[PATCH 2/2] lei_to_mail: optimize for MUAs

[Eric Wong <e@80x24.org>]

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".
---
 lib/PublicInbox/LeiToMail.pm | 30 ++++++++++++++++++++++--------
 t/lei_to_mail.t              | 16 +++++++++++-----
 t/mbox_reader.t              |  2 ++
 3 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/lib/PublicInbox/LeiToMail.pm b/lib/PublicInbox/LeiToMail.pm
index 17d48a90..1281aef4 100644
--- a/lib/PublicInbox/LeiToMail.pm
+++ b/lib/PublicInbox/LeiToMail.pm
@@ -35,7 +35,11 @@ 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];
@@ -93,6 +97,16 @@ 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) = @_;
@@ -100,9 +114,7 @@ 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;
@@ -114,9 +126,7 @@ 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);
 	}
 	$$buf .= $crlf;
 	$buf;
@@ -277,7 +287,11 @@ sub _buf2maildir {
 	} while (!sysopen($fh, $tmp, O_CREAT|O_EXCL|O_WRONLY) &&
 		$! == EEXIST && ($rand = int(rand 0x7fffffff).','));
 	if (print $fh $$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";
diff --git a/t/lei_to_mail.t b/t/lei_to_mail.t
index 083e0df4..e5ac8eac 100644
--- a/t/lei_to_mail.t
+++ b/t/lei_to_mail.t
@@ -25,7 +25,7 @@ for my $mbox (@MBOX) {
 	my $s = $cb->(PublicInbox::Eml->new($from), $kw);
 	is(substr($$s, -1, 1), "\n", "trailing LF in normal $mbox");
 	my $eml = PublicInbox::Eml->new($s);
-	is($eml->header('Status'), 'R', "Status: set by $m");
+	is($eml->header('Status'), 'OR', "Status: set by $m");
 	is($eml->header('X-Status'), 'AF', "X-Status: set by $m");
 	if ($mbox eq 'mboxcl2') {
 		like($eml->body_raw, qr/^From /, "From not escaped $m");
@@ -170,6 +170,12 @@ for my $zsfx (qw(gz bz2 xz)) { # XXX should we support zst, zz, lzo, lzma?
 	}
 }
 
+my $as_orig = sub {
+	my ($eml) = @_;
+	$eml->header_set('Status');
+	$eml->as_string;
+};
+
 unlink $fn or BAIL_OUT $!;
 if ('default deduplication uses content_hash') {
 	my $wcb = $wcb_get->('mboxo', $fn);
@@ -177,7 +183,7 @@ if ('default deduplication uses content_hash') {
 	undef $wcb; # undef to commit changes
 	my $cmp = '';
 	open my $fh, '<', $fn or BAIL_OUT $!;
-	PublicInbox::MboxReader->mboxo($fh, sub { $cmp .= shift->as_string });
+	PublicInbox::MboxReader->mboxo($fh, sub { $cmp .= $as_orig->(@_) });
 	is($cmp, $buf, 'only one message written');
 
 	local $lei->{opt} = { augment => 1 };
@@ -186,7 +192,7 @@ if ('default deduplication uses content_hash') {
 	undef $wcb; # undef to commit changes
 	open $fh, '<', $fn or BAIL_OUT $!;
 	my @x;
-	PublicInbox::MboxReader->mboxo($fh, sub { push @x, shift->as_string });
+	PublicInbox::MboxReader->mboxo($fh, sub { push @x, $as_orig->(@_) });
 	is(scalar(@x), 2, 'augmented mboxo');
 	is($x[0], $cmp, 'original message preserved');
 	is($x[1], $buf . "\nx\n", 'new message appended');
@@ -200,7 +206,7 @@ if ('default deduplication uses content_hash') {
 	undef $wcb; # commit
 	seek($tmp, 0, SEEK_SET) or BAIL_OUT $!;
 	my $cmp = '';
-	PublicInbox::MboxReader->mboxrd($tmp, sub { $cmp .= shift->as_string });
+	PublicInbox::MboxReader->mboxrd($tmp, sub { $cmp .= $as_orig->(@_) });
 	is($cmp, $buf, 'message written to stdout');
 }
 
@@ -213,7 +219,7 @@ SKIP: { # FIFO support
 	$wcb->(\(my $x = $buf), 'deadbeef', []);
 	undef $wcb; # commit
 	my $cmp = '';
-	PublicInbox::MboxReader->mboxo($cat, sub { $cmp .= shift->as_string });
+	PublicInbox::MboxReader->mboxo($cat, sub { $cmp .= $as_orig->(@_) });
 	is($cmp, $buf, 'message written to FIFO');
 }
 
diff --git a/t/mbox_reader.t b/t/mbox_reader.t
index 4ea2ae29..30a5e6e3 100644
--- a/t/mbox_reader.t
+++ b/t/mbox_reader.t
@@ -45,6 +45,8 @@ my $check_fmt = sub {
 	seek($fh, 0, SEEK_SET) or BAIL_OUT "seek: $!";
 	$reader->$fmt($fh, sub {
 		my ($eml) = @_;
+		$eml->header_set('Status');
+		$eml->header_set('Lines');
 		my $cur = shift @order;
 		my @cl = $eml->header_raw('Content-Length');
 		if ($fmt =~ /\Amboxcl/) {