// Copyright 2014 The Closure Library Authors. All Rights Reserved.
//
// 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 The SafeStyleSheet type and its builders.
*
* TODO(xtof): Link to document stating type contract.
*/
goog.provide('goog.html.SafeStyleSheet');
goog.require('goog.array');
goog.require('goog.asserts');
goog.require('goog.string');
goog.require('goog.string.Const');
goog.require('goog.string.TypedString');
/**
* A string-like object which represents a CSS style sheet and that carries the
* security type contract that its value, as a string, will not cause untrusted
* script execution (XSS) when evaluated as CSS in a browser.
*
* Instances of this type must be created via the factory method
* {@code goog.html.SafeStyleSheet.fromConstant} and not by invoking its
* constructor. The constructor intentionally takes no parameters and the type
* is immutable; hence only a default instance corresponding to the empty string
* can be obtained via constructor invocation.
*
* A SafeStyleSheet's string representation can safely be interpolated as the
* content of a style element within HTML. The SafeStyleSheet string should
* not be escaped before interpolation.
*
* Values of this type must be composable, i.e. for any two values
* {@code styleSheet1} and {@code styleSheet2} of this type,
* {@code goog.html.SafeStyleSheet.unwrap(styleSheet1) +
* goog.html.SafeStyleSheet.unwrap(styleSheet2)} must itself be a value that
* satisfies the SafeStyleSheet type constraint. This requirement implies that
* for any value {@code styleSheet} of this type,
* {@code goog.html.SafeStyleSheet.unwrap(styleSheet1)} must end in
* "beginning of rule" context.
* A SafeStyleSheet can be constructed via security-reviewed unchecked
* conversions. In this case producers of SafeStyleSheet must ensure themselves
* that the SafeStyleSheet does not contain unsafe script. Note in particular
* that {@code <} is dangerous, even when inside CSS strings, and so should
* always be forbidden or CSS-escaped in user controlled input. For example, if
* {@code </style><script>evil</script>"} were interpolated
* inside a CSS string, it would break out of the context of the original
* style element and {@code evil} would execute. Also note that within an HTML
* style (raw text) element, HTML character references, such as
* {@code &lt;}, are not allowed. See
* http://www.w3.org/TR/html5/scripting-1.html#restrictions-for-contents-of-script-elements
* (similar considerations apply to the style element).
*
* @see goog.html.SafeStyleSheet#fromConstant
* @constructor
* @final
* @struct
* @implements {goog.string.TypedString}
*/
goog.html.SafeStyleSheet = function() {
/**
* The contained value of this SafeStyleSheet. The field has a purposely
* ugly name to make (non-compiled) code that attempts to directly access this
* field stand out.
* @private {string}
*/
this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_ = '';
/**
* A type marker used to implement additional run-time type checking.
* @see goog.html.SafeStyleSheet#unwrap
* @const
* @private
*/
this.SAFE_SCRIPT_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ =
goog.html.SafeStyleSheet.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_;
};
/**
* @override
* @const
*/
goog.html.SafeStyleSheet.prototype.implementsGoogStringTypedString = true;
/**
* Type marker for the SafeStyleSheet type, used to implement additional
* run-time type checking.
* @const
* @private
*/
goog.html.SafeStyleSheet.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ = {};
/**
* Creates a new SafeStyleSheet object by concatenating values.
* @param {...(!goog.html.SafeStyleSheet|!Array<!goog.html.SafeStyleSheet>)}
* var_args Values to concatenate.
* @return {!goog.html.SafeStyleSheet}
*/
goog.html.SafeStyleSheet.concat = function(var_args) {
var result = '';
/**
* @param {!goog.html.SafeStyleSheet|!Array<!goog.html.SafeStyleSheet>}
* argument
*/
var addArgument = function(argument) {
if (goog.isArray(argument)) {
goog.array.forEach(argument, addArgument);
} else {
result += goog.html.SafeStyleSheet.unwrap(argument);
}
};
goog.array.forEach(arguments, addArgument);
return goog.html.SafeStyleSheet
.createSafeStyleSheetSecurityPrivateDoNotAccessOrElse(result);
};
/**
* Creates a SafeStyleSheet object from a compile-time constant string.
*
* {@code styleSheet} must not have any < characters in it, so that
* the syntactic structure of the surrounding HTML is not affected.
*
* @param {!goog.string.Const} styleSheet A compile-time-constant string from
* which to create a SafeStyleSheet.
* @return {!goog.html.SafeStyleSheet} A SafeStyleSheet object initialized to
* {@code styleSheet}.
