accessing it.
Then it checks the SQL Database that contains the following format:
id | m_File | m_Pass
0 | Test.txt | testpass
Any help would be appreciated.
Index.php:
<?php
echo <<<EOF
<form method="post" action="Index.php">
File:<input type="text" name="txtFilename"><br>
Password:<input type="text" name="txtPassword">
<input type="submit" value="Download" name="submit">
</form>
EOF;
function doProcess()
{
$servername = "localhost";
$username = "<username>";
$password = "<Password>";
$dbname = "<dbname>";
$filename = $_POST["txtFilename"];
$pass = $_POST["txtPassword"];
echo $filename . "<br>";
if ($filename = ""){
return;
}
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
echo "Connected successfully" . "<br>";
$sql = "SELECT id, m_Pass FROM Main WHERE m_File = '$filename'";
$result = mysqli_query($conn, $sql);
$row = mysqli_fetch_array($result, MYSQLI_ASSOC);
$m_id = $row["id"];
echo $m_id . "<br>";
if ($row["m_Pass"] == $pass){
echo "Downloading.<br>";
//Download File
$filename = utf8_decode("<Path>" . $filename);
if (file_exists($filename)) {
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($filename));
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($filename));
ob_clean();
flush();
readfile($filename);
$sql = "delete from Main where id = '$m_id'";
$result = mysqli_query($conn, $sql);
}
} else {
echo $pass . " | '" . $row["m_Pass"] . "'<br>";
echo "Bad Password.<br>";
}
echo "Done.<br>";
// Close connection
$conn->close();
}
if(isset($_POST['submit']))
{
doProcess();
}
?>

Answer 1

Got it... Turns out the SQL query command wasnt appending the $filename because of the block:
if ($filename = ""){
return;
}
And I see why... I am assigning the value not comparing lol.