aboutsummaryrefslogtreecommitdiffstats
path: root/imapsync
blob: ae051639eae13b590c8db00551fd93ec57a30b0f (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
#!/usr/bin/perl -T

#----------------------------------------------------------------------
# IMAP-to-IMAP synchronization program for QRESYNC-capable servers
# Copyright © 2015 Guilhem Moulin <guilhem@fripost.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#----------------------------------------------------------------------

use strict;
use warnings;

our $VERSION = '0.1';
my $NAME = 'imapsync';
use Getopt::Long qw/:config posix_default no_ignore_case gnu_compat
                            bundling auto_version/;
use DBI ();
use List::Util 'first';
use POSIX 'strftime';

use lib 'lib';
use Net::IMAP::Sync qw/read_config compact_set $IMAP_text $IMAP_cond/;

# Clean up PATH
$ENV{PATH} = join ':', qw{/usr/local/bin /usr/bin /bin};
delete @ENV{qw/IFS CDPATH ENV BASH_ENV/};

my %CONFIG;
sub usage(;$) {
    my $rv = shift // 0;
    if ($rv) {
        print STDERR "Usage: $NAME [OPTIONS] [COMMAND] [MAILBOX [..]]\n"
                    ."Try '$NAME --help' or consult the manpage for more information.\n";
    }
    else {
        print STDERR "Usage: $NAME [OPTIONS] [MAILBOX [..]]\n"
                    ."  or: $NAME [OPTIONS] --repair [MAILBOX [..]]\n"
                    ."  or: $NAME [OPTIONS] --delete MAILBOX [..]\n"
                    ."  or: $NAME [OPTIONS] --rename SOURCE DEST\n"
                    ."Consult the manpage for more information.\n";
    }
    exit $rv;
}
usage(1) unless GetOptions(\%CONFIG, qw/config=s quiet|q target=s@ debug help|h repair delete rename/);
usage(0) if $CONFIG{help};
my $COMMAND = do {
    my @command = grep {exists $CONFIG{$_}} qw/repair delete rename/;
    usage(1) if $#command>0;
    $command[0]
};
usage(1) if defined $COMMAND and (($COMMAND eq 'delete' and !@ARGV) or $COMMAND eq 'rename' and $#ARGV != 1);
@ARGV = map {uc $_ eq 'INBOX' ? 'INBOX' : $_ } @ARGV; # INBOX is case-insensitive


my $CONF = read_config( delete $CONFIG{config} // $NAME
                      , [qw/_ local remote/]
                      , database => qr/\A(\P{Control}+)\z/
                      , logfile => qr/\A(\/\P{Control}+)\z/
                      , 'list-mailbox' => qr/\A([\x01-\x09\x0B\x0C\x0E-\x7F]+)\z/
                      , 'list-select-opts' => qr/\A([\x21\x23\x24\x26\x27\x2B-\x5B\x5E-\x7A\x7C-\x7E]+)\z/
                      , 'ignore-mailbox' => qr/\A([\x01-\x09\x0B\x0C\x0E-\x7F]+)\z/
                      );
my ($DBFILE, $LOCKFILE, $LOGGER_FD);

{
    $DBFILE = $CONF->{_}->{database} if defined $CONF->{_};
    $DBFILE //= $CONF->{remote}->{host}.'.db' if defined $CONF->{remote};
    $DBFILE //= $CONF->{local}->{host}. '.db' if defined $CONF->{local};
    die "Missing option database" unless defined $DBFILE;

    unless ($DBFILE =~ /\A\//) {
        my $dir = ($ENV{XDG_DATA_HOME} // "$ENV{HOME}/.local/share") .'/'. $NAME;
        $dir =~ /\A(\/\p{Print}+)\z/ or die "Insecure $dir";
        $dir = $1;
        $DBFILE = $dir .'/'. $DBFILE;
        unless (-d $dir) {
            mkdir $dir, 0700 or die "Can't mkdir $dir: $!\n";
        }
    }

    $LOCKFILE = $DBFILE =~ s/([^\/]+)\z/.$1.lck/r;

    if (defined $CONF->{_} and defined $CONF->{_}->{logfile}) {
        open $LOGGER_FD, '>>', $CONF->{_}->{logfile}
            or die "Can't open $CONF->{_}->{logfile}: $!\n";
        $LOGGER_FD->autoflush(1);
    }
}
my $DBH;

# Clean after us
sub cleanup() {
    logger(undef, "Cleaning up...") if $CONFIG{debug};
    unlink $LOCKFILE if defined $LOCKFILE and -f $LOCKFILE;
    close $LOGGER_FD if defined $LOGGER_FD;
    $DBH->disconnect() if defined $DBH;
}
$SIG{$_} = sub { msg(undef, $!); cleanup(); exit 1; } foreach qw/INT TERM/;
$SIG{$_} = sub { msg(undef, $!); cleanup(); exit 0; } foreach qw/HUP/;


#############################################################################
# Lock the database
{
    if (-f $LOCKFILE) {
        open my $lock, '<', $LOCKFILE or die "Can't open $LOCKFILE: $!\n";
        my $pid = <$lock>;
        close $lock;
        chomp $pid;
        my $msg = "LOCKFILE '$LOCKFILE' exists.";
        $msg .= " (Is PID $pid running?)" if defined $pid and $pid =~ /^[0-9]+$/;
        die $msg, "\n";
    }

    open my $lock, '>', $LOCKFILE or die "Can't open $LOCKFILE: $!\n";
    print $lock $$, "\n";
    close $lock;
}


#############################################################################
# Open the database and create tables

$DBH = DBI::->connect("dbi:SQLite:dbname=$DBFILE", undef, undef, {
    AutoCommit => 0,
    RaiseError => 1,
    sqlite_see_if_its_a_number => 1, # see if the bind values are numbers or not
});
$DBH->do('PRAGMA foreign_keys = ON');