*/
goog.html.SafeStyleSheet.fromConstant = function(styleSheet) {
var styleSheetString = goog.string.Const.unwrap(styleSheet);
if (styleSheetString.length === 0) {
return goog.html.SafeStyleSheet.EMPTY;
}
// > is a valid character in CSS selectors and there's no strict need to
// block it if we already block <.
goog.asserts.assert(!goog.string.contains(styleSheetString, '<'),
"Forbidden '<' character in style sheet string: " + styleSheetString);
return goog.html.SafeStyleSheet.
createSafeStyleSheetSecurityPrivateDoNotAccessOrElse(styleSheetString);
};
/**
* Returns this SafeStyleSheet's value as a string.
*
* IMPORTANT: In code where it is security relevant that an object's type is
* indeed {@code SafeStyleSheet}, use {@code goog.html.SafeStyleSheet.unwrap}
* instead of this method. If in doubt, assume that it's security relevant. In
* particular, note that goog.html functions which return a goog.html type do
* not guarantee the returned instance is of the right type. For example:
*
* <pre>
* var fakeSafeHtml = new String('fake');
* fakeSafeHtml.__proto__ = goog.html.SafeHtml.prototype;
* var newSafeHtml = goog.html.SafeHtml.htmlEscape(fakeSafeHtml);
* // newSafeHtml is just an alias for fakeSafeHtml, it's passed through by
* // goog.html.SafeHtml.htmlEscape() as fakeSafeHtml
* // instanceof goog.html.SafeHtml.
* </pre>
*
* @see goog.html.SafeStyleSheet#unwrap
* @override
*/
goog.html.SafeStyleSheet.prototype.getTypedStringValue = function() {
return this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_;
};
if (goog.DEBUG) {
/**
* Returns a debug string-representation of this value.
*
* To obtain the actual string value wrapped in a SafeStyleSheet, use
* {@code goog.html.SafeStyleSheet.unwrap}.
*
* @see goog.html.SafeStyleSheet#unwrap
* @override
*/
goog.html.SafeStyleSheet.prototype.toString = function() {
return 'SafeStyleSheet{' +
this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_ + '}';
};
}
/**
* Performs a runtime check that the provided object is indeed a
* SafeStyleSheet object, and returns its value.
*
* @param {!goog.html.SafeStyleSheet} safeStyleSheet The object to extract from.
* @return {string} The safeStyleSheet object's contained string, unless
* the run-time type check fails. In that case, {@code unwrap} returns an
* innocuous string, or, if assertions are enabled, throws
* {@code goog.asserts.AssertionError}.
*/
goog.html.SafeStyleSheet.unwrap = function(safeStyleSheet) {
// Perform additional Run-time type-checking to ensure that
// safeStyleSheet is indeed an instance of the expected type. This
// provides some additional protection against security bugs due to
// application code that disables type checks.
// Specifically, the following checks are performed:
// 1. The object is an instance of the expected type.
// 2. The object is not an instance of a subclass.
// 3. The object carries a type marker for the expected type. "Faking" an
// object requires a reference to the type marker, which has names intended
// to stand out in code reviews.
if (safeStyleSheet instanceof goog.html.SafeStyleSheet &&
safeStyleSheet.constructor === goog.html.SafeStyleSheet &&
safeStyleSheet.SAFE_SCRIPT_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ ===
goog.html.SafeStyleSheet.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_) {
return safeStyleSheet.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_;
} else {
goog.asserts.fail(
"expected object of type SafeStyleSheet, got '" + safeStyleSheet +
"'");
return 'type_error:SafeStyleSheet';
}
};
/**
* Package-internal utility method to create SafeStyleSheet instances.
*
* @param {string} styleSheet The string to initialize the SafeStyleSheet
* object with.
* @return {!goog.html.SafeStyleSheet} The initialized SafeStyleSheet object.
* @package
*/
goog.html.SafeStyleSheet.createSafeStyleSheetSecurityPrivateDoNotAccessOrElse =
function(styleSheet) {
return new goog.html.SafeStyleSheet().initSecurityPrivateDoNotAccessOrElse_(
styleSheet);
};
/**
* Called from createSafeStyleSheetSecurityPrivateDoNotAccessOrElse(). This
* method exists only so that the compiler can dead code eliminate static
* fields (like EMPTY) when they're not accessed.
* @param {string} styleSheet
* @return {!goog.html.SafeStyleSheet}
* @private
*/
goog.html.SafeStyleSheet.prototype.initSecurityPrivateDoNotAccessOrElse_ =
function(styleSheet) {
this.privateDoNotAccessOrElseSafeStyleSheetWrappedValue_ = styleSheet;
return this;
};
/**
* A SafeStyleSheet instance corresponding to the empty string.
* @const {!goog.html.SafeStyleSheet}
*/
goog.html.SafeStyleSheet.EMPTY =
goog.html.SafeStyleSheet.
createSafeStyleSheetSecurityPrivateDoNotAccessOrElse('');
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