enhancement: add priority to direct child nodes #108

This enhancement aims to flow priority down to direct child nodes only.
Through the implementation of node levels and a level check when
marking a node to be crawled, we only assign a parent priority to a
child node if it is a direct ancestor of the original node.
This will prevent passing priority recursively and if, for example, a child
node is a top level node, filtering the priority to effectively all nodes,
which is undesirable behaviour.

classes/robot/crawler.php

@@ -306,12 +306,20 @@ public function get_queue_size() {
      * @return object|boolean The node record if the resource pointed to by the URL can and should be considered; or `false` if the
      *     URL is invalid or excluded.
      */
-    public function mark_for_crawl($baseurl, $url, $courseid = null, $priority = TOOL_CRAWLER_PRIORITY_DEFAULT) {
+    public function mark_for_crawl($baseurl, $url, $courseid = null, $priority = TOOL_CRAWLER_PRIORITY_DEFAULT,
+            $level = TOOL_CRAWLER_NODE_LEVEL_PARENT) {
 
         global $DB, $CFG;
 
         $url = $this->absolute_url($baseurl, $url);
 
+        // Strip priority from indirect child nodes. Only parent and direct children
+        // of parent nodes have priority applied to avoid recursively applying priority
+        // to all ancestors of a parent node.
+        if ($level == TOOL_CRAWLER_NODE_LEVEL_INDIRECT_CHILD) {
+            $priority = TOOL_CRAWLER_PRIORITY_DEFAULT;
+        }
+
         // Filter out non http protocols like mailto:[email protected] etc.
         $bits = parse_url($url);
         if (array_key_exists('scheme', $bits)
@@ -420,6 +428,7 @@ public function mark_for_crawl($baseurl, $url, $courseid = null, $priority = TOO
             $node->external   = self::is_external($url);
             $node->needscrawl = time();
             $node->priority = $priority;
+            $node->level = $level;
 
             if (isset($courseid)) {
                 $node->courseid = $courseid;
@@ -438,6 +447,11 @@ public function mark_for_crawl($baseurl, $url, $courseid = null, $priority = TOO
                 $node->priority = $priority;
                 $needsupdating = true;
             }
+            if ($node->level != $level) {
+                // Set the level again, in case this node has been seen again at a different
+                // level, to avoid reprocessing.
+                $node->level = $level;
+            }
             if (isset($courseid)) {
                 $node->courseid = $courseid;
                 $needsupdating = true;
@@ -901,8 +915,15 @@ private function link_from_node_to_url($from, $url, $text, $idattr) {
 
         global $DB;
 
+        // Ascertain the correct node level based on parent node level.
+        if ($from->level == TOOL_CRAWLER_NODE_LEVEL_PARENT) {
+            $level = TOOL_CRAWLER_NODE_LEVEL_DIRECT_CHILD;
+        } else {
+            $level = TOOL_CRAWLER_NODE_LEVEL_INDIRECT_CHILD;
+        }
+
         // Add the node URL to the queue.
-        $to = $this->mark_for_crawl($from->url, $url, null, $from->priority);
+        $to = $this->mark_for_crawl($from->url, $url, $from->courseid, $from->priority, $level);
         if ($to === false) {
             return false;
         }

constants.php

@@ -93,3 +93,12 @@
 define('TOOL_CRAWLER_PRIORITY_DEFAULT', 0);
 define('TOOL_CRAWLER_PRIORITY_NORMAL', 50);
 define('TOOL_CRAWLER_PRIORITY_HIGH', 100);
+
+/**
+ * Node level assigned to each node based on whether it is the parent node, or
+ * a child node discovered within a parent when crawling, or any child of a child
+ * node (or even further removed).
+ */
+define('TOOL_CRAWLER_NODE_LEVEL_PARENT', 2);
+define('TOOL_CRAWLER_NODE_LEVEL_DIRECT_CHILD', 1);
+define('TOOL_CRAWLER_NODE_LEVEL_INDIRECT_CHILD', 0);

db/install.xml

@@ -27,6 +27,8 @@
         <FIELD NAME="httpmsg" TYPE="text" NOTNULL="false" SEQUENCE="false"/>
         <FIELD NAME="errormsg" TYPE="text" NOTNULL="false" SEQUENCE="false"/>
         <FIELD NAME="priority" TYPE="int" LENGTH="10" NOTNULL="false" SEQUENCE="false" DEFAULT="0"/>
+        <FIELD NAME="level" TYPE="int" LENGTH="1" NOTNULL="false" DEFAULT="2" SEQUENCE="false" COMMENT="Node level, 2 for parent node, 1 for direct child and 0 for subsequent children."/>
+      </FIELDS>
       </FIELDS>
       <KEYS>
         <KEY NAME="primary" TYPE="primary" FIELDS="id"/>

db/upgrade.php

@@ -94,5 +94,21 @@ function xmldb_tool_crawler_upgrade($oldversion) {
         upgrade_plugin_savepoint(true, 2019100300, 'tool', 'crawler');
     }
 
+    if ($oldversion < 2020012300) {
+
+        // Define field level to be added to tool_crawler_url.
+        $table = new xmldb_table('tool_crawler_url');
+        $field = new xmldb_field('level', XMLDB_TYPE_INTEGER, '1', null, null, null, '2', 'priority');
+
+        // Conditionally launch add field level.
+        if (!$dbman->field_exists($table, $field)) {
+            $dbman->add_field($table, $field);
+        }
+
+        // Crawler savepoint reached.
+        upgrade_plugin_savepoint(true, 2020012300, 'tool', 'crawler');
+    }
+
+
     return true;
 }

version.php

@@ -27,8 +27,8 @@
 defined('MOODLE_INTERNAL') || die();
 
 
-$plugin->version   = 2020010600;        // The current plugin version (Date: YYYYMMDDXX)
-$plugin->release   = 2020010600;        // The current plugin version (Date: YYYYMMDDXX)
+$plugin->version   = 2020012300;        // The current plugin version (Date: YYYYMMDDXX)
+$plugin->release   = 2020012300;        // The current plugin version (Date: YYYYMMDDXX)
 $plugin->requires  = 2016021800;        // Requires this Moodle version.
 $plugin->component = 'tool_crawler'; // To check on upgrade, that module sits in correct place.
 $plugin->maturity  = MATURITY_STABLE;