{
    my @schema = (
        mailboxes => [
            q{idx        INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT},
            q{mailbox    TEXT    NOT NULL CHECK (mailbox != '') UNIQUE},
            q{subscribed BOOLEAN NOT NULL}
        ],
        local => [
            q{idx           INTEGER         NOT NULL PRIMARY KEY REFERENCES mailboxes(idx)},
            q{UIDVALIDITY   UNSIGNED INT    NOT NULL CHECK (UIDVALIDITY > 0)},
            q{UIDNEXT       UNSIGNED INT    NOT NULL}, # 0 initially
            q{HIGHESTMODSEQ UNSIGNED BIGINT NOT NULL}  # 0 initially
            # one-to-one correspondence between local.idx and remote.idx
        ],
        remote => [
            q{idx           INTEGER         NOT NULL PRIMARY KEY REFERENCES mailboxes(idx)},
            q{UIDVALIDITY   UNSIGNED INT    NOT NULL CHECK (UIDVALIDITY > 0)},
            q{UIDNEXT       UNSIGNED INT    NOT NULL}, # 0 initially
            q{HIGHESTMODSEQ UNSIGNED BIGINT NOT NULL}  # 0 initially
            # one-to-one correspondence between local.idx and remote.idx
        ],
        mapping => [
            q{idx  INTEGER      NOT NULL REFERENCES mailboxes(idx)},
            q{lUID UNSIGNED INT NOT NULL CHECK (lUID > 0)},
            q{rUID UNSIGNED INT NOT NULL CHECK (rUID > 0)},
            q{PRIMARY KEY (idx,lUID)},
            q{UNIQUE      (idx,rUID)}
            # also, lUID  < local.UIDNEXT and rUID < remote.UIDNEXT (except for interrupted syncs)
            # mapping.idx must be found among local.idx (and remote.idx)
        ],
    );

    # Invariants:
    #   * UIDVALIDITY never changes.
    #   * All changes for UID < {local,remote}.UIDNEXT and MODSEQ <
    #     {local,remote}.HIGHESTMODSEQ have been propagated.
    #   * No local (resp. remote) new message will ever have a UID <= local.UIDNEXT
    #     (resp. <= remote.UIDNEXT).
    #   * Any idx in `local` must be present in `remote` and vice-versa.
    #   * Any idx in `mapping` must be present in `local` and `remote`.
    while (@schema) {
        my $table = shift @schema;
        my $schema = shift @schema;
        my $sth = $DBH->table_info(undef, undef, $table, 'TABLE', {Escape => 1});
        my $row = $sth->fetch();
        die if defined $sth->fetch(); # sanity check
        unless (defined $row) {
            $DBH->do("CREATE TABLE $table (".join(', ',@$schema).")");
            $DBH->commit();
        }
    }
}

sub msg($@) {
    my $name = shift;
    return unless @_;
    logger($name, @_) if defined $LOGGER_FD and $LOGGER_FD ne \*STDERR;
    my $prefix = defined $name ? "$name: " : '';
    print STDERR $prefix, @_, "\n";
}
sub logger($@) {
    my $name = shift;
    return unless @_ and defined $LOGGER_FD;
    my $prefix = strftime "%b %e %H:%M:%S ", localtime;
    $prefix .= "$name: " if defined $name;
    $LOGGER_FD->say($prefix, @_);
}
logger(undef, ">>> $NAME $VERSION");


#############################################################################
# Connect to the local and remote IMAP servers

my $IMAP;
foreach my $name (qw/local remote/) {
    my %config = %{$CONF->{$name}};
    $config{$_} = $CONFIG{$_} foreach grep {defined $CONFIG{$_}} qw/quiet debug/;
    $config{enable} = 'QRESYNC';
    $config{name} = $name;
    $config{'logger-fd'} = $LOGGER_FD if defined $LOGGER_FD;

    $IMAP->{$name} = { client => Net::IMAP::Sync::->new(%config) };
    my $client = $IMAP->{$name}->{client};

    die "Non $_-capable IMAP server.\n" foreach $client->incapable(qw/LIST-EXTENDED LIST-STATUS UIDPLUS/);
    # XXX We should start by listing all mailboxes matching the user's LIST
    #     criterion, then issue "SET NOTIFY (mailboxes ... (...))".  But this
    #     crashes the IMAP client:
    #     http://dovecot.org/pipermail/dovecot/2015-July/101473.html
    #my $mailboxes = $client->list((uc $config{'subscribed-only'} eq 'TRUE' ? '(SUBSCRIBED)' : '' )
    #                             .$config{mailboxes}, 'SUBSCRIBED');
    # $client->notify('SELECTED', 'MAILBOXES ('.join(' ', keys %$mailboxes).')');
    # XXX NOTIFY doesn't work as expected for INBOX
    #     http://dovecot.org/pipermail/dovecot/2015-July/101514.html
    #$client->notify(qw/SELECTED SUBSCRIBED/) if $CONFIG{watch};
    # XXX We shouldn't need to ask for STATUS responses here, and use
    #     NOTIFY's STATUS indicator instead.  However Dovecot violates RFC
    #     5464: http://dovecot.org/pipermail/dovecot/2015-July/101474.html

    my $list = '"" ';
    my @params;
    if (!defined $COMMAND or $COMMAND eq 'repair') {
        $list  = '('.uc($CONF->{_}->{'list-select-opts'}).') '.$list if defined $CONF->{_}->{'list-select-opts'};
        $list .= (defined $CONF->{_}->{'list-mailbox'} ? '('.$CONF->{_}->{'list-mailbox'}.')' : '*') unless @ARGV;
        @params = ('SUBSCRIBED', 'STATUS (UIDVALIDITY UIDNEXT HIGHESTMODSEQ)');
    }
    $list .= $#ARGV == 0 ? Net::IMAP::Sync::quote($ARGV[0])
           : ('('.join(' ',map {Net::IMAP::Sync::quote($_)} @ARGV).')') if @ARGV;
    @{$IMAP->{$name}}{qw/mailboxes delims/} = $client->list($list, @params);
}


##############################################################################
#

# Add a new mailbox to the database.
my $STH_INSERT_MAILBOX= $DBH->prepare(q{INSERT INTO mailboxes (mailbox,subscribed) VALUES (?,?)});

# Get the index associated with a mailbox.
my $STH_GET_INDEX = $DBH->prepare(q{SELECT idx,subscribed FROM mailboxes WHERE mailbox = ?});

# Ensure local and remote delimiter match
sub check_delim($) {
    my $mbx = shift;
    my ($lDelims, $rDelims) = map {$IMAP->{$_}->{delims}} qw/local remote/;
    if (exists $lDelims->{$mbx} and exists $rDelims->{$mbx} and
        ((defined $lDelims->{$mbx} xor defined $rDelims->{$mbx}) or
         (defined $lDelims->{$mbx} and defined $rDelims->{$mbx} and $lDelims->{$mbx} ne $rDelims->{$mbx}))) {
        my ($ld, $rd) = ($lDelims->{$mbx}, $rDelims->{$mbx});
        $ld =~ s/([\x22\x5C])/\\$1/g if defined $ld;
        $rd =~ s/([\x22\x5C])/\\$1/g if defined $rd;
        die "Error: Hierarchy delimiter for $mbx don't match: "
           ."local \"". ($ld // '')."\", remote \"".($rd // '')."\"\n"
    }
    return exists $lDelims->{$mbx} ? $lDelims->{$mbx} : exists $rDelims->{$mbx} ? $rDelims->{$mbx} : undef;
}

