Secure your gravity forms uploads

dl-file.php

<?php
require_once('wp-load.php');
is_user_logged_in() || auth_redirect();

$upload_dir = wp_upload_dir();
//Set your path below I am using /gravity_forms/
$basedir = $upload_dir[ 'basedir' ] . '/gravity_forms/';

$file = rtrim( $basedir, '/' ) . '/' . str_replace( '..', '', isset( $_GET[ 'file' ] ) ? $_GET[ 'file' ] : '' );
if ( ! $basedir || ! is_file( $file ) ) {
 status_header( 404 );
 die( '404 &#8212; File not found.' );
}

$mime = wp_check_filetype( $file );
if( false === $mime[ 'type' ] && function_exists( 'mime_content_type' ) )
 $mime[ 'type' ] = mime_content_type( $file );

if( $mime[ 'type' ] )
 $mimetype = $mime[ 'type' ];
else
 $mimetype = 'image/' . substr( $file, strrpos( $file, '.' ) + 1 );

header( 'Content-Type: ' . $mimetype ); // always send this
if ( false === strpos( $_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS' ) )
 header( 'Content-Length: ' . filesize( $file ) );

$last_modified = gmdate( 'D, d M Y H:i:s', filemtime( $file ) );
$etag = '"' . md5( $last_modified ) . '"';
header( "Last-Modified: $last_modified GMT" );
header( 'ETag: ' . $etag );
header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + 100000000 ) . ' GMT' );

// Support for Conditional GET
$client_etag = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) : false;

if( ! isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) )
 $_SERVER['HTTP_IF_MODIFIED_SINCE'] = false;

$client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
// If string is empty, return 0. If not, attempt to parse into a timestamp
$client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;

// Make a timestamp for our most recent modification...
$modified_timestamp = strtotime($last_modified);

if ( ( $client_last_modified && $client_etag )
 ? ( ( $client_modified_timestamp >= $modified_timestamp) && ( $client_etag == $etag ) )
 : ( ( $client_modified_timestamp >= $modified_timestamp) || ( $client_etag == $etag ) )
 ) {
 status_header( 304 );
 exit;
}

// If we made it this far, just serve the file
readfile( $file );