How to send a PHP cURL POST request to a URL, receive a file and give to the user download?

Question

There's a url that when I pass some POST parameters it gives me back a file to download. What's the best way to make my server download that file and, while it downloads it sends to the user?

Thanks in advance

Answer 1

I'd use cURL for the whole thing.

I don't have a reference on me at the moment, but at least with multi-cURL, it is possible to have a callback function that is fired when a chunk of data comes in. When that happens, you echo the data out to your client.

Answer 2

It depends on what you want to do with the response, but the easiest way is just to set CURLOPT_RETURNTRANSFER and output the response:

$ch = curl_init("http://stackoverflow.com/");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$resp = curl_exec($ch);
curl_close($ch);

echo $resp;

Don't forget that curl_exec returns FALSE on failure, so you probably should check that too:

if ($resp === false) die('Unable to contact server');

If you want to save the response on the server as well (instead of the above method which is just basically a dumb proxy), you could make use of CURLOPT_WRITEFUNCTION instead.

$fp = fopen('my_file', 'w');
$ch = curl_init("http://stackoverflow.com/");
curl_setopt($ch, CURLOPT_WRITEFUNCTION, 'writefunc');
curl_exec($ch);
curl_close($ch);
fclose($fp);

function writefunc($ch, $data) {
    global $fp;
    echo $data;
    return fwrite($fp, $data);
}

The write function takes two arguments (curl handle, data), and requires a return value of the amount of data written (in our case also the amount outputted).