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third_party/google_input_tools/third_party/closure_library/closure/goog/html/safestylesheet.js

Index: third_party/google_input_tools/third_party/closure_library/closure/goog/html/safestylesheet.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 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 <}, 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 &lt; 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('');