search: favor In-Reply-To over last References iff IRT exists

Some email clients set the References headers backwards, so
trust the In-Reply-To header if (and only if) it exists and
is parseable as direct parent of the current message.

For affected repos, this will require reindexing (via
"public-inbox-index --reindex"), but there will be no
version bump for this bugfix.

diff --git a/lib/PublicInbox/SearchIdx.pm b/lib/PublicInbox/SearchIdx.pm
index 4aac0281304146c39e2eb4d25cf8575c121a84a0..832d1cbfccc06aa3ab4e5948190b5856431bb5ac 100644 (file)
--- a/lib/PublicInbox/SearchIdx.pm
+++ b/lib/PublicInbox/SearchIdx.pm
@@ -293,10 +293,10 @@ sub link_message {
        my $hdr = $mime->header_obj;
        my $refs = $hdr->header_raw('References');
        my @refs = $refs ? ($refs =~ /<([^>]+)>/g) : ();
-       if (my $irt = $hdr->header_raw('In-Reply-To')) {
-               # last References should be $irt
-               # we will de-dupe later
-               push @refs, mid_clean($irt);
+       my $irt = $hdr->header_raw('In-Reply-To');
+       if (defined $irt) {
+               $irt = mid_clean($irt);
+               $irt = undef if $mid eq $irt;
        }
 
        my $tid;
@@ -305,6 +305,15 @@ sub link_message {
                my @orig_refs = @refs;
                @refs = ();
 
+               if (defined $irt) {
+                       # to check MAX_MID_SIZE
+                       push @orig_refs, $irt;
+
+                       # below, we will ensure IRT (if specified)
+                       # is the last References
+                       $uniq{$irt} = 1;
+               }
+
                # prevent circular references via References: here:
                foreach my $ref (@orig_refs) {
                        if (length($ref) > MAX_MID_SIZE) {
@@ -315,6 +324,11 @@ sub link_message {
                        push @refs, $ref;
                }
        }
+
+       # last References should be IRT, but some mail clients do things
+       # out of order, so trust IRT over References iff IRT exists
+       push @refs, $irt if defined $irt;
+
        if (@refs) {
                $smsg->{references} = '<'.join('> <', @refs).'>';