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

Index: third_party/google_input_tools/third_party/closure_library/closure/goog/html/safestyle.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 SafeStyle type and its builders.
+ *
+ * TODO(xtof): Link to document stating type contract.
+ */
+
+goog.provide('goog.html.SafeStyle');
+
+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 sequence of CSS declarations
+ * ({@code propertyName1: propertyvalue1; propertyName2: propertyValue2; ...})
+ * 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 methods
+ * ({@code goog.html.SafeStyle.create} or
+ * {@code goog.html.SafeStyle.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 SafeStyle's string representation ({@link #getTypedStringValue()}) can
+ * safely:
+ * <ul>
+ *   <li>Be interpolated as the entire content of a *quoted* HTML style
+ *       attribute, or before already existing properties. The SafeStyle string
+ *       *must be HTML-attribute-escaped* (where " and ' are escaped) before
+ *       interpolation.
+ *   <li>Be interpolated as the entire content of a {}-wrapped block within a
+ *       stylesheet, or before already existing properties. The SafeStyle string
+ *       should not be escaped before interpolation. SafeStyle's contract also
+ *       guarantees that the string will not be able to introduce new properties
+ *       or elide existing ones.
+ *   <li>Be assigned to the style property of a DOM node. The SafeStyle string
+ *       should not be escaped before being assigned to the property.
+ * </ul>
+ *
+ * A SafeStyle may never contain literal angle brackets. Otherwise, it could
+ * be unsafe to place a SafeStyle into a &lt;style&gt; tag (where it can't
+ * be HTML escaped). For example, if the SafeStyle containing
+ * "{@code font: 'foo &lt;style/&gt;&lt;script&gt;evil&lt;/script&gt;'}" were
+ * interpolated within a &lt;style&gt; tag, this would then break out of the
+ * style context into HTML.
+ *
+ * A SafeStyle may contain literal single or double quotes, and as such the
+ * entire style string must be escaped when used in a style attribute (if
+ * this were not the case, the string could contain a matching quote that
+ * would escape from the style attribute).
+ *
+ * Values of this type must be composable, i.e. for any two values
+ * {@code style1} and {@code style2} of this type,
+ * {@code goog.html.SafeStyle.unwrap(style1) +
+ * goog.html.SafeStyle.unwrap(style2)} must itself be a value that satisfies
+ * the SafeStyle type constraint. This requirement implies that for any value
+ * {@code style} of this type, {@code goog.html.SafeStyle.unwrap(style)} must
+ * not end in a "property value" or "property name" context. For example,
+ * a value of {@code background:url("} or {@code font-} would not satisfy the
+ * SafeStyle contract. This is because concatenating such strings with a
+ * second value that itself does not contain unsafe CSS can result in an
+ * overall string that does. For example, if {@code javascript:evil())"} is
+ * appended to {@code background:url("}, the resulting string may result in
+ * the execution of a malicious script.
+ *
+ * TODO(user): Consider whether we should implement UTF-8 interchange
+ * validity checks and blacklisting of newlines (including Unicode ones) and
+ * other whitespace characters (\t, \f). Document here if so and also update
+ * SafeStyle.fromConstant().
+ *
+ * The following example values comply with this type's contract:
+ * <ul>
+ *   <li><pre>width: 1em;</pre>
+ *   <li><pre>height:1em;</pre>
+ *   <li><pre>width: 1em;height: 1em;</pre>
+ *   <li><pre>background:url('http://url');</pre>
+ * </ul>
+ * In addition, the empty string is safe for use in a CSS attribute.
