How to Automatically Start a Download in PHP?

Here is a simple function that can compress any file or directory recursively, only needs the zip extension to be loaded.

function Zip($source, $destination)
{
    if (!extension_loaded('zip') || !file_exists($source)) {
        return false;
    }

    $zip = new ZipArchive();
    if (!$zip->open($destination, ZIPARCHIVE::CREATE)) {
        return false;
    }

    $source = str_replace('\', '/', realpath($source));

    if (is_dir($source) === true)
    {
        $files = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($source), RecursiveIteratorIterator::SELF_FIRST);

        foreach ($files as $file)
        {
            $file = str_replace('\', '/', $file);

            // Ignore "." and ".." folders
            if( in_array(substr($file, strrpos($file, '/')+1), array('.', '..')) )
                continue;

            $file = realpath($file);

            if (is_dir($file) === true)
            {
                $zip->addEmptyDir(str_replace($source . '/', '', $file . '/'));
            }
            else if (is_file($file) === true)
            {
                $zip->addFromString(str_replace($source . '/', '', $file), file_get_contents($file));
            }
        }
    }
    else if (is_file($source) === true)
    {
        $zip->addFromString(basename($source), file_get_contents($source));
    }

    return $zip->close();
}

Call it like this:

Zip('/folder/to/compress/', './compressed.zip');

This is pretty easy. All you need to do is provide cURL with a callback to handle data as it comes in.

function onResponseBodyData($ch, $data)
{
    echo $data;
    return strlen($data);
}

curl_setopt($ch, CURLOPT_WRITEFUNCTION, 'onResponseBodyData');

Returning the length of data from your callback is important. It signifies how much data you processed. If you return something other than the length of data passed in (such as 0), then the request is aborted.

Now, make sure you don't have output buffering turned on, and configure your server to not buffer the entire response before sending. It will work out of the box on most configurations.

You can find more examples here: http://curl.haxx.se/libcurl/php/examples/callbacks.html