1<?php
2
3/**
4 * Takes a well formed list of tokens and fixes their nesting.
5 *
6 * HTML elements dictate which elements are allowed to be their children,
7 * for example, you can't have a p tag in a span tag.  Other elements have
8 * much more rigorous definitions: tables, for instance, require a specific
9 * order for their elements.  There are also constraints not expressible by
10 * document type definitions, such as the chameleon nature of ins/del
11 * tags and global child exclusions.
12 *
13 * The first major objective of this strategy is to iterate through all
14 * the nodes and determine whether or not their children conform to the
15 * element's definition.  If they do not, the child definition may
16 * optionally supply an amended list of elements that is valid or
17 * require that the entire node be deleted (and the previous node
18 * rescanned).
19 *
20 * The second objective is to ensure that explicitly excluded elements of
21 * an element do not appear in its children.  Code that accomplishes this
22 * task is pervasive through the strategy, though the two are distinct tasks
23 * and could, theoretically, be seperated (although it's not recommended).
24 *
25 * @note Whether or not unrecognized children are silently dropped or
26 *       translated into text depends on the child definitions.
27 *
28 * @todo Enable nodes to be bubbled out of the structure.  This is
29 *       easier with our new algorithm.
30 */
31
32class HTMLPurifier_Strategy_FixNesting extends HTMLPurifier_Strategy
33{
34
35    /**
36     * @param HTMLPurifier_Token[] $tokens
37     * @param HTMLPurifier_Config $config
38     * @param HTMLPurifier_Context $context
39     * @return array|HTMLPurifier_Token[]
40     */
41    public function execute($tokens, $config, $context)
42    {
43
44        //####################################################################//
45        // Pre-processing
46
47        // O(n) pass to convert to a tree, so that we can efficiently
48        // refer to substrings
49        $top_node = HTMLPurifier_Arborize::arborize($tokens, $config, $context);
50
51        // get a copy of the HTML definition
52        $definition = $config->getHTMLDefinition();
53
54        $excludes_enabled = !$config->get('Core.DisableExcludes');
55
56        // setup the context variable 'IsInline', for chameleon processing
57        // is 'false' when we are not inline, 'true' when it must always
58        // be inline, and an integer when it is inline for a certain
59        // branch of the document tree
60        $is_inline = $definition->info_parent_def->descendants_are_inline;
61        $context->register('IsInline', $is_inline);
62
63        // setup error collector
64        $e =& $context->get('ErrorCollector', true);
65
66        //####################################################################//
67        // Loop initialization
68
69        // stack that contains all elements that are excluded
70        // it is organized by parent elements, similar to $stack,
71        // but it is only populated when an element with exclusions is
72        // processed, i.e. there won't be empty exclusions.
73        $exclude_stack = array($definition->info_parent_def->excludes);
74
75        // variable that contains the start token while we are processing
76        // nodes. This enables error reporting to do its job
77        $node = $top_node;
78        // dummy token
79        list($token, $d) = $node->toTokenPair();
80        $context->register('CurrentNode', $node);
81        $context->register('CurrentToken', $token);
82
83        //####################################################################//
84        // Loop
85
86        // We need to implement a post-order traversal iteratively, to
87        // avoid running into stack space limits.  This is pretty tricky
88        // to reason about, so we just manually stack-ify the recursive
89        // variant:
90        //
91        //  function f($node) {
92        //      foreach ($node->children as $child) {
93        //          f($child);
94        //      }
95        //      validate($node);
96        //  }
97        //
98        // Thus, we will represent a stack frame as array($node,
99        // $is_inline, stack of children)
100        // e.g. array_reverse($node->children) - already processed
101        // children.
102
103        $parent_def = $definition->info_parent_def;
104        $stack = array(
105            array($top_node,
106                  $parent_def->descendants_are_inline,
107                  $parent_def->excludes, // exclusions
108                  0)
109            );
110
111        while (!empty($stack)) {
112            list($node, $is_inline, $excludes, $ix) = array_pop($stack);
113            // recursive call
114            $go = false;
115            $def = empty($stack) ? $definition->info_parent_def : $definition->info[$node->name];
116            while (isset($node->children[$ix])) {
117                $child = $node->children[$ix++];
118                if ($child instanceof HTMLPurifier_Node_Element) {
119                    $go = true;
120                    $stack[] = array($node, $is_inline, $excludes, $ix);
121                    $stack[] = array($child,
122                        // ToDo: I don't think it matters if it's def or
123                        // child_def, but double check this...
124                        $is_inline || $def->descendants_are_inline,
125                        empty($def->excludes) ? $excludes
126                                              : array_merge($excludes, $def->excludes),
127                        0);
128                    break;
129                }
130            };
131            if ($go) continue;
132            list($token, $d) = $node->toTokenPair();
133            // base case
134            if ($excludes_enabled && isset($excludes[$node->name])) {
135                $node->dead = true;
136                if ($e) $e->send(E_ERROR, 'Strategy_FixNesting: Node excluded');
137            } else {
138                // XXX I suppose it would be slightly more efficient to
139                // avoid the allocation here and have children
140                // strategies handle it
141                $children = array();
142                foreach ($node->children as $child) {
143                    if (!$child->dead) $children[] = $child;
144                }
145                $result = $def->child->validateChildren($children, $config, $context);
146                if ($result === true) {
147                    // nop
148                    $node->children = $children;
149                } elseif ($result === false) {
150                    $node->dead = true;
151                    if ($e) $e->send(E_ERROR, 'Strategy_FixNesting: Node removed');
152                } else {
153                    $node->children = $result;
154                    if ($e) {
155                        // XXX This will miss mutations of internal nodes. Perhaps defer to the child validators
156                        if (empty($result) && !empty($children)) {
157                            $e->send(E_ERROR, 'Strategy_FixNesting: Node contents removed');
158                        } else if ($result != $children) {
159                            $e->send(E_WARNING, 'Strategy_FixNesting: Node reorganized');
160                        }
161                    }
162                }
163            }
164        }
165
166        //####################################################################//
167        // Post-processing
168
169        // remove context variables
170        $context->destroy('IsInline');
171        $context->destroy('CurrentNode');
172        $context->destroy('CurrentToken');
173
174        //####################################################################//
175        // Return
176
177        return HTMLPurifier_Arborize::flatten($node, $config, $context);
178    }
179}
180
181// vim: et sw=4 sts=4
182