Upload external file to AWS S3 bucket using PHP SDK

I want to upload a file from an external URL directly to an Amazon S3 bucket using the PHP SDK. I managed to do this with the following code:

$s3 = new AmazonS3();
 $response = $s3->create_object($bucket, $destination, array(
   'fileUpload' => $source,
   'length' => remote_filesize($source),
   'contentType' => 'image/jpeg'
 )); 
 

Where the function remote_filesize is the following:

function remote_filesize($url) {
   ob_start();
   $ch = curl_init($url);
   curl_setopt($ch, CURLOPT_HEADER, 1);
   curl_setopt($ch, CURLOPT_NOBODY, 1);
   $ok = curl_exec($ch);
   curl_close($ch);
   $head = ob_get_contents();
   ob_end_clean();
   $regex = '/Content-Length:\s([0-9].+?)\s/';
   $count = preg_match($regex, $head, $matches);
   return isset($matches[1]) ? $matches[1] : "unknown";
 }
 

However, it would be nice if I could skip setting the filesize when uploading to Amazon since this would save me a trip to my own server. But if I remove setting the 'length' property in the $s3->create_object function, I get an error saying that the 'The stream size for the streaming upload cannot be determined.' Any ideas how to solve this problem?

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