PhabricatorPolicyAwareQuery.php
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Created: Tue, May 21, 11:16

PhabricatorPolicyAwareQuery.php
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	<?php

	/**
	* A @{class:PhabricatorQuery} which filters results according to visibility
	* policies for the querying user. Broadly, this class allows you to implement
	* a query that returns only objects the user is allowed to see.
	*
	* $results = id(new ExampleQuery())
	* ->setViewer($user)
	* ->withConstraint($example)
	* ->execute();
	*
	* Normally, you should extend @{class:PhabricatorCursorPagedPolicyAwareQuery},
	* not this class. @{class:PhabricatorCursorPagedPolicyAwareQuery} provides a
	* more practical interface for building usable queries against most object
	* types.
	*
	* NOTE: Although this class extends @{class:PhabricatorOffsetPagedQuery},
	* offset paging with policy filtering is not efficient. All results must be
	* loaded into the application and filtered here: skipping `N` rows via offset
	* is an `O(N)` operation with a large constant. Prefer cursor-based paging
	* with @{class:PhabricatorCursorPagedPolicyAwareQuery}, which can filter far
	* more efficiently in MySQL.
	*
	* @task config Query Configuration
	* @task exec Executing Queries
	* @task policyimpl Policy Query Implementation
	*/
	abstract class PhabricatorPolicyAwareQuery extends PhabricatorOffsetPagedQuery {

	private $viewer;
	private $raisePolicyExceptions;
	private $parentQuery;
	private $rawResultLimit;
	private $capabilities;
	private $workspace = array();
	private $policyFilteredPHIDs = array();
	private $canUseApplication;


	/* -( Query Configuration )------------------------------------------------ */


	/**
	* Set the viewer who is executing the query. Results will be filtered
	* according to the viewer's capabilities. You must set a viewer to execute
	* a policy query.
	*
	* @param PhabricatorUser The viewing user.
	* @return this
	* @task config
	*/
	final public function setViewer(PhabricatorUser $viewer) {
	$this->viewer = $viewer;
	return $this;
	}


	/**
	* Get the query's viewer.
	*
	* @return PhabricatorUser The viewing user.
	* @task config
	*/
	final public function getViewer() {
	return $this->viewer;
	}


	/**
	* Set the parent query of this query. This is useful for nested queries so
	* that configuration like whether or not to raise policy exceptions is
	* seamlessly passed along to child queries.
	*
	* @return this
	* @task config
	*/
	final public function setParentQuery(PhabricatorPolicyAwareQuery $query) {
	$this->parentQuery = $query;
	return $this;
	}


	/**
	* Get the parent query. See @{method:setParentQuery} for discussion.
	*
	* @return PhabricatorPolicyAwareQuery The parent query.
	* @task config
	*/
	final public function getParentQuery() {
	return $this->parentQuery;
	}


	/**
	* Hook to configure whether this query should raise policy exceptions.
	*
	* @return this
	* @task config
	*/
	final public function setRaisePolicyExceptions($bool) {
	$this->raisePolicyExceptions = $bool;
	return $this;
	}


	/**
	* @return bool
	* @task config
	*/
	final public function shouldRaisePolicyExceptions() {
	return (bool)$this->raisePolicyExceptions;
	}


	/**
	* @task config
	*/
	final public function requireCapabilities(array $capabilities) {
	$this->capabilities = $capabilities;
	return $this;
	}


	/* -( Query Execution )---------------------------------------------------- */


	/**
	* Execute the query, expecting a single result. This method simplifies
	* loading objects for detail pages or edit views.
	*
	* // Load one result by ID.
	* $obj = id(new ExampleQuery())
	* ->setViewer($user)
	* ->withIDs(array($id))
	* ->executeOne();
	* if (!$obj) {
	* return new Aphront404Response();
	* }
	*
	* If zero results match the query, this method returns `null`.
	* If one result matches the query, this method returns that result.
	*
	* If two or more results match the query, this method throws an exception.
	* You should use this method only when the query constraints guarantee at
	* most one match (e.g., selecting a specific ID or PHID).
	*
	* If one result matches the query but it is caught by the policy filter (for
	* example, the user is trying to view or edit an object which exists but
	* which they do not have permission to see) a policy exception is thrown.
	*
	* @return mixed Single result, or null.
	* @task exec
	*/
	final public function executeOne() {

