// Copyright 2006-2008, The Google Caja project.
// Modifications Copyright 2009 The Closure Library Authors.
// All Rights Reserved

/**
 * @license Portions of this code are from the google-caja project, received by
 * Google under the Apache license (http://code.google.com/p/google-caja/).
 * All other code is Copyright 2009 Google, Inc. All Rights Reserved.

// Copyright (C) 2006 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

 */

/**
 * @fileoverview An HTML sanitizer that can satisfy a variety of security
 * policies. The HTML sanitizer is built around a SAX parser and HTML element
 * and attributes schemas.
 *
 * This package provides html sanitizing and parsing functions.
 * {@code goog.string.htmlSanitize} is basically just using a custom written
 * {@code goog.string.HtmlSaxHandler} that outputs safe html as the unsafe
 * html content is parsed by {@code goog.string.HtmlParser}.
 *
 * Examples of usage of the static {@code goog.string.htmlSanitize}:
 * <pre>
 *   var safeHtml = goog.string.html.htmlSanitize('<script src="xss.js" />');
 *   el.innerHTML = safeHtml;
 * </pre>
 *
 * We use {@code goog.string.StringBuffer} for fast string concatenation, since
 * htmlSanitize is relatively heavy considering that it is designed to parse
 * large html files.
 *
 * @author msamuel@google.com (Mike Samuel)
 */

goog.provide('goog.string.html.HtmlSanitizer');
goog.provide('goog.string.html.HtmlSanitizer.AttributeType');
goog.provide('goog.string.html.HtmlSanitizer.Attributes');
goog.provide('goog.string.html.htmlSanitize');

goog.require('goog.string.StringBuffer');
goog.require('goog.string.html.HtmlParser');
goog.require('goog.string.html.HtmlSaxHandler');


/**
 * Strips unsafe tags and attributes from HTML.
 *
 * @param {string} htmlText The HTML text to sanitize.
 * @param {function(string): string=} opt_urlPolicy A transform to apply to URL
 *     attribute values.
 * @param {function(string): string=} opt_nmTokenPolicy A transform to apply to
 *     names, IDs, and classes.
 * @return {string} A sanitized HTML, safe to be embedded on the page.
 */
goog.string.html.htmlSanitize = function(
    htmlText, opt_urlPolicy, opt_nmTokenPolicy) {
  var stringBuffer = new goog.string.StringBuffer();
  var handler = new goog.string.html.HtmlSanitizer(
      stringBuffer, opt_urlPolicy, opt_nmTokenPolicy);
  var parser = new goog.string.html.HtmlParser();
  parser.parse(handler, htmlText);
  return stringBuffer.toString();
};



/**
 * An implementation of the {@code goog.string.HtmlSaxHandler} interface that
 * will take each of the html tags and sanitize it.
 *
 * @param {goog.string.StringBuffer} stringBuffer A string buffer, used to
 *     output the html as we sanitize it.
 * @param {?function(string):string=} opt_urlPolicy An optional function to be
 *     applied in URLs.
 * @param {?function(string):string=} opt_nmTokenPolicy An optional function to
 *     be applied in names.
 * @constructor
 * @implements {goog.string.html.HtmlSaxHandler}
 */
goog.string.html.HtmlSanitizer = function(
    stringBuffer, opt_urlPolicy, opt_nmTokenPolicy) {

  /**
   * The string buffer that holds the sanitized version of the html. Used
   * during the parse time.
   * @type {goog.string.StringBuffer}
   * @private
   */
  this.stringBuffer_ = stringBuffer;

  /**
   * A stack that holds how the handler is being called.
   * @type {Array}
   * @private
   */
  this.stack_ = [];

  /**
   * Whether we are ignoring what is being processed or not.
   * @type {boolean}
   * @private
   */
  this.ignoring_ = false;

  /**
   * A function to be applied to urls found on the parsing process.
   * @type {?function(string):string}
   * @private
   */
  this.urlPolicy_ = opt_urlPolicy || null;

  /**
   * A function to be applied to names fround on the parsing process.
   * @type {?function(string):string}
   * @private
   */
  this.nmTokenPolicy_ = opt_nmTokenPolicy || null;
};


/**
 * The HTML types the parser supports.
 * @enum {number}
 */
goog.string.html.HtmlSanitizer.AttributeType = {
  NONE: 0,
  URI: 1,
  URI_FRAGMENT: 11,
  SCRIPT: 2,
  STYLE: 3,
  ID: 4,
  IDREF: 5,
  IDREFS: 6,
  GLOBAL_NAME: 7,
  LOCAL_NAME: 8,
  CLASSES: 9,
  FRAME_TARGET: 10
};


