upload.php

<?php
// Allen, StackDoubleFlow
$tokens = array("mySecret", "myOtherSecret");
$blacklist_names = array("upload.php", ".htaccess");
 
$sharexdir = "./"; // File directory
$lengthofstring = 5; // Length of file name

// Random file name generation
function random_string($length) {
    $keys = array_merge(range(0,9), range('a', 'z'));
 
    for($i=0; $i < $length; $i++) {
        $key .= $keys[mt_rand(0, count($keys) - 1)];
    }
    return $key;
}
 
// Check for token
if(!isset($_POST['secret']) || !in_array($_POST['secret'], $tokens)) {
	die('Invalid Secret Key');
}

// Prepares for upload
$filename = $_FILES["sharex"]["name"];
if (!$filename) {
	$target_file = $_FILES["sharex"]["name"];
	$fileType = pathinfo($target_file, PATHINFO_EXTENSION);
	$filename = random_string($lengthofstring).'.'.$fileType;
}

if(in_array($blacklist_names, $filename)) {
	die('Invalid filename');
}
	
// Accepts and moves to directory
if (move_uploaded_file($_FILES["sharex"]["tmp_name"], $sharexdir.$filename)) {
	// Sends info to client
	$json->status = "OK";
	$json->errormsg = "";
	$json->url = $filename;
} else {
	// Warning
   die('File upload failed - CHMOD/Folder doesn\'t exist?');
}  

// Sends json
echo(json_encode($json));
?>