<Deuce> Easiest fix would be to have outbuf_append adjust outlen to be "long enough" if doubling isn't.
<Deuce>         /* Not enough room, double the size. */
<Deuce>         *outlen *= 2;
<Deuce>         if(*outp - *outbuf + len >= *outlen)
<Deuce>                 *outlen = *outp - *outbuf + len + 1
<Deuce> So yeah, blindly doubling won't work for utf-8.
<Deuce> Because a line will have more bytes than the number of characters in a line.