Rename Toolkit's webextensions component directory to better reflect what it is.

1 files changed, 2143 insertions, 0 deletions

diff --git a/toolkit/components/webextensions/Schemas.jsm b/toolkit/components/webextensions/Schemas.jsm
new file mode 100644
index 000000000..159211c79
--- /dev/null
+++ b/toolkit/components/webextensions/Schemas.jsm
@@ -0,0 +1,2143 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const Ci = Components.interfaces;
+const Cc = Components.classes;
+const Cu = Components.utils;
+const Cr = Components.results;
+
+const global = this;
+
+Cu.importGlobalProperties(["URL"]);
+
+Cu.import("resource://gre/modules/NetUtil.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+
+Cu.import("resource://gre/modules/ExtensionUtils.jsm");
+var {
+  DefaultMap,
+  instanceOf,
+} = ExtensionUtils;
+
+class DeepMap extends DefaultMap {
+  constructor() {
+    super(() => new DeepMap());
+  }
+
+  getPath(...keys) {
+    return keys.reduce((map, prop) => map.get(prop), this);
+  }
+}
+
+XPCOMUtils.defineLazyServiceGetter(this, "contentPolicyService",
+                                   "@mozilla.org/addons/content-policy;1",
+                                   "nsIAddonContentPolicy");
+
+this.EXPORTED_SYMBOLS = ["Schemas"];
+
+/* globals Schemas, URL */
+
+function readJSON(url) {
+  return new Promise((resolve, reject) => {
+    NetUtil.asyncFetch({uri: url, loadUsingSystemPrincipal: true}, (inputStream, status) => {
+      if (!Components.isSuccessCode(status)) {
+        // Convert status code to a string
+        let e = Components.Exception("", status);
+        reject(new Error(`Error while loading '${url}' (${e.name})`));
+        return;
+      }
+      try {
+        let text = NetUtil.readInputStreamToString(inputStream, inputStream.available());
+
+        // Chrome JSON files include a license comment that we need to
+        // strip off for this to be valid JSON. As a hack, we just
+        // look for the first '[' character, which signals the start
+        // of the JSON content.
+        let index = text.indexOf("[");
+        text = text.slice(index);
+
+        resolve(JSON.parse(text));
+      } catch (e) {
+        reject(e);
+      }
+    });
+  });
+}
+
+/**
+ * Defines a lazy getter for the given property on the given object. Any
+ * security wrappers are waived on the object before the property is
+ * defined, and the getter and setter methods are wrapped for the target
+ * scope.
+ *
+ * The given getter function is guaranteed to be called only once, even
+ * if the target scope retrieves the wrapped getter from the property
+ * descriptor and calls it directly.
+ *
+ * @param {object} object
+ *        The object on which to define the getter.
+ * @param {string|Symbol} prop
+ *        The property name for which to define the getter.
+ * @param {function} getter
+ *        The function to call in order to generate the final property
+ *        value.
+ */
+function exportLazyGetter(object, prop, getter) {
+  object = Cu.waiveXrays(object);
+
+  let redefine = value => {
+    if (value === undefined) {
+      delete object[prop];
+    } else {
+      Object.defineProperty(object, prop, {
+        enumerable: true,
+        configurable: true,
+        writable: true,
+        value,
+      });
+    }
+
+    getter = null;
+
+    return value;
+  };
+
+  Object.defineProperty(object, prop, {
+    enumerable: true,
+    configurable: true,
+
+    get: Cu.exportFunction(function() {
+      return redefine(getter.call(this));
+    }, object),
+
+    set: Cu.exportFunction(value => {
+      redefine(value);
+    }, object),
+  });
+}
+
+const POSTPROCESSORS = {
+  convertImageDataToURL(imageData, context) {
+    let document = context.cloneScope.document;
+    let canvas = document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");
+    canvas.width = imageData.width;
+    canvas.height = imageData.height;
+    canvas.getContext("2d").putImageData(imageData, 0, 0);
+
+    return canvas.toDataURL("image/png");
+  },
+};
+
+// Parses a regular expression, with support for the Python extended
+// syntax that allows setting flags by including the string (?im)
+function parsePattern(pattern) {
+  let flags = "";
+  let match = /^\(\?([im]*)\)(.*)/.exec(pattern);
+  if (match) {
+    [, flags, pattern] = match;
+  }
+  return new RegExp(pattern, flags);
+}
+
+function getValueBaseType(value) {
+  let t = typeof(value);
+  if (t == "object") {
+    if (value === null) {
+      return "null";
+    } else if (Array.isArray(value)) {
+      return "array";
+    } else if (Object.prototype.toString.call(value) == "[object ArrayBuffer]") {
+      return "binary";
+    }
+  } else if (t == "number") {
+    if (value % 1 == 0) {
+      return "integer";
+    }
+  }
+  return t;
+}
+
+// Methods of Context that are used by Schemas.normalize. These methods can be
+// overridden at the construction of Context.
+const CONTEXT_FOR_VALIDATION = [
+  "checkLoadURL",
+  "hasPermission",
+  "logError",
+];
+
+// Methods of Context that are used by Schemas.inject.
+// Callers of Schemas.inject should implement all of these methods.
+const CONTEXT_FOR_INJECTION = [
+  ...CONTEXT_FOR_VALIDATION,
+  "shouldInject",
+  "getImplementation",
+];
+
+/**
+ * A context for schema validation and error reporting. This class is only used
+ * internally within Schemas.
+ */
+class Context {
+  /**
+   * @param {object} params Provides the implementation of this class.
+   * @param {Array<string>} overridableMethods
+   */
+  constructor(params, overridableMethods = CONTEXT_FOR_VALIDATION) {
+    this.params = params;
+
+    this.path = [];
+    this.preprocessors = {
+      localize(value, context) {
+        return value;
+      },
+    };
+    this.postprocessors = POSTPROCESSORS;
+    this.isChromeCompat = false;
+
+    this.currentChoices = new Set();
+    this.choicePathIndex = 0;
+
+    for (let method of overridableMethods) {
+      if (method in params) {
+        this[method] = params[method].bind(params);
+      }
+    }
+
+    let props = ["preprocessors", "isChromeCompat"];
+    for (let prop of props) {
+      if (prop in params) {
+        if (prop in this && typeof this[prop] == "object") {
+          Object.assign(this[prop], params[prop]);
+        } else {
+          this[prop] = params[prop];
+        }
+      }
+    }
+  }
+
+  get choicePath() {
+    let path = this.path.slice(this.choicePathIndex);
+    return path.join(".");
+  }
+
+  get cloneScope() {
+    return this.params.cloneScope;
+  }
+
+  get url() {
+    return this.params.url;
+  }
+
+  get principal() {
+    return this.params.principal || Services.scriptSecurityManager.createNullPrincipal({});
+  }
+
+  /**
+   * Checks whether `url` may be loaded by the extension in this context.
+   *
+   * @param {string} url The URL that the extension wished to load.
+   * @returns {boolean} Whether the context may load `url`.
+   */
+  checkLoadURL(url) {
+    let ssm = Services.scriptSecurityManager;
+    try {
+      ssm.checkLoadURIStrWithPrincipal(this.principal, url,
+                                       ssm.DISALLOW_INHERIT_PRINCIPAL);
+    } catch (e) {
+      return false;
+    }
+    return true;
+  }
+
+  /**
+   * Checks whether this context has the given permission.
+   *
+   * @param {string} permission
+   *        The name of the permission to check.
+   *
+   * @returns {boolean} True if the context has the given permission.
+   */
+  hasPermission(permission) {
+    return false;
+  }
+
+  /**
+   * Returns an error result object with the given message, for return
+   * by Type normalization functions.
+   *
+   * If the context has a `currentTarget` value, this is prepended to
+   * the message to indicate the location of the error.
+   *
+   * @param {string} errorMessage
+   *        The error message which will be displayed when this is the
+   *        only possible matching schema.
