pdf_scripting_api.js

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * Turn a dictionary received from postMessage into a key event.
 * @param {Object} dict A dictionary representing the key event.
 * @return {Event} A key event.
 */
function DeserializeKeyEvent(dict) {
  var e = document.createEvent('Event');
  e.initEvent('keydown', true, true);
  e.keyCode = dict.keyCode;
  e.shiftKey = dict.shiftKey;
  e.ctrlKey = dict.ctrlKey;
  e.altKey = dict.altKey;
  e.metaKey = dict.metaKey;
  e.fromScriptingAPI = true;
  return e;
}

/**
 * Turn a key event into a dictionary which can be sent over postMessage.
 * @param {Event} event A key event.
 * @return {Object} A dictionary representing the key event.
 */
function SerializeKeyEvent(event) {
  return {
    keyCode: event.keyCode,
    shiftKey: event.shiftKey,
    ctrlKey: event.ctrlKey,
    altKey: event.altKey,
    metaKey: event.metaKey
  };
}

/**
 * An enum containing a value specifying whether the PDF is currently loading,
 * has finished loading or failed to load.
 * @enum {string}
 */
var LoadState = {LOADING: 'loading', SUCCESS: 'success', FAILED: 'failed'};

/**
 * Create a new PDFScriptingAPI. This provides a scripting interface to
 * the PDF viewer so that it can be customized by things like print preview.
 * @param {Window} window the window of the page containing the pdf viewer.
 * @param {Object} plugin the plugin element containing the pdf viewer.
 * @constructor
 */
function PDFScriptingAPI(window, plugin) {
  this.loadState_ = LoadState.LOADING;
  this.pendingScriptingMessages_ = [];
  this.setPlugin(plugin);

  window.addEventListener('message', event => {
    if (event.origin != 'chrome://pdf-viewer' &&
        event.origin != 'chrome://print') {
      console.error(
          'Received message that was not from the extension: ' + event);
      return;
    }
    switch (event.data.type) {
      case 'viewport':
        /**
         * @type {{
         *   pageX: number,
         *   pageY: number,
         *   pageWidth: number,
         *   viewportWidth: number,
         *   viewportHeight: number
         * }}
         */
        var viewportData = event.data;
        if (this.viewportChangedCallback_)
          this.viewportChangedCallback_(
              viewportData.pageX, viewportData.pageY, viewportData.pageWidth,
              viewportData.viewportWidth, viewportData.viewportHeight);
        break;
      case 'documentLoaded':
        var data = /** @type {{load_state: LoadState}} */ (event.data);
        this.loadState_ = data.load_state;
        if (this.loadCallback_)
          this.loadCallback_(this.loadState_ == LoadState.SUCCESS);
        break;
      case 'getSelectedTextReply':
        var data = /** @type {{selectedText: string}} */ (event.data);
        if (this.selectedTextCallback_) {
          this.selectedTextCallback_(data.selectedText);
          this.selectedTextCallback_ = null;
        }
        break;
      case 'sendKeyEvent':
        if (this.keyEventCallback_)
          this.keyEventCallback_(DeserializeKeyEvent(event.data.keyEvent));
        break;
    }
  }, false);
}

PDFScriptingAPI.prototype = {
  /**
   * @private
   * Send a message to the extension. If messages try to get sent before there
   * is a plugin element set, then we queue them up and send them later (this
   * can happen in print preview).
   * @param {Object} message The message to send.
   */
  sendMessage_: function(message) {
    if (this.plugin_)
      this.plugin_.postMessage(message, '*');
    else
      this.pendingScriptingMessages_.push(message);
  },

  /**
   * Sets the plugin element containing the PDF viewer. The element will usually
   * be passed into the PDFScriptingAPI constructor but may also be set later.
   * @param {Object} plugin the plugin element containing the PDF viewer.
   */
  setPlugin: function(plugin) {
    this.plugin_ = plugin;

    if (this.plugin_) {
      // Send a message to ensure the postMessage channel is initialized which
      // allows us to receive messages.
      this.sendMessage_({type: 'initialize'});
      // Flush pending messages.
      while (this.pendingScriptingMessages_.length > 0)
        this.sendMessage_(this.pendingScriptingMessages_.shift());
    }
  },

