... and that doesn't necessarily mean that malloc() failed.
We do *not* want to evict a heavy-hitter by an unfrequent element.

Note: even the implementation currently in master *did* return NULL,
so some parts of the code were just wrongly returning ENOMEM.

The implementation is now similar to set-associative caches
that x86 CPU use.  Also the API is changed a bit, leading to
slight simplification of our use patterns.

Fixes https://gitlab.labs.nic.cz/knot/resolver/issues/93.
API of a KR_EXPORT function is changed, so ABIVER is bumped.

if the score is known (and not glued), the retry
rate is <avg(rtt), 250ms>

if the NS score is unknown or worse than 250ms,
it is always retried at this rate

all other servers in the list use default rate

maintainer may wish to choose neutral or even
more favoured server selection of IPv6 servers.

-DFAVOUR_IPV6=0 makes neutral server selection
-DFAVOUR_IPV6=40 gives IPv6 40ms better chance

RTT tracking for all targets is also supported,
but no loadbalancing is done based on that yet

when doing fast retransmit, each address may be
contacted 1-N times, but previously only cumulative
RTT was tracked for the NS that sent the answer.

now the approximate query start time is subtracted
from cumulative RTT to give an idea how long it
took since the query was actually sent, and all
the NSs that didn't respond within their retransmit
windows are penalised too

bcf3f4b5 made query_finalize() to be called on
each outbound query before sending, so each
retransmitted query got different 0x20 case
and the only responses from the latest contacted
NS matched.

reverted back the old behaviour where query case
is randomised when an outbound query is generated,
not before sending

REFUSED response no longer causes retry in
iterator when operating in stub mode

example:

> daf.add 'forward 127.0.0.1@5353'

Karel Slaný authored 8 years ago and Ondřej Surý committed 8 years ago

EDNS data from the packet must be erased before attempting to send the
query again.

Marek Vavrusa authored 8 years ago and Ondřej Surý committed 8 years ago

the cookies require libknot>=2.3, Makefile didn't
check for that, and turning cookies off wasn't
possible either

Karel Slaný authored 8 years ago and Ondřej Surý committed 8 years ago

Introduced kr_rplan_push_empty() to create empty query for DNS cookies.