20 files changed, 1216 insertions, 222 deletions

diff --git a/engine/classes/ElggAttributeLoader.php b/engine/classes/ElggAttributeLoader.php
new file mode 100644
index 000000000..602bb8bae
--- /dev/null
+++ b/engine/classes/ElggAttributeLoader.php
@@ -0,0 +1,199 @@
+<?php
+
+/**
+ * Loads ElggEntity attributes from DB or validates those passed in via constructor
+ *
+ * @access private
+ */
+class ElggAttributeLoader {
+
+	/**
+	 * @var array names of attributes in all entities
+	 */
+	protected static $primary_attr_names = array(
+		'guid',
+		'type',
+		'subtype',
+		'owner_guid',
+		'container_guid',
+		'site_guid',
+		'access_id',
+		'time_created',
+		'time_updated',
+		'last_action',
+		'enabled'
+	);
+
+	/**
+	 * @var array names of secondary attributes required for the entity
+	 */
+	protected $secondary_attr_names = array();
+
+	/**
+	 * @var string entity type (not class) required for fetched primaries
+	 */
+	protected $required_type;
+
+	/**
+	 * @var array
+	 */
+	protected $initialized_attributes;
+
+	/**
+	 * @var string class of object being loaded
+	 */
+	protected $class;
+
+	/**
+	 * @var bool should access control be considered when fetching entity?
+	 */
+	public $requires_access_control = true;
+
+	/**
+	 * @var callable function used to load attributes from {prefix}entities table
+	 */
+	public $primary_loader = 'get_entity_as_row';
+
+	/**
+	 * @var callable function used to load attributes from secondary table
+	 */
+	public $secondary_loader = '';
+
+	/**
+	 * @var callable function used to load all necessary attributes
+	 */
+	public $full_loader = '';
+
+	/**
+	 * @param string $class class of object being loaded
+	 * @param string $required_type entity type this is being used to populate
+	 * @param array $initialized_attrs attributes after initializeAttributes() has been run
+	 * @throws InvalidArgumentException
+	 */
+	public function __construct($class, $required_type, array $initialized_attrs) {
+		if (!is_string($class)) {
+			throw new InvalidArgumentException('$class must be a class name.');
+		}
+		$this->class = $class;
+
+		if (!is_string($required_type)) {
+			throw new InvalidArgumentException('$requiredType must be a system entity type.');
+		}
+		$this->required_type = $required_type;
+
+		$this->initialized_attributes = $initialized_attrs;
+		unset($initialized_attrs['tables_split'], $initialized_attrs['tables_loaded']);
+		$all_attr_names = array_keys($initialized_attrs);
+		$this->secondary_attr_names = array_diff($all_attr_names, self::$primary_attr_names);
+	}
+
+	protected function isMissingPrimaries($row) {
+		return array_diff(self::$primary_attr_names, array_keys($row)) !== array();
+	}
+
+	protected function isMissingSecondaries($row) {
+		return array_diff($this->secondary_attr_names, array_keys($row)) !== array();
+	}
+
+	protected function checkType($row) {
+		if ($row['type'] !== $this->required_type) {
+			$msg = elgg_echo('InvalidClassException:NotValidElggStar', array($row['guid'], $this->class));
+			throw new InvalidClassException($msg);
+		}
+	}
+
+	/**
+	 * Get all required attributes for the entity, validating any that are passed in. Returns empty array
+	 * if can't be loaded (Check $failure_reason).
+	 *
+	 * This function splits loading between "primary" attributes (those in {prefix}entities table) and
+	 * "secondary" attributes (e.g. those in {prefix}objects_entity), but can load all at once if a
+	 * combined loader is available.
+	 *
+	 * @param mixed $row a row loaded from DB (array or stdClass) or a GUID
+	 * @return array will be empty if failed to load all attributes (access control or entity doesn't exist)
+	 *
+	 * @throws InvalidArgumentException|LogicException|IncompleteEntityException
+	 */
+	public function getRequiredAttributes($row) {
+		if (!is_array($row) && !($row instanceof stdClass)) {
+			// assume row is the GUID
+			$row = array('guid' => $row);
+		}
+		$row = (array) $row;
+		if (empty($row['guid'])) {
+			throw new InvalidArgumentException('$row must be or contain a GUID');
+		}
+
+		// these must be present to support isFullyLoaded()
+		foreach (array('tables_split', 'tables_loaded') as $key) {
+			if (isset($this->initialized_attributes[$key])) {
+				$row[$key] = $this->initialized_attributes[$key];
+			}
+		}
+
+		$was_missing_primaries = $this->isMissingPrimaries($row);
+		$was_missing_secondaries = $this->isMissingSecondaries($row);
+
+		// some types have a function to load all attributes at once, it should be faster
+		if (($was_missing_primaries || $was_missing_secondaries) && is_callable($this->full_loader)) {
+			$fetched = (array) call_user_func($this->full_loader, $row['guid']);
+			if (!$fetched) {
+				return array();
+			}
+			$row = array_merge($row, $fetched);
+			$this->checkType($row);
+		} else {
+			if ($was_missing_primaries) {
+				if (!is_callable($this->primary_loader)) {
+					throw new LogicException('Primary attribute loader must be callable');
+				}
+				if (!$this->requires_access_control) {
+					$ignoring_access = elgg_set_ignore_access();
+				}
+				$fetched = (array) call_user_func($this->primary_loader, $row['guid']);
+				if (!$this->requires_access_control) {
+					elgg_set_ignore_access($ignoring_access);
+				}
+				if (!$fetched) {
+					return array();
+				}
+				$row = array_merge($row, $fetched);
+			}
+
+			// We must test type before trying to load the secondaries so that InvalidClassException
+			// gets thrown. Otherwise the secondary loader will fail and return false.
+			$this->checkType($row);
+
+			if ($was_missing_secondaries) {
+				if (!is_callable($this->secondary_loader)) {
+					throw new LogicException('Secondary attribute loader must be callable');
+				}
+				$fetched = (array) call_user_func($this->secondary_loader, $row['guid']);
+				if (!$fetched) {
+					if ($row['type'] === 'site') {
+						// A special case is needed for sites: When vanilla ElggEntities are created and
+						// saved, these are stored w/ type "site", but with no sites_entity row. These
+						// are probably only created in the unit tests.
+						// @todo Don't save vanilla ElggEntities with type "site"
+						$row['guid'] = (int) $row['guid'];
+						return $row;
+					}
+					throw new IncompleteEntityException("Secondary loader failed to return row for {$row['guid']}");
+				}
+				$row = array_merge($row, $fetched);
+			}
+		}
+
+		// loading complete: re-check missing and check type
+		if (($was_missing_primaries && $this->isMissingPrimaries($row))
+				|| ($was_missing_secondaries && $this->isMissingSecondaries($row))) {
+			throw new LogicException('Attribute loaders failed to return proper attributes');
+		}
+
+		// guid needs to be an int  http://trac.elgg.org/ticket/4111
+		$row['guid'] = (int) $row['guid'];
+
+		return $row;
+	}
+}
diff --git a/engine/classes/ElggAutoP.php b/engine/classes/ElggAutoP.php
new file mode 100644
index 000000000..89d77e583
--- /dev/null
+++ b/engine/classes/ElggAutoP.php
@@ -0,0 +1,309 @@
+<?php
+
+/**
+ * Create wrapper P and BR elements in HTML depending on newlines. Useful when
+ * users use newlines to signal line and paragraph breaks. In all cases output
+ * should be well-formed markup.
+ *
+ * In DIV elements, Ps are only added when there would be at
+ * least two of them.
+ */
+class ElggAutoP {
+
+	public $encoding = 'UTF-8';
+
+	/**
+	 * @var DOMDocument
+	 */
+	protected $_doc = null;
+
+	/**
+	 * @var DOMXPath
+	 */
+	protected $_xpath = null;
+
+	protected $_blocks = 'address article area aside blockquote caption col colgroup dd 
+		details div dl dt fieldset figure figcaption footer form h1 h2 h3 h4 h5 h6 header 
+		hr hgroup legend map math menu nav noscript p pre section select style summary
+		table tbody td tfoot th thead tr ul ol option li';
+
+	/**
+	 * @var array
+	 */
+	protected $_inlines = 'a abbr audio b button canvas caption cite code command datalist
+		del dfn em embed i iframe img input ins kbd keygen label map mark meter object
+		output progress q rp rt ruby s samp script select small source span strong style
+		sub sup textarea time var video wbr';
+
+	/**
+	 * Descend into these elements to add Ps
+	 *
+	 * @var array
+	 */
+	protected $_descendList = 'article aside blockquote body details div footer form
+		header section';
+
+	/**
+	 * Add Ps inside these elements
+	 *
+	 * @var array
+	 */
+	protected $_alterList = 'article aside blockquote body details div footer header
+		section';
+
+	protected $_unique = '';
+
+	public function __construct() {
