PHP cURL Realtime proxy (stream file)

Question

Currently I have a script like the following:

<?php
$filename = "http://someurl.com/file.ext";
header('Content-Type: application/octet-stream');
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$filename);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 500);
$data=curl_exec($ch);
curl_close($ch);
echo $data;
?>

The problem is that the server just send the response after download the whole file. I want to make it work like a "stream", sending chunks of data as response while the file is downloaded.

Is that possible to achieve with PHP and cURL?

Answer 1

It's possible. You can use the curl option CURLOPT_WRITEFUNCTION to specify a callback where you'll receive chunks of data so you can send them directly to the client as curl downloads the file.

<?php

$filename = "http://someurl.com/file.ext";
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename="' . basename($filename) . '"');
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$filename);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 500);
curl_setopt($ch, CURLOPT_WRITEFUNCTION, function($curl, $data) {
    echo $data;
    return strlen($data);
});
curl_exec($ch);
curl_close($ch);

Answer 2

Curl will by default output the response directly, unless you specify CURLOPT_RETURNTRANSFER.

Your code will work just by removing CURLOPT_RETURNTRANSFER and the last echo:

<?php
$filename = "http://someurl.com/file.ext";
header('Content-Type: application/octet-stream');
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL,$filename);
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 500);
$data=curl_exec($ch);
curl_close($ch);
?>