Merge branch 'master' into debian

1 files changed, 389 insertions, 203 deletions

diff --git a/imapsync b/imapsync
index f80106d..00beec7 100755
--- a/imapsync
+++ b/imapsync
@@ -1,7 +1,7 @@
 #!/usr/bin/perl -T
 
 #----------------------------------------------------------------------
-# A minimal IMAP4 client for QRESYNC-capable servers
+# 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
@@ -42,7 +42,7 @@ sub usage(;$) {
     print STDERR "TODO $NAME usage\n";
     exit $rv;
 }
-usage(1) unless GetOptions(\%CONFIG, qw/debug help|h config=s quiet|q oneshot|1 check/);
+usage(1) unless GetOptions(\%CONFIG, qw/debug help|h config=s quiet|q oneshot|1 repair/);
 usage(0) if $CONFIG{help};
 
 
@@ -69,17 +69,16 @@ my ($DBFILE, $LOCKFILE);
 
     $LOCKFILE = $DBFILE =~ s/([^\/]+)\z/.$1.lck/r;
 }
-my ($DBH, $IMAP);
-
+my $DBH;
 
 # Clean after us
-sub clean() {
-    print STDERR "Cleaning...\n" if $CONFIG{debug};
+sub cleanup() {
+    print STDERR "Cleaning up...\n" if $CONFIG{debug};
     unlink $LOCKFILE if defined $LOCKFILE and -f $LOCKFILE;
-    undef $_ foreach grep defined, map {$IMAP->{$_}->{client}} keys %$IMAP;
     $DBH->disconnect() if defined $DBH;
 }
-$SIG{$_} = sub { clean(); die "$!\n"; } foreach qw/INT TERM/;
+$SIG{$_} = sub { cleanup(); print STDERR "$!\n"; exit 1; } foreach qw/INT TERM/;
+$SIG{$_} = sub { cleanup(); print STDERR "$!\n"; exit 0; } foreach qw/HUP/;
 
 
 #############################################################################
@@ -122,15 +121,15 @@ $DBH->do('PRAGMA foreign_keys = ON');
         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 CHECK (UIDNEXT > 0)},
-            q{HIGHESTMODSEQ UNSIGNED BIGINT NOT NULL CHECK (HIGHESTMODSEQ > 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 CHECK (UIDNEXT > 0)},
-            q{HIGHESTMODSEQ UNSIGNED BIGINT NOT NULL CHECK (HIGHESTMODSEQ > 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 => [
@@ -139,7 +138,7 @@ $DBH->do('PRAGMA foreign_keys = ON');
             q{rUID UNSIGNED INT NOT NULL CHECK (rUID > 0)},
             q{PRIMARY KEY (idx,lUID)},
             q{UNIQUE      (idx,rUID)}
-            # also, lUID  < local.UIDNEXT and rUID < remote.UIDNEXT
+            # also, lUID  < local.UIDNEXT and rUID < remote.UIDNEXT (except for interrupted syncs)
             # mapping.idx must be found among local.idx (and remote.idx)
         ],
     );
@@ -176,6 +175,7 @@ sub msg($@) {
 #############################################################################
 # Connect to the local and remote IMAP servers
 
+my $IMAP;
 foreach my $name (qw/local remote/) {
     my %config = %{$CONF->{$name}};
     $config{$_} = $CONFIG{$_} foreach keys %CONFIG;
@@ -406,7 +406,7 @@ sub sync_tree($$%) {
         my %mailboxes;
         $mailboxes{$_} = 1 foreach (keys %{$IMAP->{local}->{mailboxes}}, keys %{$IMAP->{remote}->{mailboxes}});
         foreach my $mbx (keys %mailboxes) {
-            die "Could not sync mailbox list.\n" if exists_mbx('local',$mbx) xor exists_mbx('remote',$mbx);
+            die "Couldn't sync mailbox list.\n" if exists_mbx('local',$mbx) xor exists_mbx('remote',$mbx);
         }
     }
 }
@@ -531,8 +531,7 @@ my $STH_GET_LOCAL_UID  = $DBH->prepare(q{SELECT lUID FROM mapping WHERE idx = ?
 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!
+# /!\ 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.
@@ -544,129 +543,209 @@ my $STH_UPDATE_LOCAL  = $DBH->prepare(q{UPDATE local  SET UIDNEXT = ?, HIGHESTMO
 my $STH_UPDATE_REMOTE = $DBH->prepare(q{UPDATE remote SET UIDNEXT = ?, HIGHESTMODSEQ = ? WHERE idx = ?});
 
