summaryrefslogtreecommitdiffstats
path: root/services/sync/modules/service.js
blob: f3837a9499bf285e5e8407e137d43f43782b3090 (plain)
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
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
/* 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/. */

this.EXPORTED_SYMBOLS = ["Service"];

var Cc = Components.classes;
var Ci = Components.interfaces;
var Cr = Components.results;
var Cu = Components.utils;

// How long before refreshing the cluster
const CLUSTER_BACKOFF = 5 * 60 * 1000; // 5 minutes

// How long a key to generate from an old passphrase.
const PBKDF2_KEY_BYTES = 16;

const CRYPTO_COLLECTION = "crypto";
const KEYS_WBO = "keys";

Cu.import("resource://gre/modules/Preferences.jsm");
Cu.import("resource://gre/modules/XPCOMUtils.jsm");
Cu.import("resource://gre/modules/Log.jsm");
Cu.import("resource://services-common/utils.js");
Cu.import("resource://services-sync/constants.js");
Cu.import("resource://services-sync/engines.js");
Cu.import("resource://services-sync/engines/clients.js");
Cu.import("resource://services-sync/identity.js");
Cu.import("resource://services-sync/policies.js");
Cu.import("resource://services-sync/record.js");
Cu.import("resource://services-sync/resource.js");
Cu.import("resource://services-sync/rest.js");
Cu.import("resource://services-sync/stages/enginesync.js");
Cu.import("resource://services-sync/stages/declined.js");
Cu.import("resource://services-sync/status.js");
Cu.import("resource://services-sync/userapi.js");
Cu.import("resource://services-sync/util.js");

const ENGINE_MODULES = {
  Addons: "addons.js",
  Bookmarks: "bookmarks.js",
  Form: "forms.js",
  History: "history.js",
  Password: "passwords.js",
  Prefs: "prefs.js",
  Tab: "tabs.js",
};

const STORAGE_INFO_TYPES = [INFO_COLLECTIONS,
                            INFO_COLLECTION_USAGE,
                            INFO_COLLECTION_COUNTS,
                            INFO_QUOTA];

// A structure mapping a (boolean) telemetry probe name to a preference name.
// The probe will record true if the pref is modified, false otherwise.
const TELEMETRY_CUSTOM_SERVER_PREFS = {
  WEAVE_CUSTOM_LEGACY_SERVER_CONFIGURATION: "services.sync.serverURL",
  WEAVE_CUSTOM_FXA_SERVER_CONFIGURATION: "identity.fxaccounts.auth.uri",
  WEAVE_CUSTOM_TOKEN_SERVER_CONFIGURATION: "services.sync.tokenServerURI",
};


function Sync11Service() {
  this._notify = Utils.notify("weave:service:");
}
Sync11Service.prototype = {

  _lock: Utils.lock,
  _locked: false,
  _loggedIn: false,

  infoURL: null,
  storageURL: null,
  metaURL: null,
  cryptoKeyURL: null,

  get serverURL() Svc.Prefs.get("serverURL"),
  set serverURL(value) {
    if (!value.endsWith("/")) {
      value += "/";
    }

    // Only do work if it's actually changing
    if (value == this.serverURL)
      return;

    // A new server most likely uses a different cluster, so clear that
    Svc.Prefs.set("serverURL", value);
    Svc.Prefs.reset("clusterURL");
  },

  get clusterURL() Svc.Prefs.get("clusterURL", ""),
  set clusterURL(value) {
    Svc.Prefs.set("clusterURL", value);
    this._updateCachedURLs();
  },

  get miscAPI() {
    // Append to the serverURL if it's a relative fragment
    let misc = Svc.Prefs.get("miscURL");
    if (misc.indexOf(":") == -1)
      misc = this.serverURL + misc;
    return misc + MISC_API_VERSION + "/";
  },

  /**
   * The URI of the User API service.
   *
   * This is the base URI of the service as applicable to all users up to
   * and including the server version path component, complete with trailing
   * forward slash.
   */
  get userAPIURI() {
    // Append to the serverURL if it's a relative fragment.
    let url = Svc.Prefs.get("userURL");
    if (!url.includes(":")) {
      url = this.serverURL + url;
    }

    return url + USER_API_VERSION + "/";
  },

  get pwResetURL() {
    return this.serverURL + "weave-password-reset";
  },

  get syncID() {
    // Generate a random syncID id we don't have one
    let syncID = Svc.Prefs.get("client.syncID", "");
    return syncID == "" ? this.syncID = Utils.makeGUID() : syncID;
  },
  set syncID(value) {
    Svc.Prefs.set("client.syncID", value);
  },

  get isLoggedIn() { return this._loggedIn; },

  get locked() { return this._locked; },
  lock: function lock() {
    if (this._locked)
      return false;
    this._locked = true;
    return true;
  },
  unlock: function unlock() {
    this._locked = false;
  },

  // A specialized variant of Utils.catch.
  // This provides a more informative error message when we're already syncing:
  // see Bug 616568.
  _catch: function _catch(func) {
    function lockExceptions(ex) {
      if (Utils.isLockException(ex)) {
        // This only happens if we're syncing already.
        this._log.info("Cannot start sync: already syncing?");
      }
    }

    return Utils.catch.call(this, func, lockExceptions);
  },

  get userBaseURL() {
    if (!this._clusterManager) {
      return null;
    }
    return this._clusterManager.getUserBaseURL();
  },

  _updateCachedURLs: function _updateCachedURLs() {
    // Nothing to cache yet if we don't have the building blocks
    if (!this.clusterURL || !this.identity.username)
      return;

    this._log.debug("Caching URLs under storage user base: " + this.userBaseURL);

    // Generate and cache various URLs under the storage API for this user
    this.infoURL = this.userBaseURL + "info/collections";
    this.storageURL = this.userBaseURL + "storage/";
    this.metaURL = this.storageURL + "meta/global";
    this.cryptoKeysURL = this.storageURL + CRYPTO_COLLECTION + "/" + KEYS_WBO;
  },

  _checkCrypto: function _checkCrypto() {
    let ok = false;

    try {
      let iv = Svc.Crypto.generateRandomIV();
      if (iv.length == 24)
        ok = true;

    } catch (e) {
      this._log.debug("Crypto check failed: " + e);
    }

    return ok;
  },

  /**
   * Here is a disgusting yet reasonable way of handling HMAC errors deep in
   * the guts of Sync. The astute reader will note that this is a hacky way of
   * implementing something like continuable conditions.
   *
   * A handler function is glued to each engine. If the engine discovers an
   * HMAC failure, we fetch keys from the server and update our keys, just as
   * we would on startup.
   *
   * If our key collection changed, we signal to the engine (via our return
   * value) that it should retry decryption.
   *
   * If our key collection did not change, it means that we already had the
   * correct keys... and thus a different client has the wrong ones. Reupload
   * the bundle that we fetched, which will bump the modified time on the
   * server and (we hope) prompt a broken client to fix itself.
   *
   * We keep track of the time at which we last applied this reasoning, because
   * thrashing doesn't solve anything. We keep a reasonable interval between
   * these remedial actions.
   */
  lastHMACEvent: 0,