+ *
+ * The following example values do NOT comply with this type's contract:
+ * <ul>
+ *   <li><pre>background: red</pre> (missing a trailing semi-colon)
+ *   <li><pre>background:</pre> (missing a value and a trailing semi-colon)
+ *   <li><pre>1em</pre> (missing an attribute name, which provides context for
+ *       the value)
+ * </ul>
+ *
+ * @see goog.html.SafeStyle#create
+ * @see goog.html.SafeStyle#fromConstant
+ * @see http://www.w3.org/TR/css3-syntax/
+ * @constructor
+ * @final
+ * @struct
+ * @implements {goog.string.TypedString}
+ */
+goog.html.SafeStyle = function() {
+  /**
+   * The contained value of this SafeStyle.  The field has a purposely
+   * ugly name to make (non-compiled) code that attempts to directly access this
+   * field stand out.
+   * @private {string}
+   */
+  this.privateDoNotAccessOrElseSafeStyleWrappedValue_ = '';
+
+  /**
+   * A type marker used to implement additional run-time type checking.
+   * @see goog.html.SafeStyle#unwrap
+   * @const
+   * @private
+   */
+  this.SAFE_STYLE_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ =
+      goog.html.SafeStyle.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_;
+};
+
+
+/**
+ * @override
+ * @const
+ */
+goog.html.SafeStyle.prototype.implementsGoogStringTypedString = true;
+
+
+/**
+ * Type marker for the SafeStyle type, used to implement additional
+ * run-time type checking.
+ * @const
+ * @private
+ */
+goog.html.SafeStyle.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ = {};
+
+
+/**
+ * Creates a SafeStyle object from a compile-time constant string.
+ *
+ * {@code style} should be in the format
+ * {@code name: value; [name: value; ...]} and must not have any < or >
+ * characters in it. This is so that SafeStyle's contract is preserved,
+ * allowing the SafeStyle to correctly be interpreted as a sequence of CSS
+ * declarations and without affecting the syntactic structure of any
+ * surrounding CSS and HTML.
+ *
+ * This method performs basic sanity checks on the format of {@code style}
+ * but does not constrain the format of {@code name} and {@code value}, except
+ * for disallowing tag characters.
+ *
+ * @param {!goog.string.Const} style A compile-time-constant string from which
+ *     to create a SafeStyle.
+ * @return {!goog.html.SafeStyle} A SafeStyle object initialized to
+ *     {@code style}.
+ */
+goog.html.SafeStyle.fromConstant = function(style) {
+  var styleString = goog.string.Const.unwrap(style);
+  if (styleString.length === 0) {
+    return goog.html.SafeStyle.EMPTY;
+  }
+  goog.html.SafeStyle.checkStyle_(styleString);
+  goog.asserts.assert(goog.string.endsWith(styleString, ';'),
+      'Last character of style string is not \';\': ' + styleString);
+  goog.asserts.assert(goog.string.contains(styleString, ':'),
+      'Style string must contain at least one \':\', to ' +
+      'specify a "name: value" pair: ' + styleString);
+  return goog.html.SafeStyle.createSafeStyleSecurityPrivateDoNotAccessOrElse(
+      styleString);
+};
+
+
+/**
+ * Checks if the style definition is valid.
+ * @param {string} style
+ * @private
+ */
+goog.html.SafeStyle.checkStyle_ = function(style) {
+  goog.asserts.assert(!/[<>]/.test(style),
+      'Forbidden characters in style string: ' + style);
+};
+
+
+/**
+ * Returns this SafeStyle's value as a string.
+ *
+ * IMPORTANT: In code where it is security relevant that an object's type is
+ * indeed {@code SafeStyle}, use {@code goog.html.SafeStyle.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.SafeStyle#unwrap
+ * @override
+ */
+goog.html.SafeStyle.prototype.getTypedStringValue = function() {
+  return this.privateDoNotAccessOrElseSafeStyleWrappedValue_;
+};
+
+
+if (goog.DEBUG) {
+  /**
+   * Returns a debug string-representation of this value.
+   *
+   * To obtain the actual string value wrapped in a SafeStyle, use
+   * {@code goog.html.SafeStyle.unwrap}.