 # Add a new mailbox.
-my $STH_NEWMAILBOX = $DBH->prepare(q{INSERT INTO mailboxes (mailbox,subscribed) VALUES (?,?)});
-my $STH_INSERT_LOCAL  = $DBH->prepare(q{INSERT INTO local  (idx,UIDVALIDITY,UIDNEXT,HIGHESTMODSEQ) VALUES (?,?,?,?)});
-my $STH_INSERT_REMOTE = $DBH->prepare(q{INSERT INTO remote (idx,UIDVALIDITY,UIDNEXT,HIGHESTMODSEQ) VALUES (?,?,?,?)});
+my $STH_INSERT_MAILBOX= $DBH->prepare(q{INSERT INTO mailboxes (mailbox,subscribed) VALUES (?,?)});
+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)
+});
 
-# Initialize $lIMAP and $rIMAP states to detect mailbox dirtyness.
-$STH_GET_CACHE->execute();
-while (defined (my $row = $STH_GET_CACHE->fetchrow_hashref())) {
-    $lIMAP->set_cache($row->{mailbox},
-        UIDVALIDITY   => $row->{lUIDVALIDITY},
-        UIDNEXT       => $row->{lUIDNEXT},
-        HIGHESTMODSEQ => ($CONFIG{check} ? 0 : $row->{lHIGHESTMODSEQ})
-    );
-    $rIMAP->set_cache($row->{mailbox},
-        UIDVALIDITY   => $row->{rUIDVALIDITY},
-        UIDNEXT       => $row->{rUIDNEXT},
-        HIGHESTMODSEQ => ($CONFIG{check} ? 0 : $row->{rHIGHESTMODSEQ})
-    );
-}
 
-# Download some missing UIDs.
-sub fix_missing($$$@) {
+# Download some missing UIDs from $source; returns the thew allocated UIDs
+sub download_missing($$$@) {
     my $idx = shift;
     my $mailbox = shift;
-    my $name = shift;
+    my $source = shift;
     my @set = @_;
+    my @uids;
+
+    my $target = $source eq 'local' ? 'remote' : 'local';
 
-    my $source = $name eq 'local' ? $lIMAP : $rIMAP;
-    my $target = $name eq 'local' ? $rIMAP : $lIMAP;
+    my ($buff, $bufflen) = ([], 0);
+    undef $buff if ($target eq 'local' ? $lIMAP : $rIMAP)->incapable('MULTIAPPEND');
 
     my $attrs = join ' ', qw/MODSEQ FLAGS INTERNALDATE ENVELOPE BODY.PEEK[]/;
-    $source->fetch(compact_set(@set), "($attrs)", sub(%) {
-        my %mail = @_;
-        return unless exists $mail{RFC822}; # not for us
+    ($source eq 'local' ? $lIMAP : $rIMAP)->fetch(compact_set(@set), "($attrs)", sub($) {
+        my $mail = shift;
+        return unless exists $mail->{RFC822}; # not for us
 
-        my $from = first { defined $_ and @$_ } @{$mail{ENVELOPE}}[2,3,4];
+        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] : '';
-        print STDERR "$name($mailbox): UID $mail{UID} from <$from> ($mail{INTERNALDATE})\n" unless $CONFIG{quiet};
+        print STDERR "$source($mailbox): UID $uid from <$from> ($mail->{INTERNALDATE})\n" unless $CONFIG{quiet};
 
