Download dynamically generated PNG in CakePHP 2

I have a QR code PNG being dynamically generated. I can access it by going to www.example.com/events/qrgen, which causes it to be displayed in the browser correctly.

Now, I would like another option that downloads the PNG file. Here is what I've tried:

// this action displays a QR code in the browser
public function qrgen() {
    $this->layout = false;
    $this->response->type('image/png');
}

// this action SHOULD make the png download
public function download_qrgen() {
    $qrUrl = Router::url(['controller'=>'events', 'action'=>'qrgen']);
    $this->response->file($qrUrl, ['download'=>true, 'name'=>'qr']);
    return $this->response;
}

// in the "qrgen" view
QRcode::png('example value', null, "M", 4, 4);

But when I access www.example.com/events/download_qrgen, it gives an error "That page could not be found", and shows the CakeResponse->file(string, array) value as: /var/www/example.com//events/qrgen.

If I try a file in my webroot, it correctly downloads the file. But I can't seem to get it to download a dynamically generated png like this.

Solution

CakeResponse::file() expects a file system path passed to it, not a URL, it's not going to make any HTTP requests to obtain the data.

You have to obtain the data yourself, and then either buffer it in a temporary file whose path in the filesystem you can pass to CakeResponse::file():

public function download_qrgen() {
    $this->layout = false;
    $qrcodeData = $this->_getViewObject()->render('qrgen');

    $temp = tmpfile();
    fwrite($temp, $qrcodeData);
    $filePath = stream_get_meta_data($temp)['uri'];

    $this->response->file($filePath, ['download' => true, 'name' => 'qr.png']);

    return $this->response;
}

or you prepare the response with the data and headers yourself:

public function download_qrgen() {
    $this->layout = false;
    $qrcodeData = $this->_getViewObject()->render('qrgen');

    $this->response->type('image/png');
    $this->response->download('qr.png');
    $this->response->length(strlen($qrcodeData));
    $this->response->header('Content-Transfer-Encoding', 'binary');
    $this->response->body($qrcodeData);

    return $this->response;
}