Rip out the current implementation of PDFHistory

The current implementation of `PDFHistory` contains a number of smaller bugs, which are *very* difficult to address without breaking other parts of its code.
Possibly the main issue with the current implementation, is that I wrote it quite some time ago, and at the time my understanding of the various edge-cases the code has to deal with was quite limited.
Currently `PDFHistory` may, despite most of those cases being fixed, in certain edge-cases lock-up the browser history, essentially preventing the user from navigating back/forward.

Hence rather than trying to iterate on `PDFHistory` to make it better, the only viable approach is unfortunately rip it out in its entirety and re-write it from scratch.

web/app.js

@@ -89,7 +89,6 @@ const DefaultExternalServices = {
 
 let PDFViewerApplication = {
   initialBookmark: document.location.hash.substring(1),
-  initialDestination: null,
   initialized: false,
   fellback: false,
   appConfig: null,
@@ -931,20 +930,11 @@ let PDFViewerApplication = {
       if (!PDFJS.disableHistory && !this.isViewerEmbedded) {
         // The browsing history is only enabled when the viewer is standalone,
         // i.e. not when it is embedded in a web page.
-        if (!this.viewerPrefs['showPreviousViewOnLoad']) {
+        let resetHistory = !this.viewerPrefs['showPreviousViewOnLoad'];
-          this.pdfHistory.clearHistoryState();
+        this.pdfHistory.initialize(id, resetHistory);
-        }
-        this.pdfHistory.initialize(this.documentFingerprint);
-
-        if (this.pdfHistory.initialDestination) {
-          this.initialDestination = this.pdfHistory.initialDestination;
-        } else if (this.pdfHistory.initialBookmark) {
-          this.initialBookmark = this.pdfHistory.initialBookmark;
-        }
       }
 
       let initialParams = {
-        destination: this.initialDestination,
         bookmark: this.initialBookmark,
         hash: null,
       };
@@ -991,14 +981,12 @@ let PDFViewerApplication = {
       }).then(() => {
         // For documents with different page sizes, once all pages are resolved,
         // ensure that the correct location becomes visible on load.
-        if (!initialParams.destination && !initialParams.bookmark &&
+        if (!initialParams.bookmark && !initialParams.hash) {
-            !initialParams.hash) {
           return;
         }
         if (pdfViewer.hasEqualPageSizes) {
           return;
         }
-        this.initialDestination = initialParams.destination;
         this.initialBookmark = initialParams.bookmark;
 
         pdfViewer.currentScaleValue = pdfViewer.currentScaleValue;
@@ -1141,12 +1129,8 @@ let PDFViewerApplication = {
     this.isInitialViewSet = true;
     this.pdfSidebar.setInitialView(sidebarView);
 
-    if (this.initialDestination) {
+    if (this.initialBookmark) {
-      this.pdfLinkService.navigateTo(this.initialDestination);
-      this.initialDestination = null;
-    } else if (this.initialBookmark) {
       this.pdfLinkService.setHash(this.initialBookmark);
-      this.pdfHistory.push({ hash: this.initialBookmark, }, true);
       this.initialBookmark = null;
     } else if (storedHash) {
       this.pdfLinkService.setHash(storedHash);
@@ -1787,10 +1771,6 @@ function webViewerUpdateViewarea(evt) {
   PDFViewerApplication.appConfig.secondaryToolbar.viewBookmarkButton.href =
     href;
 
-  // Update the current bookmark in the browsing history.
-  PDFViewerApplication.pdfHistory.updateCurrentBookmark(location.pdfOpenParams,
-                                                        location.pageNumber);
-
   // Show/hide the loading indicator in the page number input element.
   let currentPage =
     PDFViewerApplication.pdfViewer.getPageView(PDFViewerApplication.page - 1);
@@ -1814,16 +1794,14 @@ function webViewerResize() {
 }
 
 function webViewerHashchange(evt) {
-  if (PDFViewerApplication.pdfHistory.isHashChangeUnlocked) {
+  let hash = evt.hash;
-    let hash = evt.hash;
+  if (!hash) {
-    if (!hash) {
+    return;
-      return;
+  }
-    }
+  if (!PDFViewerApplication.isInitialViewSet) {
-    if (!PDFViewerApplication.isInitialViewSet) {
+    PDFViewerApplication.initialBookmark = hash;
-      PDFViewerApplication.initialBookmark = hash;
+  } else {
-    } else {
+    PDFViewerApplication.pdfLinkService.setHash(hash);
-      PDFViewerApplication.pdfLinkService.setHash(hash);
-    }
   }
 }
 
