isc_buffer_consumedlength
isc_buffer_consumedlength(source->pushback);
REQUIRE(isc_buffer_consumedlength(source->pushback) != 0 ||
REQUIRE(isc_buffer_consumedlength(source->pushback) != 0 ||
INSIST(source->ignored <= isc_buffer_consumedlength(source->pushback));
r->length = isc_buffer_consumedlength(source->pushback) -