# Return true if $mailbox exists on $name
sub mbx_exists($$) {
    my ($name, $mailbox) = @_;
    my $flags = $IMAP->{$name}->{mailboxes}->{$mailbox};
    return (defined $flags and !grep {lc $_ eq lc '\NonExistent'} @$flags) ? 1 : 0;
}

# Return true if $mailbox is subscribed to on $name
sub mbx_subscribed($$) {
    my ($name, $mailbox) = @_;
    my $flags = $IMAP->{$name}->{mailboxes}->{$mailbox};
    return (defined $flags and grep {lc $_ eq lc '\Subscribed'} @$flags) ? 1 : 0;
}


##############################################################################
# Process --delete command
#
if (defined $COMMAND and $COMMAND eq 'delete') {
    my $sth_delete_mailboxes = $DBH->prepare(q{DELETE FROM mailboxes WHERE idx = ?});
    my $sth_delete_local     = $DBH->prepare(q{DELETE FROM local     WHERE idx = ?});
    my $sth_delete_remote    = $DBH->prepare(q{DELETE FROM remote    WHERE idx = ?});
    my $sth_delete_mapping   = $DBH->prepare(q{DELETE FROM mapping   WHERE idx = ?});

    foreach my $mailbox (@ARGV) {
        $STH_GET_INDEX->execute($mailbox);
        my ($idx) = $STH_GET_INDEX->fetchrow_array();
        die if defined $STH_GET_INDEX->fetch(); # sanity check

        # delete $mailbox on servers where $mailbox exists.  note that
        # there is a race condition where the mailbox could have
        # appeared meanwhile
        foreach my $name (qw/local remote/) {
            next if defined $CONFIG{target} and !grep {$_ eq $name} @{$CONFIG{target}};
            $IMAP->{$name}->{client}->delete($mailbox) if mbx_exists($name, $mailbox);
        }

        if (defined $idx and (!defined $CONFIG{target} or grep {$_ eq 'database'} @{$CONFIG{target}})) {
            my $r1 = $sth_delete_mapping->execute($idx);
            msg('database', "WARNING: `DELETE FROM mapping WHERE idx = $idx` failed") unless $r1;
            my $r2 = $sth_delete_local->execute($idx);
            msg('database', "WARNING: `DELETE FROM local WHERE idx = $idx` failed") unless $r2;
            my $r3 = $sth_delete_remote->execute($idx);
            msg('database', "WARNING: `DELETE FROM remote WHERE idx = $idx` failed") unless $r3;
            my $r4 = $sth_delete_mailboxes->execute($idx);
            msg('database', "WARNING: `DELETE FROM mailboxes WHERE idx = $idx` failed") unless $r4;

            $DBH->commit();
            msg('database', "Removed mailbox $mailbox") if $r4;
        }
    }
    exit 0;
}


##############################################################################
# Process --rename command
#
elsif (defined $COMMAND and $COMMAND eq 'rename') {
    my ($from, $to) = @ARGV;

    # get index of the original name
    $STH_GET_INDEX->execute($from);
    my ($idx) = $STH_GET_INDEX->fetchrow_array();
    die if defined $STH_GET_INDEX->fetch(); # sanity check

    # ensure the local and remote hierarchy delimiter match
    my $delim = check_delim($from);

    # ensure the target name doesn't already exist on the servers. there
    # is a race condition where the mailbox would be created before we
    # issue the RENAME command, then the server would reply with a
    # tagged NO response
    foreach my $name (qw/local remote/) {
        next if defined $CONFIG{target} and !grep {$_ eq $name} @{$CONFIG{target}};
        if (mbx_exists($name, $to)) {
            msg($name, "ERROR: Mailbox $to exists.  Run `$NAME --delete $to` to delete.");
            exit 1;
        }
    }

    # ensure the target name doesn't already exist in the database
    $STH_GET_INDEX->execute($to);
    if (defined $STH_GET_INDEX->fetch() and
        (!defined $CONFIG{target} or grep {$_ eq 'database'} @{$CONFIG{target}})) {
        msg('database', "ERROR: Mailbox $to exists.  Run `$NAME --delete $to` to delete.");
        exit 1;
    }


    # rename $from to $to on servers where $from exists.  again there is
    # a race condition, but if $to has been created meanwhile the server
    # will reply with a tagged NO response
    foreach my $name (qw/local remote/) {
        next if defined $CONFIG{target} and !grep {$_ eq $name} @{$CONFIG{target}};
        $IMAP->{$name}->{client}->rename($from, $to) if mbx_exists($name, $from);
    }

    # rename from to $to in the database
    if (defined $idx and (!defined $CONFIG{target} or grep {$_ eq 'database'} @{$CONFIG{target}})) {
        my $sth_rename_mailbox = $DBH->prepare(q{UPDATE mailboxes SET mailbox = ? WHERE idx = ?});
        my $r = $sth_rename_mailbox->execute($to, $idx);
        msg('database', "WARNING: `UPDATE mailboxes SET mailbox = ".$DBH->quote($to)." WHERE idx = $idx` failed") unless $r;

        # for non-flat mailboxes, rename the children as well
        if (defined $delim) {
            my $prefix = $from.$delim;
            my $sth_rename_children = $DBH->prepare(q{
                UPDATE mailboxes SET mailbox = ? || SUBSTR(mailbox,?)
                WHERE SUBSTR(mailbox,1,?) = ?
            });
            $sth_rename_children->execute($to, length($prefix), length($prefix), $prefix);
        }

        $DBH->commit();
        msg('database', "Renamed mailbox $from to $to") if $r;
    }
    exit 0;
}


##############################################################################
# Synchronize mailbox and subscription lists

my @MAILBOXES;
{
    my %mailboxes;
    $mailboxes{$_} = 1 foreach keys %{$IMAP->{local}->{mailboxes}};
    $mailboxes{$_} = 1 foreach keys %{$IMAP->{remote}->{mailboxes}};
    my $sth_subscribe = $DBH->prepare(q{UPDATE mailboxes SET subscribed = ? WHERE idx = ?});

    @MAILBOXES = keys %mailboxes;
    @MAILBOXES = grep !/$CONF->{_}->{'ignore-mailbox'}/, @MAILBOXES
        if defined $CONF->{_}->{'ignore-mailbox'};

    foreach my $mailbox (@MAILBOXES) {
        check_delim($mailbox); # ensure that the delimiter match
        my ($lExists, $rExists) = map {mbx_exists($_,$mailbox)} qw/local remote/;

