Index: libraries.api.php
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/libraries/libraries.api.php,v
retrieving revision 1.2
diff -u -p -r1.2 libraries.api.php
--- libraries.api.php	23 Jul 2010 12:57:01 -0000	1.2
+++ libraries.api.php	26 Aug 2010 13:12:26 -0000
@@ -20,6 +20,10 @@
  *   - path: (optional) A relative path from the directory of the library to the
  *     actual library. Only required if the extracted download package contains
  *     the actual library files in a sub-directory.
+ *   - external: (optional) A Boolean indicating whether the library is hosted
+ *     externally. If defined, the 'library path' property has to be predefined
+ *     manually. In case of multiple variants, of which some are external and
+ *     some are not, set this to TRUE.
  *   - version callback: (optional) The name of a function that detects and
  *     returns the full version string of the library. Defaults to
  *     libraries_get_version(). The first argument is always $library, an array
@@ -30,6 +34,9 @@
  *       be declared as an associative array.
  *     - or any number of independent arguments. In this case the version
  *       arguments (see below) must be declared as an indexed array.
+ *     In case the library version is static, the 'version' property may also be
+ *     predefined (without corresponding 'version callback'), so as to not try
+ *     to detect the library's version.
  *   - version arguments: A list of arguments to pass to the version callback.
  *     The default version callback libraries_get_version() expects a single,
  *     associative array with named keys:
@@ -303,6 +310,43 @@ function hook_libraries_info() {
       ),
     ),
   );
+
+  // An example library that is external, because it defines an external
+  // variant.
+  $libraries['openlayers'] = array(
+    'title' => 'OpenLayers',
+    'vendor url' => 'http://www.openlayers.org/',
+    'download url' => 'http://openlayers.org/download/',
+    'external' => TRUE,
+    // This should determine which variant is available (the local or the
+    // remote one) with 'libraries_get_path', and then use
+    // 'libraries_get_version' conditionally with or without the 'external' flag
+    // to determine the version. Note that in case of the remote variant the
+    // library information that is passed to 'libraries_get_version' must be
+    // padded with the 'library path' property as it is defined below in the
+    // variant information of the local variant.
+    'version callback' => 'openlayers_get_version',
+    'variants' => array(
+      'local' => array(
+        'library path' => 'http://openlayers.org/api',
+        'files' => array(
+          'js' => array(
+            // This syntax makes drupal_process_attached() pass the 'external'
+            // property correctly.
+            'OpenLayers.js' => array(
+              'type' => 'external',
+            ),
+          ),
+        ),
+      ),
+      'remote' => array(
+        'files' => array(
+          'js' => array('OpenLayers.js'),
+          ),
+        ),
+      ),
+    ),
+  );
   return $libraries;
 }
 
Index: libraries.module
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/libraries/libraries.module,v
retrieving revision 1.6
diff -u -p -r1.6 libraries.module
--- libraries.module	23 Jul 2010 12:57:01 -0000	1.6
+++ libraries.module	26 Aug 2010 13:12:26 -0000
@@ -146,6 +146,7 @@ function libraries_info($library = NULL)
           'vendor url' => '',
           'download url' => '',
           'path' => '',
+          'external' => FALSE,
           'version callback' => 'libraries_get_version',
           'version arguments' => array(),
           'files' => array(),
@@ -208,20 +209,24 @@ function libraries_detect_library(&$libr
   if (!isset($library['library path'])) {
     $library['library path'] = libraries_get_path($name);
   }
-  if (!file_exists($library['library path'])) {
+  // @todo Verify 'external' condition in light of PHP stream wrappers and
+  //   http://php.net/manual/en/filesystem.configuration.php#ini.allow-url-fopen
+  if (!$library['external'] && !file_exists($library['library path'])) {
     $library['error'] = t('%library could not be found.', array('%library' => $library['title']));
     return;
   }
 
-  // Detect library version.
-  // We support both a single parameter, which is an associative array, and an
-  // indexed array of multiple parameters.
-  if (isset($library['version arguments'][0])) {
-    // Add the library as the first argument.
-    $library['version'] = call_user_func_array($library['version callback'], array_merge(array($library), $library['version arguments']));
-  }
-  else {
-    $library['version'] = $library['version callback']($library, $library['version arguments']);
+  // Detect library version, if not hard-coded.
+  if (!isset($library['version'])) {
+    // We support both a single parameter, which is an associative array, and an
+    // indexed array of multiple parameters.
+    if (isset($library['version arguments'][0])) {
+      // Add the library as the first argument.
+      $library['version'] = call_user_func_array($library['version callback'], array_merge(array($library), $library['version arguments']));
+    }
+    else {
+      $library['version'] = $library['version callback']($library, $library['version arguments']);
+    }
   }
   if (empty($library['version'])) {
     $library['error'] = t('The version of %library could not be detected.', array('%library' => $library['title']));
@@ -291,6 +296,9 @@ function libraries_detect_library(&$libr
 function libraries_load($library, $variant = NULL) {
   $library = libraries_info($library);
   libraries_detect_library($library);
+  if (!$library['installed']) {
+    return $library['error'];
+  }
   libraries_load_files($library, $variant);
 }
 