+		$this->_blocks = preg_split('@\\s+@', $this->_blocks);
+		$this->_descendList = preg_split('@\\s+@', $this->_descendList);
+		$this->_alterList = preg_split('@\\s+@', $this->_alterList);
+		$this->_inlines = preg_split('@\\s+@', $this->_inlines);
+		$this->_unique = md5(__FILE__);
+	}
+
+	/**
+	 * Intance of class for singleton pattern.
+	 * @var ElggAutoP
+	 */
+	private static $instance;
+	
+	/**
+	 * Singleton pattern.
+	 * @return ElggAutoP
+	 */
+	public static function getInstance() {
+		$className = __CLASS__;
+		if (!(self::$instance instanceof $className)) {
+			self::$instance = new $className();
+		}
+		return self::$instance;
+	}
+	
+	/**
+	 * Create wrapper P and BR elements in HTML depending on newlines. Useful when
+	 * users use newlines to signal line and paragraph breaks. In all cases output
+	 * should be well-formed markup.
+	 *
+	 * In DIV, LI, TD, and TH elements, Ps are only added when their would be at
+	 * least two of them.
+	 *
+	 * @param string $html snippet
+	 * @return string|false output or false if parse error occurred
+	 */
+	public function process($html) {
+		// normalize whitespace
+		$html = str_replace(array("\r\n", "\r"), "\n", $html);
+
+		// allows preserving entities untouched
+		$html = str_replace('&', $this->_unique . 'AMP', $html);
+
+		$this->_doc = new DOMDocument();
+	   
+		// parse to DOM, suppressing loadHTML warnings
+		// http://www.php.net/manual/en/domdocument.loadhtml.php#95463
+		libxml_use_internal_errors(true);
+
+		if (!$this->_doc->loadHTML("<html><meta http-equiv='content-type' " 
+				. "content='text/html; charset={$this->encoding}'><body>{$html}</body>"
+				. "</html>")) {
+			return false;
+		}
+
+		$this->_xpath = new DOMXPath($this->_doc);
+		// start processing recursively at the BODY element
+		$nodeList = $this->_xpath->query('//body[1]');
+		$this->_addParagraphs($nodeList->item(0));
+
+		// serialize back to HTML
+		$html = $this->_doc->saveHTML();
+
+		// split AUTOPs into multiples at /\n\n+/
+		$html = preg_replace('/(' . $this->_unique . 'NL){2,}/', '</autop><autop>', $html);
+		$html = str_replace(array($this->_unique . 'BR', $this->_unique . 'NL', '<br>'), 
+				'<br />',
+				$html);
+		$html = str_replace('<br /></autop>', '</autop>', $html);
+
+		// re-parse so we can handle new AUTOP elements
+
+		if (!$this->_doc->loadHTML($html)) {
+			return false;
+		}
+		// must re-create XPath object after DOM load
+		$this->_xpath = new DOMXPath($this->_doc);
+
+		// strip AUTOPs that only have comments/whitespace
+		foreach ($this->_xpath->query('//autop') as $autop) {
+			$hasContent = false;
+			if (trim($autop->textContent) !== '') {
+				$hasContent = true;
+			} else {
+				foreach ($autop->childNodes as $node) {
+					if ($node->nodeType === XML_ELEMENT_NODE) {
+						$hasContent = true;
+						break;
+					}
+				}
+			}
+			if (!$hasContent) {
+				// strip w/ preg_replace later (faster than moving nodes out)
+				$autop->setAttribute("r", "1");
+			}
+		}
+
+		// remove a single AUTOP inside certain elements
+		foreach ($this->_xpath->query('//div') as $el) {
+			$autops = $this->_xpath->query('./autop', $el);
+			if ($autops->length === 1) {
+				// strip w/ preg_replace later (faster than moving nodes out)
+				$autops->item(0)->setAttribute("r", "1");
+			}
+		}
+
+		$html = $this->_doc->saveHTML();
+
+		// trim to the contents of BODY
+		$bodyStart = strpos($html, '<body>');
+		$bodyEnd = strpos($html, '</body>', $bodyStart + 6);
+		$html = substr($html, $bodyStart + 6, $bodyEnd - $bodyStart - 6);
+		
+		// strip AUTOPs that should be removed
+		$html = preg_replace('@<autop r="1">(.*?)</autop>@', '\\1', $html);
+
+		// commit to converting AUTOPs to Ps
+		$html = str_replace('<autop>', "\n<p>", $html);
+		$html = str_replace('</autop>', "</p>\n", $html);
+		
+		$html = str_replace('<br>', '<br />', $html);
+		$html = str_replace($this->_unique . 'AMP', '&', $html);
+		return $html;
+	}
+
+	/**
+	 * Add P and BR elements as necessary
+	 *
+	 * @param DOMElement $el
+	 */
+	protected function _addParagraphs(DOMElement $el) {
+		// no need to recurse, just queue up
+		$elsToProcess = array($el);
+		$inlinesToProcess = array();
+		while ($el = array_shift($elsToProcess)) {
+			// if true, we can alter all child nodes, if not, we'll just call
+			// _addParagraphs on each element in the descendInto list
+			$alterInline = in_array($el->nodeName, $this->_alterList);
+
+			// inside affected elements, we want to trim leading whitespace from
+			// the first text node
+			$ltrimFirstTextNode = true;
+
+			// should we open a new AUTOP element to move inline elements into?
+			$openP = true;
+			$autop = null;
+
+			// after BR, ignore a newline
+			$isFollowingBr = false;
+
+			$node = $el->firstChild;
+			while (null !== $node) {
+				if ($alterInline) {
+					if ($openP) {
+						$openP = false;
+						// create a P to move inline content into (this may be removed later)
+						$autop = $el->insertBefore($this->_doc->createElement('autop'), $node);
+					}
+				}
+
+				$isElement = ($node->nodeType === XML_ELEMENT_NODE);
+				if ($isElement) {
+					$elName = $node->nodeName;
+				}
+				$isBlock = ($isElement && in_array($elName, $this->_blocks));
+
+				if ($alterInline) {
+					$isInline = $isElement && ! $isBlock;
+					$isText = ($node->nodeType === XML_TEXT_NODE);
+					$isLastInline = (! $node->nextSibling
+								   || ($node->nextSibling->nodeType === XML_ELEMENT_NODE
+									   && in_array($node->nextSibling->nodeName, $this->_blocks)));
+					if ($isElement) {
+						$isFollowingBr = ($node->nodeName === 'br');
+					}
+
+					if ($isText) {
+						$nodeText = $node->nodeValue;
+						if ($ltrimFirstTextNode) {
+							$nodeText = ltrim($nodeText);
+							$ltrimFirstTextNode = false;
+						}
+						if ($isFollowingBr && preg_match('@^[ \\t]*\\n[ \\t]*@', $nodeText, $m)) {
+							// if a user ends a line with <br>, don't add a second BR
+							$nodeText = substr($nodeText, strlen($m[0]));
+						}
+						if ($isLastInline) {
+							$nodeText = rtrim($nodeText);
+						}
+						$nodeText = str_replace("\n", $this->_unique . 'NL', $nodeText);
+						$tmpNode = $node;
+						$node = $node->nextSibling; // move loop to next node
+
+						// alter node in place, then move into AUTOP
+						$tmpNode->nodeValue = $nodeText;
+						$autop->appendChild($tmpNode);
+
+						continue;
+					}
+				}
+				if ($isBlock || ! $node->nextSibling) {
+					if ($isBlock) {
+						if (in_array($node->nodeName, $this->_descendList)) {
+							$elsToProcess[] = $node;
+							//$this->_addParagraphs($node);
+						}
+					}
+					$openP = true;
+					$ltrimFirstTextNode = true;
+				}
+				if ($alterInline) {
+					if (! $isBlock) {
+						$tmpNode = $node;
+						if ($isElement && false !== strpos($tmpNode->textContent, "\n")) {
+							$inlinesToProcess[] = $tmpNode;
+						}
+						$node = $node->nextSibling;
+						$autop->appendChild($tmpNode);
+						continue;
+					}
+				}
+
+				$node = $node->nextSibling;
+			}
+		}
+
+		// handle inline nodes
+		// no need to recurse, just queue up
+		while ($el = array_shift($inlinesToProcess)) {
+			$ignoreLeadingNewline = false;
+			foreach ($el->childNodes as $node) {
+				if ($node->nodeType === XML_ELEMENT_NODE) {
+					if ($node->nodeValue === 'BR') {
+						$ignoreLeadingNewline = true;
+					} else {
+						$ignoreLeadingNewline = false;
+						if (false !== strpos($node->textContent, "\n")) {
+							$inlinesToProcess[] = $node;
+						}
+					}
+					continue;
+				} elseif ($node->nodeType === XML_TEXT_NODE) {
+					$text = $node->nodeValue;
+					if ($text[0] === "\n" && $ignoreLeadingNewline) {
+						$text = substr($text, 1);
+						$ignoreLeadingNewline = false;
+					}
+					$node->nodeValue = str_replace("\n", $this->_unique . 'BR', $text);
+				}
+			}
+		}
+	}
+}
diff --git a/engine/classes/ElggEntity.php b/engine/classes/ElggEntity.php
index 77c2bbf4d..929abceb2 100644
--- a/engine/classes/ElggEntity.php
+++ b/engine/classes/ElggEntity.php
@@ -248,7 +248,9 @@ abstract class ElggEntity extends ElggData implements
 	 * @return mixed The value, or NULL if not found.
 	 */
 	public function getMetaData($name) {
-		if ((int) ($this->guid) == 0) {
+		$guid = $this->getGUID();
+
+		if (! $guid) {
 			if (isset($this->temp_metadata[$name])) {
 				// md is returned as an array only if more than 1 entry
 				if (count($this->temp_metadata[$name]) == 1) {
@@ -261,21 +263,38 @@ abstract class ElggEntity extends ElggData implements
 			}
 		}
 
