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docs/js/compiled/out/goog/html/safescript.js

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+// 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 {!Object}
+   * @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 {!Object}
+ * @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 + '\' of type ' + goog.typeOf(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('');