-        # don't bother checking for MULTIAPPEND, @set is probably rather small
-        my @mail = ($mail{RFC822}, [ grep {lc $_ ne '\recent'} @{$mail{FLAGS}} ], $mail{INTERNALDATE});
-        my ($uid) = $target->append($mailbox, @mail);
-
-        my ($lUID, $rUID) = $name eq 'local' ? ($mail{UID}, $uid) : ($uid, $mail{UID});
-        print STDERR "$name($mailbox): Adding mapping (lUID,rUID) = ($lUID,$rUID)\n";
-        $STH_INSERT_MAPPING->execute($idx, $lUID, $rUID);
+        callback_new_message($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);
+    warn "WARNING: Conflicting flag update in $mailbox for local UID $lUID ($lFlags) ".
+         "and remote UID $rUID ($rFlags). Setting both to the union ($flags).\n";
+
+    return $flags
 }
 
-# Check synchronization of a mailbox between the two servers (in a very crude way)
-my @CHECKED;
-sub check($$$$$) {
-    my ($idx, $lVanished, $lList, $rVanished, $rList) = @_;
+
+# Delete a mapping ($idx, $lUID)
+sub delete_mapping($$) {
+    my ($idx, $lUID) = @_;
+    my $r = $STH_DELETE_MAPPING->execute($idx, $lUID);
+    die if $r > 1; # sanity check
+    warn "WARNING: Can't delete (idx,lUID) = ($idx,$lUID) from the database\n" 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)
+my @REPAIR;
+sub repair($$) {
+    my ($idx, $mailbox) = @_;
+
+    # get all existing UID with their flags
+    my ($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;
+
     $STH_GET_CACHE_BY_IDX->execute($idx);
     my $cache = $STH_GET_CACHE_BY_IDX->fetchrow_hashref() // die "Missing cache for index $idx";
     die if defined $STH_GET_CACHE_BY_IDX->fetch(); # sanity check
-    my $mailbox = $cache->{mailbox};
+
+    # process each pair ($lUID,$rUID) found in the mapping table, and
+    # compare with the result from the IMAP servers to detect anomalies
 