  /*
   * Returns whether to try again.
   */
  handleHMACEvent: function handleHMACEvent() {
    let now = Date.now();

    // Leave a sizable delay between HMAC recovery attempts. This gives us
    // time for another client to fix themselves if we touch the record.
    if ((now - this.lastHMACEvent) < HMAC_EVENT_INTERVAL)
      return false;

    this._log.info("Bad HMAC event detected. Attempting recovery " +
                   "or signaling to other clients.");

    // Set the last handled time so that we don't act again.
    this.lastHMACEvent = now;

    // Fetch keys.
    let cryptoKeys = new CryptoWrapper(CRYPTO_COLLECTION, KEYS_WBO);
    try {
      let cryptoResp = cryptoKeys.fetch(this.resource(this.cryptoKeysURL)).response;

      // Save out the ciphertext for when we reupload. If there's a bug in
      // CollectionKeyManager, this will prevent us from uploading junk.
      let cipherText = cryptoKeys.ciphertext;

      if (!cryptoResp.success) {
        this._log.warn("Failed to download keys.");
        return false;
      }

      let keysChanged = this.handleFetchedKeys(this.identity.syncKeyBundle,
                                               cryptoKeys, true);
      if (keysChanged) {
        // Did they change? If so, carry on.
        this._log.info("Suggesting retry.");
        return true;              // Try again.
      }

      // If not, reupload them and continue the current sync.
      cryptoKeys.ciphertext = cipherText;
      cryptoKeys.cleartext  = null;

      let uploadResp = cryptoKeys.upload(this.resource(this.cryptoKeysURL));
      if (uploadResp.success)
        this._log.info("Successfully re-uploaded keys. Continuing sync.");
      else
        this._log.warn("Got error response re-uploading keys. " +
                       "Continuing sync; let's try again later.");

      return false;            // Don't try again: same keys.

    } catch (ex) {
      this._log.warn("Got exception \"" + ex + "\" fetching and handling " +
                     "crypto keys. Will try again later.");
      return false;
    }
  },

  handleFetchedKeys: function handleFetchedKeys(syncKey, cryptoKeys, skipReset) {
    // Don't want to wipe if we're just starting up!
    let wasBlank = this.collectionKeys.isClear;
    let keysChanged = this.collectionKeys.updateContents(syncKey, cryptoKeys);

    if (keysChanged && !wasBlank) {
      this._log.debug("Keys changed: " + JSON.stringify(keysChanged));

      if (!skipReset) {
        this._log.info("Resetting client to reflect key change.");

        if (keysChanged.length) {
          // Collection keys only. Reset individual engines.
          this.resetClient(keysChanged);
        }
        else {
          // Default key changed: wipe it all.
          this.resetClient();
        }

        this._log.info("Downloaded new keys, client reset. Proceeding.");
      }
      return true;
    }
    return false;
  },

  // The global "enabled" state comes from prefs, and will be set to false
  // whenever the UI that exposes what to sync finds all Sync engines disabled.
  get enabled() {
    return Svc.Prefs.get("enabled");
  },
  set enabled(val) {
    // There's no real reason to impose this other than to catch someone doing
    // something we don't expect with bad consequences - all setting of this
    // pref are in the UI code and external to this module.
    if (val) {
      throw new Error("Only disabling via this setter is supported");
    }
    Svc.Prefs.set("enabled", val);
  },

  /**
   * Prepare to initialize the rest of Weave after waiting a little bit
   */
  onStartup: function onStartup() {
    this._migratePrefs();

    // Status is instantiated before us and is the first to grab an instance of
    // the IdentityManager. We use that instance because IdentityManager really
    // needs to be a singleton. Ideally, the longer-lived object would spawn
    // this service instance.
    if (!Status || !Status._authManager) {
      throw new Error("Status or Status._authManager not initialized.");
    }

    this.status = Status;
    this.identity = Status._authManager;
    this.collectionKeys = new CollectionKeyManager();

    this.errorHandler = new ErrorHandler(this);

    this._log = Log.repository.getLogger("Sync.Service");
    this._log.level =
      Log.Level[Svc.Prefs.get("log.logger.service.main")];

    this._log.info("Loading Weave " + WEAVE_VERSION);

    this._clusterManager = this.identity.createClusterManager(this);
    this.recordManager = new RecordManager(this);

    this._registerEngines();

    let ua = Cc["@mozilla.org/network/protocol;1?name=http"].
      getService(Ci.nsIHttpProtocolHandler).userAgent;
    this._log.info(ua);

    if (!this._checkCrypto()) {
      this.enabled = false;
      this._log.info("Could not load the Weave crypto component. Disabling " +
                      "Weave, since it will not work correctly.");
    }

    Svc.Obs.add("weave:service:setup-complete", this);
    Svc.Prefs.observe("engine.", this);

    this.scheduler = new SyncScheduler(this);

    if (!this.enabled) {
      this._log.info("Firefox Sync disabled.");
    }

    this._updateCachedURLs();

    let status = this._checkSetup();
    if (status != STATUS_DISABLED && status != CLIENT_NOT_CONFIGURED) {
      Svc.Obs.notify("weave:engine:start-tracking");
    }

    // Telemetry probes to indicate if the user is using custom servers.
    for (let [probeName, prefName] of Iterator(TELEMETRY_CUSTOM_SERVER_PREFS)) {
      let isCustomized = Services.prefs.prefHasUserValue(prefName);
      Services.telemetry.getHistogramById(probeName).add(isCustomized);
    }

    // Send an event now that Weave service is ready.  We don't do this
    // synchronously so that observers can import this module before
    // registering an observer.
    Utils.nextTick(function onNextTick() {
      this.status.ready = true;

      // UI code uses the flag on the XPCOM service so it doesn't have
      // to load a bunch of modules.
      let xps = Cc["@mozilla.org/weave/service;1"]
                  .getService(Ci.nsISupports)
                  .wrappedJSObject;
      xps.ready = true;

      Svc.Obs.notify("weave:service:ready");
    }.bind(this));
  },

  _checkSetup: function _checkSetup() {
    if (!this.enabled) {
      return this.status.service = STATUS_DISABLED;
    }
    return this.status.checkSetup();
  },

  _migratePrefs: function _migratePrefs() {
    // Migrate old debugLog prefs.
    let logLevel = Svc.Prefs.get("log.appender.debugLog");
    if (logLevel) {
      Svc.Prefs.set("log.appender.file.level", logLevel);
      Svc.Prefs.reset("log.appender.debugLog");
    }
    if (Svc.Prefs.get("log.appender.debugLog.enabled")) {
      Svc.Prefs.set("log.appender.file.logOnSuccess", true);
      Svc.Prefs.reset("log.appender.debugLog.enabled");
    }

