Print Preview: Associating preview requests and responses using an identifier

chrome/browser/resources/print_preview/print_preview.js

 // Copyright (c) 2011 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.
 
 var localStrings = new LocalStrings();
 
 // Store the last selected printer index.
 var lastSelectedPrinterIndex = 0;
 
 // Used to disable some printing options when the preview is not modifiable.
 var previewModifiable = false;
 
 // Destination list special value constants.
 const PRINT_TO_PDF = 'Print To PDF';
 const MANAGE_PRINTERS = 'Manage Printers';
 
 // State of the print preview settings.
 var printSettings = new PrintSettings();
 
 // The name of the default or last used printer.
 var defaultOrLastUsedPrinterName = '';
 
 // True when a pending print preview request exists.
 var hasPendingPreviewRequest = false;
 
+// The ID of the last preview request.
+var lastPreviewRequestID = -1;
+
 // True when a pending print file request exists.
 var hasPendingPrintFileRequest = false;
 
 // True when preview tab is hidden.
 var isTabHidden = false;
 
 // Object holding all the pages related settings.
 var pageSettings;
 
 // Object holding all the copies related settings.
@@ skipping 214 matching lines @@
  * @return {number} duplex mode.
  */
 function getDuplexMode() {
   // Constants values matches printing::DuplexMode enum.
   const SIMPLEX = 0;
   const LONG_EDGE = 1;
   return !copiesSettings.twoSidedCheckbox.checked ? SIMPLEX : LONG_EDGE;
 }
 
 /**
- * Creates a JSON string based on the values in the printer settings.
+ * Creates an object based on the values in the printer settings.
  *
- * @return {string} JSON string with print job settings.
+ * @return {Object} Object containing print job settings.
  */
-function getSettingsJSON() {
+function getSettings() {
   var deviceName = getSelectedPrinterName();
   var printToPDF = (deviceName == PRINT_TO_PDF);
 
-  return JSON.stringify(
+  var settings =
       {'deviceName': deviceName,
        'pageRange': pageSettings.selectedPageRanges,
        'printAll': pageSettings.allPagesRadioButton.checked,
        'duplex': getDuplexMode(),
        'copies': copiesSettings.numberOfCopies,
        'collate': isCollated(),
        'landscape': isLandscape(),
        'color': isColor(),
-       'printToPDF': printToPDF});
+       'printToPDF': printToPDF,
+       'requestID': 0};
+  return settings;
 }
 
 /**
+ * @return {number} The next unused preview request id.
+ */
+function generatePreviewRequestID() {
+  return ++lastPreviewRequestID;
+}
+
+/**
  * Returns the name of the selected printer or the empty string if no
  * printer is selected.
  */
 function getSelectedPrinterName() {
   var printerList = $('printer-list')
   var selectedPrinter = printerList.selectedIndex;
   if (selectedPrinter < 0)
     return '';
   return printerList.options[selectedPrinter].value;
 }
@@ skipping 47 matching lines @@
  * Sends a message to cancel the pending print request.
  */
 function cancelPendingPrintRequest() {
   chrome.send('cancelPendingPrintRequest');
 }
 
 /**
  * Sends a message to initiate print workflow.
  */
 function sendPrintFileRequest() {
-  chrome.send('print', [getSettingsJSON()]);
+  chrome.send('print', [JSON.stringify(getSettings())]);
 }
 
 /**
  * Asks the browser to generate a preview PDF based on current print settings.
  */
 function requestPrintPreview() {
   hasPendingPreviewRequest = true;
   removeEventListeners();
   printSettings.save();
   if (!isTabHidden)
     showLoadingAnimation();
 
-  chrome.send('getPreview', [getSettingsJSON()]);
+  var settings = getSettings();
+  settings.requestID = generatePreviewRequestID();
+  chrome.send('getPreview', [JSON.stringify(settings)]);
 }
 
 /**
  * Called from PrintPreviewUI::OnFileSelectionCancelled to notify the print
  * preview tab regarding the file selection cancel event.
  */
 function fileSelectionCancelled() {
   // TODO(thestig) re-enable controls here.
 }
 
@@ skipping 166 matching lines @@
   // TODO(thestig) Make use of |pageNumber| for pipelined preview generation.
 }
 
 /**
  * Update the print preview when new preview data is available.
  * Create the PDF plugin as needed.
  * Called from PrintPreviewUI::PreviewDataIsAvailable().
  * @param {string} jobTitle The print job title.
  * @param {boolean} modifiable If the preview is modifiable.
  * @param {string} previewUid Preview unique identifier.
+ * @param {string} previewRequestId The preview request id that resulted in this
+ *     response.
  */
-function updatePrintPreview(jobTitle, modifiable, previewUid) {
+function updatePrintPreview(jobTitle,
+                            modifiable,
+                            previewUid,
+                            previewRequestId) {
+  if (lastPreviewRequestID != previewRequestId)
+    return;
   hasPendingPreviewRequest = false;
 
   if (checkIfSettingsChangedAndRegeneratePreview())
     return;
 
   previewModifiable = modifiable;
   document.title = localStrings.getStringF('printPreviewTitleFormat', jobTitle);
 
   createPDFPlugin(previewUid);
   updatePrintSummary();
@@ skipping 167 matching lines @@
   this.isLandscape = '';
 }
 
 /**
  * Takes a snapshot of the print settings.
  */
 PrintSettings.prototype.save = function() {
   this.deviceName = getSelectedPrinterName();
   this.isLandscape = isLandscape();
 }