+   * @param {string} choicesMessage
+   *        The message describing the valid what constitutes a valid
+   *        value for this schema, which will be displayed when multiple
+   *        schema choices are available and none match.
+   *
+   *        A caller may pass `null` to prevent a choice from being
+   *        added, but this should *only* be done from code processing a
+   *        choices type.
+   * @returns {object}
+   */
+  error(errorMessage, choicesMessage = undefined) {
+    if (choicesMessage !== null) {
+      let {choicePath} = this;
+      if (choicePath) {
+        choicesMessage = `.${choicePath} must ${choicesMessage}`;
+      }
+
+      this.currentChoices.add(choicesMessage);
+    }
+
+    if (this.currentTarget) {
+      return {error: `Error processing ${this.currentTarget}: ${errorMessage}`};
+    }
+    return {error: errorMessage};
+  }
+
+  /**
+   * Creates an `Error` object belonging to the current unprivileged
+   * scope. If there is no unprivileged scope associated with this
+   * context, the message is returned as a string.
+   *
+   * If the context has a `currentTarget` value, this is prepended to
+   * the message, in the same way as for the `error` method.
+   *
+   * @param {string} message
+   * @returns {Error}
+   */
+  makeError(message) {
+    let {error} = this.error(message);
+    if (this.cloneScope) {
+      return new this.cloneScope.Error(error);
+    }
+    return error;
+  }
+
+  /**
+   * Logs the given error to the console. May be overridden to enable
+   * custom logging.
+   *
+   * @param {Error|string} error
+   */
+  logError(error) {
+    Cu.reportError(error);
+  }
+
+  /**
+   * Returns the name of the value currently being normalized. For a
+   * nested object, this is usually approximately equivalent to the
+   * JavaScript property accessor for that property. Given:
+   *
+   *   { foo: { bar: [{ baz: x }] } }
+   *
+   * When processing the value for `x`, the currentTarget is
+   * 'foo.bar.0.baz'
+   */
+  get currentTarget() {
+    return this.path.join(".");
+  }
+
+  /**
+   * Executes the given callback, and returns an array of choice strings
+   * passed to {@see #error} during its execution.
+   *
+   * @param {function} callback
+   * @returns {object}
+   *          An object with a `result` property containing the return
+   *          value of the callback, and a `choice` property containing
+   *          an array of choices.
+   */
+  withChoices(callback) {
+    let {currentChoices, choicePathIndex} = this;
+
+    let choices = new Set();
+    this.currentChoices = choices;
+    this.choicePathIndex = this.path.length;
+
+    try {
+      let result = callback();
+
+      return {result, choices: Array.from(choices)};
+    } finally {
+      this.currentChoices = currentChoices;
+      this.choicePathIndex = choicePathIndex;
+
+      choices = Array.from(choices);
+      if (choices.length == 1) {
+        currentChoices.add(choices[0]);
+      } else if (choices.length) {
+        let n = choices.length - 1;
+        choices[n] = `or ${choices[n]}`;
+
+        this.error(null, `must either [${choices.join(", ")}]`);
+      }
+    }
+  }
+
+  /**
+   * Appends the given component to the `currentTarget` path to indicate
+   * that it is being processed, calls the given callback function, and
+   * then restores the original path.
+   *
+   * This is used to identify the path of the property being processed
+   * when reporting type errors.
+   *
+   * @param {string} component
+   * @param {function} callback
+   * @returns {*}
+   */
+  withPath(component, callback) {
+    this.path.push(component);
+    try {
+      return callback();
+    } finally {
+      this.path.pop();
+    }
+  }
+}
+
+/**
+ * Holds methods that run the actual implementation of the extension APIs. These
+ * methods are only called if the extension API invocation matches the signature
+ * as defined in the schema. Otherwise an error is reported to the context.
+ */
+class InjectionContext extends Context {
+  constructor(params) {
+    super(params, CONTEXT_FOR_INJECTION);
+  }
+
+  /**
+   * Check whether the API should be injected.
+   *
+   * @abstract
+   * @param {string} namespace The namespace of the API. This may contain dots,
+   *     e.g. in the case of "devtools.inspectedWindow".
+   * @param {string} [name] The name of the property in the namespace.
+   *     `null` if we are checking whether the namespace should be injected.
+   * @param {Array<string>} allowedContexts A list of additional contexts in which
+   *     this API should be available. May include any of:
+   *         "main" - The main chrome browser process.
+   *         "addon" - An addon process.
+   *         "content" - A content process.
+   * @returns {boolean} Whether the API should be injected.
+   */
+  shouldInject(namespace, name, allowedContexts) {
+    throw new Error("Not implemented");
+  }
+
+  /**
+   * Generate the implementation for `namespace`.`name`.
+   *
+   * @abstract
+   * @param {string} namespace The full path to the namespace of the API, minus
+   *     the name of the method or property. E.g. "storage.local".
+   * @param {string} name The name of the method, property or event.
+   * @returns {SchemaAPIInterface} The implementation of the API.
+   */
+  getImplementation(namespace, name) {
+    throw new Error("Not implemented");
+  }
+}
+
+/**
+ * The methods in this singleton represent the "format" specifier for
+ * JSON Schema string types.
+ *
+ * Each method either returns a normalized version of the original
+ * value, or throws an error if the value is not valid for the given
+ * format.
+ */
+const FORMATS = {
+  url(string, context) {
+    let url = new URL(string).href;
+
+    if (!context.checkLoadURL(url)) {
+      throw new Error(`Access denied for URL ${url}`);
+    }
+    return url;
+  },
+
+  relativeUrl(string, context) {
+    if (!context.url) {
+      // If there's no context URL, return relative URLs unresolved, and
+      // skip security checks for them.
+      try {
+        new URL(string);
+      } catch (e) {
+        return string;
+      }
+    }
+
+    let url = new URL(string, context.url).href;
+
+    if (!context.checkLoadURL(url)) {
+      throw new Error(`Access denied for URL ${url}`);
+    }
+    return url;
+  },
+
+  strictRelativeUrl(string, context) {
+    // Do not accept a string which resolves as an absolute URL, or any
+    // protocol-relative URL.
+    if (!string.startsWith("//")) {
+      try {
+        new URL(string);
+      } catch (e) {
+        return FORMATS.relativeUrl(string, context);
+      }
+    }
+
+    throw new SyntaxError(`String ${JSON.stringify(string)} must be a relative URL`);
+  },
+
+  contentSecurityPolicy(string, context) {
+    let error = contentPolicyService.validateAddonCSP(string);
+    if (error != null) {
+      throw new SyntaxError(error);
+    }
+    return string;
+  },
+
+  date(string, context) {
+    // A valid ISO 8601 timestamp.
+    const PATTERN = /^\d{4}-\d{2}-\d{2}(T\d{2}:\d{2}:\d{2}(\.\d{3})?(Z|([-+]\d{2}:?\d{2})))?$/;
+    if (!PATTERN.test(string)) {
+      throw new Error(`Invalid date string ${string}`);
+    }
+    // Our pattern just checks the format, we could still have invalid
+    // values (e.g., month=99 or month=02 and day=31).  Let the Date
+    // constructor do the dirty work of validating.
+    if (isNaN(new Date(string))) {
+      throw new Error(`Invalid date string ${string}`);
+    }
+    return string;
+  },
+};
+
+// Schema files contain namespaces, and each namespace contains types,
+// properties, functions, and events. An Entry is a base class for
+// types, properties, functions, and events.
+class Entry {
+  constructor(schema = {}) {
+    /**
+     * If set to any value which evaluates as true, this entry is
+     * deprecated, and any access to it will result in a deprecation
+     * warning being logged to the browser console.
+     *
+     * If the value is a string, it will be appended to the deprecation
+     * message. If it contains the substring "${value}", it will be
+     * replaced with a string representation of the value being
+     * processed.