    // Migrate old extensions.weave.* prefs if we haven't already tried.
    if (Svc.Prefs.get("migrated", false))
      return;

    // Grab the list of old pref names
    let oldPrefBranch = "extensions.weave.";
    let oldPrefNames = Cc["@mozilla.org/preferences-service;1"].
                       getService(Ci.nsIPrefService).
                       getBranch(oldPrefBranch).
                       getChildList("", {});

    // Map each old pref to the current pref branch
    let oldPref = new Preferences(oldPrefBranch);
    for (let pref of oldPrefNames)
      Svc.Prefs.set(pref, oldPref.get(pref));

    // Remove all the old prefs and remember that we've migrated
    oldPref.resetBranch("");
    Svc.Prefs.set("migrated", true);
  },

  /**
   * Register the built-in engines for certain applications
   */
  _registerEngines: function _registerEngines() {
    this.engineManager = new EngineManager(this);

    let engines = [];
    // Applications can provide this preference (comma-separated list)
    // to specify which engines should be registered on startup.
    let pref = Svc.Prefs.get("registerEngines");
    if (pref) {
      engines = pref.split(",");
    }

    let declined = [];
    pref = Svc.Prefs.get("declinedEngines");
    if (pref) {
      declined = pref.split(",");
    }

    this.clientsEngine = new ClientEngine(this);

    for (let name of engines) {
      if (!(name in ENGINE_MODULES)) {
        this._log.info("Do not know about engine: " + name);
        continue;
      }

      let ns = {};
      try {
        Cu.import("resource://services-sync/engines/" + ENGINE_MODULES[name], ns);

        let engineName = name + "Engine";
        if (!(engineName in ns)) {
          this._log.warn("Could not find exported engine instance: " + engineName);
          continue;
        }

        this.engineManager.register(ns[engineName]);
      } catch (ex) {
        this._log.warn("Could not register engine " + name + ": " +
                       CommonUtils.exceptionStr(ex));
      }
    }

    this.engineManager.setDeclined(declined);
  },

  QueryInterface: XPCOMUtils.generateQI([Ci.nsIObserver,
                                         Ci.nsISupportsWeakReference]),

  // nsIObserver

  observe: function observe(subject, topic, data) {
    switch (topic) {
      case "weave:service:setup-complete":
        let status = this._checkSetup();
        if (status != STATUS_DISABLED && status != CLIENT_NOT_CONFIGURED)
            Svc.Obs.notify("weave:engine:start-tracking");
        break;
      case "nsPref:changed":
        if (this._ignorePrefObserver)
          return;
        let engine = data.slice((PREFS_BRANCH + "engine.").length);
        this._handleEngineStatusChanged(engine);
        break;
    }
  },

  _handleEngineStatusChanged: function handleEngineDisabled(engine) {
    this._log.trace("Status for " + engine + " engine changed.");
    if (Svc.Prefs.get("engineStatusChanged." + engine, false)) {
      // The enabled status being changed back to what it was before.
      Svc.Prefs.reset("engineStatusChanged." + engine);
    } else {
      // Remember that the engine status changed locally until the next sync.
      Svc.Prefs.set("engineStatusChanged." + engine, true);
    }
  },

  /**
   * Obtain a Resource instance with authentication credentials.
   */
  resource: function resource(url) {
    let res = new Resource(url);
    res.authenticator = this.identity.getResourceAuthenticator();

    return res;
  },

  /**
   * Obtain a SyncStorageRequest instance with authentication credentials.
   */
  getStorageRequest: function getStorageRequest(url) {
    let request = new SyncStorageRequest(url);
    request.authenticator = this.identity.getRESTRequestAuthenticator();

    return request;
  },

  /**
   * Perform the info fetch as part of a login or key fetch, or
   * inside engine sync.
   */
  _fetchInfo: function (url) {
    let infoURL = url || this.infoURL;

    this._log.trace("In _fetchInfo: " + infoURL);
    let info;
    try {
      info = this.resource(infoURL).get();
    } catch (ex) {
      this.errorHandler.checkServerError(ex);
      throw ex;
    }

    // Always check for errors; this is also where we look for X-Weave-Alert.
    this.errorHandler.checkServerError(info);
    if (!info.success) {
      throw "Aborting sync: failed to get collections.";
    }
    return info;
  },

  verifyAndFetchSymmetricKeys: function verifyAndFetchSymmetricKeys(infoResponse) {

    this._log.debug("Fetching and verifying -- or generating -- symmetric keys.");

    // Don't allow empty/missing passphrase.
    // Furthermore, we assume that our sync key is already upgraded,
    // and fail if that assumption is invalidated.

    if (!this.identity.syncKey) {
      this.status.login = LOGIN_FAILED_NO_PASSPHRASE;
      this.status.sync = CREDENTIALS_CHANGED;
      return false;
    }

    let syncKeyBundle = this.identity.syncKeyBundle;
    if (!syncKeyBundle) {
      this._log.error("Sync Key Bundle not set. Invalid Sync Key?");

      this.status.login = LOGIN_FAILED_INVALID_PASSPHRASE;
      this.status.sync = CREDENTIALS_CHANGED;
      return false;
    }

    try {
      if (!infoResponse)
        infoResponse = this._fetchInfo();    // Will throw an exception on failure.

      // This only applies when the server is already at version 4.
      if (infoResponse.status != 200) {
        this._log.warn("info/collections returned non-200 response. Failing key fetch.");
        this.status.login = LOGIN_FAILED_SERVER_ERROR;
        this.errorHandler.checkServerError(infoResponse);
        return false;
      }

      let infoCollections = infoResponse.obj;

      this._log.info("Testing info/collections: " + JSON.stringify(infoCollections));

      if (this.collectionKeys.updateNeeded(infoCollections)) {
        this._log.info("collection keys reports that a key update is needed.");

        // Don't always set to CREDENTIALS_CHANGED -- we will probably take care of this.

        // Fetch storage/crypto/keys.
        let cryptoKeys;

        if (infoCollections && (CRYPTO_COLLECTION in infoCollections)) {
          try {
            cryptoKeys = new CryptoWrapper(CRYPTO_COLLECTION, KEYS_WBO);
            let cryptoResp = cryptoKeys.fetch(this.resource(this.cryptoKeysURL)).response;

            if (cryptoResp.success) {
              let keysChanged = this.handleFetchedKeys(syncKeyBundle, cryptoKeys);
              return true;
            }
            else if (cryptoResp.status == 404) {
              // On failure, ask to generate new keys and upload them.
              // Fall through to the behavior below.
              this._log.warn("Got 404 for crypto/keys, but 'crypto' in info/collections. Regenerating.");
              cryptoKeys = null;
            }
            else {
              // Some other problem.
              this.status.login = LOGIN_FAILED_SERVER_ERROR;
              this.errorHandler.checkServerError(cryptoResp);
              this._log.warn("Got status " + cryptoResp.status + " fetching crypto keys.");
              return false;
            }
          }
          catch (ex) {
            this._log.warn("Got exception \"" + ex + "\" fetching cryptoKeys.");
            // TODO: Um, what exceptions might we get here? Should we re-throw any?