@@ -2277,23 +2255,6 @@ function webViewerKeyDown(evt) {
     }
   }
 
-  if (cmd === 2) { // alt-key
-    switch (evt.keyCode) {
-      case 37: // left arrow
-        if (isViewerInPresentationMode) {
-          PDFViewerApplication.pdfHistory.back();
-          handled = true;
-        }
-        break;
-      case 39: // right arrow
-        if (isViewerInPresentationMode) {
-          PDFViewerApplication.pdfHistory.forward();
-          handled = true;
-        }
-        break;
-    }
-  }
-
   if (ensureViewerFocused && !pdfViewer.containsElement(curElement)) {
     // The page container is not focused, but a page navigation key has been
     // pressed. Change the focus to the viewer container to make sure that

web/interfaces.js

@@ -73,10 +73,13 @@ class IPDFLinkService {
  * @interface
  */
 class IPDFHistory {
-  forward() {}
+  initialize() {}
+
+  push() {}
+
   back() {}
-  push(params) {}
+
-  updateNextHashParam(hash) {}
+  forward() {}
 }
 
 /**

web/pdf_history.js

@@ -1,4 +1,4 @@
-/* Copyright 2012 Mozilla Foundation
+/* Copyright 2017 Mozilla Foundation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -12,415 +12,24 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* globals chrome */
 
 import { getGlobalEventBus } from './dom_events';
 
-function PDFHistory(options) {
+class PDFHistory {
-  this.linkService = options.linkService;
+  constructor({ linkService, eventBus, }) {
-  this.eventBus = options.eventBus || getGlobalEventBus();
+    this.linkService = linkService;
+    this.eventBus = eventBus || getGlobalEventBus();
+  }
 
-  this.initialized = false;
+  initialize(fingerprint, resetHistory = false) {}
-  this.initialDestination = null;
+
-  this.initialBookmark = null;
+  push() {}
+
+  back() {}
+
+  forward() {}
 }
 
