http: fix modification of read-only value

This fails in the rare case we get a partial send() on "\r\n"
when writing chunked HTTP responses out.

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/PublicInbox/HTTP.pm b/lib/PublicInbox/HTTP.pm
index 3dd49be3..bc10814e 100644
--- a/lib/PublicInbox/HTTP.pm
+++ b/lib/PublicInbox/HTTP.pm
@@ -316,9 +316,12 @@ sub more ($$) {
         if (MSG_MORE && !$self->{write_buf_size}) {
                 my $n = send($self->{sock}, $_[1], MSG_MORE);
                 if (defined $n) {
-                        my $dlen = length($_[1]);
-                        return 1 if $n == $dlen; # all done!
-                        $_[1] = substr($_[1], $n, $dlen - $n);
+                        my $nlen = length($_[1]) - $n;
+                        return 1 if $nlen == 0; # all done!
+                        eval { $_[1] = substr($_[1], $n, $nlen) };
+                        if ($@) { # modification of read-only value:
+                                return $self->write(substr($_[1], $n, $nlen));
+                        }
                         # fall through to normal write:
                 }
         }