DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (b20b355373b4)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547
/* 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";

var EXPORTED_SYMBOLS = [
  "Sqlite",
];

// The maximum time to wait before considering a transaction stuck and rejecting
// it. (Note that the minimum amount of time we wait is 20% less than this, see
// the `_getTimeoutPromise` method on `ConnectionData` for details).
const TRANSACTIONS_QUEUE_TIMEOUT_MS = 300000; // 5 minutes

const {XPCOMUtils} = ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
const {setTimeout} = ChromeUtils.import("resource://gre/modules/Timer.jsm");

XPCOMUtils.defineLazyModuleGetters(this, {
  AsyncShutdown: "resource://gre/modules/AsyncShutdown.jsm",
  Services: "resource://gre/modules/Services.jsm",
  OS: "resource://gre/modules/osfile.jsm",
  Log: "resource://gre/modules/Log.jsm",
  FileUtils: "resource://gre/modules/FileUtils.jsm",
  PromiseUtils: "resource://gre/modules/PromiseUtils.jsm",
});

XPCOMUtils.defineLazyServiceGetter(this, "FinalizationWitnessService",
                                   "@mozilla.org/toolkit/finalizationwitness;1",
                                   "nsIFinalizationWitnessService");

// Regular expression used by isInvalidBoundLikeQuery
var likeSqlRegex = /\bLIKE\b\s(?![@:?])/i;

// Counts the number of created connections per database basename(). This is
// used for logging to distinguish connection instances.
var connectionCounters = new Map();

// Tracks identifiers of wrapped connections, that are Storage connections
// opened through mozStorage and then wrapped by Sqlite.jsm to use its syntactic
// sugar API.  Since these connections have an unknown origin, we use this set
// to differentiate their behavior.
var wrappedConnections = new Set();

/**
 * Once `true`, reject any attempt to open or close a database.
 */
var isClosed = false;

var Debugging = {
  // Tests should fail if a connection auto closes.  The exception is
  // when finalization itself is tested, in which case this flag
  // should be set to false.
  failTestsOnAutoClose: true,
};

/**
 * Helper function to check whether LIKE is implemented using proper bindings.
 *
 * @param sql
 *        (string) The SQL query to be verified.
 * @return boolean value telling us whether query was correct or not
*/
function isInvalidBoundLikeQuery(sql) {
  return likeSqlRegex.test(sql);
}

// Displays a script error message
function logScriptError(message) {
  let consoleMessage = Cc["@mozilla.org/scripterror;1"].
                       createInstance(Ci.nsIScriptError);
  let stack = new Error();
  consoleMessage.init(message, stack.fileName, null, stack.lineNumber, 0,
                      Ci.nsIScriptError.errorFlag, "component javascript");
  Services.console.logMessage(consoleMessage);

  // This `Promise.reject` will cause tests to fail.  The debugging
  // flag can be used to suppress this for tests that explicitly
  // test auto closes.
  if (Debugging.failTestsOnAutoClose) {
    Promise.reject(new Error(message));
  }
}

/**
 * Gets connection identifier from its database file name.
 *
 * @param fileName
 *        A database file string name.
 * @return the connection identifier.
 */
function getIdentifierByFileName(fileName) {
  let number = connectionCounters.get(fileName) || 0;
  connectionCounters.set(fileName, number + 1);
  return fileName + "#" + number;
}

/**
 * Barriers used to ensure that Sqlite.jsm is shutdown after all
 * its clients.
 */
XPCOMUtils.defineLazyGetter(this, "Barriers", () => {
  let Barriers = {
    /**
     * Public barrier that clients may use to add blockers to the
     * shutdown of Sqlite.jsm. Triggered by profile-before-change.
     * Once all blockers of this barrier are lifted, we close the
     * ability to open new connections.
     */
    shutdown: new AsyncShutdown.Barrier("Sqlite.jsm: wait until all clients have completed their task"),

    /**
     * Private barrier blocked by connections that are still open.
     * Triggered after Barriers.shutdown is lifted and `isClosed` is
     * set to `true`.
     */
    connections: new AsyncShutdown.Barrier("Sqlite.jsm: wait until all connections are closed"),
  };

  /**
   * Observer for the event which is broadcasted when the finalization
   * witness `_witness` of `OpenedConnection` is garbage collected.
   *
   * The observer is passed the connection identifier of the database
   * connection that is being finalized.
   */
  let finalizationObserver = function(subject, topic, identifier) {
    let connectionData = ConnectionData.byId.get(identifier);

    if (connectionData === undefined) {
      logScriptError("Error: Attempt to finalize unknown Sqlite connection: " +
                     identifier + "\n");
      return;
    }

    ConnectionData.byId.delete(identifier);
    logScriptError("Warning: Sqlite connection '" + identifier +
                   "' was not properly closed. Auto-close triggered by garbage collection.\n");
    connectionData.close();
  };
  Services.obs.addObserver(finalizationObserver, "sqlite-finalization-witness");

  /**
   * Ensure that Sqlite.jsm:
   * - informs its clients before shutting down;
   * - lets clients open connections during shutdown, if necessary;
   * - waits for all connections to be closed before shutdown.
   */
  AsyncShutdown.profileBeforeChange.addBlocker("Sqlite.jsm shutdown blocker",
    async function() {
      await Barriers.shutdown.wait();
      // At this stage, all clients have had a chance to open (and close)
      // their databases. Some previous close operations may still be pending,
      // so we need to wait until they are complete before proceeding.

