// 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 SafeScript type and its builders.
*
* TODO(xtof): Link to document stating type contract.
*/
goog.provide('goog.html.SafeScript');
goog.require('goog.asserts');
goog.require('goog.string.Const');
goog.require('goog.string.TypedString');
/**
* A string-like object which represents JavaScript code and that carries the
* security type contract that its value, as a string, will not cause execution
* of unconstrained attacker controlled code (XSS) when evaluated as JavaScript
* in a browser.
*
* Instances of this type must be created via the factory method
* {@code goog.html.SafeScript.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 SafeScript's string representation can safely be interpolated as the
* content of a script element within HTML. The SafeScript string should not be
* escaped before interpolation.
*
* Note that the SafeScript might contain text that is attacker-controlled but
* that text should have been interpolated with appropriate escaping,
* sanitization and/or validation into the right location in the script, such
* that it is highly constrained in its effect (for example, it had to match a
* set of whitelisted words).
*
* A SafeScript can be constructed via security-reviewed unchecked
* conversions. In this case producers of SafeScript must ensure themselves that
* the SafeScript does not contain unsafe script. Note in particular that
* {@code <} is dangerous, even when inside JavaScript strings, and so should
* always be forbidden or JavaScript escaped in user controlled input. For
* example, if {@code </script><script>evil</script>"} were
* interpolated inside a JavaScript string, it would break out of the context
* of the original script element and {@code evil} would execute. Also note
* that within an HTML script (raw text) element, HTML character references,
* such as "<" are not allowed. See
* http://www.w3.org/TR/html5/scripting-1.html#restrictions-for-contents-of-script-elements.
*
* @see goog.html.SafeScript#fromConstant
* @constructor
* @final
* @struct
* @implements {goog.string.TypedString}
*/
goog.html.SafeScript = function() {
/**
* The contained value of this SafeScript. The field has a purposely
* ugly name to make (non-compiled) code that attempts to directly access this
* field stand out.
* @private {string}
*/
this.privateDoNotAccessOrElseSafeScriptWrappedValue_ = '';
/**
* A type marker used to implement additional run-time type checking.
* @see goog.html.SafeScript#unwrap
* @const
* @private
*/
this.SAFE_SCRIPT_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ =
goog.html.SafeScript.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_;
};
/**
* @override
* @const
*/
goog.html.SafeScript.prototype.implementsGoogStringTypedString = true;
/**
* Type marker for the SafeScript type, used to implement additional
* run-time type checking.
* @const
* @private
*/
goog.html.SafeScript.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ = {};
/**
* Creates a SafeScript object from a compile-time constant string.
*
* @param {!goog.string.Const} script A compile-time-constant string from which
* to create a SafeScript.
* @return {!goog.html.SafeScript} A SafeScript object initialized to
* {@code script}.
*/
goog.html.SafeScript.fromConstant = function(script) {
var scriptString = goog.string.Const.unwrap(script);
if (scriptString.length === 0) {
return goog.html.SafeScript.EMPTY;
}
return goog.html.SafeScript.createSafeScriptSecurityPrivateDoNotAccessOrElse(
scriptString);
};
/**
* Returns this SafeScript's value as a string.
*
* IMPORTANT: In code where it is security relevant that an object's type is
* indeed {@code SafeScript}, use {@code goog.html.SafeScript.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.SafeScript#unwrap
* @override
*/
goog.html.SafeScript.prototype.getTypedStringValue = function() {
return this.privateDoNotAccessOrElseSafeScriptWrappedValue_;
};
if (goog.DEBUG) {
/**
* Returns a debug string-representation of this value.
*
* To obtain the actual string value wrapped in a SafeScript, use
* {@code goog.html.SafeScript.unwrap}.
*
* @see goog.html.SafeScript#unwrap
* @override
*/
goog.html.SafeScript.prototype.toString = function() {
return 'SafeScript{' +
this.privateDoNotAccessOrElseSafeScriptWrappedValue_ + '}';
};
}
/**
* Performs a runtime check that the provided object is indeed a
* SafeScript object, and returns its value.
*
* @param {!goog.html.SafeScript} safeScript The object to extract from.
* @return {string} The safeScript 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.SafeScript.unwrap = function(safeScript) {
// Perform additional Run-time type-checking to ensure that
// safeScript 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 (safeScript instanceof goog.html.SafeScript &&
safeScript.constructor === goog.html.SafeScript &&
safeScript.SAFE_SCRIPT_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ ===
goog.html.SafeScript.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_) {
return safeScript.privateDoNotAccessOrElseSafeScriptWrappedValue_;
} else {
goog.asserts.fail(
'expected object of type SafeScript, got \'' + safeScript + '\'');
return 'type_error:SafeScript';
}
};
/**
* Package-internal utility method to create SafeScript instances.
*
* @param {string} script The string to initialize the SafeScript object with.
* @return {!goog.html.SafeScript} The initialized SafeScript object.
* @package
*/
goog.html.SafeScript.createSafeScriptSecurityPrivateDoNotAccessOrElse =
function(script) {
return new goog.html.SafeScript().initSecurityPrivateDoNotAccessOrElse_(
script);
};
/**
* Called from createSafeScriptSecurityPrivateDoNotAccessOrElse(). This
* method exists only so that the compiler can dead code eliminate static
* fields (like EMPTY) when they're not accessed.
* @param {string} script
* @return {!goog.html.SafeScript}
* @private
*/
goog.html.SafeScript.prototype.initSecurityPrivateDoNotAccessOrElse_ = function(
script) {
this.privateDoNotAccessOrElseSafeScriptWrappedValue_ = script;
return this;
};
/**
* A SafeScript instance corresponding to the empty string.
* @const {!goog.html.SafeScript}
*/
goog.html.SafeScript.EMPTY =
goog.html.SafeScript.createSafeScriptSecurityPrivateDoNotAccessOrElse('');
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