/**
 * A map of attributes to types it has.
 * @const {!Object<string,number>}
 */
goog.string.html.HtmlSanitizer.Attributes = {
  '*::class': goog.string.html.HtmlSanitizer.AttributeType.CLASSES,
  '*::dir': 0,
  '*::id': goog.string.html.HtmlSanitizer.AttributeType.ID,
  '*::lang': 0,
  '*::onclick': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::ondblclick': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onkeydown': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onkeypress': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onkeyup': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onload': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onmousedown': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onmousemove': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onmouseout': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onmouseover': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onmouseup': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::style': goog.string.html.HtmlSanitizer.AttributeType.STYLE,
  '*::title': 0,
  '*::accesskey': 0,
  '*::tabindex': 0,
  '*::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  '*::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'a::coords': 0,
  'a::href': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'a::hreflang': 0,
  'a::name': goog.string.html.HtmlSanitizer.AttributeType.GLOBAL_NAME,
  'a::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'a::rel': 0,
  'a::rev': 0,
  'a::shape': 0,
  'a::target': goog.string.html.HtmlSanitizer.AttributeType.FRAME_TARGET,
  'a::type': 0,
  'area::accesskey': 0,
  'area::alt': 0,
  'area::coords': 0,
  'area::href': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'area::nohref': 0,
  'area::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'area::shape': 0,
  'area::tabindex': 0,
  'area::target': goog.string.html.HtmlSanitizer.AttributeType.FRAME_TARGET,
  'bdo::dir': 0,
  'blockquote::cite': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'br::clear': 0,
  'button::accesskey': 0,
  'button::disabled': 0,
  'button::name': goog.string.html.HtmlSanitizer.AttributeType.LOCAL_NAME,
  'button::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'button::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'button::tabindex': 0,
  'button::type': 0,
  'button::value': 0,
  'caption::align': 0,
  'col::align': 0,
  'col::char': 0,
  'col::charoff': 0,
  'col::span': 0,
  'col::valign': 0,
  'col::width': 0,
  'colgroup::align': 0,
  'colgroup::char': 0,
  'colgroup::charoff': 0,
  'colgroup::span': 0,
  'colgroup::valign': 0,
  'colgroup::width': 0,
  'del::cite': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'del::datetime': 0,
  'dir::compact': 0,
  'div::align': 0,
  'dl::compact': 0,
  'font::color': 0,
  'font::face': 0,
  'font::size': 0,
  'form::accept': 0,
  'form::action': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'form::autocomplete': 0,
  'form::enctype': 0,
  'form::method': 0,
  'form::name': goog.string.html.HtmlSanitizer.AttributeType.GLOBAL_NAME,
  'form::onreset': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'form::onsubmit': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'form::target': goog.string.html.HtmlSanitizer.AttributeType.FRAME_TARGET,
  'h1::align': 0,
  'h2::align': 0,
  'h3::align': 0,
  'h4::align': 0,
  'h5::align': 0,
  'h6::align': 0,
  'hr::align': 0,
  'hr::noshade': 0,
  'hr::size': 0,
  'hr::width': 0,
  'img::align': 0,
  'img::alt': 0,
  'img::border': 0,
  'img::height': 0,
  'img::hspace': 0,
  'img::ismap': 0,
  'img::longdesc': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'img::name': goog.string.html.HtmlSanitizer.AttributeType.GLOBAL_NAME,
  'img::src': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'img::usemap': goog.string.html.HtmlSanitizer.AttributeType.URI_FRAGMENT,
  'img::vspace': 0,
  'img::width': 0,
  'input::accept': 0,
  'input::accesskey': 0,
  'input::autocomplete': 0,
  'input::align': 0,
  'input::alt': 0,
  'input::checked': 0,
  'input::disabled': 0,
  'input::ismap': 0,
  'input::maxlength': 0,
  'input::name': goog.string.html.HtmlSanitizer.AttributeType.LOCAL_NAME,
  'input::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'input::onchange': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'input::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'input::onselect': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'input::readonly': 0,
  'input::size': 0,
  'input::src': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'input::tabindex': 0,
  'input::type': 0,
  'input::usemap': goog.string.html.HtmlSanitizer.AttributeType.URI_FRAGMENT,
  'input::value': 0,
  'ins::cite': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'ins::datetime': 0,
  'label::accesskey': 0,
  'label::for': goog.string.html.HtmlSanitizer.AttributeType.IDREF,
  'label::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'label::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'legend::accesskey': 0,
  'legend::align': 0,
  'li::type': 0,
  'li::value': 0,
  'map::name': goog.string.html.HtmlSanitizer.AttributeType.GLOBAL_NAME,
  'menu::compact': 0,
  'ol::compact': 0,
  'ol::start': 0,
  'ol::type': 0,
  'optgroup::disabled': 0,
  'optgroup::label': 0,
  'option::disabled': 0,
  'option::label': 0,
  'option::selected': 0,
  'option::value': 0,
  'p::align': 0,
  'pre::width': 0,
  'q::cite': goog.string.html.HtmlSanitizer.AttributeType.URI,
  'select::disabled': 0,
  'select::multiple': 0,
  'select::name': goog.string.html.HtmlSanitizer.AttributeType.LOCAL_NAME,
  'select::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'select::onchange': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'select::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'select::size': 0,
  'select::tabindex': 0,
  'table::align': 0,
  'table::bgcolor': 0,
  'table::border': 0,
  'table::cellpadding': 0,
  'table::cellspacing': 0,
  'table::frame': 0,
  'table::rules': 0,
  'table::summary': 0,
  'table::width': 0,
  'tbody::align': 0,
  'tbody::char': 0,
  'tbody::charoff': 0,
  'tbody::valign': 0,
  'td::abbr': 0,
  'td::align': 0,
  'td::axis': 0,
  'td::bgcolor': 0,
  'td::char': 0,
  'td::charoff': 0,
  'td::colspan': 0,
  'td::headers': goog.string.html.HtmlSanitizer.AttributeType.IDREFS,
  'td::height': 0,
  'td::nowrap': 0,
  'td::rowspan': 0,
  'td::scope': 0,
  'td::valign': 0,
  'td::width': 0,
  'textarea::accesskey': 0,
  'textarea::cols': 0,
  'textarea::disabled': 0,
  'textarea::name': goog.string.html.HtmlSanitizer.AttributeType.LOCAL_NAME,
  'textarea::onblur': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'textarea::onchange': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'textarea::onfocus': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'textarea::onselect': goog.string.html.HtmlSanitizer.AttributeType.SCRIPT,
  'textarea::readonly': 0,
  'textarea::rows': 0,
  'textarea::tabindex': 0,
  'tfoot::align': 0,
  'tfoot::char': 0,
  'tfoot::charoff': 0,
  'tfoot::valign': 0,
  'th::abbr': 0,
  'th::align': 0,
  'th::axis': 0,
  'th::bgcolor': 0,
  'th::char': 0,
  'th::charoff': 0,
  'th::colspan': 0,
  'th::headers': goog.string.html.HtmlSanitizer.AttributeType.IDREFS,
  'th::height': 0,
  'th::nowrap': 0,
  'th::rowspan': 0,
  'th::scope': 0,
  'th::valign': 0,
  'th::width': 0,
  'thead::align': 0,
  'thead::char': 0,
  'thead::charoff': 0,
  'thead::valign': 0,
  'tr::align': 0,
  'tr::bgcolor': 0,
  'tr::char': 0,
  'tr::charoff': 0,
  'tr::valign': 0,
  'ul::compact': 0,
  'ul::type': 0
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.startTag =
    function(tagName, attribs) {
  if (this.ignoring_) {
    return;
  }
  if (!goog.string.html.HtmlParser.Elements.hasOwnProperty(tagName)) {
    return;
  }
  var eflags = goog.string.html.HtmlParser.Elements[tagName];
  if (eflags & goog.string.html.HtmlParser.EFlags.FOLDABLE) {
    return;
  } else if (eflags & goog.string.html.HtmlParser.EFlags.UNSAFE) {
    this.ignoring_ = !(eflags & goog.string.html.HtmlParser.EFlags.EMPTY);
    return;
  }
  attribs = this.sanitizeAttributes_(tagName, attribs);
  if (attribs) {
    if (!(eflags & goog.string.html.HtmlParser.EFlags.EMPTY)) {
      this.stack_.push(tagName);
    }

