gecko-dev/browser/components/sessionstore/SessionMigration.sys.mjs

/* 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, {
  E10SUtils: "resource://gre/modules/E10SUtils.sys.mjs",
});

var SessionMigrationInternal = {
  /**
   * Convert the original session restore state into a minimal state. It will
   * only contain:
   * - open windows
   *   - with tabs
   *     - with history entries with only title, url, triggeringPrincipal
   *     - with pinned state
   *     - with tab group info (hidden + group id)
   *     - with selected tab info
   *   - with selected window info
   *
   * The complete state is then wrapped into the "about:welcomeback" page as
   * form field info to be restored when restoring the state.
   */
  convertState(aStateObj) {
    let state = {
      selectedWindow: aStateObj.selectedWindow,
      _closedWindows: [],
    };
    state.windows = aStateObj.windows.map(function (oldWin) {
      var win = { extData: {} };
      win.tabs = oldWin.tabs.map(function (oldTab) {
        var tab = {};
        // Keep only titles, urls and triggeringPrincipals for history entries
        tab.entries = oldTab.entries.map(function (entry) {
          return {
            url: entry.url,
            triggeringPrincipal_base64: entry.triggeringPrincipal_base64,
            title: entry.title,
          };
        });
        tab.index = oldTab.index;
        tab.hidden = oldTab.hidden;
        tab.pinned = oldTab.pinned;
        return tab;
      });
      win.selected = oldWin.selected;
      win._closedTabs = [];
      return win;
    });
    let url = "about:welcomeback";
    let formdata = { id: { sessionData: state }, url };
    let entry = {
      url,
      triggeringPrincipal_base64: lazy.E10SUtils.SERIALIZED_SYSTEMPRINCIPAL,
    };
    return { windows: [{ tabs: [{ entries: [entry], formdata }] }] };
  },
  /**
   * Asynchronously read session restore state (JSON) from a path
   */
  readState(aPath) {
    return IOUtils.readJSON(aPath, { decompress: true });
  },
  /**
   * Asynchronously write session restore state as JSON to a path
   */
  writeState(aPath, aState) {
    return IOUtils.writeJSON(aPath, aState, {
      compress: true,
      tmpPath: `${aPath}.tmp`,
    });
  },
};

export var SessionMigration = {
  /**
   * Migrate a limited set of session data from one path to another.
   */
  migrate(aFromPath, aToPath) {
    return (async function () {
      let inState = await SessionMigrationInternal.readState(aFromPath);
      let outState = SessionMigrationInternal.convertState(inState);
      // Unfortunately, we can't use SessionStore's own SessionFile to
      // write out the data because it has a dependency on the profile dir
      // being known. When the migration runs, there is no guarantee that
      // that's true.
      await SessionMigrationInternal.writeState(aToPath, outState);
    })();
  },
};