      // Prevent any new opening.
      isClosed = true;

      // Now, wait until all databases are closed
      await Barriers.connections.wait();

      // Everything closed, no finalization events to catch
      Services.obs.removeObserver(finalizationObserver, "sqlite-finalization-witness");
    },

    function status() {
      if (isClosed) {
        // We are waiting for the connections to close. The interesting
        // status is therefore the list of connections still pending.
        return { description: "Waiting for connections to close",
                 state: Barriers.connections.state };
      }

      // We are still in the first stage: waiting for the barrier
      // to be lifted. The interesting status is therefore that of
      // the barrier.
      return { description: "Waiting for the barrier to be lifted",
               state: Barriers.shutdown.state };
  });

  return Barriers;
});

/**
 * Connection data with methods necessary for closing the connection.
 *
 * To support auto-closing in the event of garbage collection, this
 * data structure contains all the connection data of an opened
 * connection and all of the methods needed for sucessfully closing
 * it.
 *
 * By putting this information in its own separate object, it is
 * possible to store an additional reference to it without preventing
 * a garbage collection of a finalization witness in
 * OpenedConnection. When the witness detects a garbage collection,
 * this object can be used to close the connection.
 *
 * This object contains more methods than just `close`.  When
 * OpenedConnection needs to use the methods in this object, it will
 * dispatch its method calls here.
 */
function ConnectionData(connection, identifier, options = {}) {
  this._log = Log.repository.getLoggerWithMessagePrefix("Sqlite.Connection",
                                                        identifier + ": ");
  this._log.info("Opened");

  this._dbConn = connection;

  // This is a unique identifier for the connection, generated through
  // getIdentifierByFileName.  It may be used for logging or as a key in Maps.
  this._identifier = identifier;

  this._open = true;

  this._cachedStatements = new Map();
  this._anonymousStatements = new Map();
  this._anonymousCounter = 0;

  // A map from statement index to mozIStoragePendingStatement, to allow for
  // canceling prior to finalizing the mozIStorageStatements.
  this._pendingStatements = new Map();

  // Increments for each executed statement for the life of the connection.
  this._statementCounter = 0;

  // Increments whenever we request a unique operation id.
  this._operationsCounter = 0;

  if ("defaultTransactionType" in options) {
    this.defaultTransactionType = options.defaultTransactionType;
  } else {
    this.defaultTransactionType = convertStorageTransactionType(
      this._dbConn.defaultTransactionType);
  }
  this._hasInProgressTransaction = false;
  // Manages a chain of transactions promises, so that new transactions
  // always happen in queue to the previous ones.  It never rejects.
  this._transactionQueue = Promise.resolve();

  this._idleShrinkMS = options.shrinkMemoryOnConnectionIdleMS;
  if (this._idleShrinkMS) {
    this._idleShrinkTimer = Cc["@mozilla.org/timer;1"]
                              .createInstance(Ci.nsITimer);
    // We wait for the first statement execute to start the timer because
    // shrinking now would not do anything.
  }

  // Deferred whose promise is resolved when the connection closing procedure
  // is complete.
  this._deferredClose = PromiseUtils.defer();
  this._closeRequested = false;

  // An AsyncShutdown barrier used to make sure that we wait until clients
  // are done before shutting down the connection.
  this._barrier = new AsyncShutdown.Barrier(`${this._identifier}: waiting for clients`);

  Barriers.connections.client.addBlocker(
    this._identifier + ": waiting for shutdown",
    this._deferredClose.promise,
    () => ({
      identifier: this._identifier,
      isCloseRequested: this._closeRequested,
      hasDbConn: !!this._dbConn,
      hasInProgressTransaction: this._hasInProgressTransaction,
      pendingStatements: this._pendingStatements.size,
      statementCounter: this._statementCounter,
    })
  );

  // We avoid creating a timer every transaction that exists solely as a safety
  // check (e.g. one that never should fire) by reusing it if it's sufficiently
  // close to when the previous promise was created (see bug 1442353 and
  // `_getTimeoutPromise` for more info).
  this._timeoutPromise = null;
  // The last timestamp when we should consider using `this._timeoutPromise`.
  this._timeoutPromiseExpires = 0;
}

/**
 * Map of connection identifiers to ConnectionData objects
 *
 * The connection identifier is a human-readable name of the
 * database. Used by finalization witnesses to be able to close opened
 * connections on garbage collection.
 *
 * Key: _identifier of ConnectionData
 * Value: ConnectionData object
 */
ConnectionData.byId = new Map();

ConnectionData.prototype = Object.freeze({
  /**
   * Run a task, ensuring that its execution will not be interrupted by shutdown.
   *
   * As the operations of this module are asynchronous, a sequence of operations,
   * or even an individual operation, can still be pending when the process shuts
   * down. If any of this operations is a write, this can cause data loss, simply
   * because the write has not been completed (or even started) by shutdown.
   *
   * To avoid this risk, clients are encouraged to use `executeBeforeShutdown` for
   * any write operation, as follows:
   *
   * myConnection.executeBeforeShutdown("Bookmarks: Removing a bookmark",
   *   async function(db) {
   *     // The connection will not be closed and shutdown will not proceed
   *     // until this task has completed.
   *
   *     // `db` exposes the same API as `myConnection` but provides additional
   *     // logging support to help debug hard-to-catch shutdown timeouts.
   *
   *     await db.execute(...);
   * }));
   *
   * @param {string} name A human-readable name for the ongoing operation, used
   *  for logging and debugging purposes.
   * @param {function(db)} task A function that takes as argument a Sqlite.jsm
   *  db and returns a Promise.
   */
  executeBeforeShutdown(parent, name, task) {
    if (!name) {
      throw new TypeError("Expected a human-readable name as first argument");
    }
    if (typeof task != "function") {
      throw new TypeError("Expected a function as second argument");
    }
    if (this._closeRequested) {
      throw new Error(`${this._identifier}: cannot execute operation ${name}, the connection is already closing`);
    }

    // Status, used for AsyncShutdown crash reports.
    let status = {
      // The latest command started by `task`, either as a
      // sql string, or as one of "<not started>" or "<closing>".
      command: "<not started>",

      // `true` if `command` was started but not completed yet.
      isPending: false,
    };

