imap: support 8000 octet lines

RFC 2683 section 3.2.1.5 recommends it:

> For its part, a server should allow for a command line of at least
> 8000 octets.  This provides plenty of leeway for accepting reasonable
> length commands from clients.  The server should send a BAD response
> to a command that does not end within the server's maximum accepted
> command length.

To conserve memory, we won't bother reading the entire line
before sending the BAD response and disconnecting them.

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/PublicInbox/IMAP.pm b/lib/PublicInbox/IMAP.pm
index b3c449b0..2e50415d 100644
--- a/lib/PublicInbox/IMAP.pm
+++ b/lib/PublicInbox/IMAP.pm
@@ -36,7 +36,7 @@ for my $mod (qw(Email::Address::XS Mail::Address)) {
 }
 die "neither Email::Address::XS nor Mail::Address loaded: $@" if !$Address;
 
-sub LINE_MAX () { 512 } # does RFC 3501 have a limit like RFC 977?
+sub LINE_MAX () { 8000 } # RFC 2683 3.2.1.5
 
 # changing this will cause grief for clients which cache
 sub UID_BLOCK () { 50_000 }
@@ -1170,7 +1170,10 @@ sub event_step {
         my $rbuf = $self->{rbuf} // \(my $x = '');
         my $line = index($$rbuf, "\n");
         while ($line < 0) {
-                return $self->close if length($$rbuf) >= LINE_MAX;
+                if (length($$rbuf) >= LINE_MAX) {
+                        $self->write(\"\* BAD request too long\r\n");
+                        return $self->close;
+                }
                 $self->do_read($rbuf, LINE_MAX, length($$rbuf)) or return;
                 $line = index($$rbuf, "\n");
         }