	$this->setRaisePolicyExceptions(true);
	try {
	$results = $this->execute();
	} catch (Exception $ex) {
	$this->setRaisePolicyExceptions(false);
	throw $ex;
	}

	if (count($results) > 1) {
	throw new Exception("Expected a single result!");
	}

	if (!$results) {
	return null;
	}

	return head($results);
	}


	/**
	* Execute the query, loading all visible results.
	*
	* @return list<PhabricatorPolicyInterface> Result objects.
	* @task exec
	*/
	final public function execute() {
	if (!$this->viewer) {
	throw new Exception("Call setViewer() before execute()!");
	}

	$parent_query = $this->getParentQuery();
	if ($parent_query) {
	$this->setRaisePolicyExceptions(
	$parent_query->shouldRaisePolicyExceptions());
	}

	$results = array();

	$filter = $this->getPolicyFilter();

	$offset = (int)$this->getOffset();
	$limit = (int)$this->getLimit();
	$count = 0;

	if ($limit) {
	$need = $offset + $limit;
	} else {
	$need = 0;
	}

	$this->willExecute();

	do {
	if ($need) {
	$this->rawResultLimit = min($need - $count, 1024);
	} else {
	$this->rawResultLimit = 0;
	}

	if ($this->canViewerUseQueryApplication()) {
	try {
	$page = $this->loadPage();
	} catch (PhabricatorEmptyQueryException $ex) {
	$page = array();
	}
	} else {
	$page = array();
	}

	if ($page) {
	$maybe_visible = $this->willFilterPage($page);
	} else {
	$maybe_visible = array();
	}

	if ($this->shouldDisablePolicyFiltering()) {
	$visible = $maybe_visible;
	} else {
	$visible = $filter->apply($maybe_visible);

	$policy_filtered = array();
	foreach ($maybe_visible as $key => $object) {
	if (empty($visible[$key])) {
	$phid = $object->getPHID();
	if ($phid) {
	$policy_filtered[$phid] = $phid;
	}
	}
	}
	$this->addPolicyFilteredPHIDs($policy_filtered);
	}

	if ($visible) {
	$this->putObjectsInWorkspace($this->getWorkspaceMapForPage($visible));
	$visible = $this->didFilterPage($visible);
	}

	$removed = array();
	foreach ($maybe_visible as $key => $object) {
	if (empty($visible[$key])) {
	$removed[$key] = $object;
	}
	}

	$this->didFilterResults($removed);

	foreach ($visible as $key => $result) {
	++$count;

	// If we have an offset, we just ignore that many results and start
	// storing them only once we've hit the offset. This reduces memory
	// requirements for large offsets, compared to storing them all and
	// slicing them away later.
	if ($count > $offset) {
	$results[$key] = $result;
	}

	if ($need && ($count >= $need)) {
	// If we have all the rows we need, break out of the paging query.
	break 2;
	}
	}

	if (!$this->rawResultLimit) {
	// If we don't have a load count, we loaded all the results. We do
	// not need to load another page.
	break;
	}

	if (count($page) < $this->rawResultLimit) {
	// If we have a load count but the unfiltered results contained fewer
	// objects, we know this was the last page of objects; we do not need
	// to load another page because we can deduce it would be empty.
	break;
	}

	$this->nextPage($page);
	} while (true);

	$results = $this->didLoadResults($results);

	return $results;
	}

	private function getPolicyFilter() {
	$filter = new PhabricatorPolicyFilter();
	$filter->setViewer($this->viewer);
	$capabilities = $this->getRequiredCapabilities();
	$filter->requireCapabilities($capabilities);
	$filter->raisePolicyExceptions($this->shouldRaisePolicyExceptions());

	return $filter;
	}

	protected function getRequiredCapabilities() {
	if ($this->capabilities) {
	return $this->capabilities;
	}

	return array(
	PhabricatorPolicyCapability::CAN_VIEW,
	);
	}

	protected function applyPolicyFilter(array $objects, array $capabilities) {
	if ($this->shouldDisablePolicyFiltering()) {
	return $objects;
	}
	$filter = $this->getPolicyFilter();
	$filter->requireCapabilities($capabilities);
	return $filter->apply($objects);
	}

	protected function didRejectResult(PhabricatorPolicyInterface $object) {
	$this->getPolicyFilter()->rejectObject(
	$object,
	$object->getPolicy(PhabricatorPolicyCapability::CAN_VIEW),
	PhabricatorPolicyCapability::CAN_VIEW);
	}

	public function addPolicyFilteredPHIDs(array $phids) {
	$this->policyFilteredPHIDs += $phids;
	if ($this->getParentQuery()) {
	$this->getParentQuery()->addPolicyFilteredPHIDs($phids);
	}
	return $this;
	}