+		// upon first cache miss, just load/cache all the metadata and retry.
+		// if this works, the rest of this function may not be needed!
+		$cache = elgg_get_metadata_cache();
+		if ($cache->isKnown($guid, $name)) {
+			return $cache->load($guid, $name);
+		} else {
+			$cache->populateFromEntities(array($guid));
+			// in case ignore_access was on, we have to check again...
+			if ($cache->isKnown($guid, $name)) {
+				return $cache->load($guid, $name);
+			}
+		}
+
 		$md = elgg_get_metadata(array(
-			'guid' => $this->getGUID(),
+			'guid' => $guid,
 			'metadata_name' => $name,
 			'limit' => 0,
 		));
 
+		$value = null;
+
 		if ($md && !is_array($md)) {
-			return $md->value;
+			$value = $md->value;
 		} elseif (count($md) == 1) {
-			return $md[0]->value;
+			$value = $md[0]->value;
 		} else if ($md && is_array($md)) {
-			return metadata_array_to_values($md);
+			$value = metadata_array_to_values($md);
 		}
 
-		return null;
+		$cache->save($guid, $name, $value);
+
+		return $value;
 	}
 
 	/**
@@ -1007,7 +1026,7 @@ abstract class ElggEntity extends ElggData implements
 	/**
 	 * Returns the guid.
 	 *
-	 * @return int GUID
+	 * @return int|null GUID
 	 */
 	public function getGUID() {
 		return $this->get('guid');
@@ -1245,16 +1264,16 @@ abstract class ElggEntity extends ElggData implements
 	/**
 	 * Save an entity.
 	 *
-	 * @return bool/int
+	 * @return bool|int
 	 * @throws IOException
 	 */
 	public function save() {
-		$guid = (int) $this->guid;
+		$guid = $this->getGUID();
 		if ($guid > 0) {
 			cache_entity($this);
 
 			return update_entity(
-				$this->get('guid'),
+				$guid,
 				$this->get('owner_guid'),
 				$this->get('access_id'),
 				$this->get('container_guid'),
@@ -1301,10 +1320,7 @@ abstract class ElggEntity extends ElggData implements
 			$this->attributes['subtype'] = get_subtype_id($this->attributes['type'],
 				$this->attributes['subtype']);
 
-			// Cache object handle
-			if ($this->attributes['guid']) {
-				cache_entity($this);
-			}
+			cache_entity($this);
 
 			return $this->attributes['guid'];
 		}
diff --git a/engine/classes/ElggGroup.php b/engine/classes/ElggGroup.php
index 121186196..ea257f368 100644
--- a/engine/classes/ElggGroup.php
+++ b/engine/classes/ElggGroup.php
@@ -324,37 +324,18 @@ class ElggGroup extends ElggEntity
 	 * @return bool
 	 */
 	protected function load($guid) {
-		// Test to see if we have the generic stuff
-		if (!parent::load($guid)) {
-			return false;
-		}
+		$attr_loader = new ElggAttributeLoader(get_class(), 'group', $this->attributes);
+		$attr_loader->requires_access_control = !($this instanceof ElggPlugin);
+		$attr_loader->secondary_loader = 'get_group_entity_as_row';
 
-		// Only work with GUID from here
-		if ($guid instanceof stdClass) {
-			$guid = $guid->guid;
-		}
-
-		// Check the type
-		if ($this->attributes['type'] != 'group') {
-			$msg = elgg_echo('InvalidClassException:NotValidElggStar', array($guid, get_class()));
-			throw new InvalidClassException($msg);
-		}
-
-		// Load missing data
-		$row = get_group_entity_as_row($guid);
-		if (($row) && (!$this->isFullyLoaded())) {
-			// If $row isn't a cached copy then increment the counter
-			$this->attributes['tables_loaded']++;
-		}
-
-		// Now put these into the attributes array as core values
-		$objarray = (array) $row;
-		foreach ($objarray as $key => $value) {
-			$this->attributes[$key] = $value;
+		$attrs = $attr_loader->getRequiredAttributes($guid);
+		if (!$attrs) {
+			return false;
 		}
 
