1 files changed, 163 insertions, 0 deletions
diff --git a/browser/components/sessionstore/TabStateCache.jsm b/browser/components/sessionstore/TabStateCache.jsm
new file mode 100644
index 000000000..9bed315a0
--- /dev/null
+++ b/browser/components/sessionstore/TabStateCache.jsm
@@ -0,0 +1,163 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["TabStateCache"];
+
+/**
+ * A cache for tabs data.
+ *
+ * This cache implements a weak map from tabs (as XUL elements)
+ * to tab data (as objects).
+ *
+ * Note that we should never cache private data, as:
+ * - that data is used very seldom by SessionStore;
+ * - caching private data in addition to public data is memory consuming.
+ */
+this.TabStateCache = Object.freeze({
+  /**
+   * Retrieves cached data for a given |tab| or associated |browser|.
+   *
+   * @param browserOrTab (xul:tab or xul:browser)
+   *        The tab or browser to retrieve cached data for.
+   * @return (object)
+   *         The cached data stored for the given |tab|
+   *         or associated |browser|.
+   */
+  get: function (browserOrTab) {
+    return TabStateCacheInternal.get(browserOrTab);
+  },
+
+  /**
+   * Updates cached data for a given |tab| or associated |browser|.
+   *
+   * @param browserOrTab (xul:tab or xul:browser)
+   *        The tab or browser belonging to the given tab data.
+   * @param newData (object)
+   *        The new data to be stored for the given |tab|
+   *        or associated |browser|.
+   */
+  update: function (browserOrTab, newData) {
+    TabStateCacheInternal.update(browserOrTab, newData);
+  }
+});
+
+var TabStateCacheInternal = {
+  _data: new WeakMap(),
+
+  /**
+   * Retrieves cached data for a given |tab| or associated |browser|.
+   *
+   * @param browserOrTab (xul:tab or xul:browser)
+   *        The tab or browser to retrieve cached data for.
+   * @return (object)
+   *         The cached data stored for the given |tab|
+   *         or associated |browser|.
+   */
+  get: function (browserOrTab) {
+    return this._data.get(browserOrTab.permanentKey);
+  },
+
+  /**
+   * Helper function used by update (see below). For message size
+   * optimization sometimes we don't update the whole session storage
+   * only the values that have been changed.
+   *
+   * @param data (object)
+   *        The cached data where we want to update the changes.
+   * @param change (object)
+   *        The actual changed values per domain.
+   */
+  updatePartialStorageChange: function (data, change) {
+    if (!data.storage) {
+      data.storage = {};
+    }
+
+    let storage = data.storage;
+    for (let domain of Object.keys(change)) {
+      for (let key of Object.keys(change[domain])) {
+        let value = change[domain][key];
+        if (value === null) {
+          if (storage[domain] && storage[domain][key]) {
+            delete storage[domain][key];
+          }
+        } else {
+          if (!storage[domain]) {
+            storage[domain] = {};
+          }
+          storage[domain][key] = value;
+        }
+      }
+    }
+  },
+
+  /**
+   * Helper function used by update (see below). For message size
+   * optimization sometimes we don't update the whole browser history
+   * only the current index and the tail of the history from a certain
+   * index (specified by change.fromIdx)
+   *
+   * @param data (object)
+   *        The cached data where we want to update the changes.
+   * @param change (object)
+   *        Object containing the tail of the history array, and
+   *        some additional metadata.
+   */
+  updatePartialHistoryChange: function (data, change) {
+    const kLastIndex = Number.MAX_SAFE_INTEGER - 1;
+
+    if (!data.history) {
+      data.history = { entries: [] };
+    }
+
+    let history = data.history;
+    for (let key of Object.keys(change)) {
+      if (key == "entries") {
+        if (change.fromIdx != kLastIndex) {
+          history.entries.splice(change.fromIdx + 1);
+          while (change.entries.length) {
+            history.entries.push(change.entries.shift());
+          }
+        }
+      } else if (key != "fromIndex") {
+        history[key] = change[key];
+      }
+    }
+  },
+
+  /**
+   * Updates cached data for a given |tab| or associated |browser|.
+   *
+   * @param browserOrTab (xul:tab or xul:browser)
+   *        The tab or browser belonging to the given tab data.
+   * @param newData (object)
+   *        The new data to be stored for the given |tab|
+   *        or associated |browser|.
+   */
+  update: function (browserOrTab, newData) {
+    let data = this._data.get(browserOrTab.permanentKey) || {};
+
+    for (let key of Object.keys(newData)) {
+      if (key == "storagechange") {
+        this.updatePartialStorageChange(data, newData.storagechange);
+        continue;
+      }
+
+      if (key == "historychange") {
+        this.updatePartialHistoryChange(data, newData.historychange);
+        continue;
+      }
+
+      let value = newData[key];
+      if (value === null) {
+        delete data[key];
+      } else {
+        data[key] = value;
+      }
+    }
+
+    this._data.set(browserOrTab.permanentKey, data);
+  }
+};