[PATCH] SaPlugin::ListMirror: follow RFC 2919 List-ID rules

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

List-ID headers are sometimes populated with a descriptive phrase
before the angle-bracketed value and making things difficult to
match.

Tweak our handling to allow checking the angle-bracketed portion
only in accordance with RFC 2919.

Handling of all other headers and senselessly non-bracketed
values for List-ID remain unchanged.
---
 lib/PublicInbox/SaPlugin/ListMirror.pm  | 10 +++++++--
 lib/PublicInbox/SaPlugin/ListMirror.pod | 27 +++++++++++++++++--------
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/lib/PublicInbox/SaPlugin/ListMirror.pm b/lib/PublicInbox/SaPlugin/ListMirror.pm
index 9acf86c0..06903cad 100644
--- a/lib/PublicInbox/SaPlugin/ListMirror.pm
+++ b/lib/PublicInbox/SaPlugin/ListMirror.pm
@@ -1,4 +1,4 @@
-# Copyright (C) 2016-2021 all contributors <meta@public-inbox.org>
+# Copyright (C) all contributors <meta@public-inbox.org>
 # License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
 
 # SpamAssassin rules useful for running a mailing list mirror.  We want to:
@@ -39,7 +39,11 @@ sub check_list_mirror_received {
 		my $v = $pms->get($hdr) or next;
 		local $/ = "\n";
 		chomp $v;
-		next if $v ne $hval;
+		if (ref($hval)) {
+			next if $v !~ $hval;
+		} else {
+			next if $v ne $hval;
+		}
 		return 1 if $recvd !~ $host_re;
 	}
 
@@ -91,6 +95,8 @@ sub config_list_mirror {
 	$host_glob =~ s!(.)!$patmap{$1} || "\Q$1"!ge;
 	my $host_re = qr/\A\s*from\s+$host_glob(?:\s|$)/si;
 
+	(lc($hdr) eq 'list-id' && $hval =~ /<([^>]+)>/) and
+		$hval = qr/\A<\Q$1\E>\z/;
 	push @{$self->{list_mirror_check}}, [ $hdr, $hval, $host_re, $addr ];
 }
 
diff --git a/lib/PublicInbox/SaPlugin/ListMirror.pod b/lib/PublicInbox/SaPlugin/ListMirror.pod
index d931d762..e6a6c2ad 100644
--- a/lib/PublicInbox/SaPlugin/ListMirror.pod
+++ b/lib/PublicInbox/SaPlugin/ListMirror.pod
@@ -6,11 +6,11 @@ PublicInbox::SaPlugin::ListMirror - SpamAssassin plugin for mailing list mirrors
 
   loadplugin PublicInbox::SaPlugin::ListMirror
 
-Declare some mailing lists based on the expected List-Id value,
+Declare some mailing lists based on the expected List-ID value,
 expected servers, and mailing list address:
 
-  list_mirror List-Id <foo.example.com> *.example.com foo@example.com
-  list_mirror List-Id <bar.example.com> *.example.com bar@example.com
+  list_mirror List-ID <foo.example.com> *.example.com foo@example.com
+  list_mirror List-ID <bar.example.com> *.example.com bar@example.com
 
 Bump the score for messages which come from unexpected servers:
 
@@ -43,14 +43,25 @@ C<allow_user_rules 1>
 
 =item list_mirror HEADER HEADER_VALUE HOSTNAME_GLOB [LIST_ADDRESS]
 
-Declare a list based on an expected C<HEADER> matching C<HEADER_NAME>
-exactly coming from C<HOSTNAME_GLOB>.  C<LIST_ADDRESS> is optional,
+Declare a list based on an expected C<HEADER> matching C<HEADER_VALUE>
+coming from C<HOSTNAME_GLOB>.  C<LIST_ADDRESS> is optional,
 but may specify the address of the mailing list being mirrored.
 
-C<List-Id> or C<X-Mailing-List> are common values of C<HEADER>
+C<List-ID> is the recommended value of C<HEADER> as most
+mailing lists support it.
 
 An example of C<HEADER_VALUE> is C<E<lt>foo.example.orgE<gt>>
-if C<HEADER> is C<List-Id>.
+if C<HEADER> is C<List-ID>.
+
+As of public-inbox 2.0, using C<List-ID> as the C<HEADER> and a
+C<HEADER_VALUE> contained by angle brackets (E<lt>list-idE<gt>),
+matching is done in accordance with
+L<RFC 2919|https://tools.ietf.org/html/rfc2919>.  That is,
+C<HEADER_VALUE> will be a case-insensitive substring match
+and ignore the optional description C<phrase> as documented
+in RFC 2919.
+
+All other C<HEADER> values use exact matches for backwards-compatibility.
 
 C<HOSTNAME_GLOB> may be a wildcard match for machines where mail can
 come from or an exact match.
@@ -105,7 +116,7 @@ and L<http://4uok3hntl7oi7b4uf4rtfwefqeexfzil2w6kgk2jn5z2f764irre7byd.onion/meta
 
 =head1 COPYRIGHT
 
-Copyright (C) 2016-2021 all contributors L<mailto:meta@public-inbox.org>
+Copyright (C) all contributors L<mailto:meta@public-inbox.org>
 
 License: AGPL-3.0+ L<http://www.gnu.org/licenses/agpl-3.0.txt>