        $STH_GET_INDEX->execute($mailbox);
        my ($idx,$subscribed) = $STH_GET_INDEX->fetchrow_array();
        die if defined $STH_GET_INDEX->fetch(); # sanity check

        if ($lExists and $rExists) {
            # $mailbox exists on both sides
            my ($lSubscribed,$rSubscribed) = map {mbx_subscribed($_, $mailbox)} qw/local remote/;
            if (defined $idx) {
                if ($lSubscribed xor $rSubscribed) {
                    # mailbox is subscribed on only one server
                    if ($subscribed) { # unsubscribe
                        my $name = $lSubscribed ? 'local' : 'remote';
                        $IMAP->{$name}->{client}->unsubscribe($mailbox);
                    }
                    else { # subscribe
                        my $name = $lSubscribed ? 'remote' : 'local';
                        $IMAP->{$name}->{client}->subscribe($mailbox);
                    }
                    # toggle subscribtion in the database
                    $subscribed = $subscribed ? 0 : 1;
                    $sth_subscribe->execute($subscribed, $idx) or
                        msg('database', "WARNING: `UPDATE mailboxes SET subscribed = $subscribed WHERE idx = $idx` failed");
                    $DBH->commit();
                }
                # $mailbox is either subscribed on both servers, or subscribed on both
                elsif ($lSubscribed xor $subscribed) {
                    # update the database if needed
                    $sth_subscribe->execute($lSubscribed, $idx) or
                        msg('database', "WARNING: `UPDATE mailboxes SET subscribed = $lSubscribed WHERE idx = $idx` failed");
                    $DBH->commit();
                }
            }
            else {
                # add new mailbox; subscribe on both servers if $mailbox is subscribed on one of them
                my $subscribed = ($lSubscribed or $rSubscribed) ? 1 : 0;
                $STH_INSERT_MAILBOX->execute($mailbox, $subscribed);
                $IMAP->{local}->{client}->subscribe($mailbox)  if $subscribed and !$lSubscribed;
                $IMAP->{remote}->{client}->subscribe($mailbox) if $subscribed and !$rSubscribed;
                $DBH->commit();
            }
        }
        elsif ($lExists and !$rExists) {
            # $mailbox is on 'local' only
            if (defined $idx) {
                msg('database', "ERROR: Mailbox $mailbox exists.  Run `$NAME --delete $mailbox` to delete.");
                exit 1;
            }
            my $subscribed = mbx_subscribed('local', $mailbox);
            $STH_INSERT_MAILBOX->execute($mailbox, $subscribed);
            $IMAP->{remote}->{client}->create($mailbox);
            $IMAP->{remote}->{client}->subscribe($mailbox) if $subscribed;
            $DBH->commit();
        }
        elsif (!$lExists and $rExists) {
            # $mailbox is on 'remote' only
            if (defined $idx) {
                msg('database', "ERROR: Mailbox $mailbox exists.  Run `$NAME --delete $mailbox` to delete.");
                exit 1;
            }
            my $subscribed = mbx_subscribed('remote', $mailbox);
            $STH_INSERT_MAILBOX->execute($mailbox, $subscribed);
            $IMAP->{local}->{client}->create($mailbox);
            $IMAP->{local}->{client}->subscribe($mailbox) if $subscribed;
            $DBH->commit();
        }
    }
}
my ($lIMAP, $rIMAP) = map {$IMAP->{$_}->{client}} qw/local remote/;
undef $IMAP;


#############################################################################
# Synchronize messages

# Get all cached states from the database.
my $STH_GET_CACHE = $DBH->prepare(q{
    SELECT mailbox, m.idx as idx,
           l.UIDVALIDITY as lUIDVALIDITY, l.UIDNEXT as lUIDNEXT, l.HIGHESTMODSEQ as lHIGHESTMODSEQ,
           r.UIDVALIDITY as rUIDVALIDITY, r.UIDNEXT as rUIDNEXT, r.HIGHESTMODSEQ as rHIGHESTMODSEQ
    FROM mailboxes m JOIN local l ON m.idx = l.idx JOIN remote r ON m.idx = r.idx
});
my $STH_GET_CACHE_BY_IDX = $DBH->prepare(q{
    SELECT mailbox,
           l.UIDVALIDITY as lUIDVALIDITY, l.UIDNEXT as lUIDNEXT, l.HIGHESTMODSEQ as lHIGHESTMODSEQ,
           r.UIDVALIDITY as rUIDVALIDITY, r.UIDNEXT as rUIDNEXT, r.HIGHESTMODSEQ as rHIGHESTMODSEQ
    FROM mailboxes m JOIN local l ON m.idx = l.idx JOIN remote r ON m.idx = r.idx
    WHERE m.idx = ?
});

# Find local/remote UID from the map.
my $STH_GET_LOCAL_UID  = $DBH->prepare(q{SELECT lUID FROM mapping WHERE idx = ? and rUID = ?});
my $STH_GET_REMOTE_UID = $DBH->prepare(q{SELECT rUID FROM mapping WHERE idx = ? and lUID = ?});

# Delete a (idx,lUID,rUID) association.
# /!\ Don't commit before the messages have actually been EXPUNGEd on both sides!
my $STH_DELETE_MAPPING = $DBH->prepare(q{DELETE FROM mapping WHERE idx = ? and lUID = ?});

# Update the HIGHESTMODSEQ.
my $STH_UPDATE_LOCAL_HIGHESTMODSEQ  = $DBH->prepare(q{UPDATE local  SET HIGHESTMODSEQ = ? WHERE idx = ?});
my $STH_UPDATE_REMOTE_HIGHESTMODSEQ = $DBH->prepare(q{UPDATE remote SET HIGHESTMODSEQ = ? WHERE idx = ?});

# Update the HIGHESTMODSEQ and UIDNEXT.
my $STH_UPDATE_LOCAL  = $DBH->prepare(q{UPDATE local  SET UIDNEXT = ?, HIGHESTMODSEQ = ? WHERE idx = ?});
my $STH_UPDATE_REMOTE = $DBH->prepare(q{UPDATE remote SET UIDNEXT = ?, HIGHESTMODSEQ = ? WHERE idx = ?});

# Add a new mailbox.
my $STH_INSERT_LOCAL  = $DBH->prepare(q{INSERT INTO local  (idx,UIDVALIDITY,UIDNEXT,HIGHESTMODSEQ) VALUES (?,?,0,0)});
my $STH_INSERT_REMOTE = $DBH->prepare(q{INSERT INTO remote (idx,UIDVALIDITY,UIDNEXT,HIGHESTMODSEQ) VALUES (?,?,0,0)});

