Add support for, the API property, PageMode in the viewer (issue 8657)

Note that the PageMode, as specified in the API, will only be honoured when either: the user hasn't set the `sidebarViewOnLoad` preference to a non-default value, or a non-default `sidebarView` entry doesn't exist in the view history, or the "pagemode" hash parameter is included in the URL.

Since this is new functionality, the patch also includes a preference (`disablePageMode`), to make it easy to opt-out of this functionality if the user/implementor so wishes.

extensions/chromium/preferences_schema.json

@@ -102,6 +102,10 @@
       "type": "boolean",
       "default": false
     },
+    "disablePageMode": {
+      "type": "boolean",
+      "default": false
+    },
     "disableTelemetry": {
       "title": "Disable telemetry",
       "type": "boolean",

web/app.js

@@ -141,6 +141,7 @@ let PDFViewerApplication = {
     pdfBugEnabled: false,
     showPreviousViewOnLoad: true,
     defaultZoomValue: '',
+    disablePageMode: false,
     disablePageLabels: false,
     renderer: 'canvas',
     enhanceTextSelection: false,
@@ -255,6 +256,9 @@ let PDFViewerApplication = {
       preferences.get('renderInteractiveForms').then(function resolved(value) {
         viewerPrefs['renderInteractiveForms'] = value;
       }),
+      preferences.get('disablePageMode').then(function resolved(value) {
+        viewerPrefs['disablePageMode'] = value;
+      }),
       preferences.get('disablePageLabels').then(function resolved(value) {
         viewerPrefs['disablePageLabels'] = value;
       }),
@@ -883,6 +887,11 @@ let PDFViewerApplication = {
       });
     });
 
+    // Since the `setInitialView` call below depends on this being resolved,
+    // fetch it early to avoid delaying initial rendering of the PDF document.
+    let pageModePromise = pdfDocument.getPageMode().catch(
+      function() { /* Avoid breaking initial rendering; ignoring errors. */ });
+
     this.toolbar.setPagesCount(pdfDocument.numPages, false);
     this.secondaryToolbar.setPagesCount(pdfDocument.numPages);
 
@@ -939,9 +948,10 @@ let PDFViewerApplication = {
         scrollLeft: '0',
         scrollTop: '0',
         sidebarView: SidebarView.NONE,
-      }).catch(() => { /* Unable to read from storage -- ignoring errors. */ });
+      }).catch(() => { /* Unable to read from storage; ignoring errors. */ });
 
-      storePromise.then((values = {}) => {
+      Promise.all([storePromise, pageModePromise]).then(
+          ([values = {}, pageMode]) => {
         // Initialize the default values, from user preferences.
         let hash = this.viewerPrefs['defaultZoomValue'] ?
           ('zoom=' + this.viewerPrefs['defaultZoomValue']) : null;
@@ -953,6 +963,10 @@ let PDFViewerApplication = {
             ',' + values.scrollLeft + ',' + values.scrollTop;
           sidebarView = sidebarView || (values.sidebarView | 0);
         }
+        if (pageMode && !this.viewerPrefs['disablePageMode']) {
+          // Always let the user preference/history take precedence.
+          sidebarView = sidebarView || apiPageModeToSidebarView(pageMode);
+        }
         return {
           hash,
           sidebarView,
@@ -2290,6 +2304,30 @@ function webViewerKeyDown(evt) {
   }
 }
 
+/**
+ * Converts API PageMode values to the format used by `PDFSidebar`.
+ * NOTE: There's also a "FullScreen" parameter which is not possible to support,
+ *       since the Fullscreen API used in browsers requires that entering
+ *       fullscreen mode only occurs as a result of a user-initiated event.
+ * @param {string} mode - The API PageMode value.
+ * @returns {number} A value from {SidebarView}.
+ */
+function apiPageModeToSidebarView(mode) {
+  switch (mode) {
+    case 'UseNone':
+      return SidebarView.NONE;
+    case 'UseThumbs':
+      return SidebarView.THUMBS;
+    case 'UseOutlines':
+      return SidebarView.OUTLINE;
+    case 'UseAttachments':
+      return SidebarView.ATTACHMENTS;
+    case 'UseOC':
+      // Not implemented, since we don't support Optional Content Groups yet.
+  }
+  return SidebarView.NONE; // Default value.
+}
+
 /* Abstract factory for the print service. */
 let PDFPrintServiceFactory = {
   instance: {

web/default_preferences.json

@@ -17,5 +17,6 @@
   "renderer": "canvas",
   "renderInteractiveForms": false,
   "enablePrintAutoRotate": false,
+  "disablePageMode": false,
   "disablePageLabels": false
 }