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347 lines
14 KiB
PHP
347 lines
14 KiB
PHP
<?php
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/**
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* Takes a well formed list of tokens and fixes their nesting.
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*
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* HTML elements dictate which elements are allowed to be their children,
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* for example, you can't have a p tag in a span tag. Other elements have
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* much more rigorous definitions: tables, for instance, require a specific
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* order for their elements. There are also constraints not expressible by
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* document type definitions, such as the chameleon nature of ins/del
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* tags and global child exclusions.
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*
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* The first major objective of this strategy is to iterate through all the
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* nodes (not tokens) of the list of tokens and determine whether or not
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* their children conform to the element's definition. If they do not, the
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* child definition may optionally supply an amended list of elements that
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* is valid or require that the entire node be deleted (and the previous
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* node rescanned).
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*
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* The second objective is to ensure that explicitly excluded elements of
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* an element do not appear in its children. Code that accomplishes this
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* task is pervasive through the strategy, though the two are distinct tasks
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* and could, theoretically, be seperated (although it's not recommended).
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*
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* @note Whether or not unrecognized children are silently dropped or
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* translated into text depends on the child definitions.
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*
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* @todo Enable nodes to be bubbled out of the structure.
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*
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* @warning This algorithm (though it may be hard to see) proceeds from
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* a top-down fashion. Thus, parents are processed before
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* children. This is easy to implement and has a nice effiency
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* benefit, in that if a node is removed, we never waste any
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* time processing it, but it also means that if a child
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* changes in a non-encapsulated way (e.g. it is removed), we
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* need to go back and reprocess the parent to see if those
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* changes resulted in problems for the parent. See
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* [BACKTRACK] for an example of this. In the current
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* implementation, this backtracking can only be triggered when
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* a node is removed and if that node was the sole node, the
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* parent would need to be removed. As such, it is easy to see
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* that backtracking only incurs constant overhead. If more
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* sophisticated backtracking is implemented, care must be
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* taken to avoid nontermination or exponential blowup.
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*/
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class HTMLPurifier_Strategy_FixNesting extends HTMLPurifier_Strategy
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{
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public function execute($tokens, $config, $context) {
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//####################################################################//
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// Pre-processing
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// get a copy of the HTML definition
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$definition = $config->getHTMLDefinition();
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$excludes_enabled = !$config->get('Core.DisableExcludes');
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// insert implicit "parent" node, will be removed at end.
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// DEFINITION CALL
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$parent_name = $definition->info_parent;
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array_unshift($tokens, new HTMLPurifier_Token_Start($parent_name));
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$tokens[] = new HTMLPurifier_Token_End($parent_name);
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// setup the context variable 'IsInline', for chameleon processing
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// is 'false' when we are not inline, 'true' when it must always
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// be inline, and an integer when it is inline for a certain
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// branch of the document tree
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$is_inline = $definition->info_parent_def->descendants_are_inline;
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$context->register('IsInline', $is_inline);
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// setup error collector
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$e =& $context->get('ErrorCollector', true);
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//####################################################################//
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// Loop initialization
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// stack that contains the indexes of all parents,
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// $stack[count($stack)-1] being the current parent
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$stack = array();
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// stack that contains all elements that are excluded
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// it is organized by parent elements, similar to $stack,
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// but it is only populated when an element with exclusions is
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// processed, i.e. there won't be empty exclusions.
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$exclude_stack = array();
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// variable that contains the start token while we are processing
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// nodes. This enables error reporting to do its job
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$start_token = false;
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$context->register('CurrentToken', $start_token);
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//####################################################################//
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// Loop
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// iterate through all start nodes. Determining the start node
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// is complicated so it has been omitted from the loop construct
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for ($i = 0, $size = count($tokens) ; $i < $size; ) {
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//################################################################//
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// Gather information on children
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// child token accumulator
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$child_tokens = array();
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// scroll to the end of this node, report number, and collect
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// all children
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for ($j = $i, $depth = 0; ; $j++) {
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if ($tokens[$j] instanceof HTMLPurifier_Token_Start) {
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$depth++;
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// skip token assignment on first iteration, this is the
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// token we currently are on
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if ($depth == 1) continue;
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} elseif ($tokens[$j] instanceof HTMLPurifier_Token_End) {
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$depth--;
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// skip token assignment on last iteration, this is the
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// end token of the token we're currently on
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if ($depth == 0) break;
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}
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$child_tokens[] = $tokens[$j];
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}
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// $i is index of start token
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// $j is index of end token
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$start_token = $tokens[$i]; // to make token available via CurrentToken
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//################################################################//
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// Gather information on parent
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// calculate parent information
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if ($count = count($stack)) {
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$parent_index = $stack[$count-1];
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$parent_name = $tokens[$parent_index]->name;
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if ($parent_index == 0) {
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$parent_def = $definition->info_parent_def;
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} else {
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$parent_def = $definition->info[$parent_name];
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}
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} else {
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// processing as if the parent were the "root" node
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// unknown info, it won't be used anyway, in the future,
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// we may want to enforce one element only (this is
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// necessary for HTML Purifier to clean entire documents
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$parent_index = $parent_name = $parent_def = null;
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}
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// calculate context
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if ($is_inline === false) {
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// check if conditions make it inline
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if (!empty($parent_def) && $parent_def->descendants_are_inline) {
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$is_inline = $count - 1;
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}
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} else {
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// check if we're out of inline
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if ($count === $is_inline) {
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$is_inline = false;
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}
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}
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//################################################################//
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// Determine whether element is explicitly excluded SGML-style
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// determine whether or not element is excluded by checking all
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// parent exclusions. The array should not be very large, two
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// elements at most.