    // An object with the same API as `this` but with
    // additional logging. To keep logging simple, we
    // assume that `task` is not running several queries
    // concurrently.
    let loggedDb = Object.create(parent, {
      execute: {
        value: async (sql, ...rest) => {
          status.isPending = true;
          status.command = sql;
          try {
            return (await this.execute(sql, ...rest));
          } finally {
            status.isPending = false;
          }
        },
      },
      close: {
        value: async () => {
          status.isPending = false;
          status.command = "<close>";
          try {
            return (await this.close());
          } finally {
            status.isPending = false;
          }
        },
      },
      executeCached: {
        value: async (sql, ...rest) => {
          status.isPending = false;
          status.command = sql;
          try {
            return (await this.executeCached(sql, ...rest));
          } finally {
            status.isPending = false;
          }
        },
      },
    });

    let promiseResult = task(loggedDb);
    if (!promiseResult || typeof promiseResult != "object" || !("then" in promiseResult)) {
      throw new TypeError("Expected a Promise");
    }
    let key = `${this._identifier}: ${name} (${this._getOperationId()})`;
    let promiseComplete = promiseResult.catch(() => {});
    this._barrier.client.addBlocker(key, promiseComplete, {
      fetchState: () => status,
    });

    return (async () => {
      try {
        return (await promiseResult);
      } finally {
        this._barrier.client.removeBlocker(key, promiseComplete);
      }
    })();
  },
  close() {
    this._closeRequested = true;

    if (!this._dbConn) {
      return this._deferredClose.promise;
    }

    this._log.debug("Request to close connection.");
    this._clearIdleShrinkTimer();

    return this._barrier.wait().then(() => {
      if (!this._dbConn) {
        return undefined;
      }
      return this._finalize();
    });
  },

  clone(readOnly = false) {
    this.ensureOpen();

    this._log.debug("Request to clone connection.");

    let options = {
      connection: this._dbConn,
      readOnly,
    };
    if (this._idleShrinkMS)
      options.shrinkMemoryOnConnectionIdleMS = this._idleShrinkMS;

    return cloneStorageConnection(options);
  },
  _getOperationId() {
    return this._operationsCounter++;
  },
  _finalize() {
    this._log.debug("Finalizing connection.");
    // Cancel any pending statements.
    for (let [/* k */, statement] of this._pendingStatements) {
      statement.cancel();
    }
    this._pendingStatements.clear();

    // We no longer need to track these.
    this._statementCounter = 0;

    // Next we finalize all active statements.
    for (let [/* k */, statement] of this._anonymousStatements) {
      statement.finalize();
    }
    this._anonymousStatements.clear();

    for (let [/* k */, statement] of this._cachedStatements) {
      statement.finalize();
    }
    this._cachedStatements.clear();

    // This guards against operations performed between the call to this
    // function and asyncClose() finishing. See also bug 726990.
    this._open = false;

    // We must always close the connection at the Sqlite.jsm-level, not
    // necessarily at the mozStorage-level.
    let markAsClosed = () => {
      this._log.info("Closed");
      // Now that the connection is closed, no need to keep
      // a blocker for Barriers.connections.
      Barriers.connections.client.removeBlocker(this._deferredClose.promise);
      this._deferredClose.resolve();
    };
    if (wrappedConnections.has(this._identifier)) {
      wrappedConnections.delete(this._identifier);
      this._dbConn = null;
      markAsClosed();
    } else {
      this._log.debug("Calling asyncClose().");
      this._dbConn.asyncClose(markAsClosed);
      this._dbConn = null;
    }
    return this._deferredClose.promise;
  },

  executeCached(sql, params = null, onRow = null) {
    this.ensureOpen();

    if (!sql) {
      throw new Error("sql argument is empty.");
    }

    let statement = this._cachedStatements.get(sql);
    if (!statement) {
      statement = this._dbConn.createAsyncStatement(sql);
      this._cachedStatements.set(sql, statement);
    }

    this._clearIdleShrinkTimer();

    return new Promise((resolve, reject) => {
      try {
        this._executeStatement(sql, statement, params, onRow).then(
          result => {
            this._startIdleShrinkTimer();
            resolve(result);
          },
          error => {
            this._startIdleShrinkTimer();
            reject(error);
          }
        );
      } catch (ex) {
        this._startIdleShrinkTimer();
        throw ex;
      }
    });
  },

  execute(sql, params = null, onRow = null) {
    if (typeof(sql) != "string") {
      throw new Error("Must define SQL to execute as a string: " + sql);
    }

    this.ensureOpen();

    let statement = this._dbConn.createAsyncStatement(sql);
    let index = this._anonymousCounter++;

    this._anonymousStatements.set(index, statement);
    this._clearIdleShrinkTimer();

    let onFinished = () => {
      this._anonymousStatements.delete(index);
      statement.finalize();
      this._startIdleShrinkTimer();
    };

    return new Promise((resolve, reject) => {
      try {
        this._executeStatement(sql, statement, params, onRow).then(
          rows => {
            onFinished();
            resolve(rows);
          },
          error => {
            onFinished();
            reject(error);
          }
        );
      } catch (ex) {
        onFinished();
        throw ex;
      }
    });
  },

  get transactionInProgress() {
    return this._open && this._hasInProgressTransaction;
  },

  executeTransaction(func, type) {
    if (type == OpenedConnection.prototype.TRANSACTION_DEFAULT) {
      type = this.defaultTransactionType;
    } else if (!OpenedConnection.TRANSACTION_TYPES.includes(type)) {
      throw new Error("Unknown transaction type: " + type);
    }
    this.ensureOpen();

    this._log.debug("Beginning transaction");

    let promise = this._transactionQueue.then(() => {
      if (this._closeRequested) {
        throw new Error("Transaction canceled due to a closed connection.");
      }

      let transactionPromise = (async () => {
        // At this point we should never have an in progress transaction, since
        // they are enqueued.
        if (this._hasInProgressTransaction) {
          console.error("Unexpected transaction in progress when trying to start a new one.");
        }
        this._hasInProgressTransaction = true;
        try {
          // We catch errors in statement execution to detect nested transactions.
          try {
            await this.execute("BEGIN " + type + " TRANSACTION");
          } catch (ex) {
            // Unfortunately, if we are wrapping an existing connection, a
            // transaction could have been started by a client of the same
            // connection that doesn't use Sqlite.jsm (e.g. C++ consumer).
            // The best we can do is proceed without a transaction and hope
            // things won't break.
            if (wrappedConnections.has(this._identifier)) {
              this._log.warn("A new transaction could not be started cause the wrapped connection had one in progress", ex);
              // Unmark the in progress transaction, since it's managed by
              // some other non-Sqlite.jsm client.  See the comment above.
              this._hasInProgressTransaction = false;
            } else {
              this._log.warn("A transaction was already in progress, likely a nested transaction", ex);
              throw ex;
            }
          }

          let result;
          try {
            result = await func();
          } catch (ex) {
            // It's possible that the exception has been caused by trying to
            // close the connection in the middle of a transaction.
            if (this._closeRequested) {
              this._log.warn("Connection closed while performing a transaction", ex);
            } else {
              this._log.warn("Error during transaction. Rolling back", ex);
              // If we began a transaction, we must rollback it.
              if (this._hasInProgressTransaction) {
                try {
                  await this.execute("ROLLBACK TRANSACTION");
                } catch (inner) {
                  this._log.warn("Could not roll back transaction", inner);
                }
              }
            }
            // Rethrow the exception.
            throw ex;
          }

