1 files changed, 171 insertions, 0 deletions
diff --git a/browser/components/sessionstore/TabStateCache.sys.mjs b/browser/components/sessionstore/TabStateCache.sys.mjs
new file mode 100644
index 0000000000..81524c4d69
--- /dev/null
+++ b/browser/components/sessionstore/TabStateCache.sys.mjs
@@ -0,0 +1,171 @@
+/* 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/. */
+
+/**
+ * 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.
+ */
+export var TabStateCache = Object.freeze({
+  /**
+   * Retrieves cached data for a given |tab| or associated |browser|.
+   *
+   * @param permanentKey (object)
+   *        The tab or browser to retrieve cached data for.
+   * @return (object)
+   *         The cached data stored for the given |tab|
+   *         or associated |browser|.
+   */
+  get(permanentKey) {
+    return TabStateCacheInternal.get(permanentKey);
+  },
+
+  /**
+   * Updates cached data for a given |tab| or associated |browser|.
+   *
+   * @param permanentKey (object)
+   *        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(permanentKey, newData) {
+    TabStateCacheInternal.update(permanentKey, newData);
+  },
+});
+
+var TabStateCacheInternal = {
+  _data: new WeakMap(),
+
+  /**
+   * Retrieves cached data for a given |tab| or associated |browser|.
+   *
+   * @param permanentKey (object)
+   *        The tab or browser to retrieve cached data for.
+   * @return (object)
+   *         The cached data stored for the given |tab|
+   *         or associated |browser|.
+   */
+  get(permanentKey) {
+    return this._data.get(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(data, change) {
+    if (!data.storage) {
+      data.storage = {};
+    }
+
+    let storage = data.storage;
+    for (let domain of Object.keys(change)) {
+      if (!change[domain]) {
+        // We were sent null in place of the change object, which means
+        // we should delete session storage entirely for this domain.
+        delete storage[domain];
+      } else {
+        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(data, change) {
+    const kLastIndex = Number.MAX_SAFE_INTEGER - 1;
+
+    if (!data.history) {
+      data.history = { entries: [] };
+    }
+
+    let history = data.history;
+    let toIdx = history.entries.length;
+    if ("toIdx" in change) {
+      toIdx = Math.min(toIdx, change.toIdx + 1);
+    }
+
+    for (let key of Object.keys(change)) {
+      if (key == "entries") {
+        if (change.fromIdx != kLastIndex) {
+          let start = change.fromIdx + 1;
+          history.entries.splice.apply(
+            history.entries,
+            [start, toIdx - start].concat(change.entries)
+          );
+        }
+      } else if (key != "fromIdx" && key != "toIdx") {
+        history[key] = change[key];
+      }
+    }
+  },
+
+  /**
+   * Updates cached data for a given |tab| or associated |browser|.
+   *
+   * @param permanentKey (object)
+   *        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(permanentKey, newData) {
+    let data = this._data.get(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(permanentKey, data);
+  },
+};