-		// guid needs to be an int  http://trac.elgg.org/ticket/4111
-		$this->attributes['guid'] = (int)$this->attributes['guid'];
+		$this->attributes = $attrs;
+		$this->attributes['tables_loaded'] = 2;
+		cache_entity($this);
 
 		return true;
 	}
diff --git a/engine/classes/ElggGroupItemVisibility.php b/engine/classes/ElggGroupItemVisibility.php
new file mode 100644
index 000000000..2c7e2abb4
--- /dev/null
+++ b/engine/classes/ElggGroupItemVisibility.php
@@ -0,0 +1,93 @@
+<?php
+
+/**
+ * Determines if otherwise visible items should be hidden from a user due to group
+ * policy or visibility.
+ *
+ * @class      ElggGroupItemVisibility
+ * @package    Elgg.Core
+ * @subpackage Groups
+ *
+ * @access private
+ */
+class ElggGroupItemVisibility {
+
+	const REASON_MEMBERSHIP = 'membershiprequired';
+	const REASON_LOGGEDOUT = 'loggedinrequired';
+	const REASON_NOACCESS = 'noaccess';
+
+	/**
+	 * @var bool
+	 */
+	public $shouldHideItems = false;
+
+	/**
+	 * @var string
+	 */
+	public $reasonHidden = '';
+
+	/**
+	 * Determine visibility of items within a container for the current user
+	 *
+	 * @param int $container_guid GUID of a container (may/may not be a group)
+	 *
+	 * @return ElggGroupItemVisibility
+	 *
+	 * @todo Make this faster, considering it must run for every river item.
+	 */
+	static public function factory($container_guid) {
+		// cache because this may be called repeatedly during river display, and
+		// due to need to check group visibility, cache will be disabled for some
+		// get_entity() calls
+		static $cache = array();
+
+		$ret = new ElggGroupItemVisibility();
+
+		if (!$container_guid) {
+			return $ret;
+		}
+
+		$user = elgg_get_logged_in_user_entity();
+		$user_guid = $user ? $user->guid : 0;
+
+		$container_guid = (int) $container_guid;
+
+		$cache_key = "$container_guid|$user_guid";
+		if (empty($cache[$cache_key])) {
+			// compute
+
+			$container = get_entity($container_guid);
+			$is_visible = (bool) $container;
+
+			if (!$is_visible) {
+				// see if it *really* exists...
+				$prev_access = elgg_set_ignore_access();
+				$container = get_entity($container_guid);
+				elgg_set_ignore_access($prev_access);
+			}
+
+			if ($container && $container instanceof ElggGroup) {
+				/* @var ElggGroup $container */
+
+				if ($is_visible) {
+					if (!$container->isPublicMembership()) {
+						if ($user) {
+							if (!$container->isMember($user) && !$user->isAdmin()) {
+								$ret->shouldHideItems = true;
+								$ret->reasonHidden = self::REASON_MEMBERSHIP;
+							}
+						} else {
+							$ret->shouldHideItems = true;
+							$ret->reasonHidden = self::REASON_LOGGEDOUT;
+						}
+					}
+				} else {
+					$ret->shouldHideItems = true;
+					$ret->reasonHidden = self::REASON_NOACCESS;
+				}
+			}
+			$cache[$cache_key] = $ret;
+		}
+		return $cache[$cache_key];
+	}
+}
diff --git a/engine/classes/ElggMenuBuilder.php b/engine/classes/ElggMenuBuilder.php
index de0017599..d7f85685c 100644
--- a/engine/classes/ElggMenuBuilder.php
+++ b/engine/classes/ElggMenuBuilder.php
@@ -204,6 +204,9 @@ class ElggMenuBuilder {
 
 		// sort each section
 		foreach ($this->menu as $index => $section) {
+			foreach ($section as $key => $node) {
+				$section[$key]->setData('original_order', $key);
+			}
 			usort($section, $sort_callback);
 			$this->menu[$index] = $section;
 
@@ -232,10 +235,14 @@ class ElggMenuBuilder {
 	 * @return bool
 	 */
 	public static function compareByText($a, $b) {
-		$a = $a->getText();
-		$b = $b->getText();
+		$at = $a->getText();
+		$bt = $b->getText();
 
-		return strnatcmp($a, $b);
+		$result = strnatcmp($at, $bt);
+		if ($result === 0) {
+			return $a->getData('original_order') - $b->getData('original_order');
+		}
+		return $result;
 	}
 
 	/**
@@ -246,10 +253,14 @@ class ElggMenuBuilder {
 	 * @return bool
 	 */
 	public static function compareByName($a, $b) {
-		$a = $a->getName();
-		$b = $b->getName();
+		$an = $a->getName();
+		$bn = $b->getName();
 
-		return strcmp($a, $b);
+		$result = strcmp($an, $bn);
+		if ($result === 0) {
+			return $a->getData('original_order') - $b->getData('original_order');
+		}
+		return $result;
 	}
 
 	/**
@@ -260,9 +271,12 @@ class ElggMenuBuilder {
 	 * @return bool
 	 */
 	public static function compareByWeight($a, $b) {
-		$a = $a->getWeight();
-		$b = $b->getWeight();
+		$aw = $a->getWeight();
+		$bw = $b->getWeight();
 
-		return $a > $b;
+		if ($aw == $bw) {
+			return $a->getData('original_order') - $b->getData('original_order');
+		}
+		return $aw - $bw;
 	}
 }
diff --git a/engine/classes/ElggMenuItem.php b/engine/classes/ElggMenuItem.php
index 4bc9144d4..81ce6c099 100644
--- a/engine/classes/ElggMenuItem.php
+++ b/engine/classes/ElggMenuItem.php
@@ -542,6 +542,9 @@ class ElggMenuItem {
 	 * @return void
 	 */
 	public function sortChildren($sortFunction) {
+		foreach ($this->data['children'] as $key => $node) {
+			$this->data['children'][$key]->data['original_order'] = $key;
+		}
 		usort($this->data['children'], $sortFunction);
 	}
 
diff --git a/engine/classes/ElggMetadata.php b/engine/classes/ElggMetadata.php
index 634a122e5..7f45dc3ea 100644
--- a/engine/classes/ElggMetadata.php
+++ b/engine/classes/ElggMetadata.php
@@ -26,8 +26,6 @@ class ElggMetadata extends ElggExtender {
 	 * Construct a metadata object
 	 *
 	 * @param mixed $id ID of metadata or a database row as stdClass object
-	 *
-	 * @return void
 	 */
 	function __construct($id = null) {
 		$this->initializeAttributes();
@@ -54,7 +52,7 @@ class ElggMetadata extends ElggExtender {
 	 *
 	 * @param int $user_guid The GUID of the user (defaults to currently logged in user)
 	 *
-	 * @return true|false Depending on permissions
+	 * @return bool Depending on permissions
 	 */
 	function canEdit($user_guid = 0) {
 		if ($entity = get_entity($this->get('entity_guid'))) {
@@ -64,9 +62,11 @@ class ElggMetadata extends ElggExtender {
 	}
 
