Bug 943339 - Part 1: Only store a subset of session history entries to file. r=Yoric

browser/app/profile/firefox.js

@@ -858,6 +858,10 @@ pref("browser.sessionstore.max_windows_undo", 3);
 // number of crashes that can occur before the about:sessionrestore page is displayed
 // (this pref has no effect if more than 6 hours have passed since the last crash)
 pref("browser.sessionstore.max_resumed_crashes", 1);
+// number of back button session history entries to restore (-1 = all of them)
+pref("browser.sessionstore.max_serialize_back", 10);
+// number of forward button session history entries to restore (-1 = all of them)
+pref("browser.sessionstore.max_serialize_forward", -1);
 // restore_on_demand overrides MAX_CONCURRENT_TAB_RESTORES (sessionstore constant)
 // and restore_hidden_tabs. When true, tabs will not be restored until they are
 // focused (also applies to tabs that aren't visible). When false, the values

browser/components/sessionstore/src/SessionHistory.jsm

@@ -70,8 +70,26 @@ let SessionHistoryInternal = {
     let history = webNavigation.sessionHistory;
 
     if (history && history.count > 0) {
+      let oldest;
+      let maxSerializeBack =
+        Services.prefs.getIntPref("browser.sessionstore.max_serialize_back");
+      if (maxSerializeBack >= 0) {
+        oldest = Math.max(0, history.index - maxSerializeBack);
+      } else { // History.getEntryAtIndex(0, ...) is the oldest.
+        oldest = 0;
+      }
+
+      let newest;
+      let maxSerializeFwd =
+        Services.prefs.getIntPref("browser.sessionstore.max_serialize_forward");
+      if (maxSerializeFwd >= 0) {
+        newest = Math.min(history.count - 1, history.index + maxSerializeFwd);
+      } else { // History.getEntryAtIndex(history.count - 1, ...) is the newest.
+        newest = history.count - 1;
+      }
+
       try {
-        for (let i = 0; i < history.count; i++) {
+        for (let i = oldest; i <= newest; i++) {
           let shEntry = history.getEntryAtIndex(i, false);
           let entry = this.serializeEntry(shEntry, isPinned);
           data.entries.push(entry);
@@ -85,8 +103,9 @@ let SessionHistoryInternal = {
               "for the focused window/tab. See bug 669196.");
       }
 
-      // Ensure the index isn't out of bounds if an exception was thrown above.
-      data.index = Math.min(history.index + 1, data.entries.length);
+      // Set the one-based index of the currently active tab,
+      // ensuring it isn't out of bounds if an exception was thrown above.
+      data.index = Math.min(history.index - oldest + 1, data.entries.length);
     }
 
     // If either the session history isn't available yet or doesn't have any

browser/components/sessionstore/test/browser_447951.js

@@ -9,6 +9,14 @@ function test() {
   const baseURL = "http://mochi.test:8888/browser/" +
     "browser/components/sessionstore/test/browser_447951_sample.html#";
 
+  // Make sure the functionality added in bug 943339 doesn't affect the results
+  gPrefService.setIntPref("browser.sessionstore.max_serialize_back", -1);
+  gPrefService.setIntPref("browser.sessionstore.max_serialize_forward", -1);
+  registerCleanupFunction(function () {
+    gPrefService.clearUserPref("browser.sessionstore.max_serialize_back");
+    gPrefService.clearUserPref("browser.sessionstore.max_serialize_forward");
+  });
+
   let tab = gBrowser.addTab();
   whenBrowserLoaded(tab.linkedBrowser, function() {
     let tabState = { entries: [] };

docshell/shistory/public/nsISHistory.idl

@@ -63,6 +63,7 @@ interface nsISHistory: nsISupports
    * given index.
    *
    * @param index             The index value whose entry is requested.
+   *                          The oldest entry is located at index == 0.
    * @param modifyIndex       A boolean flag that indicates if the current
    *                          index of session history should be modified 
    *                          to the parameter index.