+     *
+     * If the value is any other truthy value, a generic deprecation
+     * message will be emitted.
+     */
+    this.deprecated = false;
+    if ("deprecated" in schema) {
+      this.deprecated = schema.deprecated;
+    }
+
+    /**
+     * @property {string} [preprocessor]
+     * If set to a string value, and a preprocessor of the same is
+     * defined in the validation context, it will be applied to this
+     * value prior to any normalization.
+     */
+    this.preprocessor = schema.preprocess || null;
+
+    /**
+     * @property {string} [postprocessor]
+     * If set to a string value, and a postprocessor of the same is
+     * defined in the validation context, it will be applied to this
+     * value after any normalization.
+     */
+    this.postprocessor = schema.postprocess || null;
+
+    /**
+     * @property {Array<string>} allowedContexts A list of allowed contexts
+     * to consider before generating the API.
+     * These are not parsed by the schema, but passed to `shouldInject`.
+     */
+    this.allowedContexts = schema.allowedContexts || [];
+  }
+
+  /**
+   * Preprocess the given value with the preprocessor declared in
+   * `preprocessor`.
+   *
+   * @param {*} value
+   * @param {Context} context
+   * @returns {*}
+   */
+  preprocess(value, context) {
+    if (this.preprocessor) {
+      return context.preprocessors[this.preprocessor](value, context);
+    }
+    return value;
+  }
+
+  /**
+   * Postprocess the given result with the postprocessor declared in
+   * `postprocessor`.
+   *
+   * @param {object} result
+   * @param {Context} context
+   * @returns {object}
+   */
+  postprocess(result, context) {
+    if (result.error || !this.postprocessor) {
+      return result;
+    }
+
+    let value = context.postprocessors[this.postprocessor](result.value, context);
+    return {value};
+  }
+
+  /**
+   * Logs a deprecation warning for this entry, based on the value of
+   * its `deprecated` property.
+   *
+   * @param {Context} context
+   * @param {value} [value]
+   */
+  logDeprecation(context, value = null) {
+    let message = "This property is deprecated";
+    if (typeof(this.deprecated) == "string") {
+      message = this.deprecated;
+      if (message.includes("${value}")) {
+        try {
+          value = JSON.stringify(value);
+        } catch (e) {
+          value = String(value);
+        }
+        message = message.replace(/\$\{value\}/g, () => value);
+      }
+    }
+
+    context.logError(context.makeError(message));
+  }
+
+  /**
+   * Checks whether the entry is deprecated and, if so, logs a
+   * deprecation message.
+   *
+   * @param {Context} context
+   * @param {value} [value]
+   */
+  checkDeprecated(context, value = null) {
+    if (this.deprecated) {
+      this.logDeprecation(context, value);
+    }
+  }
+
+  /**
+   * Injects JS values for the entry into the extension API
+   * namespace. The default implementation is to do nothing.
+   * `context` is used to call the actual implementation
+   * of a given function or event.
+   *
+   * @param {Array<string>} path The API path, e.g. `["storage", "local"]`.
+   * @param {string} name The method name, e.g. "get".
+   * @param {object} dest The object where `path`.`name` should be stored.
+   * @param {InjectionContext} context
+   */
+  inject(path, name, dest, context) {
+  }
+}
+
+// Corresponds either to a type declared in the "types" section of the
+// schema or else to any type object used throughout the schema.
+class Type extends Entry {
+  /**
+   * @property {Array<string>} EXTRA_PROPERTIES
+   *        An array of extra properties which may be present for
+   *        schemas of this type.
+   */
+  static get EXTRA_PROPERTIES() {
+    return ["description", "deprecated", "preprocess", "postprocess", "allowedContexts"];
+  }
+
+  /**
+   * Parses the given schema object and returns an instance of this
+   * class which corresponds to its properties.
+   *
+   * @param {object} schema
+   *        A JSON schema object which corresponds to a definition of
+   *        this type.
+   * @param {Array<string>} path
+   *        The path to this schema object from the root schema,
+   *        corresponding to the property names and array indices
+   *        traversed during parsing in order to arrive at this schema
+   *        object.
+   * @param {Array<string>} [extraProperties]
+   *        An array of extra property names which are valid for this
+   *        schema in the current context.
+   * @returns {Type}
+   *        An instance of this type which corresponds to the given
+   *        schema object.
+   * @static
+   */
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    return new this(schema);
+  }
+
+  /**
+   * Checks that all of the properties present in the given schema
+   * object are valid properties for this type, and throws if invalid.
+   *
+   * @param {object} schema
+   *        A JSON schema object.
+   * @param {Array<string>} path
+   *        The path to this schema object from the root schema,
+   *        corresponding to the property names and array indices
+   *        traversed during parsing in order to arrive at this schema
+   *        object.
+   * @param {Array<string>} [extra]
+   *        An array of extra property names which are valid for this
+   *        schema in the current context.
+   * @throws {Error}
+   *        An error describing the first invalid property found in the
+   *        schema object.
+   */
+  static checkSchemaProperties(schema, path, extra = []) {
+    let allowedSet = new Set([...this.EXTRA_PROPERTIES, ...extra]);
+
+    for (let prop of Object.keys(schema)) {
+      if (!allowedSet.has(prop)) {
+        throw new Error(`Internal error: Namespace ${path.join(".")} has invalid type property "${prop}" in type "${schema.id || JSON.stringify(schema)}"`);
+      }
+    }
+  }
+
+  // Takes a value, checks that it has the correct type, and returns a
+  // "normalized" version of the value. The normalized version will
+  // include "nulls" in place of omitted optional properties. The
+  // result of this function is either {error: "Some type error"} or
+  // {value: <normalized-value>}.
+  normalize(value, context) {
+    return context.error("invalid type");
+  }
+
+  // Unlike normalize, this function does a shallow check to see if
+  // |baseType| (one of the possible getValueBaseType results) is
+  // valid for this type. It returns true or false. It's used to fill
+  // in optional arguments to functions before actually type checking
+
+  checkBaseType(baseType) {
+    return false;
+  }
+
+  // Helper method that simply relies on checkBaseType to implement
+  // normalize. Subclasses can choose to use it or not.
+  normalizeBase(type, value, context) {
+    if (this.checkBaseType(getValueBaseType(value))) {
+      this.checkDeprecated(context, value);
+      return {value: this.preprocess(value, context)};
+    }
+
+    let choice;
+    if (/^[aeiou]/.test(type)) {
+      choice = `be an ${type} value`;
+    } else {
+      choice = `be a ${type} value`;
+    }
+
+    return context.error(`Expected ${type} instead of ${JSON.stringify(value)}`,
+                         choice);
+  }
+}
+
+// Type that allows any value.
+class AnyType extends Type {
+  normalize(value, context) {
+    this.checkDeprecated(context, value);
+    return this.postprocess({value}, context);
+  }
+
+  checkBaseType(baseType) {
+    return true;
+  }
+}
+
+// An untagged union type.
+class ChoiceType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["choices", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    let choices = schema.choices.map(t => Schemas.parseSchema(t, path));
+    return new this(schema, choices);
+  }
+
+  constructor(schema, choices) {
+    super(schema);
+    this.choices = choices;
+  }
+
+  extend(type) {
+    this.choices.push(...type.choices);
+
+    return this;
+  }
+
+  normalize(value, context) {
+    this.checkDeprecated(context, value);
+
+    let error;
+    let {choices, result} = context.withChoices(() => {
+      for (let choice of this.choices) {
+        let r = choice.normalize(value, context);
+        if (!r.error) {
+          return r;
+        }
+
+        error = r;
+      }
+    });
+
+    if (result) {
+      return result;
+    }
+    if (choices.length <= 1) {
+      return error;
+    }
+
+    let n = choices.length - 1;
+    choices[n] = `or ${choices[n]}`;
+
+    let message = `Value must either: ${choices.join(", ")}`;
+
+    return context.error(message, null);
+  }
+
+  checkBaseType(baseType) {
+    return this.choices.some(t => t.checkBaseType(baseType));
+  }
+}
+
+// This is a reference to another type--essentially a typedef.
