upload.php

<?php
/*
echo json_encode([
    'flowChunkNumber' => $_GET['flowChunkNumber'],
    'flowTotalChunks' => $_GET['flowTotalChunks'],
    'flowChunkSize' => $_GET['flowChunkSize'],
    'flowTotalSize' => $_GET['flowTotalSize'],
    'flowIdentifier' => $_GET['flowIdentifier'],
    'flowFilename' => $_GET['flowFilename'],
    'flowRelativePath' => $_GET['flowRelativePath']
]);
*/

$tempDir = __DIR__ . DIRECTORY_SEPARATOR . 'temp';
if (!file_exists($tempDir)) {
    mkdir($tempDir);
}
if ($_SERVER['REQUEST_METHOD'] === 'GET') {
    $chunkDir = $tempDir . DIRECTORY_SEPARATOR . $_GET['flowIdentifier'];
    $chunkFile = $chunkDir.'/chunk.part'.$_GET['flowChunkNumber'];
    //move_uploaded_file($_FILES['tmp_name'], $chunkDir);
    /*
    if (file_exists($chunkFile)) {
        header("HTTP/1.0 200 Ok");
    } else {
        header("HTTP/1.0 404 Not Found");
    }
    */
}
// Just imitate that the file was uploaded and stored.
sleep(2);

echo json_encode([
    'success' => true,
    'files' => $_FILES,
    'get' => $_GET,
    'post' => $_POST,
    //optional
    'flowTotalSize' => isset($_FILES['file']) ? $_FILES['file']['size'] : $_GET['flowTotalSize'],
    'flowIdentifier' => isset($_FILES['file']) ? $_FILES['file']['name'] . '-' . $_FILES['file']['size']
        : $_GET['flowIdentifier'],
    'flowFilename' => isset($_FILES['file']) ? $_FILES['file']['name'] : $_GET['flowFilename'],
    'flowRelativePath' => isset($_FILES['file']) ? $_FILES['file']['tmp_name'] : $_GET['flowRelativePath']

]);