          // See comment above about connection being closed during transaction.
          if (this._closeRequested) {
            this._log.warn("Connection closed before committing the transaction.");
            throw new Error("Connection closed before committing the transaction.");
          }

          // If we began a transaction, we must commit it.
          if (this._hasInProgressTransaction) {
            try {
              await this.execute("COMMIT TRANSACTION");
            } catch (ex) {
              this._log.warn("Error committing transaction", ex);
              throw ex;
            }
          }

          return result;
        } finally {
          this._hasInProgressTransaction = false;
        }
      })();

      // If a transaction yields on a never resolved promise, or is mistakenly
      // nested, it could hang the transactions queue forever.  Thus we timeout
      // the execution after a meaningful amount of time, to ensure in any case
      // we'll proceed after a while.
      let timeoutPromise = this._getTimeoutPromise();
      return Promise.race([transactionPromise, timeoutPromise]);
    });
    // Atomically update the queue before anyone else has a chance to enqueue
    // further transactions.
    this._transactionQueue = promise.catch(ex => { console.error(ex); });

    // Make sure that we do not shutdown the connection during a transaction.
    this._barrier.client.addBlocker(`Transaction (${this._getOperationId()})`,
      this._transactionQueue);
    return promise;
  },

  shrinkMemory() {
    this._log.info("Shrinking memory usage.");
    let onShrunk = this._clearIdleShrinkTimer.bind(this);
    return this.execute("PRAGMA shrink_memory").then(onShrunk, onShrunk);
  },

  discardCachedStatements() {
    let count = 0;
    for (let [/* k */, statement] of this._cachedStatements) {
      ++count;
      statement.finalize();
    }
    this._cachedStatements.clear();
    this._log.debug("Discarded " + count + " cached statements.");
    return count;
  },

  interrupt() {
    this._log.info("Trying to interrupt.");
    this.ensureOpen();
    this._dbConn.interrupt();
  },

  /**
   * Helper method to bind parameters of various kinds through
   * reflection.
   */
  _bindParameters(statement, params) {
    if (!params) {
      return;
    }

    function bindParam(obj, key, val) {
      let isBlob = val && typeof val == "object" &&
                   val.constructor.name == "Uint8Array";
      let args = [key, val];
      if (isBlob)
        args.push(val.length);
      let methodName =
        `bind${isBlob ? "Blob" : ""}By${typeof key == "number" ? "Index" : "Name"}`;
      obj[methodName](...args);
    }

    if (Array.isArray(params)) {
      // It's an array of separate params.
      if (params.length && (typeof(params[0]) == "object")) {
        let paramsArray = statement.newBindingParamsArray();
        for (let p of params) {
          let bindings = paramsArray.newBindingParams();
          for (let [key, value] of Object.entries(p)) {
            bindParam(bindings, key, value);
          }
          paramsArray.addParams(bindings);
        }

        statement.bindParameters(paramsArray);
        return;
      }

      // Indexed params.
      for (let i = 0; i < params.length; i++) {
        bindParam(statement, i, params[i]);
      }
      return;
    }

    // Named params.
    if (params && typeof(params) == "object") {
      for (let k in params) {
        bindParam(statement, k, params[k]);
      }
      return;
    }

    throw new Error("Invalid type for bound parameters. Expected Array or " +
                    "object. Got: " + params);
  },

  _executeStatement(sql, statement, params, onRow) {
    if (statement.state != statement.MOZ_STORAGE_STATEMENT_READY) {
      throw new Error("Statement is not ready for execution.");
    }

    if (onRow && typeof(onRow) != "function") {
      throw new Error("onRow must be a function. Got: " + onRow);
    }

    this._bindParameters(statement, params);

    let index = this._statementCounter++;

    let deferred = PromiseUtils.defer();
    let userCancelled = false;
    let errors = [];
    let rows = [];
    let handledRow = false;

    // Don't incur overhead for serializing params unless the messages go
    // somewhere.
    if (this._log.level <= Log.Level.Trace) {
      let msg = "Stmt #" + index + " " + sql;

      if (params) {
        msg += " - " + JSON.stringify(params);
      }
      this._log.trace(msg);
    } else {
      this._log.debug("Stmt #" + index + " starting");
    }

    let self = this;
    let pending = statement.executeAsync({
      handleResult(resultSet) {
        // .cancel() may not be immediate and handleResult() could be called
        // after a .cancel().
        for (let row = resultSet.getNextRow(); row && !userCancelled; row = resultSet.getNextRow()) {
          if (!onRow) {
            rows.push(row);
            continue;
          }

          handledRow = true;

          try {
            onRow(row, () => {
              userCancelled = true;
              pending.cancel();
            });
          } catch (e) {
            self._log.warn("Exception when calling onRow callback", e);
          }
        }
      },

      handleError(error) {
        self._log.info("Error when executing SQL (" +
                       error.result + "): " + error.message);
        errors.push(error);
      },

      handleCompletion(reason) {
        self._log.debug("Stmt #" + index + " finished.");
        self._pendingStatements.delete(index);

        switch (reason) {
          case Ci.mozIStorageStatementCallback.REASON_FINISHED:
          case Ci.mozIStorageStatementCallback.REASON_CANCELED:
            // If there is an onRow handler, we always instead resolve to a
            // boolean indicating whether the onRow handler was called or not.
            let result = onRow ? handledRow : rows;
            deferred.resolve(result);
            break;

          case Ci.mozIStorageStatementCallback.REASON_ERROR:
            let error = new Error("Error(s) encountered during statement execution: " + errors.map(e => e.message).join(", "));
            error.errors = errors;
            deferred.reject(error);
            break;

          default:
            deferred.reject(new Error("Unknown completion reason code: " +
                                      reason));
            break;
        }
      },
    });

    this._pendingStatements.set(index, pending);
    return deferred.promise;
  },

  ensureOpen() {
    if (!this._open) {
      throw new Error("Connection is not open.");
    }
  },

