tohex(const void *vp, size_t l)
{
	const u_char *p = (const u_char *)vp;
	char b[3], *r;
	size_t i, hl;

	if (l > 65536)
		return xstrdup("tohex: length > 65536");

	hl = l * 2 + 1;
	r = xcalloc(1, hl);
	for (i = 0; i < l; i++) {
		snprintf(b, sizeof(b), "%02x", p[i]);
		strlcat(r, b, hl);
	}
	return (r);
}