mid: truncate excessively long MIDs early

Since we support duplicate MIDs in v2, we can safely truncate
long MID terms in the database and let other normal duplicate
resolution sort it out.  It seems only spammers use excessively
long MIDs, and there'll always be abuse/misuse vectors for causing
mis-threaded messages, so it's not worth worrying about
excessively long MIDs.

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/PublicInbox/MID.pm b/lib/PublicInbox/MID.pm
index 96085399..422902f5 100644
--- a/lib/PublicInbox/MID.pm
+++ b/lib/PublicInbox/MID.pm
@@ -10,7 +10,10 @@ our @EXPORT_OK = qw/mid_clean id_compress mid2path mid_mime mid_escape MID_ESC
         mids references/;
 use URI::Escape qw(uri_escape_utf8);
 use Digest::SHA qw/sha1_hex/;
-use constant MID_MAX => 40; # SHA-1 hex length
+use constant {
+        MID_MAX => 40, # SHA-1 hex length # TODO: get rid of this
+        MAX_MID_SIZE => 244, # max term size (Xapian limitation) - length('Q')
+};
 
 sub mid_clean {
         my ($mid) = @_;
@@ -61,6 +64,12 @@ sub mids ($) {
                         push(@mids, $v);
                 }
         }
+        foreach my $i (0..$#mids) {
+                next if length($mids[$i]) <= MAX_MID_SIZE;
+                warn "Message-ID: <$mids[$i]> too long, truncating\n";
+                $mids[$i] = substr($mids[$i], 0, MAX_MID_SIZE);
+        }
+
         uniq_mids(\@mids);
 }