            // One kind of exception: HMAC failure.
            if (Utils.isHMACMismatch(ex)) {
              this.status.login = LOGIN_FAILED_INVALID_PASSPHRASE;
              this.status.sync = CREDENTIALS_CHANGED;
            }
            else {
              // In the absence of further disambiguation or more precise
              // failure constants, just report failure.
              this.status.login = LOGIN_FAILED;
            }
            return false;
          }
        }
        else {
          this._log.info("... 'crypto' is not a reported collection. Generating new keys.");
        }

        if (!cryptoKeys) {
          this._log.info("No keys! Generating new ones.");

          // Better make some and upload them, and wipe the server to ensure
          // consistency. This is all achieved via _freshStart.
          // If _freshStart fails to clear the server or upload keys, it will
          // throw.
          this._freshStart();
          return true;
        }

        // Last-ditch case.
        return false;
      }
      else {
        // No update needed: we're good!
        return true;
      }

    } catch (ex) {
      // This means no keys are present, or there's a network error.
      this._log.debug("Failed to fetch and verify keys: "
                      + Utils.exceptionStr(ex));
      this.errorHandler.checkServerError(ex);
      return false;
    }
  },

  verifyLogin: function verifyLogin(allow40XRecovery = true) {
    // If the identity isn't ready it  might not know the username...
    if (!this.identity.readyToAuthenticate) {
      this._log.info("Not ready to authenticate in verifyLogin.");
      this.status.login = LOGIN_FAILED_NOT_READY;
      return false;
    }

    if (!this.identity.username) {
      this._log.warn("No username in verifyLogin.");
      this.status.login = LOGIN_FAILED_NO_USERNAME;
      return false;
    }

    // Attaching auth credentials to a request requires access to
    // passwords, which means that Resource.get can throw MP-related
    // exceptions!
    // So we ask the identity to verify the login state after unlocking the
    // master password (ie, this call is expected to prompt for MP unlock
    // if necessary) while we still have control.
    let cb = Async.makeSpinningCallback();
    this.identity.unlockAndVerifyAuthState().then(
      result => cb(null, result),
      cb
    );
    let unlockedState = cb.wait();
    this._log.debug("Fetching unlocked auth state returned " + unlockedState);
    if (unlockedState != STATUS_OK) {
      this.status.login = unlockedState;
      return false;
    }

    try {
      // Make sure we have a cluster to verify against.
      // This is a little weird, if we don't get a node we pretend
      // to succeed, since that probably means we just don't have storage.
      if (this.clusterURL == "" && !this._clusterManager.setCluster()) {
        this.status.sync = NO_SYNC_NODE_FOUND;
        return true;
      }

      // Fetch collection info on every startup.
      let test = this.resource(this.infoURL).get();

      switch (test.status) {
        case 200:
          // The user is authenticated.

          // We have no way of verifying the passphrase right now,
          // so wait until remoteSetup to do so.
          // Just make the most trivial checks.
          if (!this.identity.syncKey) {
            this._log.warn("No passphrase in verifyLogin.");
            this.status.login = LOGIN_FAILED_NO_PASSPHRASE;
            return false;
          }

          // Go ahead and do remote setup, so that we can determine
          // conclusively that our passphrase is correct.
          if (this._remoteSetup(test)) {
            // Username/password verified.
            this.status.login = LOGIN_SUCCEEDED;
            return true;
          }

          this._log.warn("Remote setup failed.");
          // Remote setup must have failed.
          return false;

        case 401:
          this._log.warn("401: login failed.");
          // Fall through to the 404 case.

        case 404:
          // Check that we're verifying with the correct cluster
          if (allow40XRecovery && this._clusterManager.setCluster()) {
            return this.verifyLogin(false);
          }

          // We must have the right cluster, but the server doesn't expect us
          this.status.login = LOGIN_FAILED_LOGIN_REJECTED;
          return false;

        default:
          // Server didn't respond with something that we expected
          this.status.login = LOGIN_FAILED_SERVER_ERROR;
          this.errorHandler.checkServerError(test);
          return false;
      }
    } catch (ex) {
      // Must have failed on some network issue
      this._log.debug("verifyLogin failed: " + Utils.exceptionStr(ex));
      this.status.login = LOGIN_FAILED_NETWORK_ERROR;
      this.errorHandler.checkServerError(ex);
      return false;
    }
  },

  generateNewSymmetricKeys: function generateNewSymmetricKeys() {
    this._log.info("Generating new keys WBO...");
    let wbo = this.collectionKeys.generateNewKeysWBO();
    this._log.info("Encrypting new key bundle.");
    wbo.encrypt(this.identity.syncKeyBundle);

    this._log.info("Uploading...");
    let uploadRes = wbo.upload(this.resource(this.cryptoKeysURL));
    if (uploadRes.status != 200) {
      this._log.warn("Got status " + uploadRes.status + " uploading new keys. What to do? Throw!");
      this.errorHandler.checkServerError(uploadRes);
      throw new Error("Unable to upload symmetric keys.");
    }
    this._log.info("Got status " + uploadRes.status + " uploading keys.");
    let serverModified = uploadRes.obj;   // Modified timestamp according to server.
    this._log.debug("Server reports crypto modified: " + serverModified);

    // Now verify that info/collections shows them!
    this._log.debug("Verifying server collection records.");
    let info = this._fetchInfo();
    this._log.debug("info/collections is: " + info);

    if (info.status != 200) {
      this._log.warn("Non-200 info/collections response. Aborting.");
      throw new Error("Unable to upload symmetric keys.");
    }

    info = info.obj;
    if (!(CRYPTO_COLLECTION in info)) {
      this._log.error("Consistency failure: info/collections excludes " +
                      "crypto after successful upload.");
      throw new Error("Symmetric key upload failed.");
    }

    // Can't check against local modified: clock drift.
    if (info[CRYPTO_COLLECTION] < serverModified) {
      this._log.error("Consistency failure: info/collections crypto entry " +
                      "is stale after successful upload.");
      throw new Error("Symmetric key upload failed.");
    }

    // Doesn't matter if the timestamp is ahead.

