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diff --git a/lib/selection.c b/lib/selection.c
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+/* Copyright (C) CZ.NIC, z.s.p.o. <knot-resolver@labs.nic.cz>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <libknot/dname.h>
+
+#include "lib/selection.h"
+#include "lib/selection_forward.h"
+#include "lib/selection_iter.h"
+#include "lib/rplan.h"
+#include "lib/cache/api.h"
+#include "lib/resolve.h"
+
+#include "lib/utils.h"
+
+#define VERBOSE_MSG(qry, ...) kr_log_q((qry), SELECTION, __VA_ARGS__)
+
+#define DEFAULT_TIMEOUT 400
+#define MAX_TIMEOUT 10000
+#define EXPLORE_TIMEOUT_COEFFICIENT 2
+#define MAX_BACKOFF 8
+#define MINIMAL_TIMEOUT_ADDITION 20
+
+/* After TCP_TIMEOUT_THRESHOLD timeouts one transport, we'll switch to TCP. */
+#define TCP_TIMEOUT_THRESHOLD 2
+/* If the expected RTT is over TCP_RTT_THRESHOLD we switch to TCP instead. */
+#define TCP_RTT_THRESHOLD 2000
+
+/* Define ε for ε-greedy algorithm (see select_transport)
+ * as ε=EPSILON_NOMIN/EPSILON_DENOM */
+#define EPSILON_NOMIN 1
+#define EPSILON_DENOM 20
+
+static const char *kr_selection_error_str(enum kr_selection_error err) {
+ switch (err) {
+ #define X(ENAME) case KR_SELECTION_ ## ENAME: return #ENAME
+ X(OK);
+ X(QUERY_TIMEOUT);
+ X(TLS_HANDSHAKE_FAILED);
+ X(TCP_CONNECT_FAILED);
+ X(TCP_CONNECT_TIMEOUT);
+ X(REFUSED);
+ X(SERVFAIL);
+ X(FORMERR);
+ X(FORMERR_EDNS);
+ X(NOTIMPL);
+ X(OTHER_RCODE);
+ X(MALFORMED);
+ X(MISMATCHED);
+ X(TRUNCATED);
+ X(DNSSEC_ERROR);
+ X(LAME_DELEGATION);
+ X(BAD_CNAME);
+ case KR_SELECTION_NUMBER_OF_ERRORS: break; // not a valid code
+ #undef X
+ }
+ kr_assert(false); // we want to define all; compiler helps by -Wswitch (no default:)
+ return NULL;
+}
+
+
+/* Simple detection of IPv6 being broken.
+ *
+ * We follow all IPv6 timeouts and successes. Consider it broken iff we've had
+ * timeouts on several different IPv6 prefixes since the last IPv6 success.
+ * Note: unlike the rtt_state, this happens only per-process (for simplicity).
+ *
+ * ## NO6_PREFIX_* choice
+ * For our practical use we choose primarily based on root and typical TLD servers.
+ * Looking at *.{root,gtld}-servers.net, we have 7/26 AAAAs in 2001:500:00**::
+ * but adding one more byte makes these completely unique, so we choose /48.
+ * As distribution to ASs seems to be on shorter prefixes (RIPE: /32 -- /24?),
+ * we wait for several distinct prefixes.
+ */
+
+#define NO6_PREFIX_COUNT 6
+#define NO6_PREFIX_BYTES (48/8)
+static struct {
+ int len_used;
+ uint8_t addr_prefixes[NO6_PREFIX_COUNT][NO6_PREFIX_BYTES];
+} no6_est = { .len_used = 0 };
+
+bool no6_is_bad(void)
+{
+ return no6_est.len_used == NO6_PREFIX_COUNT;
+}
+
+static void no6_timed_out(const struct kr_query *qry, const uint8_t *addr)
+{
+ if (no6_is_bad()) { // we can't get worse
+ VERBOSE_MSG(qry, "NO6: timed out, but bad already\n");
+ return;
+ }
+ // If we have the address already, do nothing.
+ for (int i = 0; i < no6_est.len_used; ++i) {
+ if (memcmp(addr, no6_est.addr_prefixes[i], NO6_PREFIX_BYTES) == 0) {
+ VERBOSE_MSG(qry, "NO6: timed out, repeated prefix, timeouts %d/%d\n",
+ no6_est.len_used, (int)NO6_PREFIX_COUNT);
+ return;
+ }
+ }
+ // Append!