+class RefType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["$ref", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    let ref = schema.$ref;
+    let ns = path[0];
+    if (ref.includes(".")) {
+      [ns, ref] = ref.split(".");
+    }
+    return new this(schema, ns, ref);
+  }
+
+  // For a reference to a type named T declared in namespace NS,
+  // namespaceName will be NS and reference will be T.
+  constructor(schema, namespaceName, reference) {
+    super(schema);
+    this.namespaceName = namespaceName;
+    this.reference = reference;
+  }
+
+  get targetType() {
+    let ns = Schemas.namespaces.get(this.namespaceName);
+    let type = ns.get(this.reference);
+    if (!type) {
+      throw new Error(`Internal error: Type ${this.reference} not found`);
+    }
+    return type;
+  }
+
+  normalize(value, context) {
+    this.checkDeprecated(context, value);
+    return this.targetType.normalize(value, context);
+  }
+
+  checkBaseType(baseType) {
+    return this.targetType.checkBaseType(baseType);
+  }
+}
+
+class StringType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["enum", "minLength", "maxLength", "pattern", "format",
+            ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    let enumeration = schema.enum || null;
+    if (enumeration) {
+      // The "enum" property is either a list of strings that are
+      // valid values or else a list of {name, description} objects,
+      // where the .name values are the valid values.
+      enumeration = enumeration.map(e => {
+        if (typeof(e) == "object") {
+          return e.name;
+        }
+        return e;
+      });
+    }
+
+    let pattern = null;
+    if (schema.pattern) {
+      try {
+        pattern = parsePattern(schema.pattern);
+      } catch (e) {
+        throw new Error(`Internal error: Invalid pattern ${JSON.stringify(schema.pattern)}`);
+      }
+    }
+
+    let format = null;
+    if (schema.format) {
+      if (!(schema.format in FORMATS)) {
+        throw new Error(`Internal error: Invalid string format ${schema.format}`);
+      }
+      format = FORMATS[schema.format];
+    }
+    return new this(schema, enumeration,
+                    schema.minLength || 0,
+                    schema.maxLength || Infinity,
+                    pattern,
+                    format);
+  }
+
+  constructor(schema, enumeration, minLength, maxLength, pattern, format) {
+    super(schema);
+    this.enumeration = enumeration;
+    this.minLength = minLength;
+    this.maxLength = maxLength;
+    this.pattern = pattern;
+    this.format = format;
+  }
+
+  normalize(value, context) {
+    let r = this.normalizeBase("string", value, context);
+    if (r.error) {
+      return r;
+    }
+    value = r.value;
+
+    if (this.enumeration) {
+      if (this.enumeration.includes(value)) {
+        return this.postprocess({value}, context);
+      }
+
+      let choices = this.enumeration.map(JSON.stringify).join(", ");
+
+      return context.error(`Invalid enumeration value ${JSON.stringify(value)}`,
+                           `be one of [${choices}]`);
+    }
+
+    if (value.length < this.minLength) {
+      return context.error(`String ${JSON.stringify(value)} is too short (must be ${this.minLength})`,
+                           `be longer than ${this.minLength}`);
+    }
+    if (value.length > this.maxLength) {
+      return context.error(`String ${JSON.stringify(value)} is too long (must be ${this.maxLength})`,
+                           `be shorter than ${this.maxLength}`);
+    }
+
+    if (this.pattern && !this.pattern.test(value)) {
+      return context.error(`String ${JSON.stringify(value)} must match ${this.pattern}`,
+                           `match the pattern ${this.pattern.toSource()}`);
+    }
+
+    if (this.format) {
+      try {
+        r.value = this.format(r.value, context);
+      } catch (e) {
+        return context.error(String(e), `match the format "${this.format.name}"`);
+      }
+    }
+
+    return r;
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "string";
+  }
+
+  inject(path, name, dest, context) {
+    if (this.enumeration) {
+      exportLazyGetter(dest, name, () => {
+        let obj = Cu.createObjectIn(dest);
+        for (let e of this.enumeration) {
+          obj[e.toUpperCase()] = e;
+        }
+        return obj;
+      });
+    }
+  }
+}
+
+let SubModuleType;
+class ObjectType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["properties", "patternProperties", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    if ("functions" in schema) {
+      return SubModuleType.parseSchema(schema, path, extraProperties);
+    }
+
+    if (!("$extend" in schema)) {
+      // Only allow extending "properties" and "patternProperties".
+      extraProperties = ["additionalProperties", "isInstanceOf", ...extraProperties];
+    }
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    let parseProperty = (schema, extraProps = []) => {
+      return {
+        type: Schemas.parseSchema(schema, path,
+                                  ["unsupported", "onError", "permissions", ...extraProps]),
+        optional: schema.optional || false,
+        unsupported: schema.unsupported || false,
+        onError: schema.onError || null,
+      };
+    };
+
+    // Parse explicit "properties" object.
+    let properties = Object.create(null);
+    for (let propName of Object.keys(schema.properties || {})) {
+      properties[propName] = parseProperty(schema.properties[propName], ["optional"]);
+    }
+
+    // Parse regexp properties from "patternProperties" object.
+    let patternProperties = [];
+    for (let propName of Object.keys(schema.patternProperties || {})) {
+      let pattern;
+      try {
+        pattern = parsePattern(propName);
+      } catch (e) {
+        throw new Error(`Internal error: Invalid property pattern ${JSON.stringify(propName)}`);
+      }
+
+      patternProperties.push({
+        pattern,
+        type: parseProperty(schema.patternProperties[propName]),
+      });
+    }
+
+    // Parse "additionalProperties" schema.
+    let additionalProperties = null;
+    if (schema.additionalProperties) {
+      let type = schema.additionalProperties;
+      if (type === true) {
+        type = {"type": "any"};
+      }
+
+      additionalProperties = Schemas.parseSchema(type, path);
+    }
+
+    return new this(schema, properties, additionalProperties, patternProperties, schema.isInstanceOf || null);
+  }
+
+  constructor(schema, properties, additionalProperties, patternProperties, isInstanceOf) {
+    super(schema);
+    this.properties = properties;
+    this.additionalProperties = additionalProperties;
+    this.patternProperties = patternProperties;
+    this.isInstanceOf = isInstanceOf;
+  }
+
+  extend(type) {
+    for (let key of Object.keys(type.properties)) {
+      if (key in this.properties) {
+        throw new Error(`InternalError: Attempt to extend an object with conflicting property "${key}"`);
+      }
+      this.properties[key] = type.properties[key];
+    }
+
+    this.patternProperties.push(...type.patternProperties);
+
+    return this;
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "object";
+  }
+
+  /**
+   * Extracts the enumerable properties of the given object, including
+   * function properties which would normally be omitted by X-ray
+   * wrappers.
+   *
+   * @param {object} value
+   * @param {Context} context
+   *        The current parse context.
+   * @returns {object}
+   *        An object with an `error` or `value` property.
+   */
+  extractProperties(value, context) {
+    // |value| should be a JS Xray wrapping an object in the
+    // extension compartment. This works well except when we need to
+    // access callable properties on |value| since JS Xrays don't
+    // support those. To work around the problem, we verify that
+    // |value| is a plain JS object (i.e., not anything scary like a
+    // Proxy). Then we copy the properties out of it into a normal
+    // object using a waiver wrapper.
+
+    let klass = Cu.getClassName(value, true);
+    if (klass != "Object") {
+      throw context.error(`Expected a plain JavaScript object, got a ${klass}`,
+                          `be a plain JavaScript object`);
+    }
+
+    let properties = Object.create(null);
+
+    let waived = Cu.waiveXrays(value);
+    for (let prop of Object.getOwnPropertyNames(waived)) {
+      let desc = Object.getOwnPropertyDescriptor(waived, prop);
+      if (desc.get || desc.set) {
+        throw context.error("Objects cannot have getters or setters on properties",
+                            "contain no getter or setter properties");
+      }
+      // Chrome ignores non-enumerable properties.