    // Download and install them.
    let cryptoKeys = new CryptoWrapper(CRYPTO_COLLECTION, KEYS_WBO);
    let cryptoResp = cryptoKeys.fetch(this.resource(this.cryptoKeysURL)).response;
    if (cryptoResp.status != 200) {
      this._log.warn("Failed to download keys.");
      throw new Error("Symmetric key download failed.");
    }
    let keysChanged = this.handleFetchedKeys(this.identity.syncKeyBundle,
                                             cryptoKeys, true);
    if (keysChanged) {
      this._log.info("Downloaded keys differed, as expected.");
    }
  },

  changePassword: function changePassword(newPassword) {
    let client = new UserAPI10Client(this.userAPIURI);
    let cb = Async.makeSpinningCallback();
    client.changePassword(this.identity.username,
                          this.identity.basicPassword, newPassword, cb);

    try {
      cb.wait();
    } catch (ex) {
      this._log.debug("Password change failed: " +
                      CommonUtils.exceptionStr(ex));
      return false;
    }

    // Save the new password for requests and login manager.
    this.identity.basicPassword = newPassword;
    this.persistLogin();
    return true;
  },

  changePassphrase: function changePassphrase(newphrase) {
    return this._catch(function doChangePasphrase() {
      /* Wipe. */
      this.wipeServer();

      this.logout();

      /* Set this so UI is updated on next run. */
      this.identity.syncKey = newphrase;
      this.persistLogin();

      /* We need to re-encrypt everything, so reset. */
      this.resetClient();
      this.collectionKeys.clear();

      /* Login and sync. This also generates new keys. */
      this.sync();

      Svc.Obs.notify("weave:service:change-passphrase", true);

      return true;
    })();
  },

  startOver: function startOver() {
    this._log.trace("Invoking Service.startOver.");
    Svc.Obs.notify("weave:engine:stop-tracking");
    this.status.resetSync();

    // Deletion doesn't make sense if we aren't set up yet!
    if (this.clusterURL != "") {
      // Clear client-specific data from the server, including disabled engines.
      for (let engine of [this.clientsEngine].concat(this.engineManager.getAll())) {
        try {
          engine.removeClientData();
        } catch(ex) {
          this._log.warn("Deleting client data for " + engine.name + " failed:"
                         + Utils.exceptionStr(ex));
        }
      }
      this._log.debug("Finished deleting client data.");
    } else {
      this._log.debug("Skipping client data removal: no cluster URL.");
    }

    // We want let UI consumers of the following notification know as soon as
    // possible, so let's fake for the CLIENT_NOT_CONFIGURED status for now
    // by emptying the passphrase (we still need the password).
    this._log.info("Service.startOver dropping sync key and logging out.");
    this.identity.resetSyncKey();
    this.status.login = LOGIN_FAILED_NO_PASSPHRASE;
    this.logout();
    Svc.Obs.notify("weave:service:start-over");

    // Reset all engines and clear keys.
    this.resetClient();
    this.collectionKeys.clear();
    this.status.resetBackoff();

    // Reset Weave prefs.
    this._ignorePrefObserver = true;
    Svc.Prefs.resetBranch("");
    this._ignorePrefObserver = false;

    Svc.Prefs.set("lastversion", WEAVE_VERSION);

    this.identity.deleteSyncCredentials();

    // If necessary, reset the identity manager, then re-initialize it so the
    // FxA manager is used.  This is configurable via a pref - mainly for tests.
    let keepIdentity = false;
    try {
      keepIdentity = Services.prefs.getBoolPref("services.sync-testing.startOverKeepIdentity");
    } catch (_) { /* no such pref */ }
    if (keepIdentity) {
      Svc.Obs.notify("weave:service:start-over:finish");
      return;
    }

    this.identity.finalize().then(
      () => {
        // an observer so the FxA migration code can take some action before
        // the new identity is created.
        Svc.Obs.notify("weave:service:start-over:init-identity");
        this.identity.username = "";
        this.status.__authManager = null;
        this.identity = Status._authManager;
        this._clusterManager = this.identity.createClusterManager(this);
        Svc.Obs.notify("weave:service:start-over:finish");
      }
    ).then(null,
      err => {
        this._log.error("startOver failed to re-initialize the identity manager: " + err);
        // Still send the observer notification so the current state is
        // reflected in the UI.
        Svc.Obs.notify("weave:service:start-over:finish");
      }
    );
  },

  persistLogin: function persistLogin() {
    try {
      this.identity.persistCredentials(true);
    } catch (ex) {
      this._log.info("Unable to persist credentials: " + ex);
    }
  },

  login: function login(username, password, passphrase) {
    function onNotify() {
      this._loggedIn = false;
      if (Services.io.offline) {
        this.status.login = LOGIN_FAILED_NETWORK_ERROR;
        throw "Application is offline, login should not be called";
      }

      let initialStatus = this._checkSetup();
      if (username) {
        this.identity.username = username;
      }
      if (password) {
        this.identity.basicPassword = password;
      }
      if (passphrase) {
        this.identity.syncKey = passphrase;
      }

      if (this._checkSetup() == CLIENT_NOT_CONFIGURED) {
        throw "Aborting login, client not configured.";
      }

      // Ask the identity manager to explicitly login now.
      let cb = Async.makeSpinningCallback();
      this.identity.ensureLoggedIn().then(cb, cb);

      // Just let any errors bubble up - they've more context than we do!
      cb.wait();

      // Calling login() with parameters when the client was
      // previously not configured means setup was completed.
      if (initialStatus == CLIENT_NOT_CONFIGURED
          && (username || password || passphrase)) {
        Svc.Obs.notify("weave:service:setup-complete");
      }
      this._log.info("Logging in the user.");
      this._updateCachedURLs();

      if (!this.verifyLogin()) {
        // verifyLogin sets the failure states here.
        throw "Login failed: " + this.status.login;
      }

      this._loggedIn = true;

      return true;
    }

    let notifier = this._notify("login", "", onNotify.bind(this));
    return this._catch(this._lock("service.js: login", notifier))();
  },

  logout: function logout() {
    // If we failed during login, we aren't going to have this._loggedIn set,
    // but we still want to ask the identity to logout, so it doesn't try and
    // reuse any old credentials next time we sync.
    this._log.info("Logging out");
    this.identity.logout();
    this._loggedIn = false;

    Svc.Obs.notify("weave:service:logout:finish");
  },

  checkAccount: function checkAccount(account) {
    let client = new UserAPI10Client(this.userAPIURI);
    let cb = Async.makeSpinningCallback();

    let username = this.identity.usernameFromAccount(account);
    client.usernameExists(username, cb);

    try {
      let exists = cb.wait();
      return exists ? "notAvailable" : "available";
    } catch (ex) {
      // TODO fix API convention.
      return this.errorHandler.errorStr(ex);
    }
  },

  createAccount: function createAccount(email, password,
                                        captchaChallenge, captchaResponse) {
    let client = new UserAPI10Client(this.userAPIURI);

    // Hint to server to allow scripted user creation or otherwise
    // ignore captcha.
    if (Svc.Prefs.isSet("admin-secret")) {
      client.adminSecret = Svc.Prefs.get("admin-secret", "");
    }

    let cb = Async.makeSpinningCallback();

    client.createAccount(email, password, captchaChallenge, captchaResponse,
                         cb);

    try {
      cb.wait();
      return null;
    } catch (ex) {
      return this.errorHandler.errorStr(ex.body);
    }
  },