+   *
+   * @see goog.html.SafeStyle#unwrap
+   * @override
+   */
+  goog.html.SafeStyle.prototype.toString = function() {
+    return 'SafeStyle{' +
+        this.privateDoNotAccessOrElseSafeStyleWrappedValue_ + '}';
+  };
+}
+
+
+/**
+ * Performs a runtime check that the provided object is indeed a
+ * SafeStyle object, and returns its value.
+ *
+ * @param {!goog.html.SafeStyle} safeStyle The object to extract from.
+ * @return {string} The safeStyle 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.SafeStyle.unwrap = function(safeStyle) {
+  // Perform additional Run-time type-checking to ensure that
+  // safeStyle 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 (safeStyle instanceof goog.html.SafeStyle &&
+      safeStyle.constructor === goog.html.SafeStyle &&
+      safeStyle.SAFE_STYLE_TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_ ===
+          goog.html.SafeStyle.TYPE_MARKER_GOOG_HTML_SECURITY_PRIVATE_) {
+    return safeStyle.privateDoNotAccessOrElseSafeStyleWrappedValue_;
+  } else {
+    goog.asserts.fail(
+        'expected object of type SafeStyle, got \'' + safeStyle + '\'');
+    return 'type_error:SafeStyle';
+  }
+};
+
+
+/**
+ * Package-internal utility method to create SafeStyle instances.
+ *
+ * @param {string} style The string to initialize the SafeStyle object with.
+ * @return {!goog.html.SafeStyle} The initialized SafeStyle object.
+ * @package
+ */
+goog.html.SafeStyle.createSafeStyleSecurityPrivateDoNotAccessOrElse =
+    function(style) {
+  return new goog.html.SafeStyle().initSecurityPrivateDoNotAccessOrElse_(style);
+};
+
+
+/**
+ * Called from createSafeStyleSecurityPrivateDoNotAccessOrElse(). This
+ * method exists only so that the compiler can dead code eliminate static
+ * fields (like EMPTY) when they're not accessed.
+ * @param {string} style
+ * @return {!goog.html.SafeStyle}
+ * @private
+ */
+goog.html.SafeStyle.prototype.initSecurityPrivateDoNotAccessOrElse_ = function(
+    style) {
+  this.privateDoNotAccessOrElseSafeStyleWrappedValue_ = style;
+  return this;
+};
+
+
+/**
+ * A SafeStyle instance corresponding to the empty string.
+ * @const {!goog.html.SafeStyle}
+ */
+goog.html.SafeStyle.EMPTY =
+    goog.html.SafeStyle.createSafeStyleSecurityPrivateDoNotAccessOrElse('');
+
+
+/**
+ * The innocuous string generated by goog.html.SafeUrl.create when passed
+ * an unsafe value.
+ * @const {string}
+ */
+goog.html.SafeStyle.INNOCUOUS_STRING = 'zClosurez';
+
+
+/**
+ * Mapping of property names to their values.
+ * @typedef {!Object<string, goog.string.Const|string>}
+ */
+goog.html.SafeStyle.PropertyMap;
+
+
+/**
+ * Creates a new SafeStyle object from the properties specified in the map.
+ * @param {goog.html.SafeStyle.PropertyMap} map Mapping of property names to
+ *     their values, for example {'margin': '1px'}. Names must consist of
+ *     [-_a-zA-Z0-9]. Values might be strings consisting of
+ *     [-,.'"%_!# a-zA-Z0-9], where " and ' must be properly balanced.
+ *     Other values must be wrapped in goog.string.Const. Null value causes
+ *     skipping the property.
+ * @return {!goog.html.SafeStyle}
+ * @throws {Error} If invalid name is provided.
+ * @throws {goog.asserts.AssertionError} If invalid value is provided. With
+ *     disabled assertions, invalid value is replaced by
+ *     goog.html.SafeStyle.INNOCUOUS_STRING.
