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278 lines
10 KiB
278 lines
10 KiB
// Copyright 2014 The Closure Library Authors. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS-IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/**
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* @fileoverview The SafeStyleSheet type and its builders.
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*
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* TODO(xtof): Link to document stating type contract.
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*/
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goog.provide('goog.html.SafeStyleSheet');
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goog.require('goog.array');
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goog.require('goog.asserts');
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goog.require('goog.string');
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goog.require('goog.string.Const');
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goog.require('goog.string.TypedString');
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/**
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* A string-like object which represents a CSS style sheet and that carries the
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* security type contract that its value, as a string, will not cause untrusted
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* script execution (XSS) when evaluated as CSS in a browser.
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*
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* Instances of this type must be created via the factory method
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* {@code goog.html.SafeStyleSheet.fromConstant} and not by invoking its
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* constructor. The constructor intentionally takes no parameters and the type
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* is immutable; hence only a default instance corresponding to the empty string
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* can be obtained via constructor invocation.
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*
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* A SafeStyleSheet's string representation can safely be interpolated as the
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* content of a style element within HTML. The SafeStyleSheet string should
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* not be escaped before interpolation.
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*
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* Values of this type must be composable, i.e. for any two values
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* {@code styleSheet1} and {@code styleSheet2} of this type,
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* {@code goog.html.SafeStyleSheet.unwrap(styleSheet1) +
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* goog.html.SafeStyleSheet.unwrap(styleSheet2)} must itself be a value that
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* satisfies the SafeStyleSheet type constraint. This requirement implies that
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* for any value {@code styleSheet} of this type,
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* {@code goog.html.SafeStyleSheet.unwrap(styleSheet1)} must end in
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* "beginning of rule" context.
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* A SafeStyleSheet can be constructed via security-reviewed unchecked
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* conversions. In this case producers of SafeStyleSheet must ensure themselves
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* that the SafeStyleSheet does not contain unsafe script. Note in particular
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* that {@code <} is dangerous, even when inside CSS strings, and so should
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* always be forbidden or CSS-escaped in user controlled input. For example, if
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* {@code </style><script>evil</script>"} were interpolated
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* inside a CSS string, it would break out of the context of the original
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* style element and {@code evil} would execute. Also note that within an HTML
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* style (raw text) element, HTML character references, such as
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* {@code &lt;}, are not allowed. See
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*
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http://www.w3.org/TR/html5/scripting-1.html#restrictions-for-contents-of-script-elements
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* (similar considerations apply to the style element).
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*
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* @see goog.html.SafeStyleSheet#fromConstant
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* @constructor
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* @final
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* @struct
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* @implements {goog.string.TypedString}
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*/
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goog.html.SafeStyleSheet = function() {
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/**
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* The contained value of this SafeStyleSheet. The field has a purposely
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* ugly name to make (non-compiled) code that attempts to directly access this
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* field stand out.
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* @private {string}
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*/
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this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_ = '';
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/**
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* A type marker used to implement additional run-time type checking.
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* @see goog.html.SafeStyleSheet#unwrap
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* @const
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* @private
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*/
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this.SAFE_STYLE_SHEET_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ =
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goog.html.SafeStyleSheet.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_;
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};
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/**
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* @override
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* @const
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*/
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goog.html.SafeStyleSheet.prototype.implementsGoogStringTypedString = true;
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/**
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* Type marker for the SafeStyleSheet type, used to implement additional
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* run-time type checking.
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* @const {!Object}
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* @private
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*/
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goog.html.SafeStyleSheet.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ = {};
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/**
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* Creates a new SafeStyleSheet object by concatenating values.
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* @param {...(!goog.html.SafeStyleSheet|!Array<!goog.html.SafeStyleSheet>)}
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* var_args Values to concatenate.
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* @return {!goog.html.SafeStyleSheet}
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*/
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goog.html.SafeStyleSheet.concat = function(var_args) {
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var result = '';
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/**
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* @param {!goog.html.SafeStyleSheet|!Array<!goog.html.SafeStyleSheet>}
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* argument
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*/
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var addArgument = function(argument) {
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if (goog.isArray(argument)) {
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goog.array.forEach(argument, addArgument);
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} else {
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result += goog.html.SafeStyleSheet.unwrap(argument);
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}
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};
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goog.array.forEach(arguments, addArgument);
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return goog.html.SafeStyleSheet
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.createSafeStyleSheetSecurityPrivateDoNotAccessOrElse(result);
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};
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/**
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* Creates a SafeStyleSheet object from a compile-time constant string.
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*
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* {@code styleSheet} must not have any < characters in it, so that
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* the syntactic structure of the surrounding HTML is not affected.
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*
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* @param {!goog.string.Const} styleSheet A compile-time-constant string from
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* which to create a SafeStyleSheet.
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* @return {!goog.html.SafeStyleSheet} A SafeStyleSheet object initialized to
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* {@code styleSheet}.