-PDFHistory.prototype = {
-  /**
-   * @param {string} fingerprint
-   */
-  initialize: function pdfHistoryInitialize(fingerprint) {
-    this.initialized = true;
-    this.reInitialized = false;
-    this.allowHashChange = true;
-    this.historyUnlocked = true;
-    this.isViewerInPresentationMode = false;
-
-    this.previousHash = window.location.hash.substring(1);
-    this.currentBookmark = '';
-    this.currentPage = 0;
-    this.updatePreviousBookmark = false;
-    this.previousBookmark = '';
-    this.previousPage = 0;
-    this.nextHashParam = '';
-
-    this.fingerprint = fingerprint;
-    this.currentUid = this.uid = 0;
-    this.current = {};
-
-    var state = window.history.state;
-    if (this._isStateObjectDefined(state)) {
-      // This corresponds to navigating back to the document
-      // from another page in the browser history.
-      if (state.target.dest) {
-        this.initialDestination = state.target.dest;
-      } else {
-        this.initialBookmark = state.target.hash;
-      }
-      this.currentUid = state.uid;
-      this.uid = state.uid + 1;
-      this.current = state.target;
-    } else {
-      // This corresponds to the loading of a new document.
-      if (state && state.fingerprint &&
-        this.fingerprint !== state.fingerprint) {
-        // Reinitialize the browsing history when a new document
-        // is opened in the web viewer.
-        this.reInitialized = true;
-      }
-      this._pushOrReplaceState({ fingerprint: this.fingerprint, }, true);
-    }
-
-    var self = this;
-    window.addEventListener('popstate', function pdfHistoryPopstate(evt) {
-      if (!self.historyUnlocked) {
-        return;
-      }
-      if (evt.state) {
-        // Move back/forward in the history.
-        self._goTo(evt.state);
-        return;
-      }
-
-      // If the state is not set, then the user tried to navigate to a
-      // different hash by manually editing the URL and pressing Enter, or by
-      // clicking on an in-page link (e.g. the "current view" link).
-      // Save the current view state to the browser history.
-
-      // Note: In Firefox, history.null could also be null after an in-page
-      // navigation to the same URL, and without dispatching the popstate
-      // event: https://bugzilla.mozilla.org/show_bug.cgi?id=1183881
-
-      if (self.uid === 0) {
-        // Replace the previous state if it was not explicitly set.
-        var previousParams = (self.previousHash && self.currentBookmark &&
-          self.previousHash !== self.currentBookmark) ?
-          { hash: self.currentBookmark, page: self.currentPage, } :
-          { page: 1, };
-        replacePreviousHistoryState(previousParams, function() {
-          updateHistoryWithCurrentHash();
-        });
-      } else {
-        updateHistoryWithCurrentHash();
-      }
-    });
-
-
-    function updateHistoryWithCurrentHash() {
-      self.previousHash = window.location.hash.slice(1);
-      self._pushToHistory({ hash: self.previousHash, }, false, true);
-      self._updatePreviousBookmark();
-    }
-
-    function replacePreviousHistoryState(params, callback) {
-      // To modify the previous history entry, the following happens:
-      // 1. history.back()
-      // 2. _pushToHistory, which calls history.replaceState( ... )
-      // 3. history.forward()
-      // Because a navigation via the history API does not immediately update
-      // the history state, the popstate event is used for synchronization.
-      self.historyUnlocked = false;
-
-      // Suppress the hashchange event to avoid side effects caused by
-      // navigating back and forward.
-      self.allowHashChange = false;
-      window.addEventListener('popstate', rewriteHistoryAfterBack);
-      history.back();
-
-      function rewriteHistoryAfterBack() {
-        window.removeEventListener('popstate', rewriteHistoryAfterBack);
-        window.addEventListener('popstate', rewriteHistoryAfterForward);
-        self._pushToHistory(params, false, true);
-        history.forward();
-      }
-      function rewriteHistoryAfterForward() {
-        window.removeEventListener('popstate', rewriteHistoryAfterForward);
-        self.allowHashChange = true;
-        self.historyUnlocked = true;
-        callback();
-      }
-    }
-
-    function pdfHistoryBeforeUnload() {
-      var previousParams = self._getPreviousParams(null, true);
-      if (previousParams) {
-        var replacePrevious = (!self.current.dest &&
-        self.current.hash !== self.previousHash);
-        self._pushToHistory(previousParams, false, replacePrevious);
-        self._updatePreviousBookmark();
-      }
-      // Remove the event listener when navigating away from the document,
-      // since 'beforeunload' prevents Firefox from caching the document.
-      window.removeEventListener('beforeunload', pdfHistoryBeforeUnload);
-    }
-
-    window.addEventListener('beforeunload', pdfHistoryBeforeUnload);
-
-    window.addEventListener('pageshow', function pdfHistoryPageShow(evt) {