    this.stringBuffer_.append('<', tagName);
    for (var i = 0, n = attribs.length; i < n; i += 2) {
      var attribName = attribs[i],
          value = attribs[i + 1];
      if (value !== null && value !== void 0) {
        this.stringBuffer_.append(' ', attribName, '="',
            this.escapeAttrib_(value), '"');
      }
    }
    this.stringBuffer_.append('>');
  }
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.endTag = function(tagName) {
  if (this.ignoring_) {
    this.ignoring_ = false;
    return;
  }
  if (!goog.string.html.HtmlParser.Elements.hasOwnProperty(tagName)) {
    return;
  }
  var eflags = goog.string.html.HtmlParser.Elements[tagName];
  if (!(eflags & (goog.string.html.HtmlParser.EFlags.UNSAFE |
      goog.string.html.HtmlParser.EFlags.EMPTY |
      goog.string.html.HtmlParser.EFlags.FOLDABLE))) {
    var index;
    if (eflags & goog.string.html.HtmlParser.EFlags.OPTIONAL_ENDTAG) {
      for (index = this.stack_.length; --index >= 0;) {
        var stackEl = this.stack_[index];
        if (stackEl === tagName) {
          break;
        }
        if (!(goog.string.html.HtmlParser.Elements[stackEl] &
            goog.string.html.HtmlParser.EFlags.OPTIONAL_ENDTAG)) {
          // Don't pop non optional end tags looking for a match.
          return;
        }
      }
    } else {
      for (index = this.stack_.length; --index >= 0;) {
        if (this.stack_[index] === tagName) {
          break;
        }
      }
    }
    if (index < 0) { return; }  // Not opened.
    for (var i = this.stack_.length; --i > index;) {
      var stackEl = this.stack_[i];
      if (!(goog.string.html.HtmlParser.Elements[stackEl] &
          goog.string.html.HtmlParser.EFlags.OPTIONAL_ENDTAG)) {
        this.stringBuffer_.append('</', stackEl, '>');
      }
    }
    this.stack_.length = index;
    this.stringBuffer_.append('</', tagName, '>');
  }
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.pcdata = function(text) {
  if (!this.ignoring_) {
    this.stringBuffer_.append(text);
  }
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.rcdata = function(text) {
  if (!this.ignoring_) {
    this.stringBuffer_.append(text);
  }
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.cdata = function(text) {
  if (!this.ignoring_) {
    this.stringBuffer_.append(text);
  }
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.startDoc = function() {
  this.stack_ = [];
  this.ignoring_ = false;
};