+      if (desc.enumerable) {
+        properties[prop] = Cu.unwaiveXrays(desc.value);
+      }
+    }
+
+    return properties;
+  }
+
+  checkProperty(context, prop, propType, result, properties, remainingProps) {
+    let {type, optional, unsupported, onError} = propType;
+    let error = null;
+
+    if (unsupported) {
+      if (prop in properties) {
+        error = context.error(`Property "${prop}" is unsupported by Firefox`,
+                              `not contain an unsupported "${prop}" property`);
+      }
+    } else if (prop in properties) {
+      if (optional && (properties[prop] === null || properties[prop] === undefined)) {
+        result[prop] = null;
+      } else {
+        let r = context.withPath(prop, () => type.normalize(properties[prop], context));
+        if (r.error) {
+          error = r;
+        } else {
+          result[prop] = r.value;
+          properties[prop] = r.value;
+        }
+      }
+      remainingProps.delete(prop);
+    } else if (!optional) {
+      error = context.error(`Property "${prop}" is required`,
+                            `contain the required "${prop}" property`);
+    } else if (optional !== "omit-key-if-missing") {
+      result[prop] = null;
+    }
+
+    if (error) {
+      if (onError == "warn") {
+        context.logError(error.error);
+      } else if (onError != "ignore") {
+        throw error;
+      }
+
+      result[prop] = null;
+    }
+  }
+
+  normalize(value, context) {
+    try {
+      let v = this.normalizeBase("object", value, context);
+      if (v.error) {
+        return v;
+      }
+      value = v.value;
+
+      if (this.isInstanceOf) {
+        if (Object.keys(this.properties).length ||
+            this.patternProperties.length ||
+            !(this.additionalProperties instanceof AnyType)) {
+          throw new Error("InternalError: isInstanceOf can only be used with objects that are otherwise unrestricted");
+        }
+
+        if (!instanceOf(value, this.isInstanceOf)) {
+          return context.error(`Object must be an instance of ${this.isInstanceOf}`,
+                               `be an instance of ${this.isInstanceOf}`);
+        }
+
+        // This is kind of a hack, but we can't normalize things that
+        // aren't JSON, so we just return them.
+        return this.postprocess({value}, context);
+      }
+
+      let properties = this.extractProperties(value, context);
+      let remainingProps = new Set(Object.keys(properties));
+
+      let result = {};
+      for (let prop of Object.keys(this.properties)) {
+        this.checkProperty(context, prop, this.properties[prop], result,
+                           properties, remainingProps);
+      }
+
+      for (let prop of Object.keys(properties)) {
+        for (let {pattern, type} of this.patternProperties) {
+          if (pattern.test(prop)) {
+            this.checkProperty(context, prop, type, result,
+                               properties, remainingProps);
+          }
+        }
+      }
+
+      if (this.additionalProperties) {
+        for (let prop of remainingProps) {
+          let type = this.additionalProperties;
+          let r = context.withPath(prop, () => type.normalize(properties[prop], context));
+          if (r.error) {
+            return r;
+          }
+          result[prop] = r.value;
+        }
+      } else if (remainingProps.size == 1) {
+        return context.error(`Unexpected property "${[...remainingProps]}"`,
+                             `not contain an unexpected "${[...remainingProps]}" property`);
+      } else if (remainingProps.size) {
+        let props = [...remainingProps].sort().join(", ");
+        return context.error(`Unexpected properties: ${props}`,
+                             `not contain the unexpected properties [${props}]`);
+      }
+
+      return this.postprocess({value: result}, context);
+    } catch (e) {
+      if (e.error) {
+        return e;
+      }
+      throw e;
+    }
+  }
+}
+
+// This type is just a placeholder to be referred to by
+// SubModuleProperty. No value is ever expected to have this type.
+SubModuleType = class SubModuleType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["functions", "events", "properties", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    // The path we pass in here is only used for error messages.
+    path = [...path, schema.id];
+    let functions = schema.functions.map(fun => Schemas.parseFunction(path, fun));
+
+    return new this(functions);
+  }
+
+  constructor(functions) {
+    super();
+    this.functions = functions;
+  }
+};
+
+class NumberType extends Type {
+  normalize(value, context) {
+    let r = this.normalizeBase("number", value, context);
+    if (r.error) {
+      return r;
+    }
+
+    if (isNaN(r.value) || !Number.isFinite(r.value)) {
+      return context.error("NaN and infinity are not valid",
+                           "be a finite number");
+    }
+
+    return r;
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "number" || baseType == "integer";
+  }
+}
+
+class IntegerType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["minimum", "maximum", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    return new this(schema, schema.minimum || -Infinity, schema.maximum || Infinity);
+  }
+
+  constructor(schema, minimum, maximum) {
+    super(schema);
+    this.minimum = minimum;
+    this.maximum = maximum;
+  }
+
+  normalize(value, context) {
+    let r = this.normalizeBase("integer", value, context);
+    if (r.error) {
+      return r;
+    }
+    value = r.value;
+
+    // Ensure it's between -2**31 and 2**31-1
+    if (!Number.isSafeInteger(value)) {
+      return context.error("Integer is out of range",
+                           "be a valid 32 bit signed integer");
+    }
+
+    if (value < this.minimum) {
+      return context.error(`Integer ${value} is too small (must be at least ${this.minimum})`,
+                           `be at least ${this.minimum}`);
+    }
+    if (value > this.maximum) {
+      return context.error(`Integer ${value} is too big (must be at most ${this.maximum})`,
+                           `be no greater than ${this.maximum}`);
+    }
+
+    return this.postprocess(r, context);
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "integer";
+  }
+}
+
+class BooleanType extends Type {
+  normalize(value, context) {
+    return this.normalizeBase("boolean", value, context);
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "boolean";
+  }
+}
+
+class ArrayType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["items", "minItems", "maxItems", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    let items = Schemas.parseSchema(schema.items, path);
+
+    return new this(schema, items, schema.minItems || 0, schema.maxItems || Infinity);
+  }
+
+  constructor(schema, itemType, minItems, maxItems) {
+    super(schema);
+    this.itemType = itemType;
+    this.minItems = minItems;
+    this.maxItems = maxItems;
+  }
+
+  normalize(value, context) {
+    let v = this.normalizeBase("array", value, context);
+    if (v.error) {
+      return v;
+    }
+    value = v.value;
+
+    let result = [];
+    for (let [i, element] of value.entries()) {
+      element = context.withPath(String(i), () => this.itemType.normalize(element, context));
+      if (element.error) {
+        return element;
+      }
+      result.push(element.value);
+    }
+
+    if (result.length < this.minItems) {
+      return context.error(`Array requires at least ${this.minItems} items; you have ${result.length}`,
+                           `have at least ${this.minItems} items`);
+    }
+
+    if (result.length > this.maxItems) {
+      return context.error(`Array requires at most ${this.maxItems} items; you have ${result.length}`,
+                           `have at most ${this.maxItems} items`);
+    }
+
+    return this.postprocess({value: result}, context);
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "array";
+  }
+}
+
+class FunctionType extends Type {
+  static get EXTRA_PROPERTIES() {
+    return ["parameters", "async", "returns", ...super.EXTRA_PROPERTIES];
+  }
+
+  static parseSchema(schema, path, extraProperties = []) {
+    this.checkSchemaProperties(schema, path, extraProperties);
+
+    let isAsync = !!schema.async;
+    let isExpectingCallback = typeof schema.async === "string";
+    let parameters = null;
+    if ("parameters" in schema) {
+      parameters = [];
+      for (let param of schema.parameters) {
+        // Callbacks default to optional for now, because of promise
+        // handling.