-      // If the entire viewer (including the PDF file) is cached in
-      // the browser, we need to reattach the 'beforeunload' event listener
-      // since the 'DOMContentLoaded' event is not fired on 'pageshow'.
-      window.addEventListener('beforeunload', pdfHistoryBeforeUnload);
-    });
-
-    self.eventBus.on('presentationmodechanged', function(e) {
-      self.isViewerInPresentationMode = e.active;
-    });
-  },
-
-  clearHistoryState: function pdfHistory_clearHistoryState() {
-    this._pushOrReplaceState(null, true);
-  },
-
-  _isStateObjectDefined: function pdfHistory_isStateObjectDefined(state) {
-    return (state && state.uid >= 0 &&
-    state.fingerprint && this.fingerprint === state.fingerprint &&
-    state.target && state.target.hash) ? true : false;
-  },
-
-  _pushOrReplaceState: function pdfHistory_pushOrReplaceState(stateObj,
-                                                              replace) {
-    // history.state.chromecomState is managed by chromecom.js.
-    if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('CHROME') &&
-        window.history.state && 'chromecomState' in window.history.state) {
-      stateObj = stateObj || {};
-      stateObj.chromecomState = window.history.state.chromecomState;
-    }
-    if (replace) {
-      if (typeof PDFJSDev === 'undefined' ||
-          PDFJSDev.test('GENERIC || CHROME')) {
-        window.history.replaceState(stateObj, '', document.URL);
-      } else {
-        window.history.replaceState(stateObj, '');
-      }
-    } else {
-      if (typeof PDFJSDev === 'undefined' ||
-          PDFJSDev.test('GENERIC || CHROME')) {
-        window.history.pushState(stateObj, '', document.URL);
-      } else {
-        window.history.pushState(stateObj, '');
-      }
-      if (typeof PDFJSDev !== 'undefined' && PDFJSDev.test('CHROME') &&
-          top === window) {
-        chrome.runtime.sendMessage('showPageAction');
-      }
-    }
-  },
-
-  get isHashChangeUnlocked() {
-    if (!this.initialized) {
-      return true;
-    }
-    return this.allowHashChange;
-  },
-
-  _updatePreviousBookmark: function pdfHistory_updatePreviousBookmark() {
-    if (this.updatePreviousBookmark &&
-      this.currentBookmark && this.currentPage) {
-      this.previousBookmark = this.currentBookmark;
-      this.previousPage = this.currentPage;
-      this.updatePreviousBookmark = false;
-    }
-  },
-
-  updateCurrentBookmark: function pdfHistoryUpdateCurrentBookmark(bookmark,
-                                                                  pageNum) {
-    if (this.initialized) {
-      this.currentBookmark = bookmark.substring(1);
-      this.currentPage = pageNum | 0;
-      this._updatePreviousBookmark();
-    }
-  },
-
-  updateNextHashParam: function pdfHistoryUpdateNextHashParam(param) {
-    if (this.initialized) {
-      this.nextHashParam = param;
-    }
-  },
-
-  push: function pdfHistoryPush(params, isInitialBookmark) {
-    if (!(this.initialized && this.historyUnlocked)) {
-      return;
-    }
-    if (params.dest && !params.hash) {
-      params.hash = (this.current.hash && this.current.dest &&
-      this.current.dest === params.dest) ?
-        this.current.hash :
-        this.linkService.getDestinationHash(params.dest).split('#')[1];
-    }
-    if (params.page) {
-      params.page |= 0;
-    }
-    if (isInitialBookmark) {
-      var target = window.history.state.target;
-      if (!target) {
-        // Invoked when the user specifies an initial bookmark,
-        // thus setting initialBookmark, when the document is loaded.
-        this._pushToHistory(params, false);
-        this.previousHash = window.location.hash.substring(1);
-      }
-      this.updatePreviousBookmark = this.nextHashParam ? false : true;
-      if (target) {
-        // If the current document is reloaded,
-        // avoid creating duplicate entries in the history.
-        this._updatePreviousBookmark();
-      }
-      return;
-    }
-    if (this.nextHashParam) {
-      if (this.nextHashParam === params.hash) {
-        this.nextHashParam = null;
-        this.updatePreviousBookmark = true;
-        return;
-      }
-      this.nextHashParam = null;
-    }
-
-    if (params.hash) {
-      if (this.current.hash) {
-        if (this.current.hash !== params.hash) {
-          this._pushToHistory(params, true);
-        } else {
-          if (!this.current.page && params.page) {
-            this._pushToHistory(params, false, true);
-          }
-          this.updatePreviousBookmark = true;
-        }
-      } else {
-        this._pushToHistory(params, true);
-      }
-    } else if (this.current.page && params.page &&
-      this.current.page !== params.page) {
-      this._pushToHistory(params, true);
-    }
-  },
-
-  _getPreviousParams: function pdfHistory_getPreviousParams(onlyCheckPage,
-                                                            beforeUnload) {
-    if (!(this.currentBookmark && this.currentPage)) {
-      return null;
-    } else if (this.updatePreviousBookmark) {