# Insert or retrieve a (idx,lUID,rUID) association.
my $STH_INSERT_MAPPING = $DBH->prepare(q{INSERT INTO mapping (idx,lUID,rUID) VALUES (?,?,?)});
my $STH_GET_MAPPING    = $DBH->prepare(q{SELECT lUID,rUID FROM mapping WHERE idx = ?});

# Get the list of interrupted mailbox syncs.
my $STH_LIST_INTERRUPTED = $DBH->prepare(q{
    SELECT mbx.idx, mailbox
    FROM mailboxes mbx JOIN local l ON mbx.idx = l.idx JOIN remote r ON mbx.idx = r.idx JOIN mapping ON mbx.idx = mapping.idx
    WHERE (lUID >= l.UIDNEXT OR rUID >= r.UIDNEXT)
    GROUP BY mbx.idx
});

# For an interrupted mailbox sync, get the pairs (lUID,rUID) that have
# already been downloaded.
my $STH_GET_INTERRUPTED_BY_IDX = $DBH->prepare(q{
    SELECT lUID, rUID
    FROM mapping m JOIN local l ON m.idx = l.idx JOIN remote r ON m.idx = r.idx
    WHERE m.idx = ? AND (lUID >= l.UIDNEXT OR rUID >= r.UIDNEXT)
});


# Download some missing UIDs from $source; returns the thew allocated UIDs
sub download_missing($$$@) {
    my $idx = shift;
    my $mailbox = shift;
    my $source = shift;
    my @set = @_;
    my @uids;

    my $target = $source eq 'local' ? 'remote' : 'local';

    my ($buff, $bufflen) = ([], 0);
    undef $buff if ($target eq 'local' ? $lIMAP : $rIMAP)->incapable('MULTIAPPEND');

    my $attrs = join ' ', qw/MODSEQ FLAGS INTERNALDATE ENVELOPE BODY.PEEK[]/;
    ($source eq 'local' ? $lIMAP : $rIMAP)->fetch(compact_set(@set), "($attrs)", sub($) {
        my $mail = shift;
        return unless exists $mail->{RFC822}; # not for us

        my $uid = $mail->{UID};
        my $from = first { defined $_ and @$_ } @{$mail->{ENVELOPE}}[2,3,4];
        $from = (defined $from and @$from) ? $from->[0]->[2].'@'.$from->[0]->[3] : '';
        msg(undef, "$source($mailbox): UID $uid from <$from> ($mail->{INTERNALDATE})") unless $CONFIG{quiet};

        callback_new_message($idx, $mailbox, $source, $mail, \@uids, $buff, \$bufflen)
    });
    push @uids, callback_new_message_flush($idx, $mailbox, $source, @$buff) if defined $buff and @$buff;
    return @uids;
}


# Solve a flag update conflict (by taking the union of the two flag lists).
sub flag_conflict($$$$$) {
    my ($mailbox, $lUID, $lFlags, $rUID, $rFlags) = @_;

    my %flags = map {$_ => 1} (split(/ /, $lFlags), split(/ /, $rFlags));
    my $flags = join ' ', sort(keys %flags);
    msg(undef, "WARNING: Conflicting flag update in $mailbox for local UID $lUID ($lFlags) ".
               "and remote UID $rUID ($rFlags). Setting both to the union ($flags).");

    return $flags
}


# Delete a mapping ($idx, $lUID)
sub delete_mapping($$) {
    my ($idx, $lUID) = @_;
    my $r = $STH_DELETE_MAPPING->execute($idx, $lUID);
    die if $r > 1; # sanity check
    msg('database', "WARNING: Can't delete (idx,lUID) = ($idx,$lUID)") if $r == 0;
}


# Check and repair synchronization of a mailbox between the two servers
# (in a very crude way, by downloading all existing UID with their flags)
sub repair($) {
    my $mailbox = shift;

    $STH_GET_INDEX->execute($mailbox);
    my ($idx) = $STH_GET_INDEX->fetchrow_array();
    die if defined $STH_GET_INDEX->fetch(); # sanity check

    return unless defined $idx; # not in the database
    $lIMAP->select($mailbox);
    $rIMAP->select($mailbox);

    $STH_GET_CACHE_BY_IDX->execute($idx);
    my $cache = $STH_GET_CACHE_BY_IDX->fetchrow_hashref() // return; # no cache
    die if defined $STH_GET_CACHE_BY_IDX->fetch(); # sanity check

    # get all existing UID with their flags
    my ($lVanished, $lModified) = $lIMAP->pull_updates(1);
    my ($rVanished, $rModified) = $rIMAP->pull_updates(1);

    my %lVanished = map {$_ => 1} @$lVanished;
    my %rVanished = map {$_ => 1} @$rVanished;

    my (@lToRemove, %lToUpdate, @lMissing);
    my (@rToRemove, %rToUpdate, @rMissing);
    my @delete_mapping;

    # process each pair ($lUID,$rUID) found in the mapping table, and
    # compare with the result from the IMAP servers to detect anomalies

    $STH_GET_MAPPING->execute($idx);
    while (defined (my $row = $STH_GET_MAPPING->fetch())) {
        my ($lUID, $rUID) = @$row;
        if (defined $lModified->{$lUID} and defined $rModified->{$rUID}) {
            # both $lUID and $rUID are known; see sync_known_messages
            # for the sync algorithm
            my ($lFlags, $rFlags) = ($lModified->{$lUID}->[1], $rModified->{$rUID}->[1]);
            if ($lFlags eq $rFlags) {
                # no conflict
            }
            elsif ($lModified->{$lUID}->[0] <= $cache->{lHIGHESTMODSEQ} and
                   $rModified->{$rUID}->[0] >  $cache->{rHIGHESTMODSEQ}) {
                # set $lUID to $rFlags
                $lToUpdate{$rFlags} //= [];
                push @{$lToUpdate{$rFlags}}, $lUID;
            }
            elsif ($lModified->{$lUID}->[0] >  $cache->{lHIGHESTMODSEQ} and
                   $rModified->{$rUID}->[0] <= $cache->{rHIGHESTMODSEQ}) {
                # set $rUID to $lFlags
                $rToUpdate{$lFlags} //= [];
                push @{$rToUpdate{$lFlags}}, $rUID;
            }
            else {
                # conflict
                msg(undef, "WARNING: Missed flag update in $mailbox for (lUID,rUID) = ($lUID,$rUID). Repairing.")
                    if $lModified->{$lUID}->[0] <= $cache->{lHIGHESTMODSEQ} and
                       $rModified->{$rUID}->[0] <= $cache->{rHIGHESTMODSEQ};
                # set both $lUID and $rUID to the union of $lFlags and $rFlags
                my $flags = flag_conflict($mailbox, $lUID => $lFlags, $rUID => $rFlags);
                $lToUpdate{$flags} //= [];
                push @{$lToUpdate{$flags}}, $lUID;
                $rToUpdate{$flags} //= [];
                push @{$rToUpdate{$flags}}, $rUID;
            }
        }
        elsif (!defined $lModified->{$lUID} and !defined $rModified->{$rUID}) {
            unless ($lVanished{$lUID} and $rVanished{$rUID}) {
                msg(undef, "WARNING: Pair (lUID,rUID) = ($lUID,$rUID) vanished from $mailbox. Repairing.");
                push @delete_mapping, $lUID;
            }
        }
        elsif (!defined $lModified->{$lUID}) {
            push @delete_mapping, $lUID;
            if ($lVanished{$lUID}) {
                push @rToRemove, $rUID;
            } else {
                msg("local($mailbox)", "WARNING: UID $lUID disappeared. Downloading remote UID $rUID again.");
                push @rMissing, $rUID;
            }
        }
        elsif (!defined $rModified->{$rUID}) {
            push @delete_mapping, $lUID;
            if ($rVanished{$rUID}) {
                push @lToRemove, $lUID;
            } else {
                msg("remote($mailbox)", "WARNING: UID $rUID disappeared. Downloading local UID $lUID again.");
                push @lMissing, $lUID;
            }
        }