  _clearIdleShrinkTimer() {
    if (!this._idleShrinkTimer) {
      return;
    }

    this._idleShrinkTimer.cancel();
  },

  _startIdleShrinkTimer() {
    if (!this._idleShrinkTimer) {
      return;
    }

    this._idleShrinkTimer.initWithCallback(this.shrinkMemory.bind(this),
                                           this._idleShrinkMS,
                                           this._idleShrinkTimer.TYPE_ONE_SHOT);
  },

  // Returns a promise that will resolve after a time comprised between 80% of
  // `TRANSACTIONS_QUEUE_TIMEOUT_MS` and `TRANSACTIONS_QUEUE_TIMEOUT_MS`. Use
  // this promise instead of creating several individual timers to reduce the
  // overhead due to timers (see bug 1442353).
  _getTimeoutPromise() {
    if (this._timeoutPromise && Cu.now() <= this._timeoutPromiseExpires) {
      return this._timeoutPromise;
    }
    let timeoutPromise = new Promise((resolve, reject) => {
      setTimeout(() => {
        // Clear out this._timeoutPromise if it hasn't changed since we set it.
        if (this._timeoutPromise == timeoutPromise) {
          this._timeoutPromise = null;
        }
        reject(new Error("Transaction timeout, most likely caused by unresolved pending work."));
      }, TRANSACTIONS_QUEUE_TIMEOUT_MS);
    });
    this._timeoutPromise = timeoutPromise;
    this._timeoutPromiseExpires = Cu.now() + TRANSACTIONS_QUEUE_TIMEOUT_MS * 0.2;
    return this._timeoutPromise;
  },
});

/**
 * Opens a connection to a SQLite database.
 *
 * The following parameters can control the connection:
 *
 *   path -- (string) The filesystem path of the database file to open. If the
 *       file does not exist, a new database will be created.
 *
 *   sharedMemoryCache -- (bool) Whether multiple connections to the database
 *       share the same memory cache. Sharing the memory cache likely results
 *       in less memory utilization. However, sharing also requires connections
 *       to obtain a lock, possibly making database access slower. Defaults to
 *       true.
 *
 *   shrinkMemoryOnConnectionIdleMS -- (integer) If defined, the connection
 *       will attempt to minimize its memory usage after this many
 *       milliseconds of connection idle. The connection is idle when no
 *       statements are executing. There is no default value which means no
 *       automatic memory minimization will occur. Please note that this is
 *       *not* a timer on the idle service and this could fire while the
 *       application is active.
 *
 *   readOnly -- (bool) Whether to open the database with SQLITE_OPEN_READONLY
 *       set. If used, writing to the database will fail. Defaults to false.
 *
 *   ignoreLockingMode -- (bool) Whether to ignore locks on the database held
 *       by other connections. If used, implies readOnly. Defaults to false.
 *       USE WITH EXTREME CAUTION. This mode WILL produce incorrect results or
 *       return "false positive" corruption errors if other connections write
 *       to the DB at the same time.
 *
 * FUTURE options to control:
 *
 *   special named databases
 *   pragma TEMP STORE = MEMORY
 *   TRUNCATE JOURNAL
 *   SYNCHRONOUS = full
 *
 * @param options
 *        (Object) Parameters to control connection and open options.
 *
 * @return Promise<OpenedConnection>
 */
function openConnection(options) {
  let log = Log.repository.getLogger("Sqlite.ConnectionOpener");

  if (!options.path) {
    throw new Error("path not specified in connection options.");
  }

  if (isClosed) {
    throw new Error("Sqlite.jsm has been shutdown. Cannot open connection to: " + options.path);
  }

  // Retains absolute paths and normalizes relative as relative to profile.
  let path = OS.Path.join(OS.Constants.Path.profileDir, options.path);

  let sharedMemoryCache = "sharedMemoryCache" in options ?
                            options.sharedMemoryCache : true;

  let openedOptions = {};

  if ("shrinkMemoryOnConnectionIdleMS" in options) {
    if (!Number.isInteger(options.shrinkMemoryOnConnectionIdleMS)) {
      throw new Error("shrinkMemoryOnConnectionIdleMS must be an integer. " +
                      "Got: " + options.shrinkMemoryOnConnectionIdleMS);
    }

    openedOptions.shrinkMemoryOnConnectionIdleMS =
      options.shrinkMemoryOnConnectionIdleMS;
  }

  if ("defaultTransactionType" in options) {
    let defaultTransactionType = options.defaultTransactionType;
    if (!OpenedConnection.TRANSACTION_TYPES.includes(defaultTransactionType)) {
      throw new Error("Unknown default transaction type: " +
                      defaultTransactionType);
    }

    openedOptions.defaultTransactionType = defaultTransactionType;
  }

  let file = FileUtils.File(path);
  let identifier = getIdentifierByFileName(OS.Path.basename(path));

  log.info("Opening database: " + path + " (" + identifier + ")");

  return new Promise((resolve, reject) => {
    let dbOptions = Cc["@mozilla.org/hash-property-bag;1"].
                    createInstance(Ci.nsIWritablePropertyBag);
    if (!sharedMemoryCache) {
      dbOptions.setProperty("shared", false);
    }
    if (options.readOnly) {
      dbOptions.setProperty("readOnly", true);
    }
    if (options.ignoreLockingMode) {
      dbOptions.setProperty("ignoreLockingMode", true);
      dbOptions.setProperty("readOnly", true);
    }

    dbOptions = dbOptions.enumerator.hasMoreElements() ? dbOptions : null;

    Services.storage.openAsyncDatabase(file, dbOptions, (status, connection) => {
      if (!connection) {
        log.warn(`Could not open connection to ${path}: ${status}`);
        let error = new Components.Exception(`Could not open connection to ${path}: ${status}`,
                                              status);
        reject(error);
        return;
      }
      log.info("Connection opened");
      try {
        resolve(
          new OpenedConnection(connection.QueryInterface(Ci.mozIStorageAsyncConnection),
                               identifier, openedOptions));
      } catch (ex) {
        log.warn("Could not open database", ex);
        connection.asyncClose();
        reject(ex);
      }
    });
  });
}