-      this.updatePreviousBookmark = false;
-    }
-    if (this.uid > 0 && !(this.previousBookmark && this.previousPage)) {
-      // Prevent the history from getting stuck in the current state,
-      // effectively preventing the user from going back/forward in
-      // the history.
-      //
-      // This happens if the current position in the document didn't change
-      // when the history was previously updated. The reasons for this are
-      // either:
-      // 1. The current zoom value is such that the document does not need to,
-      //    or cannot, be scrolled to display the destination.
-      // 2. The previous destination is broken, and doesn't actally point to a
-      //    position within the document.
-      //    (This is either due to a bad PDF generator, or the user making a
-      //     mistake when entering a destination in the hash parameters.)
-      return null;
-    }
-    if ((!this.current.dest && !onlyCheckPage) || beforeUnload) {
-      if (this.previousBookmark === this.currentBookmark) {
-        return null;
-      }
-    } else if (this.current.page || onlyCheckPage) {
-      if (this.previousPage === this.currentPage) {
-        return null;
-      }
-    } else {
-      return null;
-    }
-    var params = { hash: this.currentBookmark, page: this.currentPage, };
-    if (this.isViewerInPresentationMode) {
-      params.hash = null;
-    }
-    return params;
-  },
-
-  _stateObj: function pdfHistory_stateObj(params) {
-    return { fingerprint: this.fingerprint, uid: this.uid, target: params, };
-  },
-
-  _pushToHistory: function pdfHistory_pushToHistory(params,
-                                                    addPrevious, overwrite) {
-    if (!this.initialized) {
-      return;
-    }
-    if (!params.hash && params.page) {
-      params.hash = ('page=' + params.page);
-    }
-    if (addPrevious && !overwrite) {
-      var previousParams = this._getPreviousParams();
-      if (previousParams) {
-        var replacePrevious = (!this.current.dest &&
-        this.current.hash !== this.previousHash);
-        this._pushToHistory(previousParams, false, replacePrevious);
-      }
-    }
-    this._pushOrReplaceState(this._stateObj(params),
-      (overwrite || this.uid === 0));
-    this.currentUid = this.uid++;
-    this.current = params;
-    this.updatePreviousBookmark = true;
-  },
-
-  _goTo: function pdfHistory_goTo(state) {
-    if (!(this.initialized && this.historyUnlocked &&
-      this._isStateObjectDefined(state))) {
-      return;
-    }
-    if (!this.reInitialized && state.uid < this.currentUid) {
-      var previousParams = this._getPreviousParams(true);
-      if (previousParams) {
-        this._pushToHistory(this.current, false);
-        this._pushToHistory(previousParams, false);
-        this.currentUid = state.uid;
-        window.history.back();
-        return;
-      }
-    }
-    this.historyUnlocked = false;
-
-    if (state.target.dest) {
-      this.linkService.navigateTo(state.target.dest);
-    } else {
-      this.linkService.setHash(state.target.hash);
-    }
-    this.currentUid = state.uid;
-    if (state.uid > this.uid) {
-      this.uid = state.uid;
-    }
-    this.current = state.target;
-    this.updatePreviousBookmark = true;
-
-    var currentHash = window.location.hash.substring(1);
-    if (this.previousHash !== currentHash) {
-      this.allowHashChange = false;
-    }
-    this.previousHash = currentHash;
-
-    this.historyUnlocked = true;
-  },
-
-  back: function pdfHistoryBack() {
-    this.go(-1);
-  },
-
-  forward: function pdfHistoryForward() {
-    this.go(1);
-  },
-
-  go: function pdfHistoryGo(direction) {
-    if (this.initialized && this.historyUnlocked) {
-      var state = window.history.state;
-      if (direction === -1 && state && state.uid > 0) {
-        window.history.back();
-      } else if (direction === 1 && state && state.uid < (this.uid - 1)) {
-        window.history.forward();
-      }
-    }
-  },
-};
-
 export {
   PDFHistory,
 };

web/pdf_link_service.js

@@ -115,14 +115,6 @@ class PDFLinkService {
         pageNumber,
         destArray: explicitDest,
       });
-
-      if (this.pdfHistory) { // Update the browsing history, if enabled.
-        this.pdfHistory.push({
-          dest: explicitDest,
-          hash: namedDest,
-          page: pageNumber,
-        });
-      }
     };
 
     new Promise((resolve, reject) => {
@@ -190,9 +182,6 @@ class PDFLinkService {
       }
       // borrowing syntax from "Parameters for Opening PDF Files"
       if ('nameddest' in params) {
-        if (this.pdfHistory) {
-          this.pdfHistory.updateNextHashParam(params.nameddest);
-        }
         this.navigateTo(params.nameddest);
         return;
       }
@@ -270,9 +259,6 @@ class PDFLinkService {
       } catch (ex) {}
 
       if (typeof dest === 'string' || isValidExplicitDestination(dest)) {
-        if (this.pdfHistory) {
-          this.pdfHistory.updateNextHashParam(dest);
-        }
         this.navigateTo(dest);
         return;
       }