 	/**
-	 * Save matadata object
+	 * Save metadata object
 	 *
-	 * @return int the metadata object id
+	 * @return int|bool the metadata object id or true if updated
+	 *
+	 * @throws IOException
 	 */
 	function save() {
 		if ($this->id > 0) {
@@ -89,7 +89,13 @@ class ElggMetadata extends ElggExtender {
 	 * @return bool
 	 */
 	function delete() {
-		return elgg_delete_metastring_based_object_by_id($this->id, 'metadata');
+		$success = elgg_delete_metastring_based_object_by_id($this->id, 'metadata');
+		if ($success) {
+			// we mark unknown here because this deletes only one value
+			// under this name, and there may be others remaining.
+			elgg_get_metadata_cache()->markUnknown($this->entity_guid, $this->name);
+		}
+		return $success;
 	}
 
 	/**
@@ -99,17 +105,27 @@ class ElggMetadata extends ElggExtender {
 	 * @since 1.8
 	 */
 	function disable() {
-		return elgg_set_metastring_based_object_enabled_by_id($this->id, 'no', 'metadata');
+		$success = elgg_set_metastring_based_object_enabled_by_id($this->id, 'no', 'metadata');
+		if ($success) {
+			// we mark unknown here because this disables only one value
+			// under this name, and there may be others remaining.
+			elgg_get_metadata_cache()->markUnknown($this->entity_guid, $this->name);
+		}
+		return $success;
 	}
 
 	/**
-	 * Disable the metadata
+	 * Enable the metadata
 	 *
 	 * @return bool
 	 * @since 1.8
 	 */
 	function enable() {
-		return elgg_set_metastring_based_object_enabled_by_id($this->id, 'yes', 'metadata');
+		$success = elgg_set_metastring_based_object_enabled_by_id($this->id, 'yes', 'metadata');
+		if ($success) {
+			elgg_get_metadata_cache()->markUnknown($this->entity_guid, $this->name);
+		}
+		return $success;
 	}
 
 	/**
diff --git a/engine/classes/ElggObject.php b/engine/classes/ElggObject.php
index b4bae6825..6263f84f6 100644
--- a/engine/classes/ElggObject.php
+++ b/engine/classes/ElggObject.php
@@ -99,37 +99,18 @@ class ElggObject extends ElggEntity {
 	 * @throws InvalidClassException
 	 */
 	protected function load($guid) {
-		// Load data from entity table if needed
-		if (!parent::load($guid)) {
-			return false;
-		}
+		$attr_loader = new ElggAttributeLoader(get_class(), 'object', $this->attributes);
+		$attr_loader->requires_access_control = !($this instanceof ElggPlugin);
+		$attr_loader->secondary_loader = 'get_object_entity_as_row';
 
-		// Only work with GUID from here
-		if ($guid instanceof stdClass) {
-			$guid = $guid->guid;
-		}
-
-		// Check the type
-		if ($this->attributes['type'] != 'object') {
-			$msg = elgg_echo('InvalidClassException:NotValidElggStar', array($guid, get_class()));
-			throw new InvalidClassException($msg);
-		}
-
-		// Load missing data
-		$row = get_object_entity_as_row($guid);
-		if (($row) && (!$this->isFullyLoaded())) {
-			// If $row isn't a cached copy then increment the counter
-			$this->attributes['tables_loaded']++;
-		}
-
-		// Now put these into the attributes array as core values
-		$objarray = (array) $row;
-		foreach ($objarray as $key => $value) {
-			$this->attributes[$key] = $value;
+		$attrs = $attr_loader->getRequiredAttributes($guid);
+		if (!$attrs) {
+			return false;
 		}
 
-		// guid needs to be an int  http://trac.elgg.org/ticket/4111
-		$this->attributes['guid'] = (int)$this->attributes['guid'];
+		$this->attributes = $attrs;
+		$this->attributes['tables_loaded'] = 2;
+		cache_entity($this);
 
 		return true;
 	}
@@ -149,7 +130,7 @@ class ElggObject extends ElggEntity {
 
 		// Save ElggObject-specific attributes
 		return create_object_entity($this->get('guid'), $this->get('title'),
-			$this->get('description'), $this->get('container_guid'));
+			$this->get('description'));
 	}
 
 	/**
@@ -223,7 +204,7 @@ class ElggObject extends ElggEntity {
 
 		// must be member of group
 		if (elgg_instanceof($this->getContainerEntity(), 'group')) {
-			if (!$this->getContainerEntity()->canWriteToContainer(get_user($user_guid))) {
+			if (!$this->getContainerEntity()->canWriteToContainer($user_guid)) {
 				return false;
 			}
 		}
diff --git a/engine/classes/ElggPAM.php b/engine/classes/ElggPAM.php
index 0681a909b..f07095fc1 100644
--- a/engine/classes/ElggPAM.php
+++ b/engine/classes/ElggPAM.php
@@ -53,11 +53,17 @@ class ElggPAM {
 
 		foreach ($_PAM_HANDLERS[$this->policy] as $k => $v) {
 			$handler = $v->handler;
+			if (!is_callable($handler)) {
+				continue;
+			}
+			/* @var callable $handler */
+
 			$importance = $v->importance;
 
 			try {
 				// Execute the handler
-				$result = $handler($credentials);
+				// @todo don't assume $handler is a global function
+				$result = call_user_func($handler, $credentials);
 				if ($result) {
 					$authenticated = true;
 				} elseif ($result === false) {
diff --git a/engine/classes/ElggPlugin.php b/engine/classes/ElggPlugin.php
index 8c9093834..32b5f952a 100644
--- a/engine/classes/ElggPlugin.php
+++ b/engine/classes/ElggPlugin.php
@@ -36,8 +36,9 @@ class ElggPlugin extends ElggObject {
 	 * @warning Unlike other ElggEntity objects, you cannot null instantiate
 	 *          ElggPlugin. You must point it to an actual plugin GUID or location.
 	 *
-	 * @param mixed $plugin The GUID of the ElggPlugin object or the path of
-	 *                      the plugin to load.
+	 * @param mixed $plugin The GUID of the ElggPlugin object or the path of the plugin to load.
+	 *
+	 * @throws PluginException
 	 */
 	public function __construct($plugin) {
 		if (!$plugin) {
@@ -76,68 +77,8 @@ class ElggPlugin extends ElggObject {
 			// load the rest of the plugin
 			parent::__construct($existing_guid);
 		}
-	}
-
-	/**
-	 * Overridden from ElggEntity and ElggObject::load(). Core always inits plugins with
-	 * a query joined to the objects_entity table, so all the info is there.
-	 *
-	 * @param mixed $guid GUID of an ElggObject or the stdClass object from entities table
-	 *
-	 * @return bool
-	 * @throws InvalidClassException
-	 */
-	protected function load($guid) {
-
-		$expected_attributes = $this->attributes;
-		unset($expected_attributes['tables_split']);
-		unset($expected_attributes['tables_loaded']);
-
-		// this was loaded with a full join
-		$needs_loaded = false;
-
-		if ($guid instanceof stdClass) {
-			$row = (array) $guid;
-			$missing_attributes = array_diff_key($expected_attributes, $row);
-			if ($missing_attributes) {
-				$needs_loaded = true;
-				$old_guid = $guid;
-				$guid = $row['guid'];
-			} else {
-				$this->attributes = $row;
-			}
-		} else {
-			$needs_loaded = true;
-		}
 
