235 lines
8.4 KiB
JavaScript
235 lines
8.4 KiB
JavaScript
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// 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 SafeScript 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.SafeScript');
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goog.require('goog.asserts');
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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 JavaScript code and that carries the
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* security type contract that its value, as a string, will not cause execution
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* of unconstrained attacker controlled code (XSS) when evaluated as JavaScript
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* 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.SafeScript.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 SafeScript's string representation can safely be interpolated as the
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* content of a script element within HTML. The SafeScript string should not be
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* escaped before interpolation.
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*
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* Note that the SafeScript might contain text that is attacker-controlled but
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* that text should have been interpolated with appropriate escaping,
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* sanitization and/or validation into the right location in the script, such
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* that it is highly constrained in its effect (for example, it had to match a
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* set of whitelisted words).
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*
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* A SafeScript can be constructed via security-reviewed unchecked
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* conversions. In this case producers of SafeScript must ensure themselves that
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* the SafeScript does not contain unsafe script. Note in particular that
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* {@code <} is dangerous, even when inside JavaScript strings, and so should
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* always be forbidden or JavaScript escaped in user controlled input. For
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* example, if {@code </script><script>evil</script>"} were
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* interpolated inside a JavaScript string, it would break out of the context
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* of the original script element and {@code evil} would execute. Also note
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* that within an HTML script (raw text) element, HTML character references,
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* such as "<" are not allowed. See
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* http://www.w3.org/TR/html5/scripting-1.html#restrictions-for-contents-of-script-elements.
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*
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* @see goog.html.SafeScript#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.SafeScript = function() {
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/**
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* The contained value of this SafeScript. 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.privateDoNotAccessOrElseSafeScriptWrappedValue_ = '';
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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.SafeScript#unwrap
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* @const
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* @private
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*/
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this.SAFE_SCRIPT_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ =
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goog.html.SafeScript.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.SafeScript.prototype.implementsGoogStringTypedString = true;
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/**
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* Type marker for the SafeScript 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.SafeScript.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ = {};
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/**
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* Creates a SafeScript object from a compile-time constant string.
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*
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* @param {!goog.string.Const} script A compile-time-constant string from which
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* to create a SafeScript.
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* @return {!goog.html.SafeScript} A SafeScript object initialized to
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* {@code script}.
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*/
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goog.html.SafeScript.fromConstant = function(script) {
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var scriptString = goog.string.Const.unwrap(script);
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if (scriptString.length === 0) {
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return goog.html.SafeScript.EMPTY;
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}
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return goog.html.SafeScript.createSafeScriptSecurityPrivateDoNotAccessOrElse(
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scriptString);
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};
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/**
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* Returns this SafeScript'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 SafeScript}, use {@code goog.html.SafeScript.unwrap} instead of
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* this method. If in doubt, assume that it's security relevant. In particular,
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* note that goog.html functions which return a goog.html type do not guarantee
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* 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.SafeScript#unwrap
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* @override
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*/
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goog.html.SafeScript.prototype.getTypedStringValue = function() {
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return this.privateDoNotAccessOrElseSafeScriptWrappedValue_;
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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 SafeScript, use
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* {@code goog.html.SafeScript.unwrap}.
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*
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* @see goog.html.SafeScript#unwrap
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* @override
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*/
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goog.html.SafeScript.prototype.toString = function() {
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return 'SafeScript{' +
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this.privateDoNotAccessOrElseSafeScriptWrappedValue_ + '}';
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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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* SafeScript object, and returns its value.
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*
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* @param {!goog.html.SafeScript} safeScript The object to extract from.
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* @return {string} The safeScript 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.SafeScript.unwrap = function(safeScript) {
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// Perform additional Run-time type-checking to ensure that
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// safeScript 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 (safeScript instanceof goog.html.SafeScript &&
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safeScript.constructor === goog.html.SafeScript &&
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safeScript.SAFE_SCRIPT_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ ===
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goog.html.SafeScript.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_) {
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return safeScript.privateDoNotAccessOrElseSafeScriptWrappedValue_;
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} else {
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goog.asserts.fail('expected object of type SafeScript, got \'' +
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safeScript + '\' of type ' + goog.typeOf(safeScript));
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return 'type_error:SafeScript';
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}
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};
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/**
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* Package-internal utility method to create SafeScript instances.
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*
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* @param {string} script The string to initialize the SafeScript object with.
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* @return {!goog.html.SafeScript} The initialized SafeScript object.
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* @package
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*/
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goog.html.SafeScript.createSafeScriptSecurityPrivateDoNotAccessOrElse =
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function(script) {
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return new goog.html.SafeScript().initSecurityPrivateDoNotAccessOrElse_(
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script);
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};
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/**
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* Called from createSafeScriptSecurityPrivateDoNotAccessOrElse(). 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} script
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* @return {!goog.html.SafeScript}
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* @private
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*/
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goog.html.SafeScript.prototype.initSecurityPrivateDoNotAccessOrElse_ = function(
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script) {
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this.privateDoNotAccessOrElseSafeScriptWrappedValue_ = script;
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return this;
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};
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/**
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* A SafeScript instance corresponding to the empty string.
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* @const {!goog.html.SafeScript}
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*/
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goog.html.SafeScript.EMPTY =
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goog.html.SafeScript.createSafeScriptSecurityPrivateDoNotAccessOrElse('');
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