PHP cURL文件获取内容始终为空

I've created an endpoint in Paw (and/or Postman) for handling file uploads. It works great!

It's pretty simple. And in my application I can do something like:

echo file_get_contents('php://input');

And it will print out an encoded representation of the image/file (a cute kitten).

The problem is, I cannot seem to reproduce this behaviour using just cURL (Current application uses Guzzle).

When I try something like:

$target_url = 'http://my-document-handling-service.net:8000/documents';

$request = curl_init($target_url);

curl_setopt($request, CURLOPT_POST, true);
curl_setopt($request, CURLOPT_RETURNTRANSFER, true);
curl_setopt($request, CURLOPT_POSTREDIR, 3);

curl_setopt(
    $request,
    CURLOPT_POSTFIELDS,
    array(
      'file' => '/Users/xxxxxxx-xxxx/Documents/kitten-test-upload-image-1.jpg'
    ));

echo curl_exec($request);

curl_close($request);

The body (file_get_contents()) is always empty. I don't really understand cURL I've always just used Guzzle - but now I have to use cURL and I can't get the body.

What am I doing wrong?