  // Stuff we need to do after login, before we can really do
  // anything (e.g. key setup).
  _remoteSetup: function _remoteSetup(infoResponse) {
    let reset = false;

    this._log.debug("Fetching global metadata record");
    let meta = this.recordManager.get(this.metaURL);

    // Checking modified time of the meta record.
    if (infoResponse &&
        (infoResponse.obj.meta != this.metaModified) &&
        (!meta || !meta.isNew)) {

      // Delete the cached meta record...
      this._log.debug("Clearing cached meta record. metaModified is " +
          JSON.stringify(this.metaModified) + ", setting to " +
          JSON.stringify(infoResponse.obj.meta));

      this.recordManager.del(this.metaURL);

      // ... fetch the current record from the server, and COPY THE FLAGS.
      let newMeta = this.recordManager.get(this.metaURL);

      // If we got a 401, we do not want to create a new meta/global - we
      // should be able to get the existing meta after we get a new node.
      if (this.recordManager.response.status == 401) {
        this._log.debug("Fetching meta/global record on the server returned 401.");
        this.errorHandler.checkServerError(this.recordManager.response);
        return false;
      }

      if (!this.recordManager.response.success || !newMeta) {
        this._log.debug("No meta/global record on the server. Creating one.");
        newMeta = new WBORecord("meta", "global");
        newMeta.payload.syncID = this.syncID;
        newMeta.payload.storageVersion = STORAGE_VERSION;
        newMeta.payload.declined = this.engineManager.getDeclined();

        newMeta.isNew = true;

        this.recordManager.set(this.metaURL, newMeta);
        if (!newMeta.upload(this.resource(this.metaURL)).success) {
          this._log.warn("Unable to upload new meta/global. Failing remote setup.");
          return false;
        }
      } else {
        // If newMeta, then it stands to reason that meta != null.
        newMeta.isNew   = meta.isNew;
        newMeta.changed = meta.changed;
      }

      // Switch in the new meta object and record the new time.
      meta              = newMeta;
      this.metaModified = infoResponse.obj.meta;
    }

    let remoteVersion = (meta && meta.payload.storageVersion)?
      meta.payload.storageVersion : "";

    this._log.debug(["Weave Version:", WEAVE_VERSION, "Local Storage:",
      STORAGE_VERSION, "Remote Storage:", remoteVersion].join(" "));

    // Check for cases that require a fresh start. When comparing remoteVersion,
    // we need to convert it to a number as older clients used it as a string.
    if (!meta || !meta.payload.storageVersion || !meta.payload.syncID ||
        STORAGE_VERSION > parseFloat(remoteVersion)) {

      this._log.info("One of: no meta, no meta storageVersion, or no meta syncID. Fresh start needed.");

      // abort the server wipe if the GET status was anything other than 404 or 200
      let status = this.recordManager.response.status;
      if (status != 200 && status != 404) {
        this.status.sync = METARECORD_DOWNLOAD_FAIL;
        this.errorHandler.checkServerError(this.recordManager.response);
        this._log.warn("Unknown error while downloading metadata record. " +
                       "Aborting sync.");
        return false;
      }

      if (!meta)
        this._log.info("No metadata record, server wipe needed");
      if (meta && !meta.payload.syncID)
        this._log.warn("No sync id, server wipe needed");

      reset = true;

      this._log.info("Wiping server data");
      this._freshStart();

      if (status == 404)
        this._log.info("Metadata record not found, server was wiped to ensure " +
                       "consistency.");
      else // 200
        this._log.info("Wiped server; incompatible metadata: " + remoteVersion);

      return true;
    }
    else if (remoteVersion > STORAGE_VERSION) {
      this.status.sync = VERSION_OUT_OF_DATE;
      this._log.warn("Upgrade required to access newer storage version.");
      return false;
    }
    else if (meta.payload.syncID != this.syncID) {

      this._log.info("Sync IDs differ. Local is " + this.syncID + ", remote is " + meta.payload.syncID);
      this.resetClient();
      this.collectionKeys.clear();
      this.syncID = meta.payload.syncID;
      this._log.debug("Clear cached values and take syncId: " + this.syncID);

      if (!this.upgradeSyncKey(meta.payload.syncID)) {
        this._log.warn("Failed to upgrade sync key. Failing remote setup.");
        return false;
      }

      if (!this.verifyAndFetchSymmetricKeys(infoResponse)) {
        this._log.warn("Failed to fetch symmetric keys. Failing remote setup.");
        return false;
      }

      // bug 545725 - re-verify creds and fail sanely
      if (!this.verifyLogin()) {
        this.status.sync = CREDENTIALS_CHANGED;
        this._log.info("Credentials have changed, aborting sync and forcing re-login.");
        return false;
      }

      return true;
    }
    else {
      if (!this.upgradeSyncKey(meta.payload.syncID)) {
        this._log.warn("Failed to upgrade sync key. Failing remote setup.");
        return false;
      }

      if (!this.verifyAndFetchSymmetricKeys(infoResponse)) {
        this._log.warn("Failed to fetch symmetric keys. Failing remote setup.");
        return false;
      }

      return true;
    }
  },

  /**
   * Return whether we should attempt login at the start of a sync.
   *
   * Note that this function has strong ties to _checkSync: callers
   * of this function should typically use _checkSync to verify that
   * any necessary login took place.
   */
  _shouldLogin: function _shouldLogin() {
    return this.enabled &&
           !Services.io.offline &&
           !this.isLoggedIn;
  },

  /**
   * Determine if a sync should run.
   *
   * @param ignore [optional]
   *        array of reasons to ignore when checking
   *
   * @return Reason for not syncing; not-truthy if sync should run
   */
  _checkSync: function _checkSync(ignore) {
    let reason = "";
    if (!this.enabled)
      reason = kSyncWeaveDisabled;
    else if (Services.io.offline)
      reason = kSyncNetworkOffline;
    else if (this.status.minimumNextSync > Date.now())
      reason = kSyncBackoffNotMet;
    else if ((this.status.login == MASTER_PASSWORD_LOCKED) &&
             Utils.mpLocked())
      reason = kSyncMasterPasswordLocked;
    else if (Svc.Prefs.get("firstSync") == "notReady")
      reason = kFirstSyncChoiceNotMade;

    if (ignore && ignore.indexOf(reason) != -1)
      return "";

    return reason;
  },

  sync: function sync() {
    if (!this.enabled) {
      this._log.debug("Not syncing as Sync is disabled.");
      return;
    }
    let dateStr = new Date().toLocaleFormat(LOG_DATE_FORMAT);
    this._log.debug("User-Agent: " + SyncStorageRequest.prototype.userAgent);
    this._log.info("Starting sync at " + dateStr);
    this._catch(function () {
      // Make sure we're logged in.
      if (this._shouldLogin()) {
        this._log.debug("In sync: should login.");
        if (!this.login()) {
          this._log.debug("Not syncing: login returned false.");
          return;
        }
      }
      else {
        this._log.trace("In sync: no need to login.");
      }
      return this._lockedSync.apply(this, arguments);
    })();
  },