        delete $lModified->{$lUID};
        delete $lVanished{$lUID};
        delete $rModified->{$rUID};
        delete $rVanished{$rUID};
    }

    # remove messages on the IMAP side; will increase HIGHESTMODSEQ
    $lIMAP->remove_message(@lToRemove) if @lToRemove;
    $rIMAP->remove_message(@rToRemove) if @rToRemove;

    # remove entries in the table
    delete_mapping($idx, $_) foreach @delete_mapping;
    $DBH->commit() if @delete_mapping;

    # push flag updates; will increase HIGHESTMODSEQ
    while (my ($lFlags,$lUIDs) = each %lToUpdate) {
        $lIMAP->push_flag_updates($lFlags, @$lUIDs);
    }
    while (my ($rFlags,$rUIDs) = each %rToUpdate) {
        $rIMAP->push_flag_updates($rFlags, @$rUIDs);
    }


    # Process UID found in IMAP but not in the mapping table.
    msg("remote($mailbox)", "WARNING: No match for vanished local UID $_. Ignoring.") foreach keys %lVanished;
    msg("local($mailbox)", "WARNING: No match for vanished remote UID $_. Ignoring.") foreach keys %rVanished;

    foreach my $lUID (keys %$lModified) {
        msg("remote($mailbox)", "WARNING: No match for modified local UID $lUID. Downloading again.");
        push @lMissing, $lUID;
    }
    foreach my $rUID (keys %$rModified) {
        msg("local($mailbox)", "WARNING: No match for modified remote UID $rUID. Downloading again.");
        push @rMissing, $rUID;
    }

    # download missing UIDs; will increase UIDNEXT and HIGHESTMODSEQ
    my @rIgnore = download_missing($idx, $mailbox, 'local',  @lMissing) if @lMissing;
    my @lIgnore = download_missing($idx, $mailbox, 'remote', @rMissing) if @rMissing;

    # download new messages; this will also update UIDNEXT and HIGHESTMODSEQ in the database
    sync_messages($idx, $mailbox, \@lIgnore, \@rIgnore);
}


# Sync known messages.  Since pull_updates is the last method call on
# $lIMAP and $rIMAP, it is safe to call get_cache on either object after
# this function, in order to update the HIGHESTMODSEQ.
# Return true if an update was detected, and false otherwise
sub sync_known_messages($$) {
    my ($idx, $mailbox) = @_;
    my $update = 0;

    # loop since processing might produce VANISHED or unsollicited FETCH responses
    while (1) {
        my ($lVanished, $lModified, $rVanished, $rModified);

        ($lVanished, $lModified) = $lIMAP->pull_updates();
        ($rVanished, $rModified) = $rIMAP->pull_updates();

        # repeat until we have nothing pending
        return $update unless %$lModified or %$rModified or @$lVanished or @$rVanished;
        $update = 1;

        # process VANISHED messages
        # /!\ this might modify the VANISHED or MODIFIED cache!
        if (@$lVanished or @$rVanished) {
            my %lVanished = map {$_ => 1} @$lVanished;
            my %rVanished = map {$_ => 1} @$rVanished;

            # For each vanished UID, get the corresponding one on the
            # other side (from the DB); consider it as to be removed if
            # it hasn't been removed already.

            my (@lToRemove, @rToRemove);
            foreach my $lUID (@$lVanished) {
                $STH_GET_REMOTE_UID->execute($idx, $lUID);
                my ($rUID) = $STH_GET_REMOTE_UID->fetchrow_array();
                die if defined $STH_GET_REMOTE_UID->fetchrow_arrayref(); # sanity check
                if (!defined $rUID) {
                    msg("remote($mailbox)", "WARNING: No match for vanished local UID $lUID. Ignoring.");
                }
                elsif (!exists $rVanished{$rUID}) {
                    push @rToRemove, $rUID;
                }
            }
            foreach my $rUID (@$rVanished) {
                $STH_GET_LOCAL_UID->execute($idx, $rUID);
                my ($lUID) = $STH_GET_LOCAL_UID->fetchrow_array();
                die if defined $STH_GET_LOCAL_UID->fetchrow_arrayref(); # sanity check
                if (!defined $lUID) {
                    msg("local($mailbox)", "WARNING: No match for vanished remote UID $rUID. Ignoring.");
                }
                elsif (!exists $lVanished{$lUID}) {
                    push @lToRemove, $lUID;
                }
            }

            $lIMAP->remove_message(@lToRemove) if @lToRemove;
            $rIMAP->remove_message(@rToRemove) if @rToRemove;

            # remove existing mappings
            foreach my $lUID (@$lVanished, @lToRemove) {
                delete_mapping($idx, $lUID);
            }
        }

        # process FLAG updates
        # /!\ this might modify the VANISHED or MODIFIED cache!
        if (%$lModified or %$rModified) {
            my (%lToUpdate, %rToUpdate);

            # Take flags updates on both sides, and get the
            # corresponding UIDs on the other side (from the DB).
            # If it wasn't modified there, make it such; if it was
            # modified with the same flags list, ignore that message;
            # otherwise there is a conflict, and take the union.
            #
            # Group by flags in order to limit the number of round
            # trips.