/**
 * @override
 */
goog.string.html.HtmlSanitizer.prototype.endDoc = function() {
  for (var i = this.stack_.length; --i >= 0;) {
    this.stringBuffer_.append('</', this.stack_[i], '>');
  }
  this.stack_.length = 0;
};


/**
 * Escapes HTML special characters in attribute values as HTML entities.
 *
 * TODO(user): use {@code goog.string.htmlEscape} instead ?
 * @param {string} s The string to be escaped.
 * @return {string} An escaped version of {@code s}.
 * @private
 */
goog.string.html.HtmlSanitizer.prototype.escapeAttrib_ = function(s) {
  // Escaping '=' defangs many UTF-7 and SGML short-tag attacks.
  return s.replace(goog.string.html.HtmlParser.AMP_RE, '&amp;').
      replace(goog.string.html.HtmlParser.LT_RE, '&lt;').
      replace(goog.string.html.HtmlParser.GT_RE, '&gt;').
      replace(goog.string.html.HtmlParser.QUOTE_RE, '&#34;').
      replace(goog.string.html.HtmlParser.EQUALS_RE, '&#61;');
};


/**
 * Sanitizes attributes found on html entities.
 * @param {string} tagName The name of the tag in which the {@code attribs} were
 *     found.
 * @param {Array<?string>} attribs An array of attributes.
 * @return {Array<?string>} A sanitized version of the {@code attribs}.
 * @private
 */
goog.string.html.HtmlSanitizer.prototype.sanitizeAttributes_ =
    function(tagName, attribs) {
  for (var i = 0; i < attribs.length; i += 2) {
    var attribName = attribs[i];
    var value = attribs[i + 1];
    var atype = null, attribKey;
    if ((attribKey = tagName + '::' + attribName,
        goog.string.html.HtmlSanitizer.Attributes.hasOwnProperty(attribKey)) ||
        (attribKey = '*::' + attribName,
        goog.string.html.HtmlSanitizer.Attributes.hasOwnProperty(attribKey))) {
      atype = goog.string.html.HtmlSanitizer.Attributes[attribKey];
    }
    if (atype !== null) {
      switch (atype) {
        case 0: break;
        case goog.string.html.HtmlSanitizer.AttributeType.SCRIPT:
        case goog.string.html.HtmlSanitizer.AttributeType.STYLE:
          value = null;
          break;
        case goog.string.html.HtmlSanitizer.AttributeType.ID:
        case goog.string.html.HtmlSanitizer.AttributeType.IDREF:
        case goog.string.html.HtmlSanitizer.AttributeType.IDREFS:
        case goog.string.html.HtmlSanitizer.AttributeType.GLOBAL_NAME:
        case goog.string.html.HtmlSanitizer.AttributeType.LOCAL_NAME:
        case goog.string.html.HtmlSanitizer.AttributeType.CLASSES:
          value = this.nmTokenPolicy_ ?
              this.nmTokenPolicy_(/** @type {string} */ (value)) : value;
          break;
        case goog.string.html.HtmlSanitizer.AttributeType.URI:
          value = this.urlPolicy_ && this.urlPolicy_(
              /** @type {string} */ (value));
          break;
        case goog.string.html.HtmlSanitizer.AttributeType.URI_FRAGMENT:
          if (value && '#' === value.charAt(0)) {
            value = this.nmTokenPolicy_ ? this.nmTokenPolicy_(value) : value;
            if (value) { value = '#' + value; }
          } else {
            value = null;
          }
          break;
        default:
          value = null;
          break;
      }
    } else {
      value = null;
    }
    attribs[i + 1] = value;
  }
  return attribs;
};