-		if ($needs_loaded) {
-			$entity = (array) get_entity_as_row($guid);
-			$object = (array) get_object_entity_as_row($guid);
-
-			if (!$entity || !$object) {
-				return false;
-			}
-			
-			$this->attributes = array_merge($this->attributes, $entity, $object);
-		}
-
-		$this->attributes['tables_loaded'] = 2;
-
-		// Check the type
-		if ($this->attributes['type'] != 'object') {
-			$msg = elgg_echo('InvalidClassException:NotValidElggStar', array($guid, get_class()));
-			throw new InvalidClassException($msg);
-		}
-
-		// guid needs to be an int  http://trac.elgg.org/ticket/4111
-		$this->attributes['guid'] = (int)$this->attributes['guid'];
-
-		// cache the entity
-		if ($this->attributes['guid']) {
-			cache_entity($this);
-		}
-
-		return true;
+		_elgg_cache_plugin_by_id($this);
 	}
 
 	/**
diff --git a/engine/classes/ElggPluginManifest.php b/engine/classes/ElggPluginManifest.php
index a4f5bb95d..6912c2b08 100644
--- a/engine/classes/ElggPluginManifest.php
+++ b/engine/classes/ElggPluginManifest.php
@@ -130,7 +130,7 @@ class ElggPluginManifest {
 		}
 
 		// see if we need to construct the xml object.
-		if ($manifest instanceof XmlElement) {
+		if ($manifest instanceof ElggXMLElement) {
 			$manifest_obj = $manifest;
 		} else {
 			if (substr(trim($manifest), 0, 1) == '<') {
diff --git a/engine/classes/ElggPluginManifestParser.php b/engine/classes/ElggPluginManifestParser.php
index b0480d4d8..af152b561 100644
--- a/engine/classes/ElggPluginManifestParser.php
+++ b/engine/classes/ElggPluginManifestParser.php
@@ -53,10 +53,10 @@ abstract class ElggPluginManifestParser {
 	/**
 	 * Loads the manifest XML to be parsed.
 	 *
-	 * @param XmlElement $xml    The Manifest XML object to be parsed
-	 * @param object     $caller The object calling this parser.
+	 * @param ElggXmlElement $xml    The Manifest XML object to be parsed
+	 * @param object         $caller The object calling this parser.
 	 */
-	public function __construct(XmlElement $xml, $caller) {
+	public function __construct(ElggXMLElement $xml, $caller) {
 		$this->manifestObject = $xml;
 		$this->caller = $caller;
 	}
diff --git a/engine/classes/ElggSession.php b/engine/classes/ElggSession.php
index 13a33736c..9750f063e 100644
--- a/engine/classes/ElggSession.php
+++ b/engine/classes/ElggSession.php
@@ -54,7 +54,7 @@ class ElggSession implements ArrayAccess {
 	 *
 	 * @param mixed $key Name
 	 *
-	 * @return void
+	 * @return mixed
 	 */
 	function offsetGet($key) {
 		if (!ElggSession::$__localcache) {
@@ -98,7 +98,7 @@ class ElggSession implements ArrayAccess {
 	 *
 	 * @param int $offset Offset
 	 *
-	 * @return int
+	 * @return bool
 	 */
 	function offsetExists($offset) {
 		if (isset(ElggSession::$__localcache[$offset])) {
@@ -112,6 +112,8 @@ class ElggSession implements ArrayAccess {
 		if ($this->offsetGet($offset)) {
 			return true;
 		}
+
+		return false;
 	}
 
 
@@ -132,10 +134,10 @@ class ElggSession implements ArrayAccess {
 	 * @param string $key   Name
 	 * @param mixed  $value Value
 	 *
-	 * @return mixed
+	 * @return void
 	 */
 	function set($key, $value) {
-		return $this->offsetSet($key, $value);
+		$this->offsetSet($key, $value);
 	}
 
 	/**
@@ -143,9 +145,9 @@ class ElggSession implements ArrayAccess {
 	 *
 	 * @param string $key Name
 	 *
-	 * @return bool
+	 * @return void
 	 */
 	function del($key) {
-		return $this->offsetUnset($key);
+		$this->offsetUnset($key);
 	}
 }
diff --git a/engine/classes/ElggSite.php b/engine/classes/ElggSite.php
index 401939005..f7f5b68ea 100644
--- a/engine/classes/ElggSite.php
+++ b/engine/classes/ElggSite.php
@@ -117,37 +117,18 @@ class ElggSite extends ElggEntity {
 	 * @throws InvalidClassException
 	 */
 	protected function load($guid) {
-		// Test to see if we have the generic stuff
-		if (!parent::load($guid)) {
-			return false;
-		}
+		$attr_loader = new ElggAttributeLoader(get_class(), 'site', $this->attributes);
+		$attr_loader->requires_access_control = !($this instanceof ElggPlugin);
+		$attr_loader->secondary_loader = 'get_site_entity_as_row';
 
-		// Only work with GUID from here
-		if ($guid instanceof stdClass) {
-			$guid = $guid->guid;
-		}
-
-		// Check the type
-		if ($this->attributes['type'] != 'site') {
-			$msg = elgg_echo('InvalidClassException:NotValidElggStar', array($guid, get_class()));
-			throw new InvalidClassException($msg);
-		}
-
-		// Load missing data
-		$row = get_site_entity_as_row($guid);
-		if (($row) && (!$this->isFullyLoaded())) {
-			// If $row isn't a cached copy then increment the counter
-			$this->attributes['tables_loaded']++;
-		}
-
-		// Now put these into the attributes array as core values
-		$objarray = (array) $row;
-		foreach ($objarray as $key => $value) {
-			$this->attributes[$key] = $value;
+		$attrs = $attr_loader->getRequiredAttributes($guid);
+		if (!$attrs) {
+			return false;
 		}
 
-		// guid needs to be an int  http://trac.elgg.org/ticket/4111
-		$this->attributes['guid'] = (int)$this->attributes['guid'];
+		$this->attributes = $attrs;
+		$this->attributes['tables_loaded'] = 2;
+		cache_entity($this);
 
 		return true;
 	}
diff --git a/engine/classes/ElggStaticVariableCache.php b/engine/classes/ElggStaticVariableCache.php
index 787d35a32..17d849400 100644
--- a/engine/classes/ElggStaticVariableCache.php
+++ b/engine/classes/ElggStaticVariableCache.php
@@ -21,8 +21,8 @@ class ElggStaticVariableCache extends ElggSharedMemoryCache {
 	 * This function creates a variable cache in a static variable in
 	 * memory, optionally with a given namespace (to avoid overlap).
 	 *
-	 * @param string $namespace The namespace for this cache to write to
-	 * note, namespaces of the same name are shared!
+	 * @param string $namespace The namespace for this cache to write to.
+	 * @note namespaces of the same name are shared!
 	 */
 	function __construct($namespace = 'default') {
 		$this->setNamespace($namespace);
diff --git a/engine/classes/ElggUser.php b/engine/classes/ElggUser.php
index d7bb89265..6c1cdc1de 100644
--- a/engine/classes/ElggUser.php
+++ b/engine/classes/ElggUser.php
@@ -106,37 +106,17 @@ class ElggUser extends ElggEntity
 	 * @return bool
 	 */
 	protected function load($guid) {
-		// Test to see if we have the generic stuff
-		if (!parent::load($guid)) {
-			return false;
-		}
+		$attr_loader = new ElggAttributeLoader(get_class(), 'user', $this->attributes);
+		$attr_loader->secondary_loader = 'get_user_entity_as_row';
 
-		// Only work with GUID from here
-		if ($guid instanceof stdClass) {
-			$guid = $guid->guid;
-		}
-
-		// Check the type
-		if ($this->attributes['type'] != 'user') {
-			$msg = elgg_echo('InvalidClassException:NotValidElggStar', array($guid, get_class()));
-			throw new InvalidClassException($msg);
-		}
-
-		// Load missing data
-		$row = get_user_entity_as_row($guid);
-		if (($row) && (!$this->isFullyLoaded())) {
-			// If $row isn't a cached copy then increment the counter
-			$this->attributes['tables_loaded']++;
-		}
-
-		// Now put these into the attributes array as core values
-		$objarray = (array) $row;
-		foreach ($objarray as $key => $value) {
-			$this->attributes[$key] = $value;
+		$attrs = $attr_loader->getRequiredAttributes($guid);
+		if (!$attrs) {
+			return false;
 		}
 