	/**
	* Return a map of all object PHIDs which were loaded in the query but
	* filtered out by policy constraints. This allows a caller to distinguish
	* between objects which do not exist (or, at least, were filtered at the
	* content level) and objects which exist but aren't visible.
	*
	* @return map<phid, phid> Map of object PHIDs which were filtered
	* by policies.
	* @task exec
	*/
	public function getPolicyFilteredPHIDs() {
	return $this->policyFilteredPHIDs;
	}


	/* -( Query Workspace )---------------------------------------------------- */


	/**
	* Put a map of objects into the query workspace. Many queries perform
	* subqueries, which can eventually end up loading the same objects more than
	* once (often to perform policy checks).
	*
	* For example, loading a user may load the user's profile image, which might
	* load the user object again in order to verify that the viewer has
	* permission to see the file.
	*
	* The "query workspace" allows queries to load objects from elsewhere in a
	* query block instead of refetching them.
	*
	* When using the query workspace, it's important to obey two rules:
	*
	* **Never put objects into the workspace which the viewer may not be able
	* to see**. You need to apply all policy filtering //before// putting
	* objects in the workspace. Otherwise, subqueries may read the objects and
	* use them to permit access to content the user shouldn't be able to view.
	*
	* Fully enrich objects pulled from the workspace. After pulling objects
	* from the workspace, you still need to load and attach any additional
	* content the query requests. Otherwise, a query might return objects without
	* requested content.
	*
	* Generally, you do not need to update the workspace yourself: it is
	* automatically populated as a side effect of objects surviving policy
	* filtering.
	*
	* @param map<phid, PhabricatorPolicyInterface> Objects to add to the query
	* workspace.
	* @return this
	* @task workspace
	*/
	public function putObjectsInWorkspace(array $objects) {
	assert_instances_of($objects, 'PhabricatorPolicyInterface');

	$viewer_phid = $this->getViewer()->getPHID();

	// The workspace is scoped per viewer to prevent accidental contamination.
	if (empty($this->workspace[$viewer_phid])) {
	$this->workspace[$viewer_phid] = array();
	}

	$this->workspace[$viewer_phid] += $objects;

	return $this;
	}


	/**
	* Retrieve objects from the query workspace. For more discussion about the
	* workspace mechanism, see @{method:putObjectsInWorkspace}. This method
	* searches both the current query's workspace and the workspaces of parent
	* queries.
	*
	* @param list<phid> List of PHIDs to retreive.
	* @return this
	* @task workspace
	*/
	public function getObjectsFromWorkspace(array $phids) {
	$viewer_phid = $this->getViewer()->getPHID();

	$results = array();
	foreach ($phids as $key => $phid) {
	if (isset($this->workspace[$viewer_phid][$phid])) {
	$results[$phid] = $this->workspace[$viewer_phid][$phid];
	unset($phids[$key]);
	}
	}

	if ($phids && $this->getParentQuery()) {
	$results += $this->getParentQuery()->getObjectsFromWorkspace($phids);
	}

	return $results;
	}


	/**
	* Convert a result page to a `<phid, PhabricatorPolicyInterface>` map.
	*
	* @param list<PhabricatorPolicyInterface> Objects.
	* @return map<phid, PhabricatorPolicyInterface> Map of objects which can
	* be put into the workspace.
	* @task workspace
	*/
	protected function getWorkspaceMapForPage(array $results) {
	$map = array();
	foreach ($results as $result) {
	$phid = $result->getPHID();
	if ($phid !== null) {
	$map[$phid] = $result;
	}
	}

	return $map;
	}


	/* -( Policy Query Implementation )---------------------------------------- */


	/**
	* Get the number of results @{method:loadPage} should load. If the value is
	* 0, @{method:loadPage} should load all available results.
	*
	* @return int The number of results to load, or 0 for all results.
	* @task policyimpl
	*/
	final protected function getRawResultLimit() {
	return $this->rawResultLimit;
	}


	/**
	* Hook invoked before query execution. Generally, implementations should
	* reset any internal cursors.
	*
	* @return void
	* @task policyimpl
	*/
	protected function willExecute() {
	return;
	}


