Fixes #2552 - Implement SVG validation

Use https://github.com/darylldoyle/svg-sanitizer to check for malicious code inside svg, throw an error code 415 when triggered in the API.

include/svg-sanitizer/ElementReference/Resolver.php

@@ -0,0 +1,169 @@
+<?php
+namespace enshrined\svgSanitize\ElementReference;
+
+use enshrined\svgSanitize\data\XPath;
+use enshrined\svgSanitize\Exceptions\NestingException;
+use enshrined\svgSanitize\Helper;
+
+class Resolver
+{
+    /**
+     * @var XPath
+     */
+    protected $xPath;
+
+    /**
+     * @var Subject[]
+     */
+    protected $subjects = [];
+
+    /**
+     * @var array DOMElement[]
+     */
+    protected $elementsToRemove = [];
+
+    /**
+     * @var int
+     */
+    protected $useNestingLimit;
+
+    public function __construct(XPath $xPath, $useNestingLimit)
+    {
+        $this->xPath = $xPath;
+        $this->useNestingLimit = $useNestingLimit;
+    }
+
+    public function collect()
+    {
+        $this->collectIdentifiedElements();
+        $this->processReferences();
+        $this->determineInvalidSubjects();
+    }
+
+    /**
+     * Resolves one subject by element.
+     *
+     * @param \DOMElement $element
+     * @param bool $considerChildren Whether to search in Subject's children as well
+     * @return Subject|null
+     */
+    public function findByElement(\DOMElement $element, $considerChildren = false)
+    {
+        foreach ($this->subjects as $subject) {
+            if (
+                $element === $subject->getElement()
+                || $considerChildren && Helper::isElementContainedIn($element, $subject->getElement())
+            ) {
+                return $subject;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Resolves subjects (plural!) by element id - in theory malformed
+     * DOM might have same ids assigned to different elements and leaving
+     * it to client/browser implementation which element to actually use.
+     *
+     * @param string $elementId
+     * @return Subject[]
+     */
+    public function findByElementId($elementId)
+    {
+        return array_filter(
+            $this->subjects,
+            function (Subject $subject) use ($elementId) {
+                return $elementId === $subject->getElementId();
+            }
+        );
+    }
+
+    /**
+     * Collects elements having `id` attribute (those that can be referenced).
+     */
+    protected function collectIdentifiedElements()
+    {
+        /** @var \DOMNodeList|\DOMElement[] $elements */
+        $elements = $this->xPath->query('//*[@id]');
+        foreach ($elements as $element) {
+            $this->subjects[$element->getAttribute('id')] = new Subject($element, $this->useNestingLimit);
+        }
+    }
+
+    /**
+     * Processes references from and to elements having `id` attribute concerning
+     * their occurrence in `<use ... xlink:href="#identifier">` statements.
+     */
+    protected function processReferences()
+    {
+        $useNodeName = $this->xPath->createNodeName('use');
+        foreach ($this->subjects as $subject) {
+            $useElements = $this->xPath->query(
+                $useNodeName . '[@href or @xlink:href]',
+                $subject->getElement()
+            );
+
+            /** @var \DOMElement $useElement */
+            foreach ($useElements as $useElement) {
+                $useId = Helper::extractIdReferenceFromHref(
+                    Helper::getElementHref($useElement)
+                );
+                if ($useId === null || !isset($this->subjects[$useId])) {
+                    continue;
+                }
+                $subject->addUse($this->subjects[$useId]);
+                $this->subjects[$useId]->addUsedIn($subject);
+            }
+        }
+    }
+
+    /**
+     * Determines and tags infinite loops.
+     */
+    protected function determineInvalidSubjects()
+    {
+        foreach ($this->subjects as $subject) {
+
+            if (in_array($subject->getElement(), $this->elementsToRemove)) {
+                continue;
+            }
+
+            $useId = Helper::extractIdReferenceFromHref(
+                Helper::getElementHref($subject->getElement())
+            );
+
+            try {
+                if ($useId === $subject->getElementId()) {
+                    $this->markSubjectAsInvalid($subject);
+                } elseif ($subject->hasInfiniteLoop()) {
+                    $this->markSubjectAsInvalid($subject);
+                }
+            } catch (NestingException $e) {
+                $this->elementsToRemove[] = $e->getElement();
+                $this->markSubjectAsInvalid($subject);
+            }
+        }
+    }
+
+    /**
+     * Get all the elements that caused a nesting exception.
+     *
+     * @return array
+     */
+    public function getElementsToRemove() {
+        return $this->elementsToRemove;
+    }
+
+    /**
+     * The Subject is invalid for some reason, therefore we should
+     * remove it and all it's child usages.
+     *
+     * @param Subject $subject
+     */
+    protected function markSubjectAsInvalid(Subject $subject) {
+        $this->elementsToRemove = array_merge(
+            $this->elementsToRemove,
+            $subject->clearInternalAndGetAffectedElements()
+        );
+    }
+}