@@ -308,7 +316,7 @@ function libraries_load_files($library, 
 
   // If a variant was specified, override the top-level properties with the
   // variant properties.
-  if (!empty($variant) && !empty($library['variants'][$variant]['installed'])) {
+  if (!empty($variant) && $library['variants'][$variant]['installed']) {
     $library = array_merge($library, $library['variants'][$variant]);
   }
 
@@ -378,6 +386,9 @@ function libraries_load_files($library, 
  *   - cols: (optional) The maximum number of characters per line to take into
  *     account. Defaults to 200. In case of minified or compressed files, this
  *     prevents reading the entire file into memory.
+ *   - external: (optional) A boolean indicating whether the file is external.
+ *     The 'library path' property must be set to the (external) base path of
+ *     the file in the library declaration.
  *
  * @return
  *   A string containing the version of the library.
@@ -391,12 +402,17 @@ function libraries_get_version($library,
     'pattern' => '',
     'lines' => 20,
     'cols' => 200,
+    'external' => FALSE,
   );
 
-  $file = DRUPAL_ROOT . '/' . $library['library path'] . '/' . $options['file'];
-  if (empty($options['file']) || !file_exists($file)) {
+  // Construct the file path.
+  $file = $library['library path'] . '/' . $options['file'];
+  $file = ($options['external'] ? $file : DRUPAL_ROOT . '/' . $file);
+
+  if (empty($library['library path']) || empty($options['file']) || !file_exists($file)) {
     return;
   }
+
   $file = fopen($file, 'r');
   while ($options['lines'] && $line = fgets($file, $options['cols'])) {
     if (preg_match($options['pattern'], $line, $version)) {
Index: tests/libraries.test
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/libraries/tests/libraries.test,v
retrieving revision 1.3
diff -u -p -r1.3 libraries.test
--- tests/libraries.test	23 Jul 2010 12:57:01 -0000	1.3
+++ tests/libraries.test	26 Aug 2010 13:12:26 -0000
@@ -103,6 +103,16 @@ class LibrariesTestCase extends DrupalWe
     libraries_detect_library($library);
     $this->assertEqual($library['variants']['example_variant_1']['installed'], TRUE, 'Existing variant found.');
 
+    // Test external library.
+    $library = libraries_info('example_external');
+    libraries_detect_library($library);
+    $this->assertEqual($library['installed'], TRUE, 'External library found.');
+
+    // Test external library with version callback.
+    $library = libraries_info('example_external_version');
+    libraries_detect_library($library);
+    $this->assertEqual($library['version'], '2', 'Library version of an external library found.');
+
     // Test loading of a simple library with a top-level files property.
     $this->drupalGet('libraries_test/simple');
     $this->assertRaw('example_installed_1.js', 'A JavaScript file is loaded correctly.');
Index: tests/libraries_test.module
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/libraries/tests/libraries_test.module,v
retrieving revision 1.2
diff -u -p -r1.2 libraries_test.module
--- tests/libraries_test.module	23 Jul 2010 12:57:01 -0000	1.2
+++ tests/libraries_test.module	26 Aug 2010 13:12:26 -0000
@@ -276,6 +276,26 @@ function libraries_test_libraries_info()
     ),
   );
 
+  // Test detection of an externally hosted library using hard-coded version.
+  $libraries['example_external'] = array(
+    'external' => TRUE,
+    'library path' => url(NULL, array('absolute' => TRUE)) . drupal_get_path('module', 'libraries') . '/tests/example',
+    'version' => '1.26',
+  );
+  // Test version detection of an externally hosted library.
+  $libraries['example_external_version'] = array(
+    'external' => TRUE,
+    'library path' => url(NULL, array('absolute' => TRUE)) . drupal_get_path('module', 'libraries') . '/tests/example',
+    'version callback' => 'libraries_get_version',
+    'version arguments' => array(
+      'file' => 'example_installed.txt',
+      // Version 2
+      'pattern' => '/Version (\d+)/',
+      'lines' => 5,
+      'external' => TRUE,
+    ),
+  );
+
   return $libraries;
 }