/**
 * Creates a clone of an existing and open Storage connection.  The clone has
 * the same underlying characteristics of the original connection and is
 * returned in form of an OpenedConnection handle.
 *
 * The following parameters can control the cloned connection:
 *
 *   connection -- (mozIStorageAsyncConnection) The original Storage connection
 *       to clone.  It's not possible to clone connections to memory databases.
 *
 *   readOnly -- (boolean) - If true the clone will be read-only.  If the
 *       original connection is already read-only, the clone will be, regardless
 *       of this option.  If the original connection is using the shared cache,
 *       this parameter will be ignored and the clone will be as privileged as
 *       the original connection.
 *   shrinkMemoryOnConnectionIdleMS -- (integer) If defined, the connection
 *       will attempt to minimize its memory usage after this many
 *       milliseconds of connection idle. The connection is idle when no
 *       statements are executing. There is no default value which means no
 *       automatic memory minimization will occur. Please note that this is
 *       *not* a timer on the idle service and this could fire while the
 *       application is active.
 *
 *
 * @param options
 *        (Object) Parameters to control connection and clone options.
 *
 * @return Promise<OpenedConnection>
 */
function cloneStorageConnection(options) {
  let log = Log.repository.getLogger("Sqlite.ConnectionCloner");

  let source = options && options.connection;
  if (!source) {
    throw new TypeError("connection not specified in clone options.");
  }
  if (!(source instanceof Ci.mozIStorageAsyncConnection)) {
    throw new TypeError("Connection must be a valid Storage connection.");
  }

  if (isClosed) {
    throw new Error("Sqlite.jsm has been shutdown. Cannot clone connection to: " + source.databaseFile.path);
  }

  let openedOptions = {};

  if ("shrinkMemoryOnConnectionIdleMS" in options) {
    if (!Number.isInteger(options.shrinkMemoryOnConnectionIdleMS)) {
      throw new TypeError("shrinkMemoryOnConnectionIdleMS must be an integer. " +
                          "Got: " + options.shrinkMemoryOnConnectionIdleMS);
    }
    openedOptions.shrinkMemoryOnConnectionIdleMS =
      options.shrinkMemoryOnConnectionIdleMS;
  }

  let path = source.databaseFile.path;
  let identifier = getIdentifierByFileName(OS.Path.basename(path));

  log.info("Cloning database: " + path + " (" + identifier + ")");

  return new Promise((resolve, reject) => {
    source.asyncClone(!!options.readOnly, (status, connection) => {
      if (!connection) {
        log.warn("Could not clone connection: " + status);
        reject(new Error("Could not clone connection: " + status));
      }
      log.info("Connection cloned");
      try {
        let conn = connection.QueryInterface(Ci.mozIStorageAsyncConnection);
        resolve(new OpenedConnection(conn, identifier, openedOptions));
      } catch (ex) {
        log.warn("Could not clone database", ex);
        connection.asyncClose();
        reject(ex);
      }
    });
  });
}

/**
 * Wraps an existing and open Storage connection with Sqlite.jsm API.  The
 * wrapped connection clone has the same underlying characteristics of the
 * original connection and is returned in form of an OpenedConnection handle.
 *
 * Clients are responsible for closing both the Sqlite.jsm wrapper and the
 * underlying mozStorage connection.
 *
 * The following parameters can control the wrapped connection:
 *
 *   connection -- (mozIStorageAsyncConnection) The original Storage connection
 *       to wrap.
 *
 * @param options
 *        (Object) Parameters to control connection and wrap options.
 *
 * @return Promise<OpenedConnection>
 */
function wrapStorageConnection(options) {
  let log = Log.repository.getLogger("Sqlite.ConnectionWrapper");

  let connection = options && options.connection;
  if (!connection || !(connection instanceof Ci.mozIStorageAsyncConnection)) {
    throw new TypeError("connection not specified or invalid.");
  }

  if (isClosed) {
    throw new Error("Sqlite.jsm has been shutdown. Cannot wrap connection to: " + connection.databaseFile.path);
  }

  let identifier = getIdentifierByFileName(connection.databaseFile.leafName);

  log.info("Wrapping database: " + identifier);
  return new Promise(resolve => {
    try {
      let conn = connection.QueryInterface(Ci.mozIStorageAsyncConnection);
      let wrapper = new OpenedConnection(conn, identifier);
      // We must not handle shutdown of a wrapped connection, since that is
      // already handled by the opener.
      wrappedConnections.add(identifier);
      resolve(wrapper);
    } catch (ex) {
      log.warn("Could not wrap database", ex);
      throw ex;
    }
  });
}

/**
 * Handle on an opened SQLite database.
 *
 * This is essentially a glorified wrapper around mozIStorageConnection.
 * However, it offers some compelling advantages.
 *
 * The main functions on this type are `execute` and `executeCached`. These are
 * ultimately how all SQL statements are executed. It's worth explaining their
 * differences.
 *
 * `execute` is used to execute one-shot SQL statements. These are SQL
 * statements that are executed one time and then thrown away. They are useful
 * for dynamically generated SQL statements and clients who don't care about
 * performance (either their own or wasting resources in the overall
 * application). Because of the performance considerations, it is recommended
 * to avoid `execute` unless the statement you are executing will only be
 * executed once or seldomly.
 *
 * `executeCached` is used to execute a statement that will presumably be
 * executed multiple times. The statement is parsed once and stuffed away
 * inside the connection instance. Subsequent calls to `executeCached` will not
 * incur the overhead of creating a new statement object. This should be used
 * in preference to `execute` when a specific SQL statement will be executed
 * multiple times.
 *
 * Instances of this type are not meant to be created outside of this file.
 * Instead, first open an instance of `UnopenedSqliteConnection` and obtain
 * an instance of this type by calling `open`.
 *
 * FUTURE IMPROVEMENTS
 *
 *   Ability to enqueue operations. Currently there can be race conditions,
 *   especially as far as transactions are concerned. It would be nice to have
 *   an enqueueOperation(func) API that serially executes passed functions.
 *
 *   Support for SAVEPOINT (named/nested transactions) might be useful.
 *
 * @param connection
 *        (mozIStorageConnection) Underlying SQLite connection.
 * @param identifier
 *        (string) The unique identifier of this database. It may be used for
 *        logging or as a key in Maps.
 * @param options [optional]
 *        (object) Options to control behavior of connection. See
 *        `openConnection`.
 */
function OpenedConnection(connection, identifier, options = {}) {
  // Store all connection data in a field distinct from the
  // witness. This enables us to store an additional reference to this
  // field without preventing garbage collection of
  // OpenedConnection. On garbage collection, we will still be able to
  // close the database using this extra reference.
  this._connectionData = new ConnectionData(connection, identifier, options);