	/**
	* Load a raw page of results. Generally, implementations should load objects
	* from the database. They should attempt to return the number of results
	* hinted by @{method:getRawResultLimit}.
	*
	* @return list<PhabricatorPolicyInterface> List of filterable policy objects.
	* @task policyimpl
	*/
	abstract protected function loadPage();


	/**
	* Update internal state so that the next call to @{method:loadPage} will
	* return new results. Generally, you should adjust a cursor position based
	* on the provided result page.
	*
	* @param list<PhabricatorPolicyInterface> The current page of results.
	* @return void
	* @task policyimpl
	*/
	abstract protected function nextPage(array $page);


	/**
	* Hook for applying a page filter prior to the privacy filter. This allows
	* you to drop some items from the result set without creating problems with
	* pagination or cursor updates. You can also load and attach data which is
	* required to perform policy filtering.
	*
	* Generally, you should load non-policy data and perform non-policy filtering
	* later, in @{method:didFilterPage}. Strictly fewer objects will make it that
	* far (so the program will load less data) and subqueries from that context
	* can use the query workspace to further reduce query load.
	*
	* This method will only be called if data is available. Implementations
	* do not need to handle the case of no results specially.
	*
	* @param list<wild> Results from `loadPage()`.
	* @return list<PhabricatorPolicyInterface> Objects for policy filtering.
	* @task policyimpl
	*/
	protected function willFilterPage(array $page) {
	return $page;
	}

	/**
	* Hook for performing additional non-policy loading or filtering after an
	* object has satisfied all policy checks. Generally, this means loading and
	* attaching related data.
	*
	* Subqueries executed during this phase can use the query workspace, which
	* may improve performance or make circular policies resolvable. Data which
	* is not necessary for policy filtering should generally be loaded here.
	*
	* This callback can still filter objects (for example, if attachable data
	* is discovered to not exist), but should not do so for policy reasons.
	*
	* This method will only be called if data is available. Implementations do
	* not need to handle the case of no results specially.
	*
	* @param list<wild> Results from @{method:willFilterPage()}.
	* @return list<PhabricatorPolicyInterface> Objects after additional
	* non-policy processing.
	*/
	protected function didFilterPage(array $page) {
	return $page;
	}


	/**
	* Hook for removing filtered results from alternate result sets. This
	* hook will be called with any objects which were returned by the query but
	* filtered for policy reasons. The query should remove them from any cached
	* or partial result sets.
	*
	* @param list<wild> List of objects that should not be returned by alternate
	* result mechanisms.
	* @return void
	* @task policyimpl
	*/
	protected function didFilterResults(array $results) {
	return;
	}


	/**
	* Hook for applying final adjustments before results are returned. This is
	* used by @{class:PhabricatorCursorPagedPolicyAwareQuery} to reverse results
	* that are queried during reverse paging.
	*
	* @param list<PhabricatorPolicyInterface> Query results.
	* @return list<PhabricatorPolicyInterface> Final results.
	* @task policyimpl
	*/
	protected function didLoadResults(array $results) {
	return $results;
	}


	/**
	* Allows a subclass to disable policy filtering. This method is dangerous.
	* It should be used only if the query loads data which has already been
	* filtered (for example, because it wraps some other query which uses
	* normal policy filtering).
	*
	* @return bool True to disable all policy filtering.
	* @task policyimpl
	*/
	protected function shouldDisablePolicyFiltering() {
	return false;
	}


	/**
	* If this query belongs to an application, return the application class name
	* here. This will prevent the query from returning results if the viewer can
	* not access the application.
	*
	* If this query does not belong to an application, return `null`.
	*
	* @return string\|null Application class name.
	*/
	abstract public function getQueryApplicationClass();


	/**
	* Determine if the viewer has permission to use this query's application.
	* For queries which aren't part of an application, this method always returns
	* true.
	*
	* @return bool True if the viewer has application-level permission to
	* execute the query.
	*/
	public function canViewerUseQueryApplication() {
	if ($this->canUseApplication === null) {
	$class = $this->getQueryApplicationClass();
	if (!$class) {
	$this->canUseApplication = true;
	} else {
	$result = id(new PhabricatorApplicationQuery())
	->setViewer($this->getViewer())
	->withClasses(array($class))
	->execute();

	$this->canUseApplication = (bool)$result;
	}
	}

	return $this->canUseApplication;
	}

	}

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