     $STH_GET_MAPPING->execute($idx);
-    my %missing = ( local => [], remote => [] );
     while (defined (my $row = $STH_GET_MAPPING->fetch())) {
         my ($lUID, $rUID) = @$row;
-        if (defined $lList->{$lUID} and defined $rList->{$rUID}) {
-            # both $lUID and $rUID are known
-            if ($lList->{$lUID}->[0] <= $cache->{lHIGHESTMODSEQ} and
-                $rList->{$rUID}->[0] <= $cache->{rHIGHESTMODSEQ}) {
-                # old stuff
-                if ($lList->{$lUID}->[1] ne $rList->{$rUID}->[1]) {
-                    warn "WARNING: Missed flag update in $mailbox for (lUID,rUID) = ($lUID,$rUID). Fixing...\n";
-                    # keep it in the hash references so we fix it automatically
-                }
-                else {
-                    # no conflict, remove it from the hashes
-                    delete $lList->{$lUID};
-                    delete $rList->{$rUID};
-                }
+        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 {
-                # delete the old stuff
-                delete $lList->{$lUID} if $lList->{$lUID}->[0] <= $cache->{lHIGHESTMODSEQ};
-                delete $rList->{$rUID} if $rList->{$rUID}->[0] <= $cache->{rHIGHESTMODSEQ};
+                # conflict
+                warn "WARNING: Missed flag update in $mailbox for (lUID,rUID) = ($lUID,$rUID). Repairing.\n"
+                    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 $lList->{$lUID} and !defined $rList->{$rUID}) {
+        elsif (!defined $lModified->{$lUID} and !defined $rModified->{$rUID}) {
             unless ($lVanished{$lUID} and $rVanished{$rUID}) {
-                # will be deleted from the database later
-                warn "WARNING: Pair (lUID,rUID) = ($lUID,$rUID) vanished from $mailbox\n";
-                $lVanished{$lUID} = 1;
-                $rVanished{$rUID} = 1;
+                warn "WARNING: Pair (lUID,rUID) = ($lUID,$rUID) vanished from $mailbox. Repairing.\n";
+                push @delete_mapping, $lUID;
             }
         }
-        elsif (!defined $lList->{$lUID}) {
-            unless ($lVanished{$lUID}) {
-                warn "WARNING: local($mailbox): No match for remote UID $rUID. Downloading again...\n";
-                push @{$missing{remote}}, $rUID;
-                delete $rList->{$rUID};
+        elsif (!defined $lModified->{$lUID}) {
+            push @delete_mapping, $lUID;
+            if ($lVanished{$lUID}) {
+                push @rToRemove, $rUID;
+            } else {
+                warn "local($mailbox): WARNING: UID $lUID disappeared. Downloading remote UID $rUID again.\n";
+                push @rMissing, $rUID;
             }
         }
-        elsif (!defined $rList->{$rUID}) {
-            unless ($rVanished{$rUID}) {
-                warn "WARNING: remote($mailbox): No match for local UID $lUID. Downloading again...\n";
-                push @{$missing{local}}, $lUID;
-                delete $lList->{$lUID};
+        elsif (!defined $rModified->{$rUID}) {
+            push @delete_mapping, $lUID;
+            if ($rVanished{$rUID}) {
+                push @lToRemove, $lUID;
+            } else {
+                warn "remote($mailbox): WARNING: UID $rUID disappeared. Downloading local UID $lUID again.\n";
+                push @lMissing, $lUID;
             }
         }
-        $lList->{$lUID} = $lList->{$lUID}->[1] if defined $lList->{$lUID};
-        $rList->{$rUID} = $rList->{$rUID}->[1] if defined $rList->{$rUID};
+
+        delete $lModified->{$lUID};
+        delete $lVanished{$lUID};
+        delete $rModified->{$rUID};
+        delete $rVanished{$rUID};
     }
 
-    # we'll complain later for modified UIDs without an entry in the database
+    # 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;
 
-    @$lVanished = keys %lVanished;
-    @$rVanished = keys %rVanished;
-    push @CHECKED, $idx;
-    return %missing;
+    # push flag updates; will increase HIGHESTMODSEQ
+    while (my ($lFlags,$lUIDs) = each %lToUpdate) {
+        $lIMAP->push_flag_updates($lFlags, @$lUIDs);
+    }
+    while (my ($rFlags,$rUIDs) = each %rToUpdate) {
+        $rIMAP->push_flag_updates($rFlags, @$rUIDs);
+    }
+
+
+    # Process UID found in IMAP but not in the mapping table.
+    warn "remote($mailbox): WARNING: No match for vanished local UID $_. Ignoring.\n" foreach keys %lVanished;
+    warn "local($mailbox): WARNING: No match for vanished remote UID $_. Ignoring.\n" foreach keys %rVanished;
+
+    foreach my $lUID (keys %$lModified) {
+        warn "remote($mailbox): WARNING: No match for modified local UID $lUID. Downloading again.\n";
+        push @lMissing, $lUID;
+    }
+    foreach my $rUID (keys %$rModified) {
+        warn "local($mailbox): WARNING: No match for modified remote UID $rUID. Downloading again.\n";
+        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);
 }
 
 
@@ -680,15 +759,13 @@ sub sync_known_messages($$) {
 
     # loop since processing might produce VANISHED or unsollicited FETCH responses
     while (1) {
-        my ($lVanished, $lModified, $rVanished, $rModified, %missing);
+        my ($lVanished, $lModified, $rVanished, $rModified);
 