  /**
   * Sync up engines with the server.
   */
  _lockedSync: function _lockedSync() {
    return this._lock("service.js: sync",
                      this._notify("sync", "", function onNotify() {

      let histogram = Services.telemetry.getHistogramById("WEAVE_START_COUNT");
      histogram.add(1);

      let synchronizer = new EngineSynchronizer(this);
      let cb = Async.makeSpinningCallback();
      synchronizer.onComplete = cb;

      synchronizer.sync();
      // wait() throws if the first argument is truthy, which is exactly what
      // we want.
      let result = cb.wait();

      histogram = Services.telemetry.getHistogramById("WEAVE_COMPLETE_SUCCESS_COUNT");
      histogram.add(1);

      // We successfully synchronized.
      // Check if the identity wants to pre-fetch a migration sentinel from
      // the server.
      // If we have no clusterURL, we are probably doing a node reassignment
      // so don't attempt to get it in that case.
      //if (this.clusterURL) {
      //  this.identity.prefetchMigrationSentinel(this);
      //}

      // Now let's update our declined engines.
      let meta = this.recordManager.get(this.metaURL);
      if (!meta) {
        this._log.warn("No meta/global; can't update declined state.");
        return;
      }

      let declinedEngines = new DeclinedEngines(this);
      let didChange = declinedEngines.updateDeclined(meta, this.engineManager);
      if (!didChange) {
        this._log.info("No change to declined engines. Not reuploading meta/global.");
        return;
      }

      this.uploadMetaGlobal(meta);
    }))();
  },

  /**
   * Upload meta/global, throwing the response on failure.
   */
  uploadMetaGlobal: function (meta) {
    this._log.debug("Uploading meta/global: " + JSON.stringify(meta));

    // It would be good to set the X-If-Unmodified-Since header to `timestamp`
    // for this PUT to ensure at least some level of transactionality.
    // Unfortunately, the servers don't support it after a wipe right now
    // (bug 693893), so we're going to defer this until bug 692700.
    let res = this.resource(this.metaURL);
    let response = res.put(meta);
    if (!response.success) {
      throw response;
    }
    this.recordManager.set(this.metaURL, meta);
  },

  /**
   * Get a migration sentinel for the Firefox Accounts migration.
   * Returns a JSON blob - it is up to callers of this to make sense of the
   * data.
   *
   * Returns a promise that resolves with the sentinel, or null.
   */
  getFxAMigrationSentinel: function() {
    if (this._shouldLogin()) {
      this._log.debug("In getFxAMigrationSentinel: should login.");
      if (!this.login()) {
        this._log.debug("Can't get migration sentinel: login returned false.");
        return Promise.resolve(null);
      }
    }
    if (!this.identity.syncKeyBundle) {
      this._log.error("Can't get migration sentinel: no syncKeyBundle.");
      return Promise.resolve(null);
    }
    try {
      let collectionURL = this.storageURL + "meta/fxa_credentials";
      let cryptoWrapper = this.recordManager.get(collectionURL);
      if (!cryptoWrapper || !cryptoWrapper.payload) {
        // nothing to decrypt - .decrypt is noisy in that case, so just bail
        // now.
        return Promise.resolve(null);
      }
      // If the payload has a sentinel it means we must have put back the
      // decrypted version last time we were called.
      if (cryptoWrapper.payload.sentinel) {
        return Promise.resolve(cryptoWrapper.payload.sentinel);
      }
      // If decryption fails it almost certainly means the key is wrong - but
      // it's not clear if we need to take special action for that case?
      let payload = cryptoWrapper.decrypt(this.identity.syncKeyBundle);
      // After decrypting the ciphertext is lost, so we just stash the
      // decrypted payload back into the wrapper.
      cryptoWrapper.payload = payload;
      return Promise.resolve(payload.sentinel);
    } catch (ex) {
      this._log.error("Failed to fetch the migration sentinel: ${}", ex);
      return Promise.resolve(null);
    }
  },

  /**
   * Set a migration sentinel for the Firefox Accounts migration.
   * Accepts a JSON blob - it is up to callers of this to make sense of the
   * data.
   *
   * Returns a promise that resolves with a boolean which indicates if the
   * sentinel was successfully written.
   */
  setFxAMigrationSentinel: function(sentinel) {
    if (this._shouldLogin()) {
      this._log.debug("In setFxAMigrationSentinel: should login.");
      if (!this.login()) {
        this._log.debug("Can't set migration sentinel: login returned false.");
        return Promise.resolve(false);
      }
    }
    if (!this.identity.syncKeyBundle) {
      this._log.error("Can't set migration sentinel: no syncKeyBundle.");
      return Promise.resolve(false);
    }
    try {
      let collectionURL = this.storageURL + "meta/fxa_credentials";
      let cryptoWrapper = new CryptoWrapper("meta", "fxa_credentials");
      cryptoWrapper.cleartext.sentinel = sentinel;

      cryptoWrapper.encrypt(this.identity.syncKeyBundle);

      let res = this.resource(collectionURL);
      let response = res.put(cryptoWrapper.toJSON());

      if (!response.success) {
        throw response;
      }
      this.recordManager.set(collectionURL, cryptoWrapper);
    } catch (ex) {
      this._log.error("Failed to set the migration sentinel: ${}", ex);
      return Promise.resolve(false);
    }
    return Promise.resolve(true);
  },

  /**
   * If we have a passphrase, rather than a 25-alphadigit sync key,
   * use the provided sync ID to bootstrap it using PBKDF2.
   *
   * Store the new 'passphrase' back into the identity manager.
   *
   * We can check this as often as we want, because once it's done the
   * check will no longer succeed. It only matters that it happens after
   * we decide to bump the server storage version.
   */
  upgradeSyncKey: function upgradeSyncKey(syncID) {
    let p = this.identity.syncKey;

    if (!p) {
      return false;
    }

    // Check whether it's already a key that we generated.
    if (Utils.isPassphrase(p)) {
      this._log.info("Sync key is up-to-date: no need to upgrade.");
      return true;
    }

    // Otherwise, let's upgrade it.
    // N.B., we persist the sync key without testing it first...

    let s = btoa(syncID);        // It's what WeaveCrypto expects. *sigh*
    let k = Utils.derivePresentableKeyFromPassphrase(p, s, PBKDF2_KEY_BYTES);   // Base 32.

    if (!k) {
      this._log.error("No key resulted from derivePresentableKeyFromPassphrase. Failing upgrade.");
      return false;
    }

    this._log.info("Upgrading sync key...");
    this.identity.syncKey = k;
    this._log.info("Saving upgraded sync key...");
    this.persistLogin();
    this._log.info("Done saving.");
    return true;
  },