  // Store the extra reference in a map with connection identifier as
  // key.
  ConnectionData.byId.set(this._connectionData._identifier,
                          this._connectionData);

  // Make a finalization witness. If this object is garbage collected
  // before its `forget` method has been called, an event with topic
  // "sqlite-finalization-witness" is broadcasted along with the
  // connection identifier string of the database.
  this._witness = FinalizationWitnessService.make(
    "sqlite-finalization-witness",
    this._connectionData._identifier);
}

OpenedConnection.TRANSACTION_TYPES = ["DEFERRED", "IMMEDIATE", "EXCLUSIVE"];

// Converts a `mozIStorageAsyncConnection::TRANSACTION_*` constant into the
// corresponding `OpenedConnection.TRANSACTION_TYPES` constant.
function convertStorageTransactionType(type) {
  if (!(type in OpenedConnection.TRANSACTION_TYPES)) {
    throw new Error("Unknown storage transaction type: " + type);
  }
  return OpenedConnection.TRANSACTION_TYPES[type];
}

OpenedConnection.prototype = Object.freeze({
  TRANSACTION_DEFAULT: "DEFAULT",
  TRANSACTION_DEFERRED: "DEFERRED",
  TRANSACTION_IMMEDIATE: "IMMEDIATE",
  TRANSACTION_EXCLUSIVE: "EXCLUSIVE",

  /**
   * Returns a handle to the underlying `mozIStorageAsyncConnection`. This is
   * ⚠️ **extremely unsafe** ⚠️ because `Sqlite.jsm` continues to manage the
   * connection's lifecycle, including transactions and shutdown blockers.
   * Misusing the raw connection can easily lead to data loss, memory leaks,
   * and errors.
   *
   * Consumers of the raw connection **must not** close or re-wrap it,
   * and should not run statements concurrently with `Sqlite.jsm`.
   *
   * It's _much_ safer to open a `mozIStorage{Async}Connection` yourself,
   * and access it from JavaScript via `Sqlite.wrapStorageConnection`.
   * `unsafeRawConnection` is an escape hatch for cases where you can't
   * do that.
   *
   * Please do _not_ add new uses of `unsafeRawConnection` without review
   * from a storage peer.
   */
  get unsafeRawConnection() {
    return this._connectionData._dbConn;
  },

  /**
   * The integer schema version of the database.
   *
   * This is 0 if not schema version has been set.
   *
   * @return Promise<int>
   */
  getSchemaVersion(schemaName = "main") {
    return this.execute(`PRAGMA ${schemaName}.user_version`).then(
      function onSuccess(result) {
        if (result == null) {
          return 0;
        }
        return result[0].getInt32(0);
      }
    );
  },

  setSchemaVersion(value, schemaName = "main") {
    if (!Number.isInteger(value)) {
      // Guarding against accidental SQLi
      throw new TypeError("Schema version must be an integer. Got " + value);
    }
    this._connectionData.ensureOpen();
    return this.execute(`PRAGMA ${schemaName}.user_version = ${value}`);
  },

  /**
   * Close the database connection.
   *
   * This must be performed when you are finished with the database.
   *
   * Closing the database connection has the side effect of forcefully
   * cancelling all active statements. Therefore, callers should ensure that
   * all active statements have completed before closing the connection, if
   * possible.
   *
   * The returned promise will be resolved once the connection is closed.
   * Successive calls to close() return the same promise.
   *
   * IMPROVEMENT: Resolve the promise to a closed connection which can be
   * reopened.
   *
   * @return Promise<>
   */
  close() {
    // Unless cleanup has already been done by a previous call to
    // `close`, delete the database entry from map and tell the
    // finalization witness to forget.
    if (ConnectionData.byId.has(this._connectionData._identifier)) {
      ConnectionData.byId.delete(this._connectionData._identifier);
      this._witness.forget();
    }
    return this._connectionData.close();
  },

  /**
   * Clones this connection to a new Sqlite one.
   *
   * The following parameters can control the cloned connection:
   *
   * @param readOnly
   *        (boolean) - If true the clone will be read-only.  If the original
   *        connection is already read-only, the clone will be, regardless of
   *        this option.  If the original connection is using the shared cache,
   *        this parameter will be ignored and the clone will be as privileged as
   *        the original connection.
   *
   * @return Promise<OpenedConnection>
   */
  clone(readOnly = false) {
    return this._connectionData.clone(readOnly);
  },

  executeBeforeShutdown(name, task) {
    return this._connectionData.executeBeforeShutdown(this, name, task);
  },

  /**
   * Execute a SQL statement and cache the underlying statement object.
   *
   * This function executes a SQL statement and also caches the underlying
   * derived statement object so subsequent executions are faster and use
   * less resources.
   *
   * This function optionally binds parameters to the statement as well as
   * optionally invokes a callback for every row retrieved.
   *
   * By default, no parameters are bound and no callback will be invoked for
   * every row.
   *
   * Bound parameters can be defined as an Array of positional arguments or
   * an object mapping named parameters to their values. If there are no bound
   * parameters, the caller can pass nothing or null for this argument.
   *
   * Callers are encouraged to pass objects rather than Arrays for bound
   * parameters because they prevent foot guns. With positional arguments, it
   * is simple to modify the parameter count or positions without fixing all
   * users of the statement. Objects/named parameters are a little safer
   * because changes in order alone won't result in bad things happening.
   *
   * When `onRow` is not specified, all returned rows are buffered before the
   * returned promise is resolved. For INSERT or UPDATE statements, this has
   * no effect because no rows are returned from these. However, it has
   * implications for SELECT statements.
   *
   * If your SELECT statement could return many rows or rows with large amounts
   * of data, for performance reasons it is recommended to pass an `onRow`
   * handler. Otherwise, the buffering may consume unacceptable amounts of
   * resources.
   *
   * If the second parameter of an `onRow` handler is called during execution
   * of the `onRow` handler, the execution of the statement is immediately
   * cancelled. Subsequent rows will not be processed and no more `onRow`
   * invocations will be made. The promise is resolved immediately.
   *
   * If an exception is thrown by the `onRow` handler, the exception is logged
   * and processing of subsequent rows occurs as if nothing happened. The
   * promise is still resolved (not rejected).
   *
   * The return value is a promise that will be resolved when the statement
   * has completed fully.
   *
   * The promise will be rejected with an `Error` instance if the statement
   * did not finish execution fully. The `Error` may have an `errors` property.
   * If defined, it will be an Array of objects describing individual errors.
   * Each object has the properties `result` and `message`. `result` is a
   * numeric error code and `message` is a string description of the problem.
   *
   * @param name
   *        (string) The name of the registered statement to execute.
   * @param params optional
   *        (Array or object) Parameters to bind.
   * @param onRow optional
   *        (function) Callback to receive each row from result.
   */
  executeCached(sql, params = null, onRow = null) {
    if (isInvalidBoundLikeQuery(sql)) {
      throw new Error("Please enter a LIKE clause with bindings");
    }
    return this._connectionData.executeCached(sql, params, onRow);
  },