-        my $check = ($CONFIG{check} and !grep { $idx == $_} @CHECKED) ? 1 : 0;
-        ($lVanished, $lModified) = $lIMAP->pull_updates($check);
-        ($rVanished, $rModified) = $rIMAP->pull_updates($check);
-        %missing = check($idx, $lVanished, $lModified, $rVanished, $rModified) if $check;
+        ($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 or %missing;
+        return $update unless %$lModified or %$rModified or @$lVanished or @$rVanished;
         $update = 1;
 
         # process VANISHED messages
@@ -707,7 +784,7 @@ sub sync_known_messages($$) {
                 my ($rUID) = $STH_GET_REMOTE_UID->fetchrow_array();
                 die if defined $STH_GET_REMOTE_UID->fetchrow_arrayref(); # sanity check
                 if (!defined $rUID) {
-                    warn "WARNING: remote($mailbox): No match for local vanished UID $lUID. Ignoring...\n";
+                    warn "remote($mailbox): WARNING: No match for vanished local UID $lUID. Ignoring.\n";
                 }
                 elsif (!exists $rVanished{$rUID}) {
                     push @rToRemove, $rUID;
@@ -718,21 +795,19 @@ sub sync_known_messages($$) {
                 my ($lUID) = $STH_GET_LOCAL_UID->fetchrow_array();
                 die if defined $STH_GET_LOCAL_UID->fetchrow_arrayref(); # sanity check
                 if (!defined $lUID) {
-                    warn "WARNING: local($mailbox): No match for remote vanished UID $rUID. Ignoring...\n";
+                    warn "local($mailbox): WARNING: No match for vanished remote UID $rUID. Ignoring.\n";
                 }
                 elsif (!exists $lVanished{$lUID}) {
                     push @lToRemove, $lUID;
                 }
             }
 
-            $lIMAP->remove(@lToRemove) if @lToRemove;
-            $rIMAP->remove(@rToRemove) if @rToRemove;
+            $lIMAP->remove_message(@lToRemove) if @lToRemove;
+            $rIMAP->remove_message(@rToRemove) if @rToRemove;
 
             # remove existing mappings
             foreach my $lUID (@$lVanished, @lToRemove) {
-                my $r = $STH_DELETE_MAPPING->execute($idx, $lUID);
-                die if $r > 1; # sanity check
-                warn "WARNING: Can't delete (idx,lUID) = ($idx,$lUID) from the database\n" if $r == 0;
+                delete_mapping($idx, $lUID);
             }
         }
 
@@ -755,15 +830,11 @@ sub sync_known_messages($$) {
                 my ($rUID) = $STH_GET_REMOTE_UID->fetchrow_array();
                 die if defined $STH_GET_REMOTE_UID->fetchrow_arrayref(); # sanity check
                 if (!defined $rUID) {
-                    warn "WARNING: remote($mailbox): No match for local updated UID $lUID. Downloading again...\n";
-                    push @{$missing{local}}, $lUID;
+                    warn "remote($mailbox): WARNING: No match for modified local UID $lUID. Try '--repair'.\n";
                 }
                 elsif (defined (my $rFlags = $rModified->{$rUID})) {
                     unless ($lFlags eq $rFlags) {
-                        my %flags = map {$_ => 1} (split(/ /, $lFlags), split(/ /, $rFlags));
-                        my $flags = join ' ', sort(keys %flags);
-                        warn "WARNING: Conflicting FLAG update for lUID $lUID ($lFlags) and".
-                             "rUID $rUID ($rFlags).  Setting both to the union ($flags).\n";
+                        my $flags = flag_conflict($mailbox, $lUID => $lFlags, $rUID => $rFlags);
                         $lToUpdate{$flags} //= [];
                         push @{$lToUpdate{$flags}}, $lUID;
                         $rToUpdate{$flags} //= [];
@@ -780,8 +851,7 @@ sub sync_known_messages($$) {
                 my ($lUID) = $STH_GET_LOCAL_UID->fetchrow_array();
                 die if defined $STH_GET_LOCAL_UID->fetchrow_arrayref(); # sanity check
                 if (!defined $lUID) {
-                    warn "WARNING: local($mailbox): No match for remote updated UID $rUID. Downloading again...\n";
-                    push @{$missing{remote}}, $rUID;
+                    warn "local($mailbox): WARNING: No match for modified remote UID $rUID. Try '--repair'.\n";
                 }
                 elsif (!exists $lModified->{$lUID}) {
                     # conflicts are taken care of above
@@ -790,9 +860,6 @@ sub sync_known_messages($$) {
                 }
             }
 