+        let isCallback = isAsync && param.name == schema.async;
+        if (isCallback) {
+          isExpectingCallback = false;
+        }
+
+        parameters.push({
+          type: Schemas.parseSchema(param, path, ["name", "optional", "default"]),
+          name: param.name,
+          optional: param.optional == null ? isCallback : param.optional,
+          default: param.default == undefined ? null : param.default,
+        });
+      }
+    }
+    if (isExpectingCallback) {
+      throw new Error(`Internal error: Expected a callback parameter with name ${schema.async}`);
+    }
+
+    let hasAsyncCallback = false;
+    if (isAsync) {
+      hasAsyncCallback = (parameters &&
+                          parameters.length &&
+                          parameters[parameters.length - 1].name == schema.async);
+
+      if (schema.returns) {
+        throw new Error("Internal error: Async functions must not have return values.");
+      }
+      if (schema.allowAmbiguousOptionalArguments && !hasAsyncCallback) {
+        throw new Error("Internal error: Async functions with ambiguous arguments must declare the callback as the last parameter");
+      }
+    }
+
+    return new this(schema, parameters, isAsync, hasAsyncCallback);
+  }
+
+  constructor(schema, parameters, isAsync, hasAsyncCallback) {
+    super(schema);
+    this.parameters = parameters;
+    this.isAsync = isAsync;
+    this.hasAsyncCallback = hasAsyncCallback;
+  }
+
+  normalize(value, context) {
+    return this.normalizeBase("function", value, context);
+  }
+
+  checkBaseType(baseType) {
+    return baseType == "function";
+  }
+}
+
+// Represents a "property" defined in a schema namespace with a
+// particular value. Essentially this is a constant.
+class ValueProperty extends Entry {
+  constructor(schema, name, value) {
+    super(schema);
+    this.name = name;
+    this.value = value;
+  }
+
+  inject(path, name, dest, context) {
+    dest[name] = this.value;
+  }
+}
+
+// Represents a "property" defined in a schema namespace that is not a
+// constant.
+class TypeProperty extends Entry {
+  constructor(schema, namespaceName, name, type, writable) {
+    super(schema);
+    this.namespaceName = namespaceName;
+    this.name = name;
+    this.type = type;
+    this.writable = writable;
+  }
+
+  throwError(context, msg) {
+    throw context.makeError(`${msg} for ${this.namespaceName}.${this.name}.`);
+  }
+
+  inject(path, name, dest, context) {
+    if (this.unsupported) {
+      return;
+    }
+
+    let apiImpl = context.getImplementation(path.join("."), name);
+
+    let getStub = () => {
+      this.checkDeprecated(context);
+      return apiImpl.getProperty();
+    };
+
+    let desc = {
+      configurable: false,
+      enumerable: true,
+
+      get: Cu.exportFunction(getStub, dest),
+    };
+
+    if (this.writable) {
+      let setStub = (value) => {
+        let normalized = this.type.normalize(value, context);
+        if (normalized.error) {
+          this.throwError(context, normalized.error);
+        }
+
+        apiImpl.setProperty(normalized.value);
+      };
+
+      desc.set = Cu.exportFunction(setStub, dest);
+    }
+
+    Object.defineProperty(dest, name, desc);
+  }
+}
+
+class SubModuleProperty extends Entry {
+  // A SubModuleProperty represents a tree of objects and properties
+  // to expose to an extension. Currently we support only a limited
+  // form of sub-module properties, where "$ref" points to a
+  // SubModuleType containing a list of functions and "properties" is
+  // a list of additional simple properties.
+  //
+  // name: Name of the property stuff is being added to.
+  // namespaceName: Namespace in which the property lives.
+  // reference: Name of the type defining the functions to add to the property.
+  // properties: Additional properties to add to the module (unsupported).
+  constructor(schema, name, namespaceName, reference, properties) {
+    super(schema);
+    this.name = name;
+    this.namespaceName = namespaceName;
+    this.reference = reference;
+    this.properties = properties;
+  }
+
+  inject(path, name, dest, context) {
+    exportLazyGetter(dest, name, () => {
+      let obj = Cu.createObjectIn(dest);
+
+      let ns = Schemas.namespaces.get(this.namespaceName);
+      let type = ns.get(this.reference);
+      if (!type && this.reference.includes(".")) {
+        let [namespaceName, ref] = this.reference.split(".");
+        ns = Schemas.namespaces.get(namespaceName);
+        type = ns.get(ref);
+      }
+      if (!type || !(type instanceof SubModuleType)) {
+        throw new Error(`Internal error: ${this.namespaceName}.${this.reference} is not a sub-module`);
+      }
+
+      let functions = type.functions;
+      for (let fun of functions) {
+        let subpath = path.concat(name);
+        let namespace = subpath.join(".");
+        let allowedContexts = fun.allowedContexts.length ? fun.allowedContexts : ns.defaultContexts;
+        if (context.shouldInject(namespace, fun.name, allowedContexts)) {
+          fun.inject(subpath, fun.name, obj, context);
+        }
+      }
+
+      // TODO: Inject this.properties.
+
+      return obj;
+    });
+  }
+}
+
+// This class is a base class for FunctionEntrys and Events. It takes
+// care of validating parameter lists (i.e., handling of optional
+// parameters and parameter type checking).
+class CallEntry extends Entry {
+  constructor(schema, path, name, parameters, allowAmbiguousOptionalArguments) {
+    super(schema);
+    this.path = path;
+    this.name = name;
+    this.parameters = parameters;
+    this.allowAmbiguousOptionalArguments = allowAmbiguousOptionalArguments;
+  }
+
+  throwError(context, msg) {
+    throw context.makeError(`${msg} for ${this.path.join(".")}.${this.name}.`);
+  }
+
+  checkParameters(args, context) {
+    let fixedArgs = [];
+
+    // First we create a new array, fixedArgs, that is the same as
+    // |args| but with default values in place of omitted optional parameters.
+    let check = (parameterIndex, argIndex) => {
+      if (parameterIndex == this.parameters.length) {
+        if (argIndex == args.length) {
+          return true;
+        }
+        return false;
+      }
+
+      let parameter = this.parameters[parameterIndex];
+      if (parameter.optional) {
+        // Try skipping it.
+        fixedArgs[parameterIndex] = parameter.default;
+        if (check(parameterIndex + 1, argIndex)) {
+          return true;
+        }
+      }
+
+      if (argIndex == args.length) {
+        return false;
+      }
+
+      let arg = args[argIndex];
+      if (!parameter.type.checkBaseType(getValueBaseType(arg))) {
+        // For Chrome compatibility, use the default value if null or undefined
+        // is explicitly passed but is not a valid argument in this position.
+        if (parameter.optional && (arg === null || arg === undefined)) {
+          fixedArgs[parameterIndex] = Cu.cloneInto(parameter.default, global);
+        } else {
+          return false;
+        }
+      } else {
+        fixedArgs[parameterIndex] = arg;
+      }
+
+      return check(parameterIndex + 1, argIndex + 1);
+    };
+
+    if (this.allowAmbiguousOptionalArguments) {
+      // When this option is set, it's up to the implementation to
+      // parse arguments.
+      // The last argument for asynchronous methods is either a function or null.
+      // This is specifically done for runtime.sendMessage.
+      if (this.hasAsyncCallback && typeof(args[args.length - 1]) != "function") {
+        args.push(null);
+      }
+      return args;
+    }
+    let success = check(0, 0);
+    if (!success) {
+      this.throwError(context, "Incorrect argument types");
+    }
+
+    // Now we normalize (and fully type check) all non-omitted arguments.
+    fixedArgs = fixedArgs.map((arg, parameterIndex) => {
+      if (arg === null) {
+        return null;
+      }
+      let parameter = this.parameters[parameterIndex];
+      let r = parameter.type.normalize(arg, context);
+      if (r.error) {
+        this.throwError(context, `Type error for parameter ${parameter.name} (${r.error})`);
+      }
+      return r.value;
+    });
+
+    return fixedArgs;
+  }
+}
+
+// Represents a "function" defined in a schema namespace.