            while (my ($lUID,$lFlags) = each %$lModified) {
                $STH_GET_REMOTE_UID->execute($idx, $lUID);
                my ($rUID) = $STH_GET_REMOTE_UID->fetchrow_array();
                die if defined $STH_GET_REMOTE_UID->fetchrow_arrayref(); # sanity check
                if (!defined $rUID) {
                    msg("remote($mailbox)", "WARNING: No match for modified local UID $lUID. Try '--repair'.");
                }
                elsif (defined (my $rFlags = $rModified->{$rUID})) {
                    unless ($lFlags eq $rFlags) {
                        my $flags = flag_conflict($mailbox, $lUID => $lFlags, $rUID => $rFlags);
                        $lToUpdate{$flags} //= [];
                        push @{$lToUpdate{$flags}}, $lUID;
                        $rToUpdate{$flags} //= [];
                        push @{$rToUpdate{$flags}}, $rUID;
                    }
                }
                else {
                    $rToUpdate{$lFlags} //= [];
                    push @{$rToUpdate{$lFlags}}, $rUID;
                }
            }
            while (my ($rUID,$rFlags) = each %$rModified) {
                $STH_GET_LOCAL_UID->execute($idx, $rUID);
                my ($lUID) = $STH_GET_LOCAL_UID->fetchrow_array();
                die if defined $STH_GET_LOCAL_UID->fetchrow_arrayref(); # sanity check
                if (!defined $lUID) {
                    msg("local($mailbox)", "WARNING: No match for modified remote UID $rUID. Try '--repair'.");
                }
                elsif (!exists $lModified->{$lUID}) {
                    # conflicts are taken care of above
                    $lToUpdate{$rFlags} //= [];
                    push @{$lToUpdate{$rFlags}}, $lUID;
                }
            }

            while (my ($lFlags,$lUIDs) = each %lToUpdate) {
                $lIMAP->push_flag_updates($lFlags, @$lUIDs);
            }
            while (my ($rFlags,$rUIDs) = each %rToUpdate) {
                $rIMAP->push_flag_updates($rFlags, @$rUIDs);
            }
        }
    }
}


# The callback to use when FETCHing new messages from $name to add it to
# the other one.
# If defined, the array reference $UIDs will be fed with the newly added
# UIDs.
# If defined, $buff contains the list of messages to be appended with
# MULTIAPPEND.  In that case callback_new_message_flush should be called
# after the FETCH.
sub callback_new_message($$$$;$$$) {
    my ($idx, $mailbox, $name, $mail, $UIDs, $buff, $bufflen) = @_;
    return unless exists $mail->{RFC822}; # not for us

    my $length = length $mail->{RFC822};
    if ($length == 0) {
        msg("$name($mailbox)", "WARNING: Ignoring new 0-length message (UID $mail->{UID})");
        return;
    }

    my @UIDs;
    unless (defined $buff) {
        @UIDs = callback_new_message_flush($idx, $mailbox, $name, $mail);
    }
    else {
        # use MULTIAPPEND (RFC 3502)
        # proceed by batches of 1MB to save roundtrips without blowing up the memory
        if (@$buff and $$bufflen + $length > 1048576) {
            @UIDs = callback_new_message_flush($idx, $mailbox, $name, @$buff);
            @$buff = ();
            $$bufflen = 0;
        }
        push @$buff, $mail;
        $$bufflen += $length;
    }
    push @$UIDs, @UIDs if defined $UIDs;
}


# Add the given @messages (multiple messages are only allowed for
# MULTIAPPEND-capable servers) from $name to the other server.
# Returns the list of newly allocated UIDs.
sub callback_new_message_flush($$$@) {
    my ($idx, $mailbox, $name, @messages) = @_;

    my $imap = $name eq 'local' ? $rIMAP : $lIMAP; # target client
    my @sUID = map {$_->{UID}} @messages;
    my @tUID = $imap->append($mailbox, @messages);
    die unless $#sUID == $#tUID; # sanity check

    my ($lUIDs, $rUIDs) = $name eq 'local' ? (\@sUID,\@tUID) : (\@tUID,\@sUID);
    for (my $k=0; $k<=$#messages; $k++) {
        logger(undef, "Adding mapping (lUID,rUID) = ($lUIDs->[$k],$rUIDs->[$k]) for $mailbox")
            if $CONFIG{debug};
        $STH_INSERT_MAPPING->execute($idx, $lUIDs->[$k], $rUIDs->[$k]);
    }
    $DBH->commit(); # commit only once per batch

    return @tUID;
}


# Sync both known and new messages
# If the array references $lIgnore and $rIgnore are not empty, skip
# the given UIDs.
sub sync_messages($$;$$) {
    my ($idx, $mailbox, $lIgnore, $rIgnore) = @_;

    my %ignore = (local => ($lIgnore // []), remote => ($rIgnore // []));
    my $loop;
    do {
        # get new messages from $source (except @{$ignore{$source}}) and APPEND them to $target
        foreach my $source (qw/remote local/) { # pull remote mails first
            my $target = $source eq 'remote' ? 'local' : 'remote';
            my $buff    = [] unless ($target eq 'local' ? $lIMAP : $rIMAP)->incapable('MULTIAPPEND');
            my $bufflen = 0;
            my @tUIDs;

            ($source eq 'remote' ? $rIMAP : $lIMAP)->pull_new_messages(sub($) {
                callback_new_message($idx, $mailbox, $source, shift, \@tUIDs, $buff, \$bufflen)
            }, @{$ignore{$source}});

            push @tUIDs, callback_new_message_flush($idx, $mailbox, $source, @$buff)
                if defined $buff and @$buff;
            push @{$ignore{$target}}, @tUIDs;

            $loop = @tUIDs ? 1 : 0;
        }
        # since $source modifies $target's UIDNEXT upon new mails, we
        # need to check again the first $source (remote) whenever the
        # last one (local) added new messages to it
    }
    while ($loop);

    # both local and remote UIDNEXT are now up to date; proceed with
    # pending flag updates and vanished messages
    sync_known_messages($idx, $mailbox);

    # don't store the new UIDNEXTs before to avoid downloading these
    # mails again in the event of a crash
    $STH_UPDATE_LOCAL->execute($lIMAP->get_cache( qw/UIDNEXT HIGHESTMODSEQ/), $idx) or
        msg('database', "WARNING: Can't update remote UIDNEXT/HIGHESTMODSEQ for $mailbox");
    $STH_UPDATE_REMOTE->execute($rIMAP->get_cache(qw/UIDNEXT HIGHESTMODSEQ/), $idx) or
        msg('database', "WARNING: Can't update remote UIDNEXT/HIGHESTMODSEQ for $mailbox");
    $DBH->commit();
}


