Downloading a file appears to corrupt it and increase its size by one byte


I have an issue when downloading a file from my server.

Uploading it goes well, but when downloading it, I notice that the file is slightly corruptet. It’s 1 byte larger then when I uploaded it, and it seams to be corrupted.

For example, on my local machine before I upload the file:

$> od -x a.txt

0000000 6554 7473 000a

$> wc -c a.txt

5 a.txt

Now, after the file is uploaded, I’ve checked with the same commands and I get the exact same output.

However, after i download it back to my local machine, I get the following output:

$> od -x a.txt

0000000 540a 7365 0a74

$> wc -c a.txt

6 a.txt

As you can see, the content has changed and the filesize has increased.

In this example, the file is a simple text-file that can be opened either way, but when I try it with a pdf for example, I get error codes when trying to opened the downloaded file:

mupdf b.pdf 
error: cannot recognize version marker
warning: trying to repair broken xref
warning: repairing PDF document
error: no objects found
mupdf: error: cannot open document

Running this command before uploading it gives me no errors.

Here is the code I use to download files. I’m rather sure that the issue is there somewhere:

public function downloadFile($request, $response, $args)
    global $em;
    $fileId = $args['fileId'];
    $fileEntity = $em->getRepository('Entity\UploadedFile')->find($fileId);

    $directory = $this->getUploadDirectory();

    if (empty($fileEntity)) {
        throw new \CustomException('UploadFile with id ' . $fileId . ' not found', 123);

    $filePath = $fileEntity->getPath();

    $file = $directory . '/' . $filePath;

    $alias = $fileEntity->getAlias();

    $fh = fopen($file, 'rb');

    $stream = new \Slim\Http\Stream($fh);

    $filesize = filesize($file);

    return $response->withHeader('Content-Type', 'application/octet-stream')
        ->withHeader('Content-Description', 'File Transfer')
        ->withHeader('Content-Type', 'application/octet-stream')
        ->withHeader('Content-Disposition', 'attachment; filename="' . $alias . '"')
        ->withHeader('Content-Transfer-Encoding', 'binary')
        ->withHeader('Expires', '0')
        ->withHeader('Cache-Control', 'must-revalidate, post-check=0, pre-check=0')
        ->withHeader('Pragma', 'public')
        ->withHeader('Content-Length', $filesize)

Note that I have turned off gzip - it makes no difference.

Anyone has a clue about what’s behind this error? There is always the 1 byte size increase no matter how big the file is!

Thanks in advance!