-            fix_missing($idx, $mailbox, 'local',  @{$missing{local}})  if @{$missing{local}  // []};
-            fix_missing($idx, $mailbox, 'remote', @{$missing{remote}}) if @{$missing{remote} // []};
-
             while (my ($lFlags,$lUIDs) = each %lToUpdate) {
                 $lIMAP->push_flag_updates($lFlags, @$lUIDs);
             }
@@ -804,81 +871,99 @@ sub sync_known_messages($$) {
 }
 
 
-# Sync known and new messages
-sub sync_messages($$) {
-    my ($idx, $mailbox) = @_;
-
-    my %mapping;
-    foreach my $source (qw/remote local/) {
-        my $target = $source eq 'local' ? $rIMAP : $lIMAP;
-        my $multiappend;
-
-        my @newmails;
-        my $buffer = 0; # sum of the RFC822 sizes in @newmails
-
-        my (@sUID, @tUID);
+# The callback to use when FETCHing new messages from $name to add it to
+# the other one.
+# If defined, the array reference $UIDs will be fed with the newly added
+# UIDs.
+# If defined, $buff contains the list of messages to be appended with
+# MULTIAPPEND.  In that case callback_new_message_flush should be called
+# after the FETCH.
+sub callback_new_message($$$$;$$$) {
+    my ($idx, $mailbox, $name, $mail, $UIDs, $buff, $bufflen) = @_;
+    return unless exists $mail->{RFC822}; # not for us
+
+    my $length = length $mail->{RFC822};
+    if ($length == 0) {
+        warn "$name($mailbox): WARNING: Ignoring new 0-length message (UID $mail->{UID})\n";
+        return;
+    }
 
-        # don't fetch again the messages we've just added
-        my @ignore = $source eq 'local' ? keys %mapping : values %mapping;
+    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;
+}
 
-        ($source eq 'local' ? $lIMAP : $rIMAP)->pull_new_messages(sub(%) {
-            my %mail = @_;
-            return unless exists $mail{RFC822}; # not for us
 
-            my @mail = ($mail{RFC822}, [ grep {lc $_ ne '\recent'} @{$mail{FLAGS}} ], $mail{INTERNALDATE});
-            push @sUID, $mail{UID};
+# 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) = @_;
 
-            # use MULTIAPPEND if possible (RFC 3502) to save round-trips
-            $multiappend //= !$target->incapable('MULTIAPPEND');
+    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
 
-            if (!$multiappend) {
-                my ($uid) = $target->append($mailbox, @mail);
-                push @tUID, $uid;
-            }
-            else {
-                # proceed by batch of 1MB to save roundtrips without blowing up the memory
-                if (@newmails and $buffer + length($mail{RFC822}) > 1048576) {
-                    push @tUID, $target->append($mailbox, @newmails);
-                    @newmails = ();
-                    $buffer = 0;
-                }
-                push @newmails, @mail;
-                $buffer += length $mail{RFC822};
-            }
-        }, @ignore);
-        push @tUID, $target->append($mailbox, @newmails) if @newmails;
-
-        die unless $#sUID == $#tUID; # sanity check
-        foreach my $k (0 .. $#sUID) {
-            my ($lUID,$rUID) = $source eq 'local' ? ($sUID[$k],$tUID[$k]) : ($tUID[$k],$sUID[$k]);
-            die if exists $mapping{$lUID}; # sanity check
-            $mapping{$lUID} = $rUID;
-        }
+    my ($lUIDs, $rUIDs) = $name eq 'local' ? (\@sUID,\@tUID) : (\@tUID,\@sUID);
+    for (my $k=0; $k<=$#messages; $k++) {
+        print STDERR "Adding mapping (lUID,rUID) = ($lUIDs->[$k],$rUIDs->[$k]) for $mailbox\n"
+            if $CONFIG{debug};
+        $STH_INSERT_MAPPING->execute($idx, $lUIDs->[$k], $rUIDs->[$k]);
     }
+    $DBH->commit(); # commit only once per batch
 