+class FunctionEntry extends CallEntry {
+  constructor(schema, path, name, type, unsupported, allowAmbiguousOptionalArguments, returns, permissions) {
+    super(schema, path, name, type.parameters, allowAmbiguousOptionalArguments);
+    this.unsupported = unsupported;
+    this.returns = returns;
+    this.permissions = permissions;
+
+    this.isAsync = type.isAsync;
+    this.hasAsyncCallback = type.hasAsyncCallback;
+  }
+
+  inject(path, name, dest, context) {
+    if (this.unsupported) {
+      return;
+    }
+
+    if (this.permissions && !this.permissions.some(perm => context.hasPermission(perm))) {
+      return;
+    }
+
+    exportLazyGetter(dest, name, () => {
+      let apiImpl = context.getImplementation(path.join("."), name);
+
+      let stub;
+      if (this.isAsync) {
+        stub = (...args) => {
+          this.checkDeprecated(context);
+          let actuals = this.checkParameters(args, context);
+          let callback = null;
+          if (this.hasAsyncCallback) {
+            callback = actuals.pop();
+          }
+          if (callback === null && context.isChromeCompat) {
+            // We pass an empty stub function as a default callback for
+            // the `chrome` API, so promise objects are not returned,
+            // and lastError values are reported immediately.
+            callback = () => {};
+          }
+          return apiImpl.callAsyncFunction(actuals, callback);
+        };
+      } else if (!this.returns) {
+        stub = (...args) => {
+          this.checkDeprecated(context);
+          let actuals = this.checkParameters(args, context);
+          return apiImpl.callFunctionNoReturn(actuals);
+        };
+      } else {
+        stub = (...args) => {
+          this.checkDeprecated(context);
+          let actuals = this.checkParameters(args, context);
+          return apiImpl.callFunction(actuals);
+        };
+      }
+      return Cu.exportFunction(stub, dest);
+    });
+  }
+}
+
+// Represents an "event" defined in a schema namespace.
+class Event extends CallEntry {
+  constructor(schema, path, name, type, extraParameters, unsupported, permissions) {
+    super(schema, path, name, extraParameters);
+    this.type = type;
+    this.unsupported = unsupported;
+    this.permissions = permissions;
+  }
+
+  checkListener(listener, context) {
+    let r = this.type.normalize(listener, context);
+    if (r.error) {
+      this.throwError(context, "Invalid listener");
+    }
+    return r.value;
+  }
+
+  inject(path, name, dest, context) {
+    if (this.unsupported) {
+      return;
+    }
+
+    if (this.permissions && !this.permissions.some(perm => context.hasPermission(perm))) {
+      return;
+    }
+
+    exportLazyGetter(dest, name, () => {
+      let apiImpl = context.getImplementation(path.join("."), name);
+
+      let addStub = (listener, ...args) => {
+        listener = this.checkListener(listener, context);
+        let actuals = this.checkParameters(args, context);
+        apiImpl.addListener(listener, actuals);
+      };
+
+      let removeStub = (listener) => {
+        listener = this.checkListener(listener, context);
+        apiImpl.removeListener(listener);
+      };
+
+      let hasStub = (listener) => {
+        listener = this.checkListener(listener, context);
+        return apiImpl.hasListener(listener);
+      };
+
+      let obj = Cu.createObjectIn(dest);
+
+      Cu.exportFunction(addStub, obj, {defineAs: "addListener"});
+      Cu.exportFunction(removeStub, obj, {defineAs: "removeListener"});
+      Cu.exportFunction(hasStub, obj, {defineAs: "hasListener"});
+
+      return obj;
+    });
+  }
+}
+
+const TYPES = Object.freeze(Object.assign(Object.create(null), {
+  any: AnyType,
+  array: ArrayType,
+  boolean: BooleanType,
+  function: FunctionType,
+  integer: IntegerType,
+  number: NumberType,
+  object: ObjectType,
+  string: StringType,
+}));
+
+this.Schemas = {
+  initialized: false,
+
+  // Maps a schema URL to the JSON contained in that schema file. This
+  // is useful for sending the JSON across processes.
+  schemaJSON: new Map(),
+
+  // Map[<schema-name> -> Map[<symbol-name> -> Entry]]
+  // This keeps track of all the schemas that have been loaded so far.
+  namespaces: new Map(),
+
+  register(namespaceName, symbol, value) {
+    let ns = this.namespaces.get(namespaceName);
+    if (!ns) {
+      ns = new Map();
+      ns.name = namespaceName;
+      ns.permissions = null;
+      ns.allowedContexts = [];
+      ns.defaultContexts = [];
+      this.namespaces.set(namespaceName, ns);
+    }
+    ns.set(symbol, value);
+  },
+
+  parseSchema(schema, path, extraProperties = []) {
+    let allowedProperties = new Set(extraProperties);
+
+    if ("choices" in schema) {
+      return ChoiceType.parseSchema(schema, path, allowedProperties);
+    } else if ("$ref" in schema) {
+      return RefType.parseSchema(schema, path, allowedProperties);
+    }
+
+    if (!("type" in schema)) {
+      throw new Error(`Unexpected value for type: ${JSON.stringify(schema)}`);
+    }
+
+    allowedProperties.add("type");
+
+    let type = TYPES[schema.type];
+    if (!type) {
+      throw new Error(`Unexpected type ${schema.type}`);
+    }
+    return type.parseSchema(schema, path, allowedProperties);
+  },
+
+  parseFunction(path, fun) {
+    let f = new FunctionEntry(fun, path, fun.name,
+                              this.parseSchema(fun, path,
+                                               ["name", "unsupported", "returns",
+                                                "permissions",
+                                                "allowAmbiguousOptionalArguments"]),
+                              fun.unsupported || false,
+                              fun.allowAmbiguousOptionalArguments || false,
+                              fun.returns || null,
+                              fun.permissions || null);
+    return f;
+  },
+
+  loadType(namespaceName, type) {
+    if ("$extend" in type) {
+      this.extendType(namespaceName, type);
+    } else {
+      this.register(namespaceName, type.id, this.parseSchema(type, [namespaceName], ["id"]));
+    }
+  },
+
+  extendType(namespaceName, type) {
+    let ns = Schemas.namespaces.get(namespaceName);
+    let targetType = ns && ns.get(type.$extend);
+
+    // Only allow extending object and choices types for now.
+    if (targetType instanceof ObjectType) {
+      type.type = "object";
+    } else if (!targetType) {
+      throw new Error(`Internal error: Attempt to extend a nonexistant type ${type.$extend}`);
+    } else if (!(targetType instanceof ChoiceType)) {
+      throw new Error(`Internal error: Attempt to extend a non-extensible type ${type.$extend}`);
+    }
+
+    let parsed = this.parseSchema(type, [namespaceName], ["$extend"]);
+    if (parsed.constructor !== targetType.constructor) {
+      throw new Error(`Internal error: Bad attempt to extend ${type.$extend}`);
+    }
+
+    targetType.extend(parsed);
+  },
+
+  loadProperty(namespaceName, name, prop) {
+    if ("$ref" in prop) {
+      if (!prop.unsupported) {
+        this.register(namespaceName, name, new SubModuleProperty(prop, name, namespaceName, prop.$ref,
+                                                                 prop.properties || {}));
+      }
+    } else if ("value" in prop) {
+      this.register(namespaceName, name, new ValueProperty(prop, name, prop.value));
+    } else {
+      // We ignore the "optional" attribute on properties since we
+      // don't inject anything here anyway.
