1 files changed, 120 insertions, 0 deletions
diff --git a/services/settings/SyncHistory.sys.mjs b/services/settings/SyncHistory.sys.mjs
new file mode 100644
index 0000000000..f609eb26f7
--- /dev/null
+++ b/services/settings/SyncHistory.sys.mjs
@@ -0,0 +1,120 @@
+/* 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/. */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  KeyValueService: "resource://gre/modules/kvstore.sys.mjs",
+});
+
+/**
+ * A helper to keep track of synchronization statuses.
+ *
+ * We rely on a different storage backend than for storing Remote Settings data,
+ * because the eventual goal is to be able to detect `IndexedDB` issues and act
+ * accordingly.
+ */
+export class SyncHistory {
+  // Internal reference to underlying rkv store.
+  #store;
+
+  /**
+   * @param {String} source the synchronization source (eg. `"settings-sync"`)
+   * @param {Object} options
+   * @param {int} options.size Maximum number of entries per source.
+   */
+  constructor(source, { size } = { size: 100 }) {
+    this.source = source;
+    this.size = size;
+  }
+
+  /**
+   * Store the synchronization status. The ETag is converted and stored as
+   * a millisecond epoch timestamp.
+   * The entries with the oldest timestamps will be deleted to maintain the
+   * history size under the configured maximum.
+   *
+   * @param {String} etag the ETag value from the server (eg. `"1647961052593"`)
+   * @param {String} status the synchronization status (eg. `"success"`)
+   * @param {Object} infos optional additional information to keep track of
+   */
+  async store(etag, status, infos = {}) {
+    const rkv = await this.#init();
+    const timestamp = parseInt(etag.replace('"', ""), 10);
+    if (Number.isNaN(timestamp)) {
+      throw new Error(`Invalid ETag value ${etag}`);
+    }
+    const key = `v1-${this.source}\t${timestamp}`;
+    const value = { timestamp, status, infos };
+    await rkv.put(key, JSON.stringify(value));
+    // Trim old entries.
+    const allEntries = await this.list();
+    for (let i = this.size; i < allEntries.length; i++) {
+      let { timestamp } = allEntries[i];
+      await rkv.delete(`v1-${this.source}\t${timestamp}`);
+    }
+  }
+
+  /**
+   * Retrieve the stored history entries for a certain source, sorted by
+   * timestamp descending.
+   *
+   * @returns {Array<Object>} a list of objects
+   */
+  async list() {
+    const rkv = await this.#init();
+    const entries = [];
+    // The "from" and "to" key parameters to nsIKeyValueStore.enumerate()
+    // are inclusive and exclusive, respectively, and keys are tuples
+    // of source and datetime joined by a tab (\t), which is character code 9;
+    // so enumerating ["source", "source\n"), where the line feed (\n)
+    // is character code 10, enumerates all pairs with the given source.
+    for (const { value } of await rkv.enumerate(
+      `v1-${this.source}`,
+      `v1-${this.source}\n`
+    )) {
+      try {
+        const stored = JSON.parse(value);
+        entries.push({ ...stored, datetime: new Date(stored.timestamp) });
+      } catch (e) {
+        // Ignore malformed entries.
+        console.error(e);
+      }
+    }
+    // Sort entries by `timestamp` descending.
+    entries.sort((a, b) => (a.timestamp > b.timestamp ? -1 : 1));
+    return entries;
+  }
+
+  /**
+   * Return the most recent entry.
+   */
+  async last() {
+    // List is sorted from newer to older.
+    return (await this.list())[0];
+  }
+
+  /**
+   * Wipe out the **whole** store.
+   */
+  async clear() {
+    const rkv = await this.#init();
+    await rkv.clear();
+  }
+
+  /**
+   * Initialize the rkv store in the user profile.
+   *
+   * @returns {Object} the underlying `KeyValueService` instance.
+   */
+  async #init() {
+    if (!this.#store) {
+      // Get and cache a handle to the kvstore.
+      const dir = PathUtils.join(PathUtils.profileDir, "settings");
+      await IOUtils.makeDirectory(dir);
+      this.#store = await lazy.KeyValueService.getOrCreate(dir, "synchistory");
+    }
+    return this.#store;
+  }
+}