# Wait up to $timout seconds for notifications on either IMAP server.
# Then issue a NOOP so the connection doesn't terminate for inactivity.
sub wait_notifications(;$) {
    my $timeout = shift // 300;

    while ($timeout > 0) {
        my $r1 = $lIMAP->slurp();
        my $r2 = $rIMAP->slurp();
        last if $r1 or $r2; # got update!

        sleep 1;
        if (--$timeout == 0) {
            $lIMAP->noop();
            $rIMAP->noop();
            # might have got updates so exit the loop
        }
    }
}


#############################################################################
# Resume interrupted mailbox syncs.
#
my ($MAILBOX, $IDX);
$STH_LIST_INTERRUPTED->execute();
while (defined (my $row = $STH_LIST_INTERRUPTED->fetchrow_arrayref())) {
    next unless grep { $_ eq $row->[1] } @MAILBOXES; # skip ignored mailbox
    ($IDX, $MAILBOX) = @$row;
    msg(undef, "Resuming interrupted sync for $MAILBOX");

    my %lUIDs;
    $STH_GET_INTERRUPTED_BY_IDX->execute($IDX);
    while (defined (my $row = $STH_GET_INTERRUPTED_BY_IDX->fetchrow_arrayref())) {
        $lUIDs{$row->[0]} = $row->[1]; # pair ($lUID, $rUID)
    }
    die unless %lUIDs; # sanity check

    $lIMAP->select($MAILBOX);
    $rIMAP->select($MAILBOX);

    # FETCH all messages with their FLAGS to detect messages that have
    # vanished meanwhile, or for which there was a flag update.

    my (%lList, %rList); # The lists of existing local and remote UIDs
    my $attrs = '('.join(' ', qw/MODSEQ FLAGS/).')';
    $lIMAP->fetch(compact_set(keys   %lUIDs), $attrs, sub($){ $lList{shift->{UID}} = 1 });
    $rIMAP->fetch(compact_set(values %lUIDs), $attrs, sub($){ $rList{shift->{UID}} = 1 });

    my (@lToRemove, @rToRemove);
    while (my ($lUID,$rUID) = each %lUIDs) {
        next if $lList{$lUID} and $rList{$rUID}; # exists on both
        push @lToRemove, $lUID if $lList{$lUID};
        push @rToRemove, $rUID if $rList{$rUID};

        delete_mapping($IDX, $lUID);
    }

    $lIMAP->remove_message(@lToRemove) if @lToRemove;
    $rIMAP->remove_message(@rToRemove) if @rToRemove;
    $DBH->commit() if @lToRemove or @rToRemove; # /!\ commit *after* remove_message!

    # ignore deleted messages
    delete @lList{@lToRemove};
    delete @rList{@rToRemove};

    # Resume the sync, but skip messages that have already been
    # downloaded.  Flag updates will be processed automatically since
    # the _MODIFIED internal cache has been initialized with all our
    # UIDs.  (Since there is no reliable HIGHESTMODSEQ, any flag
    # difference is treated as a conflict.)
    sync_messages($IDX, $MAILBOX, [keys %lList], [keys %rList]);
}


#############################################################################
# Initialize $lIMAP and $rIMAP states to detect mailbox dirtyness.
#
my %KNOWN_INDEXES;
$STH_GET_CACHE->execute();
while (defined (my $row = $STH_GET_CACHE->fetchrow_hashref())) {
    $lIMAP->set_cache($row->{mailbox},
        UIDVALIDITY   => $row->{lUIDVALIDITY},
        UIDNEXT       => $row->{lUIDNEXT},
        HIGHESTMODSEQ => $row->{lHIGHESTMODSEQ}
    );
    $rIMAP->set_cache($row->{mailbox},
        UIDVALIDITY   => $row->{rUIDVALIDITY},
        UIDNEXT       => $row->{rUIDNEXT},
        HIGHESTMODSEQ => $row->{rHIGHESTMODSEQ}
    );
    $KNOWN_INDEXES{$row->{idx}} = 1;
}

if (defined $COMMAND and $COMMAND eq 'repair') {
    repair($_) foreach @MAILBOXES;
    exit 0;
}


while(1) {
    while(1) {
        my $cache;
        my $update = 0;
        if (defined $MAILBOX and ($lIMAP->is_dirty($MAILBOX) or $rIMAP->is_dirty($MAILBOX))) {
            # $MAILBOX is dirty on either the local or remote mailbox
            sync_messages($IDX, $MAILBOX);
        }
        else {
            $MAILBOX = $lIMAP->next_dirty_mailbox(@MAILBOXES) // $rIMAP->next_dirty_mailbox(@MAILBOXES) // last;
            $MAILBOX = 'INBOX' if uc $MAILBOX eq 'INBOX'; # INBOX is case insensitive

            $STH_GET_INDEX->execute($MAILBOX);
            ($IDX) = $STH_GET_INDEX->fetchrow_array();
            die if defined $STH_GET_INDEX->fetch(); # sanity check
            die unless defined $IDX; # sanity check;

            $lIMAP->select($MAILBOX);
            $rIMAP->select($MAILBOX);

            if (!$KNOWN_INDEXES{$IDX}) {
                $STH_INSERT_LOCAL->execute( $IDX, $lIMAP->uidvalidity($MAILBOX));
                $STH_INSERT_REMOTE->execute($IDX, $rIMAP->uidvalidity($MAILBOX));

                # no need to commit before the first mapping (lUID,rUID)
                $KNOWN_INDEXES{$IDX} = 1;
            }
            elsif (sync_known_messages($IDX, $MAILBOX)) {
                # sync updates to known messages before fetching new messages
                # get_cache is safe after pull_update
                $STH_UPDATE_LOCAL_HIGHESTMODSEQ->execute( $lIMAP->get_cache('HIGHESTMODSEQ'), $IDX) or
                    msg('database', "WARNING: Can't update local HIGHESTMODSEQ for $MAILBOX");
                $STH_UPDATE_REMOTE_HIGHESTMODSEQ->execute($rIMAP->get_cache('HIGHESTMODSEQ'), $IDX) or
                    msg('database', "WARNING: Can't update remote HIGHESTMODSEQ for $MAILBOX");
                $DBH->commit();
            }
            sync_messages($IDX, $MAILBOX);
        }
    }
    # clean state!
    exit 0 unless defined $COMMAND and $COMMAND eq 'watch';
    wait_notifications(900);
}

END { cleanup(); }