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$excluded = false;
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if (!empty($exclude_stack) && $excludes_enabled) {
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foreach ($exclude_stack as $lookup) {
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if (isset($lookup[$tokens[$i]->name])) {
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$excluded = true;
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// no need to continue processing
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break;
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}
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}
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}
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//################################################################//
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// Perform child validation
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if ($excluded) {
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// there is an exclusion, remove the entire node
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$result = false;
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$excludes = array(); // not used, but good to initialize anyway
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} else {
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// DEFINITION CALL
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if ($i === 0) {
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// special processing for the first node
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$def = $definition->info_parent_def;
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} else {
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$def = $definition->info[$tokens[$i]->name];
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}
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if (!empty($def->child)) {
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// have DTD child def validate children
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$result = $def->child->validateChildren(
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$child_tokens, $config, $context);
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} else {
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// weird, no child definition, get rid of everything
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$result = false;
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}
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// determine whether or not this element has any exclusions
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$excludes = $def->excludes;
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}
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// $result is now a bool or array
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//################################################################//
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// Process result by interpreting $result
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if ($result === true || $child_tokens === $result) {
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// leave the node as is
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// register start token as a parental node start
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$stack[] = $i;
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// register exclusions if there are any
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if (!empty($excludes)) $exclude_stack[] = $excludes;
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// move cursor to next possible start node
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$i++;
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} elseif($result === false) {
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// remove entire node
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if ($e) {
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if ($excluded) {
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$e->send(E_ERROR, 'Strategy_FixNesting: Node excluded');
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} else {
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$e->send(E_ERROR, 'Strategy_FixNesting: Node removed');
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}
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}
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// calculate length of inner tokens and current tokens
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$length = $j - $i + 1;
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// perform removal
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array_splice($tokens, $i, $length);
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// update size
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$size -= $length;
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// there is no start token to register,
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// current node is now the next possible start node
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// unless it turns out that we need to do a double-check
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// this is a rought heuristic that covers 100% of HTML's
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// cases and 99% of all other cases. A child definition
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// that would be tricked by this would be something like:
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// ( | a b c) where it's all or nothing. Fortunately,
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// our current implementation claims that that case would
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// not allow empty, even if it did
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if (!$parent_def->child->allow_empty) {
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// we need to do a double-check [BACKTRACK]
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$i = $parent_index;
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array_pop($stack);
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}
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// PROJECTED OPTIMIZATION: Process all children elements before
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// reprocessing parent node.
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} else {
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// replace node with $result
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// calculate length of inner tokens
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$length = $j - $i - 1;
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if ($e) {
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if (empty($result) && $length) {
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$e->send(E_ERROR, 'Strategy_FixNesting: Node contents removed');
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} else {
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$e->send(E_WARNING, 'Strategy_FixNesting: Node reorganized');
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}
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}
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// perform replacement
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array_splice($tokens, $i + 1, $length, $result);
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// update size
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$size -= $length;
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$size += count($result);
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// register start token as a parental node start
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$stack[] = $i;
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// register exclusions if there are any
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if (!empty($excludes)) $exclude_stack[] = $excludes;
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// move cursor to next possible start node
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$i++;
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}
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//################################################################//
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// Scroll to next start node
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// We assume, at this point, that $i is the index of the token
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// that is the first possible new start point for a node.
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// Test if the token indeed is a start tag, if not, move forward
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// and test again.
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$size = count($tokens);
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while ($i < $size and !$tokens[$i] instanceof HTMLPurifier_Token_Start) {
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if ($tokens[$i] instanceof HTMLPurifier_Token_End) {
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// pop a token index off the stack if we ended a node
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array_pop($stack);
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// pop an exclusion lookup off exclusion stack if
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// we ended node and that node had exclusions
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if ($i == 0 || $i == $size - 1) {
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// use specialized var if it's the super-parent
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$s_excludes = $definition->info_parent_def->excludes;
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} else {
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$s_excludes = $definition->info[$tokens[$i]->name]->excludes;
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}
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if ($s_excludes) {
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array_pop($exclude_stack);
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}
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}
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$i++;
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}
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}
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//####################################################################//
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// Post-processing
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// remove implicit parent tokens at the beginning and end
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array_shift($tokens);
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array_pop($tokens);
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// remove context variables
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$context->destroy('IsInline');
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$context->destroy('CurrentToken');
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//####################################################################//
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// Return
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return $tokens;
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}
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}
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// vim: et sw=4 sts=4
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