  /**
   * Execute a one-shot SQL statement.
   *
   * If you find yourself feeding the same SQL string in this function, you
   * should *not* use this function and instead use `executeCached`.
   *
   * See `executeCached` for the meaning of the arguments and extended usage info.
   *
   * @param sql
   *        (string) SQL to execute.
   * @param params optional
   *        (Array or Object) Parameters to bind to the statement.
   * @param onRow optional
   *        (function) Callback to receive result of a single row.
   */
  execute(sql, params = null, onRow = null) {
    if (isInvalidBoundLikeQuery(sql)) {
      throw new Error("Please enter a LIKE clause with bindings");
    }
    return this._connectionData.execute(sql, params, onRow);
  },

  /**
   * The default behavior for transactions run on this connection.
   */
  get defaultTransactionType() {
    return this._connectionData.defaultTransactionType;
  },

  /**
   * Whether a transaction is currently in progress.
   */
  get transactionInProgress() {
    return this._connectionData.transactionInProgress;
  },

  /**
   * Perform a transaction.
   *
   * *****************************************************************************
   * YOU SHOULD _NEVER_ NEST executeTransaction CALLS FOR ANY REASON, NOR
   * DIRECTLY, NOR THROUGH OTHER PROMISES.
   * FOR EXAMPLE, NEVER DO SOMETHING LIKE:
   *   await executeTransaction(async function () {
   *     ...some_code...
   *     await executeTransaction(async function () { // WRONG!
   *       ...some_code...
   *     })
   *     await someCodeThatExecuteTransaction(); // WRONG!
   *     await neverResolvedPromise; // WRONG!
   *   });
   * NESTING CALLS WILL BLOCK ANY FUTURE TRANSACTION UNTIL A TIMEOUT KICKS IN.
   * *****************************************************************************
   *
   * A transaction is specified by a user-supplied function that is an
   * async function. The function receives this connection instance as its argument.
   *
   * The supplied function is expected to return promises. These are often
   * promises created by calling `execute` and `executeCached`. If the
   * generator is exhausted without any errors being thrown, the
   * transaction is committed. If an error occurs, the transaction is
   * rolled back.
   *
   * The returned value from this function is a promise that will be resolved
   * once the transaction has been committed or rolled back. The promise will
   * be resolved to whatever value the supplied function resolves to. If
   * the transaction is rolled back, the promise is rejected.
   *
   * @param func
   *        (function) What to perform as part of the transaction.
   * @param type optional
   *        One of the TRANSACTION_* constants attached to this type.
   */
  executeTransaction(func, type = this.TRANSACTION_DEFAULT) {
    return this._connectionData.executeTransaction(() => func(this), type);
  },

  /**
   * Whether a table exists in the database (both persistent and temporary tables).
   *
   * @param name
   *        (string) Name of the table.
   *
   * @return Promise<bool>
   */
  tableExists(name) {
    return this.execute(
      "SELECT name FROM (SELECT * FROM sqlite_master UNION ALL " +
                        "SELECT * FROM sqlite_temp_master) " +
      "WHERE type = 'table' AND name=?",
      [name])
      .then(function onResult(rows) {
        return Promise.resolve(rows.length > 0);
      }
    );
  },

  /**
   * Whether a named index exists (both persistent and temporary tables).
   *
   * @param name
   *        (string) Name of the index.
   *
   * @return Promise<bool>
   */
  indexExists(name) {
    return this.execute(
      "SELECT name FROM (SELECT * FROM sqlite_master UNION ALL " +
                        "SELECT * FROM sqlite_temp_master) " +
      "WHERE type = 'index' AND name=?",
      [name])
      .then(function onResult(rows) {
        return Promise.resolve(rows.length > 0);
      }
    );
  },

  /**
   * Free up as much memory from the underlying database connection as possible.
   *
   * @return Promise<>
   */
  shrinkMemory() {
    return this._connectionData.shrinkMemory();
  },

  /**
   * Discard all cached statements.
   *
   * Note that this relies on us being non-interruptible between
   * the insertion or retrieval of a statement in the cache and its
   * execution: we finalize all statements, which is only safe if
   * they will not be executed again.
   *
   * @return (integer) the number of statements discarded.
   */
  discardCachedStatements() {
    return this._connectionData.discardCachedStatements();
  },

  /**
   * Interrupts pending database operations returning at the first opportunity.
   * Statement execution will throw an NS_ERROR_ABORT failure.
   * Can only be used on read-only connections.
   */
  interrupt() {
    this._connectionData.interrupt();
  },
});

var Sqlite = {
  openConnection,
  cloneStorageConnection,
  wrapStorageConnection,
  /**
   * Shutdown barrier client. May be used by clients to perform last-minute
   * cleanup prior to the shutdown of this module.
   *
   * See the documentation of AsyncShutdown.Barrier.prototype.client.
   */
  get shutdown() {
    return Barriers.shutdown.client;
  },
  failTestsOnAutoClose(enabled) {
    Debugging.failTestsOnAutoClose = enabled;
  },
};