+ */
+goog.html.SafeStyle.create = function(map) {
+  var style = '';
+  for (var name in map) {
+    if (!/^[-_a-zA-Z0-9]+$/.test(name)) {
+      throw Error('Name allows only [-_a-zA-Z0-9], got: ' + name);
+    }
+    var value = map[name];
+    if (value == null) {
+      continue;
+    }
+    if (value instanceof goog.string.Const) {
+      value = goog.string.Const.unwrap(value);
+      // These characters can be used to change context and we don't want that
+      // even with const values.
+      goog.asserts.assert(!/[{;}]/.test(value), 'Value does not allow [{;}].');
+    } else if (!goog.html.SafeStyle.VALUE_RE_.test(value)) {
+      goog.asserts.fail(
+          'String value allows only [-,."\'%_!# a-zA-Z0-9], got: ' + value);
+      value = goog.html.SafeStyle.INNOCUOUS_STRING;
+    } else if (!goog.html.SafeStyle.hasBalancedQuotes_(value)) {
+      goog.asserts.fail('String value requires balanced quotes, got: ' + value);
+      value = goog.html.SafeStyle.INNOCUOUS_STRING;
+    }
+    style += name + ':' + value + ';';
+  }
+  if (!style) {
+    return goog.html.SafeStyle.EMPTY;
+  }
+  goog.html.SafeStyle.checkStyle_(style);
+  return goog.html.SafeStyle.createSafeStyleSecurityPrivateDoNotAccessOrElse(
+      style);
+};
+
+
+/**
+ * Checks that quotes (" and ') are properly balanced inside a string. Assumes
+ * that neither escape (\) nor any other character that could result in
+ * breaking out of a string parsing context are allowed;
+ * see http://www.w3.org/TR/css3-syntax/#string-token-diagram.
+ * @param {string} value Untrusted CSS property value.
+ * @return {boolean} True if property value is safe with respect to quote
+ *     balancedness.
+ * @private
+ */
+goog.html.SafeStyle.hasBalancedQuotes_ = function(value) {
+  var outsideSingle = true;
+  var outsideDouble = true;
+  for (var i = 0; i < value.length; i++) {
+    var c = value.charAt(i);
+    if (c == "'" && outsideDouble) {
+      outsideSingle = !outsideSingle;
+    } else if (c == '"' && outsideSingle) {
+      outsideDouble = !outsideDouble;
+    }
+  }
+  return outsideSingle && outsideDouble;
+};
+
+
+// Keep in sync with the error string in create().
+/**
+ * Regular expression for safe values.
+ *
+ * Quotes (" and ') are allowed, but a check must be done elsewhere to ensure
+ * they're balanced.
+ *
+ * ',' allows multiple values to be assigned to the same property
+ * (e.g. background-attachment or font-family) and hence could allow
+ * multiple values to get injected, but that should pose no risk of XSS.
+ * @const {!RegExp}
+ * @private
+ */
+goog.html.SafeStyle.VALUE_RE_ = /^[-,."'%_!# a-zA-Z0-9]+$/;
+
+
+/**
+ * Creates a new SafeStyle object by concatenating the values.
+ * @param {...(!goog.html.SafeStyle|!Array<!goog.html.SafeStyle>)} var_args
+ *     SafeStyles to concatenate.
+ * @return {!goog.html.SafeStyle}
+ */
+goog.html.SafeStyle.concat = function(var_args) {
+  var style = '';
+
+  /**
+   * @param {!goog.html.SafeStyle|!Array<!goog.html.SafeStyle>} argument
+   */
+  var addArgument = function(argument) {
+    if (goog.isArray(argument)) {
+      goog.array.forEach(argument, addArgument);
+    } else {
+      style += goog.html.SafeStyle.unwrap(argument);
+    }
+  };
+
+  goog.array.forEach(arguments, addArgument);
+  if (!style) {
+    return goog.html.SafeStyle.EMPTY;
+  }
+  return goog.html.SafeStyle.createSafeStyleSecurityPrivateDoNotAccessOrElse(
+      style);
+};