Untitled

<?php
$file = $_GET["filename"];
    $file_name = basename($file);
    header("Content-Type: application/zip");
    header("Content-Disposition: attachment; filename=$file_name");
    header("Content-Length: " . filesize($file)); //added this line
    readfile($file);
?>

<a href="<?php echo $_GET["filename"]; ?>" target="_blank">click here</a>

Download.php is getting the parameter filename value correctly but says

Warning: Cannot modify header information - headers already sent by (output started at /home/content/72/11973872/html/filerepairtool/down/download.php:9) in /home/content/72/11973872/html/filerepairtool/down/download.php on line 20

Warning: Cannot modify header information - headers already sent by (output started at /home/content/72/11973872/html/filerepairtool/down/download.php:9) in /home/content/72/11973872/html/filerepairtool/down/download.php on line 21

<?php
include 'file.php';
?>

<?php
$file = $_GET["filename"];
    $file_name = basename($file);
    header("Content-Type: application/zip");
    header("Content-Disposition: attachment; filename=$file_name");
    header("Content-Length: " . filesize($file)); //added this line
    readfile($file);
?>

<!DOCTYPE html>
<head>
<title>Page title</title>
<body>
Hello world

<?php
$file = $_GET["filename"];
    $file_name = basename($file);
    header("Content-Type: application/zip");
    header("Content-Disposition: attachment; filename=$file_name");
    header("Content-Length: " . filesize($file)); //added this line
    readfile($file);
?>
</body>
</html>