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*/
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goog.html.SafeStyleSheet.fromConstant = function(styleSheet) {
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var styleSheetString = goog.string.Const.unwrap(styleSheet);
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if (styleSheetString.length === 0) {
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return goog.html.SafeStyleSheet.EMPTY;
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}
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// > is a valid character in CSS selectors and there's no strict need to
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// block it if we already block <.
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goog.asserts.assert(
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!goog.string.contains(styleSheetString, '<'),
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"Forbidden '<' character in style sheet string: " + styleSheetString);
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return goog.html.SafeStyleSheet
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.createSafeStyleSheetSecurityPrivateDoNotAccessOrElse(styleSheetString);
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};
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/**
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* Returns this SafeStyleSheet's value as a string.
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*
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* IMPORTANT: In code where it is security relevant that an object's type is
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* indeed {@code SafeStyleSheet}, use {@code goog.html.SafeStyleSheet.unwrap}
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* instead of this method. If in doubt, assume that it's security relevant. In
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* particular, note that goog.html functions which return a goog.html type do
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* not guarantee the returned instance is of the right type. For example:
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*
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* <pre>
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* var fakeSafeHtml = new String('fake');
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* fakeSafeHtml.__proto__ = goog.html.SafeHtml.prototype;
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* var newSafeHtml = goog.html.SafeHtml.htmlEscape(fakeSafeHtml);
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* // newSafeHtml is just an alias for fakeSafeHtml, it's passed through by
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* // goog.html.SafeHtml.htmlEscape() as fakeSafeHtml
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* // instanceof goog.html.SafeHtml.
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* </pre>
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*
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* @see goog.html.SafeStyleSheet#unwrap
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* @override
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*/
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goog.html.SafeStyleSheet.prototype.getTypedStringValue = function() {
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return this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_;
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};
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if (goog.DEBUG) {
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/**
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* Returns a debug string-representation of this value.
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*
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* To obtain the actual string value wrapped in a SafeStyleSheet, use
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* {@code goog.html.SafeStyleSheet.unwrap}.
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*
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* @see goog.html.SafeStyleSheet#unwrap
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* @override
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*/
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goog.html.SafeStyleSheet.prototype.toString = function() {
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return 'SafeStyleSheet{' +
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this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_ + '}';
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};
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}
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/**
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* Performs a runtime check that the provided object is indeed a
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* SafeStyleSheet object, and returns its value.
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*
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* @param {!goog.html.SafeStyleSheet} safeStyleSheet The object to extract from.
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* @return {string} The safeStyleSheet object's contained string, unless
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* the run-time type check fails. In that case, {@code unwrap} returns an
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* innocuous string, or, if assertions are enabled, throws
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* {@code goog.asserts.AssertionError}.
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*/
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goog.html.SafeStyleSheet.unwrap = function(safeStyleSheet) {
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// Perform additional Run-time type-checking to ensure that
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// safeStyleSheet is indeed an instance of the expected type. This
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// provides some additional protection against security bugs due to
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// application code that disables type checks.
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// Specifically, the following checks are performed:
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// 1. The object is an instance of the expected type.
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// 2. The object is not an instance of a subclass.
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// 3. The object carries a type marker for the expected type. "Faking" an
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// object requires a reference to the type marker, which has names intended
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// to stand out in code reviews.
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if (safeStyleSheet instanceof goog.html.SafeStyleSheet &&
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safeStyleSheet.constructor === goog.html.SafeStyleSheet &&
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safeStyleSheet
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.SAFE_STYLE_SHEET_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ ===
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goog.html.SafeStyleSheet.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_) {
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return safeStyleSheet.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_;
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} else {
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goog.asserts.fail('expected object of type SafeStyleSheet, got \'' +
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safeStyleSheet + '\' of type ' + goog.typeOf(safeStyleSheet));
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return 'type_error:SafeStyleSheet';
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}
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};
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/**
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* Package-internal utility method to create SafeStyleSheet instances.
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*
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* @param {string} styleSheet The string to initialize the SafeStyleSheet
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* object with.
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* @return {!goog.html.SafeStyleSheet} The initialized SafeStyleSheet object.
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* @package
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*/
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goog.html.SafeStyleSheet.createSafeStyleSheetSecurityPrivateDoNotAccessOrElse =
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function(styleSheet) {
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return new goog.html.SafeStyleSheet().initSecurityPrivateDoNotAccessOrElse_(
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styleSheet);
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};
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/**
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* Called from createSafeStyleSheetSecurityPrivateDoNotAccessOrElse(). This
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* method exists only so that the compiler can dead code eliminate static
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* fields (like EMPTY) when they're not accessed.
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* @param {string} styleSheet
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* @return {!goog.html.SafeStyleSheet}
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* @private
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*/
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goog.html.SafeStyleSheet.prototype.initSecurityPrivateDoNotAccessOrElse_ =
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function(styleSheet) {
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this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_ = styleSheet;
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return this;
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};
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/**
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* A SafeStyleSheet instance corresponding to the empty string.
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* @const {!goog.html.SafeStyleSheet}
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*/
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goog.html.SafeStyleSheet.EMPTY =
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goog.html.SafeStyleSheet
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.createSafeStyleSheetSecurityPrivateDoNotAccessOrElse('');
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