-    # new mailbox
-    if (!defined $$idx) {
-        my $subscribed = (grep { $_ eq $mailbox} @SUBSCRIPTIONS) ? 1 : 0;
-        $STH_NEWMAILBOX->execute($mailbox, $subscribed);
-        $STH_GET_INDEX->execute($mailbox);
-        ($$idx) = $STH_GET_INDEX->fetchrow_array();
-        die if !defined $$idx or defined $STH_GET_INDEX->fetchrow_arrayref(); # sanity check
-
-        # there might be flag updates pending
-        sync_known_messages($$idx, $mailbox);
-        $STH_INSERT_LOCAL->execute($$idx,  $lIMAP->get_cache(qw/UIDVALIDITY UIDNEXT HIGHESTMODSEQ/));
-        $STH_INSERT_REMOTE->execute($$idx, $rIMAP->get_cache(qw/UIDVALIDITY UIDNEXT HIGHESTMODSEQ/));
-    }
-    else {
-        # update known mailbox
-        sync_known_messages($$idx, $mailbox);
-        $STH_UPDATE_LOCAL->execute($lIMAP->get_cache( qw/UIDNEXT HIGHESTMODSEQ/), $$idx);
-        $STH_UPDATE_REMOTE->execute($rIMAP->get_cache(qw/UIDNEXT HIGHESTMODSEQ/), $$idx);
-    }
+    return @tUID;
+}
 
-    while (my ($lUID,$rUID) = each %mapping) {
-        $STH_INSERT_MAPPING->execute($$idx, $lUID, $rUID);
-    }
+
+# Sync both known and new messages
+# If the array references $lIgnore and $rIgnore are not empty, skip
+# the given UIDs.
+sub sync_messages($$;$$) {
+    my ($idx, $mailbox, $lIgnore, $rIgnore) = @_;
+    my ($buff, $bufflen, @lUIDs);
+
+    # get new messages from remote (except @$rIgnore) and APPEND them to local
+    ($buff, $bufflen) = ([], 0);
+    undef $buff if $lIMAP->incapable('MULTIAPPEND');
+    $rIMAP->pull_new_messages(sub($) {
+        callback_new_message($idx, $mailbox, 'remote', shift, \@lUIDs, $buff, \$bufflen)
+    }, @{$rIgnore // []});
+    push @lUIDs, callback_new_message_flush($idx, $mailbox, 'remote', @$buff)
+        if defined $buff and @$buff;
+
+    # get new messages from local (except @$lIgnore and the newly allocated local
+    # UIDs @lUIDs) and APPEND them to remote
+    ($buff, $bufflen) = ([], 0);
+    undef $buff if $rIMAP->incapable('MULTIAPPEND');
+    $lIMAP->pull_new_messages(sub($) {
+        callback_new_message($idx, $mailbox, 'local', shift, undef, $buff, \$bufflen)
+    }, @{$lIgnore // []}, @lUIDs);
+    callback_new_message_flush($idx, $mailbox, 'local', @$buff)
+        if defined $buff and @$buff;
+
+    # 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);
+    $STH_UPDATE_REMOTE->execute($rIMAP->get_cache(qw/UIDNEXT HIGHESTMODSEQ/), $idx);
     $DBH->commit();
 }
 