  /**
   * Sets the callback which will be run when the PDF viewport changes.
   * @param {Function} callback the callback to be called.
   */
  setViewportChangedCallback: function(callback) {
    this.viewportChangedCallback_ = callback;
  },

  /**
   * Sets the callback which will be run when the PDF document has finished
   * loading. If the document is already loaded, it will be run immediately.
   * @param {Function} callback the callback to be called.
   */
  setLoadCallback: function(callback) {
    this.loadCallback_ = callback;
    if (this.loadState_ != LoadState.LOADING && this.loadCallback_)
      this.loadCallback_(this.loadState_ == LoadState.SUCCESS);
  },

  /**
   * Sets a callback that gets run when a key event is fired in the PDF viewer.
   * @param {Function} callback the callback to be called with a key event.
   */
  setKeyEventCallback: function(callback) {
    this.keyEventCallback_ = callback;
  },

  /**
   * Resets the PDF viewer into print preview mode.
   * @param {string} url the url of the PDF to load.
   * @param {boolean} grayscale whether or not to display the PDF in grayscale.
   * @param {Array<number>} pageNumbers an array of the page numbers.
   * @param {boolean} modifiable whether or not the document is modifiable.
   */
  resetPrintPreviewMode: function(url, grayscale, pageNumbers, modifiable) {
    this.loadState_ = LoadState.LOADING;
    this.sendMessage_({
      type: 'resetPrintPreviewMode',
      url: url,
      grayscale: grayscale,
      pageNumbers: pageNumbers,
      modifiable: modifiable
    });
  },

  /**
   * Load a page into the document while in print preview mode.
   * @param {string} url the url of the pdf page to load.
   * @param {number} index the index of the page to load.
   */
  loadPreviewPage: function(url, index) {
    this.sendMessage_({type: 'loadPreviewPage', url: url, index: index});
  },

  /**
   * Select all the text in the document. May only be called after document
   * load.
   */
  selectAll: function() {
    this.sendMessage_({type: 'selectAll'});
  },

  /**
   * Get the selected text in the document. The callback will be called with the
   * text that is selected. May only be called after document load.
   * @param {Function} callback a callback to be called with the selected text.
   * @return {boolean} true if the function is successful, false if there is an
   *     outstanding request for selected text that has not been answered.
   */
  getSelectedText: function(callback) {
    if (this.selectedTextCallback_)
      return false;
    this.selectedTextCallback_ = callback;
    this.sendMessage_({type: 'getSelectedText'});
    return true;
  },

  /**
   * Print the document. May only be called after document load.
   */
  print: function() {
    this.sendMessage_({type: 'print'});
  },

  /**
   * Send a key event to the extension.
   * @param {Event} keyEvent the key event to send to the extension.
   */
  sendKeyEvent: function(keyEvent) {
    this.sendMessage_(
        {type: 'sendKeyEvent', keyEvent: SerializeKeyEvent(keyEvent)});
  },
};

/**
 * Creates a PDF viewer with a scripting interface. This is basically 1) an
 * iframe which is navigated to the PDF viewer extension and 2) a scripting
 * interface which provides access to various features of the viewer for use
 * by print preview and accessibility.
 * @param {string} src the source URL of the PDF to load initially.
 * @return {HTMLIFrameElement} the iframe element containing the PDF viewer.
 */
function PDFCreateOutOfProcessPlugin(src) {
  var client = new PDFScriptingAPI(window, null);
  var iframe = assertInstanceof(
      window.document.createElement('iframe'), HTMLIFrameElement);
  iframe.setAttribute('src', 'pdf_preview.html?' + src);
  // Prevent the frame from being tab-focusable.
  iframe.setAttribute('tabindex', '-1');

  iframe.onload = function() {
    client.setPlugin(iframe.contentWindow);
  };

  // Add the functions to the iframe so that they can be called directly.
  iframe.setViewportChangedCallback =
      client.setViewportChangedCallback.bind(client);
  iframe.setLoadCallback = client.setLoadCallback.bind(client);
  iframe.setKeyEventCallback = client.setKeyEventCallback.bind(client);
  iframe.resetPrintPreviewMode = client.resetPrintPreviewMode.bind(client);
  iframe.loadPreviewPage = client.loadPreviewPage.bind(client);
  iframe.sendKeyEvent = client.sendKeyEvent.bind(client);
  return iframe;
}