+      let type = this.parseSchema(prop, [namespaceName], ["optional", "writable"]);
+      this.register(namespaceName, name, new TypeProperty(prop, namespaceName, name, type, prop.writable || false));
+    }
+  },
+
+  loadFunction(namespaceName, fun) {
+    let f = this.parseFunction([namespaceName], fun);
+    this.register(namespaceName, fun.name, f);
+  },
+
+  loadEvent(namespaceName, event) {
+    let extras = event.extraParameters || [];
+    extras = extras.map(param => {
+      return {
+        type: this.parseSchema(param, [namespaceName], ["name", "optional", "default"]),
+        name: param.name,
+        optional: param.optional || false,
+        default: param.default == undefined ? null : param.default,
+      };
+    });
+
+    // We ignore these properties for now.
+    /* eslint-disable no-unused-vars */
+    let returns = event.returns;
+    let filters = event.filters;
+    /* eslint-enable no-unused-vars */
+
+    let type = this.parseSchema(event, [namespaceName],
+                                ["name", "unsupported", "permissions",
+                                 "extraParameters", "returns", "filters"]);
+
+    let e = new Event(event, [namespaceName], event.name, type, extras,
+                      event.unsupported || false,
+                      event.permissions || null);
+    this.register(namespaceName, event.name, e);
+  },
+
+  init() {
+    if (this.initialized) {
+      return;
+    }
+    this.initialized = true;
+
+    if (Services.appinfo.processType == Services.appinfo.PROCESS_TYPE_CONTENT) {
+      let data = Services.cpmm.initialProcessData;
+      let schemas = data["Extension:Schemas"];
+      if (schemas) {
+        this.schemaJSON = schemas;
+      }
+      Services.cpmm.addMessageListener("Schema:Add", this);
+    }
+
+    this.flushSchemas();
+  },
+
+  receiveMessage(msg) {
+    switch (msg.name) {
+      case "Schema:Add":
+        this.schemaJSON.set(msg.data.url, msg.data.schema);
+        this.flushSchemas();
+        break;
+
+      case "Schema:Delete":
+        this.schemaJSON.delete(msg.data.url);
+        this.flushSchemas();
+        break;
+    }
+  },
+
+  flushSchemas() {
+    XPCOMUtils.defineLazyGetter(this, "namespaces",
+                                () => this.parseSchemas());
+  },
+
+  parseSchemas() {
+    Object.defineProperty(this, "namespaces", {
+      enumerable: true,
+      configurable: true,
+      value: new Map(),
+    });
+
+    for (let json of this.schemaJSON.values()) {
+      try {
+        this.loadSchema(json);
+      } catch (e) {
+        Cu.reportError(e);
+      }
+    }
+
+    return this.namespaces;
+  },
+
+  loadSchema(json) {
+    for (let namespace of json) {
+      let name = namespace.namespace;
+
+      let types = namespace.types || [];
+      for (let type of types) {
+        this.loadType(name, type);
+      }
+
+      let properties = namespace.properties || {};
+      for (let propertyName of Object.keys(properties)) {
+        this.loadProperty(name, propertyName, properties[propertyName]);
+      }
+
+      let functions = namespace.functions || [];
+      for (let fun of functions) {
+        this.loadFunction(name, fun);
+      }
+
+      let events = namespace.events || [];
+      for (let event of events) {
+        this.loadEvent(name, event);
+      }
+
+      let ns = this.namespaces.get(name);
+      ns.permissions = namespace.permissions || null;
+      ns.allowedContexts = namespace.allowedContexts || [];
+      ns.defaultContexts = namespace.defaultContexts || [];
+    }
+  },
+
+  load(url) {
+    if (Services.appinfo.processType != Services.appinfo.PROCESS_TYPE_CONTENT) {
+      return readJSON(url).then(json => {
+        this.schemaJSON.set(url, json);
+
+        let data = Services.ppmm.initialProcessData;
+        data["Extension:Schemas"] = this.schemaJSON;
+
+        Services.ppmm.broadcastAsyncMessage("Schema:Add", {url, schema: json});
+
+        this.flushSchemas();
+      });
+    }
+  },
+
+  unload(url) {
+    this.schemaJSON.delete(url);
+
+    let data = Services.ppmm.initialProcessData;
+    data["Extension:Schemas"] = this.schemaJSON;
+
+    Services.ppmm.broadcastAsyncMessage("Schema:Delete", {url});
+
+    this.flushSchemas();
+  },
+
+  /**
+   * Checks whether a given object has the necessary permissions to
+   * expose the given namespace.
+   *
+   * @param {string} namespace
+   *        The top-level namespace to check permissions for.
+   * @param {object} wrapperFuncs
+   *        Wrapper functions for the given context.
+   * @param {function} wrapperFuncs.hasPermission
+   *        A function which, when given a string argument, returns true
+   *        if the context has the given permission.
+   * @returns {boolean}
+   *        True if the context has permission for the given namespace.
+   */
+  checkPermissions(namespace, wrapperFuncs) {
+    let ns = this.namespaces.get(namespace);
+    if (ns && ns.permissions) {
+      return ns.permissions.some(perm => wrapperFuncs.hasPermission(perm));
+    }
+    return true;
+  },
+
+  exportLazyGetter,
+
+  /**
+   * Inject registered extension APIs into `dest`.
+   *
+   * @param {object} dest The root namespace for the APIs.
+   *     This object is usually exposed to extensions as "chrome" or "browser".
+   * @param {object} wrapperFuncs An implementation of the InjectionContext
+   *     interface, which runs the actual functionality of the generated API.
+   */
+  inject(dest, wrapperFuncs) {
+    let context = new InjectionContext(wrapperFuncs);
+
+    let createNamespace = ns => {
+      let obj = Cu.createObjectIn(dest);
+
+      for (let [name, entry] of ns) {
+        let allowedContexts = entry.allowedContexts;
+        if (!allowedContexts.length) {
+          allowedContexts = ns.defaultContexts;
+        }
+
+        if (context.shouldInject(ns.name, name, allowedContexts)) {
+          entry.inject([ns.name], name, obj, context);
+        }
+      }
+
+      // Remove the namespace object if it is empty
+      if (Object.keys(obj).length) {
+        return obj;
+      }
+    };
+
+    let createNestedNamespaces = (parent, namespaces) => {
+      for (let [prop, namespace] of namespaces) {
+        if (namespace instanceof DeepMap) {
+          exportLazyGetter(parent, prop, () => {
+            let obj = Cu.createObjectIn(parent);
+            createNestedNamespaces(obj, namespace);
+            return obj;
+          });
+        } else {
+          exportLazyGetter(parent, prop,
+                           () => createNamespace(namespace));
+        }
+      }
+    };
+
+    let nestedNamespaces = new DeepMap();
+    for (let ns of this.namespaces.values()) {
+      if (ns.permissions && !ns.permissions.some(perm => context.hasPermission(perm))) {
+        continue;
+      }
+
+      if (!wrapperFuncs.shouldInject(ns.name, null, ns.allowedContexts)) {
+        continue;
+      }
+
+      if (ns.name.includes(".")) {
+        let path = ns.name.split(".");
+        let leafName = path.pop();
+
+        let parent = nestedNamespaces.getPath(...path);
+
+        parent.set(leafName, ns);
+      } else {
+        exportLazyGetter(dest, ns.name,
+                         () => createNamespace(ns));
+      }
+    }
+
+    createNestedNamespaces(dest, nestedNamespaces);
+  },
+
+  /**
+   * Normalize `obj` according to the loaded schema for `typeName`.
+   *
+   * @param {object} obj The object to normalize against the schema.
+   * @param {string} typeName The name in the format namespace.propertyname
+   * @param {object} context An implementation of Context. Any validation errors
+   *     are reported to the given context.
+   * @returns {object} The normalized object.
+   */
+  normalize(obj, typeName, context) {
+    let [namespaceName, prop] = typeName.split(".");
+    let ns = this.namespaces.get(namespaceName);
+    let type = ns.get(prop);
+
+    return type.normalize(obj, new Context(context));
+  },
+};