[PATCH 2/7] view: display redundant headers in permalink

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

Mail headers can contain multiple headers of any type, so ensure
we don't hide any information we're getting in the per-message
permalink views.

This means it's possible to have multiple From, Date, To, Cc,
Subject, and In-Reply-To headers displayed.

The thread indices are a special case, I guess, since we run
out of space on the line if the headers too long and tools like
mutt only show the first one.
---
 lib/PublicInbox/Linkify.pm | 29 +++++++++++++++
 lib/PublicInbox/View.pm    | 75 ++++++++++++++++++++++----------------
 2 files changed, 73 insertions(+), 31 deletions(-)

diff --git a/lib/PublicInbox/Linkify.pm b/lib/PublicInbox/Linkify.pm
index 175f8d72..5b83742c 100644
--- a/lib/PublicInbox/Linkify.pm
+++ b/lib/PublicInbox/Linkify.pm
@@ -89,4 +89,33 @@ sub linkify_2 {
 	$_[1];
 }
 
+# single pass linkification of <Message-ID@example.com> within $str
+# with $pfx being the URL prefix
+sub linkify_mids {
+	my ($self, $pfx, $str) = @_;
+	$$str =~ s!<([^>]+)>!
+		my $msgid = PublicInbox::Hval->new_msgid($1);
+		my $html = $msgid->as_html;
+		my $href = $msgid->{href};
+		$href = ascii_html($href); # for IDN
+
+		# salt this, as this could be exploited to show
+		# links in the HTML which don't show up in the raw mail.
+		my $key = sha1_hex($html . $SALT);
+		$self->{$key} = [ $href, $html ];
+		'<PI-LINK-'. $key . '>';
+		!ge;
+	$$str = ascii_html($$str);
+	$$str =~ s!\bPI-LINK-([a-f0-9]{40})\b!
+		my $key = $1;
+		my $repl = $_[0]->{$key};
+		if (defined $repl) {
+			"<a\nhref=\"$pfx/$repl->[0]/\">$repl->[1]</a>";
+		} else {
+			# false positive or somebody tried to mess with us
+			$key;
+		}
+	!ge;
+}
+
 1;
diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index aeb32fc8..1aa014fd 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -190,8 +190,8 @@ sub fold_addresses ($) {
 
 sub _hdr_names_html ($$) {
 	my ($hdr, $field) = @_;
-	my $val = $hdr->header($field) or return '';
-	ascii_html(join(', ', PublicInbox::Address::names($val)));
+	my @vals = $hdr->header($field) or return '';
+	ascii_html(join(', ', PublicInbox::Address::names(join(',', @vals))));
 }
 
 sub nr_to_s ($$$) {
@@ -643,12 +643,11 @@ sub _msg_html_prepare {
 	if ($over) {
 		$ctx->{-upfx} = '../';
 	}
-	my @title;
-	my $v;
-	if (defined($v = $hdr->header('From'))) {
+	my @title; # (Subject[0], From[0])
+	for my $v ($hdr->header('From')) {
 		$v = PublicInbox::Hval->new($v);
 		my @n = PublicInbox::Address::names($v->raw);
-		$title[1] = ascii_html(join(', ', @n));
+		$title[1] //= ascii_html(join(', ', @n));
 		$v = $v->as_html;
 		if ($obfs_ibx) {
 			obfuscate_addrs($obfs_ibx, $v);
@@ -657,26 +656,31 @@ sub _msg_html_prepare {
 		$rv .= "From: $v\n" if $v ne '';
 	}
 	foreach my $h (qw(To Cc)) {
-		defined($v = $hdr->header($h)) or next;
-		fold_addresses($v);
-		$v = ascii_html($v);
-		obfuscate_addrs($obfs_ibx, $v) if $obfs_ibx;
-		$rv .= "$h: $v\n" if $v ne '';
+		for my $v ($hdr->header($h)) {
+			fold_addresses($v);
+			$v = ascii_html($v);
+			obfuscate_addrs($obfs_ibx, $v) if $obfs_ibx;
+			$rv .= "$h: $v\n" if $v ne '';
+		}
 	}
-	if (defined($v = $hdr->header('Subject')) && ($v ne '')) {
-		$v = ascii_html($v);
-		obfuscate_addrs($obfs_ibx, $v) if $obfs_ibx;
-		if ($over) {
-			$rv .= qq(Subject: <a\nhref="#r"\nid=t>$v</a>\n);
-		} else {
-			$rv .= "Subject: $v\n";
+	my @subj = $hdr->header('Subject');
+	if (@subj) {
+		for my $v (@subj) {
+			$v = ascii_html($v);
+			obfuscate_addrs($obfs_ibx, $v) if $obfs_ibx;
+			$rv .= 'Subject: ';
+			if ($over) {
+				$rv .= qq(<a\nhref="#r"\nid=t>$v</a>\n);
+			} else {
+				$rv .= "$v\n";
+			}
+			$title[0] //= $v;
 		}
-		$title[0] = $v;
 	} else { # dummy anchor for thread skeleton at bottom of page
 		$rv .= qq(<a\nhref="#r"\nid=t></a>) if $over;
 		$title[0] = '(no subject)';
 	}
-	if (defined($v = $hdr->header('Date'))) {
+	for my $v ($hdr->header('Date')) {
 		$v = ascii_html($v);
 		obfuscate_addrs($obfs_ibx, $v) if $obfs_ibx; # possible :P
 		$rv .= "Date: $v\n";
@@ -727,8 +731,9 @@ sub thread_skel {
 	$$dst .= "$nr+ messages / $expand";
 	$$dst .= qq!  <a\nhref="#b">top</a>\n!;
 
-	my $subj = $hdr->header('Subject');
-	defined $subj or $subj = '';
+	# nb: mutt only shows the first Subject in the index pane
+	# when multiple Subject: headers are present, so we follow suit:
+	my $subj = $hdr->header('Subject') // '';
 	$subj = '(no subject)' if $subj eq '';
 	$ctx->{prev_subj} = [ split(/ /, subject_normalized($subj)) ];
 	$ctx->{cur} = $mid;
@@ -746,21 +751,29 @@ sub thread_skel {
 sub _parent_headers {
 	my ($hdr, $over) = @_;
 	my $rv = '';
-
-	my $refs = references($hdr);
-	my $irt = pop @$refs;
-	if (defined $irt) {
-		my $v = PublicInbox::Hval->new_msgid($irt);
-		my $html = $v->as_html;
-		my $href = $v->{href};
-		$rv .= "In-Reply-To: &lt;";
-		$rv .= "<a\nhref=\"../$href/\">$html</a>&gt;\n";
+	my @irt = $hdr->header_raw('In-Reply-To');
+	my $refs;
+	if (@irt) {
+		my $lnk = PublicInbox::Linkify->new;
+		$rv .= "In-Reply-To: $_\n" for @irt;
+		$lnk->linkify_mids('..', \$rv);
+	} else {
+		$refs = references($hdr);
+		my $irt = pop @$refs;
+		if (defined $irt) {
+			my $v = PublicInbox::Hval->new_msgid($irt);
+			my $html = $v->as_html;
+			my $href = $v->{href};
+			$rv .= "In-Reply-To: &lt;";
+			$rv .= "<a\nhref=\"../$href/\">$html</a>&gt;\n";
+		}
 	}
 
 	# do not display References: if search is present,
 	# we show the thread skeleton at the bottom, instead.
 	return $rv if $over;
 
+	$refs //= references($hdr);
 	if (@$refs) {
 		@$refs = map { linkify_ref_no_over($_) } @$refs;
 		$rv .= 'References: '. join("\n\t", @$refs) . "\n";