MDL-36903 Pre-check the ZIP download before executing the mdeploy.php…

… utility

This patch makes Moodle call HTTP HEAD method via cURL to see if the ZIP
is expected to be downloadable by mdeploy.php. This is mainly intended
for SSL certificates check.

admin/renderer.php

@@ -1211,8 +1211,13 @@ protected function plugin_available_update_info(available_update_info $updateinf
             if (empty($impediments)) {
                 $widget = $deployer->make_confirm_widget($updateinfo);
                 $box .= $this->output->render($widget);
-            } else if (isset($impediments['notwritable'])) {
-                $box .= $this->output->help_icon('notwritable', 'core_plugin', get_string('notwritable', 'core_plugin'));
+            } else {
+                if (isset($impediments['notwritable'])) {
+                    $box .= $this->output->help_icon('notwritable', 'core_plugin', get_string('notwritable', 'core_plugin'));
+                }
+                if (isset($impediments['notdownloadable'])) {
+                    $box .= $this->output->help_icon('notdownloadable', 'core_plugin', get_string('notdownloadable', 'core_plugin'));
+                }
             }
         }
 

lang/en/plugin.php

@@ -43,10 +43,14 @@
 $string['nonehighlightedinfo'] = 'Display the list of all installed plugins anyway';
 $string['noneinstalled'] = 'No plugins of this type are installed';
 $string['notes'] = 'Notes';
+$string['notdownloadable'] = 'Can not download the package';
+$string['notdownloadable_help'] = 'ZIP package with the update can not be downloaded automatically. Please refer to the documentation page for more help.';
+$string['notdownloadable_link'] = 'admin/mdeploy/notdownloadable';
 $string['notwritable'] = 'Plugin files not writable';
 $string['notwritable_help'] = 'You have enabled automatic updates deployment and there is available update for this plugin. However, the plugin files are not writable by the web server so the update can not be installed at the moment.
 
 Make the plugin folder and all its contents writable to be able to install the available update automatically.';
+$string['notwritable_link'] = 'admin/mdeploy/notwritable';
 $string['numtotal'] = 'Installed: {$a}';
 $string['numdisabled'] = 'Disabled: {$a}';
 $string['numextension'] = 'Contributions: {$a}';

lib/pluginlib.php

@@ -1589,6 +1589,10 @@ public function deployment_impediments(available_update_info $info) {
             $impediments['missingdownloadmd5'] = true;
         }
 
+        if (!empty($info->download) and !$this->update_downloadable($info->download)) {
+            $impediments['notdownloadable'] = true;
+        }
+
         if (!$this->component_writable($info->component)) {
             $impediments['notwritable'] = true;
         }
@@ -1917,6 +1921,40 @@ protected function component_writable($component) {
         return $this->directory_writable($directory);
     }
 
+    /**
+     * Checks if the mdeploy.php will be able to fetch the ZIP from the given URL
+     *
+     * This is mainly supposed to check if the transmission over HTTPS would
+     * work. That is, if the CA certificates are present at the server.
+     *
+     * @param string $downloadurl the URL of the ZIP package to download
+     * @return bool
+     */
+    protected function update_downloadable($downloadurl) {
+        global $CFG;
+
+        $curloptions = array(
+            'CURLOPT_SSL_VERIFYHOST' => 2,      // this is the default in {@link curl} class but just in case
+            'CURLOPT_SSL_VERIFYPEER' => true,
+        );
+
+        $cacertfile = $CFG->dataroot.'/moodleorgca.crt';
+        if (is_readable($cacertfile)) {
+            // Do not use CA certs provided by the operating system. Instead,
+            // use this CA cert to verify the updates provider.
+            $curloptions['CURLOPT_CAINFO'] = $cacertfile;
+        }
+
+        $curl = new curl(array('proxy' => true));
+        $result = $curl->head($downloadurl, $curloptions);
+        $errno = $curl->get_errno();
+        if (empty($errno)) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
     /**
      * Checks if the directory and all its contents (recursively) is writable
      *