  _freshStart: function _freshStart() {
    this._log.info("Fresh start. Resetting client and considering key upgrade.");
    this.resetClient();
    this.collectionKeys.clear();
    this.upgradeSyncKey(this.syncID);

    // Wipe the server.
    let wipeTimestamp = this.wipeServer();

    // Upload a new meta/global record.
    let meta = new WBORecord("meta", "global");
    meta.payload.syncID = this.syncID;
    meta.payload.storageVersion = STORAGE_VERSION;
    meta.payload.declined = this.engineManager.getDeclined();
    meta.isNew = true;

    // uploadMetaGlobal throws on failure -- including race conditions.
    // If we got into a race condition, we'll abort the sync this way, too.
    // That's fine. We'll just wait till the next sync. The client that we're
    // racing is probably busy uploading stuff right now anyway.
    this.uploadMetaGlobal(meta);

    // Wipe everything we know about except meta because we just uploaded it
    let engines = [this.clientsEngine].concat(this.engineManager.getAll());
    let collections = engines.map(engine => engine.name);
    // TODO: there's a bug here. We should be calling resetClient, no?

    // Generate, upload, and download new keys. Do this last so we don't wipe
    // them...
    this.generateNewSymmetricKeys();
  },

  /**
   * Wipe user data from the server.
   *
   * @param collections [optional]
   *        Array of collections to wipe. If not given, all collections are
   *        wiped by issuing a DELETE request for `storageURL`.
   *
   * @return the server's timestamp of the (last) DELETE.
   */
  wipeServer: function wipeServer(collections) {
    let response;
    if (!collections) {
      // Strip the trailing slash.
      let res = this.resource(this.storageURL.slice(0, -1));
      res.setHeader("X-Confirm-Delete", "1");
      try {
        response = res.delete();
      } catch (ex) {
        this._log.debug("Failed to wipe server: " + CommonUtils.exceptionStr(ex));
        throw ex;
      }
      if (response.status != 200 && response.status != 404) {
        this._log.debug("Aborting wipeServer. Server responded with " +
                        response.status + " response for " + this.storageURL);
        throw response;
      }
      return response.headers["x-weave-timestamp"];
    }

    let timestamp;
    for (let name of collections) {
      let url = this.storageURL + name;
      try {
        response = this.resource(url).delete();
      } catch (ex) {
        this._log.debug("Failed to wipe '" + name + "' collection: " +
                        Utils.exceptionStr(ex));
        throw ex;
      }

      if (response.status != 200 && response.status != 404) {
        this._log.debug("Aborting wipeServer. Server responded with " +
                        response.status + " response for " + url);
        throw response;
      }

      if ("x-weave-timestamp" in response.headers) {
        timestamp = response.headers["x-weave-timestamp"];
      }
    }

    return timestamp;
  },

  /**
   * Wipe all local user data.
   *
   * @param engines [optional]
   *        Array of engine names to wipe. If not given, all engines are used.
   */
  wipeClient: function wipeClient(engines) {
    // If we don't have any engines, reset the service and wipe all engines
    if (!engines) {
      // Clear out any service data
      this.resetService();

      engines = [this.clientsEngine].concat(this.engineManager.getAll());
    }
    // Convert the array of names into engines
    else {
      engines = this.engineManager.get(engines);
    }

    // Fully wipe each engine if it's able to decrypt data
    for each (let engine in engines) {
      if (engine.canDecrypt()) {
        engine.wipeClient();
      }
    }

    // Save the password/passphrase just in-case they aren't restored by sync
    this.persistLogin();
  },

  /**
   * Wipe all remote user data by wiping the server then telling each remote
   * client to wipe itself.
   *
   * @param engines [optional]
   *        Array of engine names to wipe. If not given, all engines are used.
   */
  wipeRemote: function wipeRemote(engines) {
    try {
      // Make sure stuff gets uploaded.
      this.resetClient(engines);

      // Clear out any server data.
      this.wipeServer(engines);

      // Only wipe the engines provided.
      if (engines) {
        engines.forEach(function(e) {
            this.clientsEngine.sendCommand("wipeEngine", [e]);
          }, this);
      }
      // Tell the remote machines to wipe themselves.
      else {
        this.clientsEngine.sendCommand("wipeAll", []);
      }

      // Make sure the changed clients get updated.
      this.clientsEngine.sync();
    } catch (ex) {
      this.errorHandler.checkServerError(ex);
      throw ex;
    }
  },

  /**
   * Reset local service information like logs, sync times, caches.
   */
  resetService: function resetService() {
    this._catch(function reset() {
      this._log.info("Service reset.");

      // Pretend we've never synced to the server and drop cached data
      this.syncID = "";
      this.recordManager.clearCache();
    })();
  },

  /**
   * Reset the client by getting rid of any local server data and client data.
   *
   * @param engines [optional]
   *        Array of engine names to reset. If not given, all engines are used.
   */
  resetClient: function resetClient(engines) {
    this._catch(function doResetClient() {
      // If we don't have any engines, reset everything including the service
      if (!engines) {
        // Clear out any service data
        this.resetService();

        engines = [this.clientsEngine].concat(this.engineManager.getAll());
      }
      // Convert the array of names into engines
      else {
        engines = this.engineManager.get(engines);
      }

      // Have each engine drop any temporary meta data
      for (let engine of engines) {
        engine.resetClient();
      }
    })();
  },

  /**
   * Fetch storage info from the server.
   *
   * @param type
   *        String specifying what info to fetch from the server. Must be one
   *        of the INFO_* values. See Sync Storage Server API spec for details.
   * @param callback
   *        Callback function with signature (error, data) where `data' is
   *        the return value from the server already parsed as JSON.
   *
   * @return RESTRequest instance representing the request, allowing callers
   *         to cancel the request.
   */
  getStorageInfo: function getStorageInfo(type, callback) {
    if (STORAGE_INFO_TYPES.indexOf(type) == -1) {
      throw "Invalid value for 'type': " + type;
    }

    let info_type = "info/" + type;
    this._log.trace("Retrieving '" + info_type + "'...");
    let url = this.userBaseURL + info_type;
    return this.getStorageRequest(url).get(function onComplete(error) {
      // Note: 'this' is the request.
      if (error) {
        this._log.debug("Failed to retrieve '" + info_type + "': " +
                        Utils.exceptionStr(error));
        return callback(error);
      }
      if (this.response.status != 200) {
        this._log.debug("Failed to retrieve '" + info_type +
                        "': server responded with HTTP" +
                        this.response.status);
        return callback(this.response);
      }

      let result;
      try {
        result = JSON.parse(this.response.body);
      } catch (ex) {
        this._log.debug("Server returned invalid JSON for '" + info_type +
                        "': " + this.response.body);
        return callback(ex);
      }
      this._log.trace("Successfully retrieved '" + info_type + "'.");
      return callback(null, result);
    });
  },
};

this.Service = new Sync11Service();
Service.onStartup();