lei_to_mail: optimize for MUAs

Instead of optimizing our own performance, this optimizes
our data to reduce work done by the MUA consumer.

Maildir and mbox destinations no longer support any notion of
the IMAP \Recent flag.  JMAP has no functioning \Recent
equivalent, and neither do we.

In practice, having MUAs (e.g. mutt) clear the \Recent flag when
committing changes to the mbox is expensive: it creates a
rename(2) storm with Maildir and overwrites the entire mbox.

For mboxcl2 (and mboxcl), we'll further optimize mutt behavior
by setting the Lines: header in addition to Content-Length.

With these changes, mutt exits instantaneously on mboxcl2,
mboxcl, and Maildirs generated by "lei q".

1 files changed, 22 insertions, 8 deletions

diff --git a/lib/PublicInbox/LeiToMail.pm b/lib/PublicInbox/LeiToMail.pm
index 8d030227..dcf6d8a3 100644
--- a/lib/PublicInbox/LeiToMail.pm
+++ b/lib/PublicInbox/LeiToMail.pm
@@ -34,7 +34,11 @@ my %kw2status = (
 sub _mbox_hdr_buf ($$$) {
         my ($eml, $type, $kw) = @_;
         $eml->header_set($_) for (qw(Lines Bytes Content-Length));
-        my %hdr; # set Status, X-Status
+
+        # Messages are always 'O' (non-\Recent in IMAP), it saves
+        # MUAs the trouble of rewriting the mbox if no other
+        # changes are made
+        my %hdr = (Status => [ 'O' ]); # set Status, X-Status
         for my $k (@$kw) {
                 if (my $ent = $kw2status{$k}) {
                         push @{$hdr{$ent->[0]}}, $ent->[1];
@@ -92,6 +96,16 @@ sub eml2mboxo {
         $buf;
 }
 
+sub _mboxcl_common ($$$) {
+        my ($buf, $bdy, $crlf) = @_;
+        # add Lines: so mutt won't have to add it on MUA close
+        my $lines = $$bdy =~ tr!\n!\n!;
+        $$buf .= 'Content-Length: '.length($$bdy).$crlf.
+                'Lines: '.$lines.$crlf.$crlf;
+        substr($$bdy, 0, 0, $$buf); # prepend header
+        $_[0] = $bdy;
+}
+
 # mboxcl still escapes "From " lines
 sub eml2mboxcl {
         my ($eml, $kw) = @_;
@@ -99,9 +113,7 @@ sub eml2mboxcl {
         my $crlf = $eml->{crlf};
         if (my $bdy = delete $eml->{bdy}) {
                 $$bdy =~ s/^From />From /gm;
-                $$buf .= 'Content-Length: '.length($$bdy).$crlf.$crlf;
-                substr($$bdy, 0, 0, $$buf); # prepend header
-                $buf = $bdy;
+                _mboxcl_common($buf, $bdy, $crlf);
         }
         $$buf .= $crlf;
         $buf;
@@ -113,9 +125,7 @@ sub eml2mboxcl2 {
         my $buf = _mbox_hdr_buf($eml, 'mboxcl2', $kw);
         my $crlf = $eml->{crlf};
         if (my $bdy = delete $eml->{bdy}) {
-                $$buf .= 'Content-Length: '.length($$bdy).$crlf.$crlf;
-                substr($$bdy, 0, 0, $$buf); # prepend header
-                $buf = $bdy;
+                _mboxcl_common($buf, $bdy, $crlf);
         }
         $$buf .= $crlf;
         $buf;
@@ -276,7 +286,11 @@ sub _buf2maildir {
         } while (!sysopen($fh, $tmp, O_CREAT|O_EXCL|O_WRONLY) &&
                 $! == EEXIST && ($rand = int(rand 0x7fffffff).','));
         if (print $fh $$buf and close($fh)) {
-                $dst .= $sfx eq '' ? 'new/' : 'cur/';
+                # ignore new/ and write only to cur/, otherwise MUAs
+                # with R/W access to the Maildir will end up doing
+                # a mass rename which can take a while with thousands
+                # of messages.
+                $dst .= 'cur/';
                 $rand = '';
                 do {
                         $final = $dst.$rand."oid=$oid:2,$sfx";