@@ -903,39 +988,140 @@ sub wait_notifications(;$) {
 }
 
 
-my ($mailbox, $idx);
+# Resume interrupted mailbox syncs.
+my ($MAILBOX, $IDX);
+$STH_LIST_INTERRUPTED->execute();
+while (defined (my $row = $STH_LIST_INTERRUPTED->fetchrow_arrayref())) {
+    ($IDX, $MAILBOX) = @$row;
+    print STDERR "Resuming interrupted sync for $MAILBOX\n";
+
+    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 $rIMAP states to detect mailbox dirtyness.
+$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}
+    );
+    push @REPAIR, $row->{mailbox} if $CONFIG{repair} and
+        (!@ARGV or grep { $_ eq $row->{mailbox} } @ARGV);
+}
+
+while (@REPAIR) {
+    $MAILBOX = shift @REPAIR;
+
+    $STH_GET_INDEX->execute($MAILBOX);
+    ($IDX) = $STH_GET_INDEX->fetchrow_array();
+    die if defined $STH_GET_INDEX->fetch(); # sanity check
+
+    $lIMAP->select($MAILBOX);
+    $rIMAP->select($MAILBOX);
+    repair($IDX, $MAILBOX);
+}
+if ($CONFIG{repair}) {
+    cleanup();
+    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);
+        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(@ARGV) // $rIMAP->next_dirty_mailbox(@ARGV) // last;
-            $mailbox = 'INBOX' if uc $mailbox eq 'INBOX'; # INBOX is case insensitive
+            $MAILBOX = $lIMAP->next_dirty_mailbox(@ARGV) // $rIMAP->next_dirty_mailbox(@ARGV) // last;
+            $MAILBOX = 'INBOX' if uc $MAILBOX eq 'INBOX'; # INBOX is case insensitive
 
-            $STH_GET_INDEX->execute($mailbox);
-            ($idx) = $STH_GET_INDEX->fetchrow_array();
+            $STH_GET_INDEX->execute($MAILBOX);
+            ($IDX) = $STH_GET_INDEX->fetchrow_array();
             die if defined $STH_GET_INDEX->fetch(); # sanity check
 
-            $lIMAP->select($mailbox);
-            $rIMAP->select($mailbox);
+            $lIMAP->select($MAILBOX);
+            $rIMAP->select($MAILBOX);
+
+            # new mailbox
+            if (!defined $IDX) {
+                my $subscribed = (grep { $_ eq $MAILBOX} @SUBSCRIPTIONS) ? 1 : 0;
+                $STH_INSERT_MAILBOX->execute($MAILBOX, $subscribed);
+                $STH_GET_INDEX->execute($MAILBOX);
+                ($IDX) = $STH_GET_INDEX->fetchrow_array();
+                die if !defined $IDX or defined $STH_GET_INDEX->fetchrow_arrayref(); # sanity check
 
-            # sync updates to known messages before fetching new messages
-            if (defined $idx and sync_known_messages($idx, $mailbox)) {
+                $STH_INSERT_LOCAL->execute( $IDX, $lIMAP->uidvalidity($MAILBOX));
+                $STH_INSERT_REMOTE->execute($IDX, $rIMAP->uidvalidity($MAILBOX));
+
+                # don't commit before the first mapping (lUID,rUID)
+            }
+            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);
-                $STH_UPDATE_REMOTE_HIGHESTMODSEQ->execute($rIMAP->get_cache('HIGHESTMODSEQ'), $idx);
+                $STH_UPDATE_LOCAL_HIGHESTMODSEQ->execute( $lIMAP->get_cache('HIGHESTMODSEQ'), $IDX);
+                $STH_UPDATE_REMOTE_HIGHESTMODSEQ->execute($rIMAP->get_cache('HIGHESTMODSEQ'), $IDX);
                 $DBH->commit();
             }
-            sync_messages(\$idx, $mailbox);
+            sync_messages($IDX, $MAILBOX);
         }
     }
     # clean state!
-    exit 0 if $CONFIG{oneshot} or $CONFIG{check};
+    if ($CONFIG{oneshot}) {
+        cleanup();
+        exit 0;
+    }
     wait_notifications(900);
 }
 
-END { clean (); }
+END { cleanup(); }