How to call functions from another module in hook_language_negotiation_info()?

Question

I am writing a new custom module which is dependent on geoip module. I'm trying to add another language negotiation in the language detection configurations which would trigger a callback function defined in the module. Now How do I call the function defined in geoip.module file? I tried calling the function directly and after a module_load_include and both do not work.

/**
 * Implement hook_language_negotiation_info
 */
function my_module_language_negotiation_info() {
  return array(
      'geoip_language_provider' => array(
          'callbacks' => array(
              'language' => '_my_module_language_callback',
          ),
          'file' => drupal_get_path( 'module', 'my_module' ) . '/my_module.module',
          'weight' => -4,
          'name' => t( 'My Module GeoIP Negotiation Provider' ),
          'description'=> t( 'This redirects the user to correct language based on their IP.' ),
          'cache' => 0,
      ),
  );
}

function _my_module_language_callback() {
  module_load_include( 'module', 'geoip' );

  //Returns array of languages based on country code. Eg. array( 'CN' => 'zh-hans',)
  $languages = _my_module_language_mapping();
  $country_code = geoip_country_code();
  $default_langcode = language_default( 'language' );

  if( !isset( $languages[$country_code] ) ) {
    watchdog( 'geoip_language', 'The country code is not in the language mapping.' );
    return $default_langcode;
  }

  return $languages[$country_code];
}

Answer 1

Not sure if this is the correct reason for this behaviour or not but it seems like the language negotiation process runs before the modules and the themes are bootstrapped in Drupal which would explain why the function is not available by default.

Changed the module_load_include to actually include the file directly by calling drupal_get_filename and requiring the file and it worked.

function _my_module_language_callback() {
  $geoip_file = drupal_get_filename('module', 'geoip');
  if( file_exists( $geoip_file ) ) {
    require_once DRUPAL_ROOT . DIRECTORY_SEPARATOR . $geoip_file;
  }

  $languages = _my_module_language_mapping();
  if( function_exists( 'geoip_country_code' ) ) {
    $country_code = geoip_country_code();
  }
  $default_langcode = language_default( 'language' );

  if( !isset( $country_code ) ) {
    watchdog( 'geoip_language', 'Country Code could not be identified by IP.' );
    return $default_langcode;
  }

  if( !isset( $languages[$country_code] ) ) {
    watchdog( 'geoip_language', 'The country code is not in the language mapping.' );
    return $default_langcode;
  }

  return $languages[$country_code];
}

Answer 2

First you have to read the module documentation to see if It provide a way to use It's own functions and instructions on how to use them. Also, you have to check if the function you're calling is in that module or in another file (for example, an inc file). If the function is in an inc file you can call it with something like:

module_load_include('inc', 'geoip');
// this cals geoip.inc

or like

module_load_include('inc', 'geoip.field');
// this cals geoip.field.inc

Answer 3

Your language negotiation callback is called from drupal_bootstrap() before Drupal is completely bootstrapped; as such not all the enabled modules are loaded. In fact, it is called during the DRUPAL_BOOTSTRAP_LANGUAGE phase, which is right before the DRUPAL_BOOTSTRAP_FULL phase.
You just need to use drupal_load() to load the module file as drupal_load('module', 'geoip').

Keep in mind that your language negotiation callback is also called from authorize.php, via drupal_initialize_language(), the same function used from drupal_bootstrap(). If you are going to load that module in your language negotiation callback, be sure it works also when autorize.php is used from Drupal, which means when installing a module from the user interface, for example.