Basic file server for use with saving coverage info

basicFileServer.php

<?php

function finishRequest($responseCode) {
    http_response_code($responseCode);
    die();
}
$storageDirectory = "upload";

$fileName = $_GET['hash'];
if (!ctype_alnum($fileName) || strlen($fileName) < 5) {
    finishRequest(400);
}


if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $uploadFile = isset($_FILES['report']['tmp_name']) ?
        $_FILES['report']['tmp_name'] :
        ''
    ;
    if (!$uploadFile) {
        finishRequest(400);
    }
    if (!is_writable($storageDirectory)) {
        finishRequest(503);
    }

    $fileName = "$storageDirectory/$fileName.gz";
    $gz = gzopen($fileName,'w9');
    gzwrite($gz, file_get_contents($uploadFile));
    gzclose($gz);
    finishRequest(201);
}

$fileName = "$storageDirectory/$fileName*.gz";
$foundFiles = glob($fileName);

if (count($foundFiles) !== 1) {
    finishRequest(204);
}

$fileName = current($foundFiles);

header("Content-Type: text/plain; charset=UTF-8");
if (strpos($_SERVER["HTTP_ACCEPT_ENCODING"], 'gzip') === false) {
   readgzfile($fileName);
   finishRequest(200);
}
header("Content-Encoding: gzip");
header("Content-Length: ".filesize($fileName));
readfile($fileName);