-		// guid needs to be an int  http://trac.elgg.org/ticket/4111
-		$this->attributes['guid'] = (int)$this->attributes['guid'];
+		$this->attributes = $attrs;
+		$this->attributes['tables_loaded'] = 2;
+		cache_entity($this);
 
 		return true;
 	}
diff --git a/engine/classes/ElggVolatileMetadataCache.php b/engine/classes/ElggVolatileMetadataCache.php
new file mode 100644
index 000000000..8a33c198d
--- /dev/null
+++ b/engine/classes/ElggVolatileMetadataCache.php
@@ -0,0 +1,347 @@
+<?php
+/**
+ * ElggVolatileMetadataCache
+ * In memory cache of known metadata values stored by entity.
+ *
+ * @package    Elgg.Core
+ * @subpackage Cache
+ *
+ * @access private
+ */
+class ElggVolatileMetadataCache {
+
+	/**
+	 * The cached values (or null for known to be empty). If the portion of the cache
+	 * is synchronized, missing values are assumed to indicate that values do not
+	 * exist in storage, otherwise, we don't know what's there.
+	 *
+	 * @var array
+	 */
+	protected $values = array();
+
+	/**
+	 * Does the cache know that it contains all names fetch-able from storage?
+	 * The keys are entity GUIDs and either the value exists (true) or it's not set.
+	 *
+	 * @var array
+	 */
+	protected $isSynchronized = array();
+
+	/**
+	 * @var null|bool
+	 */
+	protected $ignoreAccess = null;
+
+	/**
+	 * @param int $entity_guid
+	 *
+	 * @param array $values
+	 */
+	public function saveAll($entity_guid, array $values) {
+		if (!$this->getIgnoreAccess()) {
+			$this->values[$entity_guid] = $values;
+			$this->isSynchronized[$entity_guid] = true;
+		}
+	}
+
+	/**
+	 * @param int $entity_guid
+	 *
+	 * @return array
+	 */
+	public function loadAll($entity_guid) {
+		if (isset($this->values[$entity_guid])) {
+			return $this->values[$entity_guid];
+		} else {
+			return array();
+		}
+	}
+
+	/**
+	 * Declare that there may be fetch-able metadata names in storage that this
+	 * cache doesn't know about
+	 *
+	 * @param int $entity_guid
+	 */
+	public function markOutOfSync($entity_guid) {
+		unset($this->isSynchronized[$entity_guid]);
+	}
+
+	/**
+	 * @param $entity_guid
+	 *
+	 * @return bool
+	 */
+	public function isSynchronized($entity_guid) {
+		return isset($this->isSynchronized[$entity_guid]);
+	}
+
+	/**
+	 * @param int $entity_guid
+	 *
+	 * @param string $name
+	 *
+	 * @param array|int|string|null $value  null means it is known that there is no
+	 *                                      fetch-able metadata under this name
+	 * @param bool $allow_multiple
+	 */
+	public function save($entity_guid, $name, $value, $allow_multiple = false) {
+		if ($this->getIgnoreAccess()) {
+			// we don't know if what gets saves here will be available to user once
+			// access control returns, hence it's best to forget :/
+			$this->markUnknown($entity_guid, $name);
+		} else {
+			if ($allow_multiple) {
+				if ($this->isKnown($entity_guid, $name)) {
+					$existing = $this->load($entity_guid, $name);
+					if ($existing !== null) {
+						$existing = (array) $existing;
+						$existing[] = $value;
+						$value = $existing;
+					}
+				} else {
+					// we don't know whether there are unknown values, so it's
+					// safest to leave that assumption
+					$this->markUnknown($entity_guid, $name);
+					return;
+				}
+			}
+			$this->values[$entity_guid][$name] = $value;
+		}
+	}
+
+	/**
+	 * Warning: You should always call isKnown() beforehand to verify that this
+	 * function's return value should be trusted (otherwise a null return value
+	 * is ambiguous).
+	 *
+	 * @param int $entity_guid
+	 *
+	 * @param string $name
+	 *
+	 * @return array|string|int|null null = value does not exist
+	 */
+	public function load($entity_guid, $name) {
+		if (isset($this->values[$entity_guid]) && array_key_exists($name, $this->values[$entity_guid])) {
+			return $this->values[$entity_guid][$name];
+		} else {
+			return null;
+		}
+	}
+
+	/**
+	 * Forget about this metadata entry. We don't want to try to guess what the
+	 * next fetch from storage will return
+	 *
+	 * @param int $entity_guid
+	 *
+	 * @param string $name
+	 */
+	public function markUnknown($entity_guid, $name) {
+		unset($this->values[$entity_guid][$name]);
+		$this->markOutOfSync($entity_guid);
+	}
+
+	/**
+	 * If true, load() will return an accurate value for this name
+	 *
+	 * @param int $entity_guid
+	 *
+	 * @param string $name
+	 *
+	 * @return bool
+	 */
+	public function isKnown($entity_guid, $name) {
+		if (isset($this->isSynchronized[$entity_guid])) {
+			return true;
+		} else {
+			return (isset($this->values[$entity_guid]) && array_key_exists($name, $this->values[$entity_guid]));
+		}
+
+	}
+
+	/**
+	 * Declare that metadata under this name is known to be not fetch-able from storage
+	 *
+	 * @param int $entity_guid
+	 *
+	 * @param string $name
+	 *
+	 * @return array
+	 */
+	public function markEmpty($entity_guid, $name) {
+		$this->values[$entity_guid][$name] = null;
+	}
+
+	/**
+	 * Forget about all metadata for an entity
+	 *
+	 * @param int $entity_guid
+	 */
+	public function clear($entity_guid) {
+		$this->values[$entity_guid] = array();
+		$this->markOutOfSync($entity_guid);
+	}
+
+	/**
+	 * Clear entire cache and mark all entities as out of sync
+	 */
+	public function flush() {
+		$this->values = array();
+		$this->isSynchronized = array();
+	}
+
+	/**
+	 * Use this value instead of calling elgg_get_ignore_access(). By default that
+	 * function will be called.
+	 *
+	 * This setting makes this component a little more loosely-coupled.
+	 *
+	 * @param bool $ignore
+	 */
+	public function setIgnoreAccess($ignore) {
+		$this->ignoreAccess = (bool) $ignore;
+	}
+
+	/**
+	 * Tell the cache to call elgg_get_ignore_access() to determing access status.
+	 */
+	public function unsetIgnoreAccess() {
+		$this->ignoreAccess = null;
+	}
+
+	/**
+	 * @return bool
+	 */
+	protected function getIgnoreAccess() {
+		if (null === $this->ignoreAccess) {
+			return elgg_get_ignore_access();
+		} else {
+			return $this->ignoreAccess;
+		}
+	}
+
+	/**
+	 * Invalidate based on options passed to the global *_metadata functions
+	 *
+	 * @param string $action  Action performed on metadata. "delete", "disable", or "enable"
+	 *
+	 * @param array $options  Options passed to elgg_(delete|disable|enable)_metadata
+	 *
+	 *   "guid" if given, invalidation will be limited to this entity
+	 *
+	 *   "metadata_name" if given, invalidation will be limited to metadata with this name
+	 */
+	public function invalidateByOptions($action, array $options) {
+		// remove as little as possible, optimizing for common cases
