Secure file download from other server

Question

This is an unusual one. Let's say I have two web servers A and B. How would I go about making a link to a file from a Drupal website on server A to a file on server B such that the link is secure (the link to the file can't be accessed directly/shared)? I would have some control over server B, but it would just be a standard web server.

The reason for wanting this is that I need to serve some files to users behind the "Great Firewall of China", but the website is within China.

Answer 1

The first thing that pops to mind is to create a custom module, with a menu callback to obfuscate the real url. This is the same way the drupal private filesystem (private://) handles this.

• Create a menu entry in your custom module's hook_menu() to obfuscate the real url and perform access checks.

  function my_module_menu() {
    $items['my-module/download'] = array(
      'title' => 'File download',
      'page callback' => 'my_module_page_callback',
      'access callback' => TRUE, // Let the page callback handle the checks.
      'type' => MENU_CALLBACK,
    );
  }
  

• Have the page callback transfer the file and check access. Based on file_download().

  function my_module_page_callback() {
    $args = func_get_args(); // Get the path elements after `my-module/download`
    $target = implode('/', $args); // Join them into a string.
    $uri = 'http://some-other-server.com/files/' . $target;
  
  
    if (function_to_check_if_file_exists($uri)) { // Define this function yourself.
      $headers = array('Content-Type' => 'file mime-type'); // Set the correct mime-type for the file here.
  
      if (function_to_check_access()) { // Define this function yourself.
        file_transfer($uri, $headers);
      }
      drupal_access_denied();
    }
    else {
      drupal_not_found();
    }
    drupal_exit();
  }
  

Accessing an url like example.com/my-module/download/documents/1.pdf should now serve a file from http://some-other-server.com/files/documents/1.pdf.

In order to register the files you will have to construct a file object, set the uri to my-module/download/[remote-path] and save the file to the file_managed table. Then attach the file to a node. There might be better ways for this, but this is what I can think of now.

$f = (object) array(
  'uid'         => 1,
  'filename'    => '',
  'uri'         => 'my-module/download/[remote-path]',
  'filemime'    => '',
  'filesize'    => 12345,
  'status'      => 1,
);
file_save($f);

$node = node_load(1);
$node->field_file[LANGUAGE_NONE][0] = (array)$f; // Add a file field on a content type and use the name here.
node_save($node);