nntp: ensure Message-ID is not folded for leafnode

Leafnode cannot handle Message-ID headers which are too long and
require folding via Email::Simple::Header.  Since there are
already many of these messages in git with the header already
folded, we need to handle the unfolding when emitting the
message via NNTP.

As far as we know, Leafnode is the only client software
incapable of handling this case.

2 files changed, 27 insertions, 0 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index 1d07220d..d409e782 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -519,6 +519,13 @@ sub _header ($) {
         my $hdr = $_[0]->header_obj->as_string;
         utf8::encode($hdr);
         $hdr =~ s/(?<!\r)\n/\r\n/sg;
+
+        # for leafnode compatibility, we need to ensure Message-ID headers
+        # are only a single line.  We can't subclass Email::Simple::Header
+        # and override _default_fold_at in here, either; since that won't
+        # affect messages already in the archive.
+        $hdr =~ s/^(Message-ID:)[ \t]*\r\n[ \t]+([^\r]+)\r\n/$1 $2\r\n/igsm;
+
         $hdr
 }
 
diff --git a/t/nntpd.t b/t/nntpd.t
index c73cc122..cce21eeb 100644
--- a/t/nntpd.t
+++ b/t/nntpd.t
@@ -231,6 +231,26 @@ EOF
                 ok($date >= $t0, 'valid date after start');
                 ok($date <= $t1, 'valid date before stop');
         }
+        if ('leafnode interop') {
+                my $for_leafnode = PublicInbox::MIME->new(<<"");
+From: longheader\@example.com
+To: $addr
+Subject: none
+Date: Fri, 02 Oct 1993 00:00:00 +0000
+
+                my $long_hdr = 'for-leafnode-'.('y'x200).'@example.com';
+                $for_leafnode->header_set('Message-ID', "<$long_hdr>");
+                $im->add($for_leafnode);
+                $im->done;
+                if ($version == 1) {
+                        my $s = PublicInbox::SearchIdx->new($mainrepo, 1);
+                        $s->index_sync;
+                }
+                my $hdr = $n->head("<$long_hdr>");
+                my $expect = qr/\AMessage-ID: /i . qr/\Q<$long_hdr>\E/;
+                ok(scalar(grep(/$expect/, @$hdr)), 'Message-ID not folded');
+                ok(scalar(grep(/^Path:/, @$hdr)), 'Path: header found');
+        }
 
         # pipelined requests:
         {