+		if (empty($options['guid'])) {
+			// safest to clear everything unless we want to make this even more complex :(
+			$this->flush();
+		} else {
+			if (empty($options['metadata_name'])) {
+				// safest to clear the whole entity
+				$this->clear($options['guid']);
+			} else {
+				switch ($action) {
+					case 'delete':
+						$this->markEmpty($options['guid'], $options['metadata_name']);
+						break;
+					default:
+						$this->markUnknown($options['guid'], $options['metadata_name']);
+				}
+			}
+		}
+	}
+
+	/**
+	 * @param int|array $guids
+	 */
+	public function populateFromEntities($guids) {
+		if (empty($guids)) {
+			return;
+		}
+		if (!is_array($guids)) {
+			$guids = array($guids);
+		}
+		$guids = array_unique($guids);
+
+		// could be useful at some point in future
+		//$guids = $this->filterMetadataHeavyEntities($guids);
+
+		$db_prefix = elgg_get_config('dbprefix');
+		$options = array(
+			'guids' => $guids,
+			'limit' => 0,
+			'callback' => false,
+			'joins' => array(
+				"JOIN {$db_prefix}metastrings v ON n_table.value_id = v.id",
+				"JOIN {$db_prefix}metastrings n ON n_table.name_id = n.id",
+			),
+			'selects' => array('n.string AS name', 'v.string AS value'),
+			'order_by' => 'n_table.entity_guid, n_table.time_created ASC',
+
+			// @todo don't know why this is necessary
+			'wheres' => array(get_access_sql_suffix('n_table')),
+		);
+		$data = elgg_get_metadata($options);
+
+		// build up metadata for each entity, save when GUID changes (or data ends)
+		$last_guid = null;
+		$metadata = array();
+		$last_row_idx = count($data) - 1;
+		foreach ($data as $i => $row) {
+			$name = $row->name;
+			$value = ($row->value_type === 'text') ? $row->value : (int) $row->value;
+			$guid = $row->entity_guid;
+			if ($guid !== $last_guid) {
+				if ($last_guid) {
+					$this->saveAll($last_guid, $metadata);
+				}
+				$metadata = array();
+			}
+			if (isset($metadata[$name])) {
+				$metadata[$name] = (array) $metadata[$name];
+				$metadata[$name][] = $value;
+			} else {
+				$metadata[$name] = $value;
+			}
+			if (($i == $last_row_idx)) {
+				$this->saveAll($guid, $metadata);
+			}
+			$last_guid = $guid;
+		}
+	}
+
+	/**
+	 * Filter out entities whose concatenated metadata values (INTs casted as string)
+	 * exceed a threshold in characters. This could be used to avoid overpopulating the
+	 * cache if RAM usage becomes an issue.
+	 *
+	 * @param array $guids GUIDs of entities to examine
+	 *
+	 * @param int $limit Limit in characters of all metadata (with ints casted to strings)
+	 *
+	 * @return array
+	 */
+	public function filterMetadataHeavyEntities(array $guids, $limit = 1024000) {
+		$db_prefix = elgg_get_config('dbprefix');
+
+		$options = array(
+			'guids' => $guids,
+			'limit' => 0,
+			'callback' => false,
+			'joins' => "JOIN {$db_prefix}metastrings v ON n_table.value_id = v.id",
+			'selects' => array('SUM(LENGTH(v.string)) AS bytes'),
+			'order_by' => 'n_table.entity_guid, n_table.time_created ASC',
+			'group_by' => 'n_table.entity_guid',
+		);
+		$data = elgg_get_metadata($options);
+		// don't cache if metadata for entity is over 10MB (or rolled INT)
+		foreach ($data as $row) {
+			if ($row->bytes > $limit || $row->bytes < 0) {
+				array_splice($guids, array_search($row->entity_guid, $guids), 1);
+			}
+		}
+		return $guids;
+	}
+}
diff --git a/engine/classes/ElggXMLElement.php b/engine/classes/ElggXMLElement.php
new file mode 100644
index 000000000..65a13912c
--- /dev/null
+++ b/engine/classes/ElggXMLElement.php
@@ -0,0 +1,115 @@
+<?php
+/**
+ * A parser for XML that uses SimpleXMLElement
+ *
+ * @package    Elgg.Core
+ * @subpackage XML
+ */
+class ElggXMLElement {
+	/**
+	 * @var SimpleXMLElement
+	 */
+	private $_element;
+
+	/**
+	 * Creates an ElggXMLParser from a string or existing SimpleXMLElement
+	 * 
+	 * @param string|SimpleXMLElement $xml The XML to parse
+	 */
+	public function __construct($xml) {
+		if ($xml instanceof SimpleXMLElement) {
+			$this->_element = $xml;
+		} else {
+			$this->_element = new SimpleXMLElement($xml);
+		}
+	}
+
+	/**
+	 * @return string The name of the element
+	 */
+	public function getName() {
+		return $this->_element->getName();
+	}
+
+	/**
+	 * @return array:string The attributes
+	 */
+	public function getAttributes() {
+		//include namespace declarations as attributes
+		$xmlnsRaw = $this->_element->getNamespaces();
+		$xmlns = array();
+		foreach ($xmlnsRaw as $key => $val) {
+			$label = 'xmlns' . ($key ? ":$key" : $key);
+			$xmlns[$label] = $val;
+		}
+		//get attributes and merge with namespaces
+		$attrRaw = $this->_element->attributes();
+		$attr = array();
+		foreach ($attrRaw as $key => $val) {
+			$attr[$key] = $val;
+		}
+		$attr = array_merge((array) $xmlns, (array) $attr);
+		$result = array();
+		foreach ($attr as $key => $val) {
+			$result[$key] = (string) $val;
+		}
+		return $result;
+	}
+
+	/**
+	 * @return string CData
+	 */
+	public function getContent() {
+		return (string) $this->_element;
+	}
+
+	/**
+	 * @return array:ElggXMLElement Child elements
+	 */
+	public function getChildren() {
+		$children = $this->_element->children();
+		$result = array();
+		foreach ($children as $val) {
+			$result[] = new ElggXMLElement($val);
+		}
+
+		return $result;
+	}
+
+	function __get($name) {
+		switch ($name) {
+			case 'name':
+				return $this->getName();
+				break;
+			case 'attributes':
+				return $this->getAttributes();
+				break;
+			case 'content':
+				return $this->getContent();
+				break;
+			case 'children':
+				return $this->getChildren();
+				break;
+		}
+		return null;
+	}
+
+	function __isset($name) {
+		switch ($name) {
+			case 'name':
+				return $this->getName() !== null;
+				break;
+			case 'attributes':
+				return $this->getAttributes() !== null;
+				break;
+			case 'content':
+				return $this->getContent() !== null;
+				break;
+			case 'children':
+				return $this->getChildren() !== null;
+				break;
+		}
+		return false;
+	}
+
+}
\ No newline at end of file
diff --git a/engine/classes/IncompleteEntityException.php b/engine/classes/IncompleteEntityException.php
new file mode 100644
index 000000000..8c86edcc6
--- /dev/null
+++ b/engine/classes/IncompleteEntityException.php
@@ -0,0 +1,10 @@
+<?php
+/**
+ * IncompleteEntityException
+ * Thrown when constructing an entity that is missing its secondary entity table
+ *
+ * @package    Elgg.Core
+ * @subpackage Exception
+ * @access private
+ */
+class IncompleteEntityException extends Exception {}