+ memcpy(no6_est.addr_prefixes[no6_est.len_used++], addr, NO6_PREFIX_BYTES);
+ VERBOSE_MSG(qry, "NO6: timed out, appended, timeouts %d/%d\n",
+ no6_est.len_used, (int)NO6_PREFIX_COUNT);
+}
+
+static inline void no6_success(const struct kr_query *qry)
+{
+ if (no6_est.len_used) {
+ VERBOSE_MSG(qry, "NO6: success, zeroing %d/%d\n",
+ no6_est.len_used, (int)NO6_PREFIX_COUNT);
+ }
+ no6_est.len_used = 0;
+}
+
+
+/* Simple cache interface follows */
+
+static knot_db_val_t cache_key(const uint8_t *ip, size_t len)
+{
+ // CACHE_KEY_DEF: '\0' + 'S' + raw IP
+ const size_t key_len = len + 2;
+ uint8_t *key_data = malloc(key_len);
+ key_data[0] = '\0';
+ key_data[1] = 'S';
+ memcpy(key_data + 2, ip, len);
+ knot_db_val_t key = {
+ .len = key_len,
+ .data = key_data,
+ };
+ return key;
+}
+
+/* First value of timeout will be calculated as SRTT+4*VARIANCE
+ * by calc_timeout(), so it'll be equal to DEFAULT_TIMEOUT. */
+static const struct rtt_state default_rtt_state = { .srtt = 0,
+ .variance = DEFAULT_TIMEOUT / 4,
+ .consecutive_timeouts = 0,
+ .dead_since = 0 };
+
+struct rtt_state get_rtt_state(const uint8_t *ip, size_t len,
+ struct kr_cache *cache)
+{
+ struct rtt_state state;
+ knot_db_val_t value;
+ knot_db_t *db = cache->db;
+ struct kr_cdb_stats *stats = &cache->stats;
+
+ knot_db_val_t key = cache_key(ip, len);
+
+ if (cache->api->read(db, stats, &key, &value, 1)) {
+ state = default_rtt_state;
+ } else if (kr_fails_assert(value.len == sizeof(struct rtt_state))) {
+ // shouldn't happen but let's be more robust
+ state = default_rtt_state;
+ } else { // memcpy is safe for unaligned case (on non-x86)
+ memcpy(&state, value.data, sizeof(state));
+ }
+
+ free(key.data);
+ return state;
+}
+
+int put_rtt_state(const uint8_t *ip, size_t len, struct rtt_state state,
+ struct kr_cache *cache)
+{
+ knot_db_t *db = cache->db;
+ struct kr_cdb_stats *stats = &cache->stats;
+
+ knot_db_val_t key = cache_key(ip, len);
+ knot_db_val_t value = { .len = sizeof(struct rtt_state),
+ .data = &state };
+
+ int ret = cache->api->write(db, stats, &key, &value, 1);
+ cache->api->commit(db, stats);
+
+ free(key.data);
+ return ret;
+}
+
+void bytes_to_ip(uint8_t *bytes, size_t len, uint16_t port, union kr_sockaddr *dst)
+{
+ switch (len) {
+ case sizeof(struct in_addr):
+ dst->ip4.sin_family = AF_INET;
+ memcpy(&dst->ip4.sin_addr, bytes, len);
+ dst->ip4.sin_port = htons(port);
+ break;
+ case sizeof(struct in6_addr):
+ memset(&dst->ip6, 0, sizeof(dst->ip6)); // avoid uninit surprises
+ dst->ip6.sin6_family = AF_INET6;
+ memcpy(&dst->ip6.sin6_addr, bytes, len);
+ dst->ip6.sin6_port = htons(port);
+ break;
+ default:
+ kr_assert(false);
+ }
+}
+
+uint8_t *ip_to_bytes(const union kr_sockaddr *src, size_t len)
+{
+ switch (len) {
+ case sizeof(struct in_addr):
+ return (uint8_t *)&src->ip4.sin_addr;
+ case sizeof(struct in6_addr):
+ return (uint8_t *)&src->ip6.sin6_addr;
+ default:
+ kr_assert(false);
+ return NULL;
+ }
+}
+
+static bool no_rtt_info(struct rtt_state s)
+{
+ return s.srtt == 0 && s.consecutive_timeouts == 0;
+}
+
+static unsigned back_off_timeout(uint32_t to, int pow)
+{
+ pow = MIN(pow, MAX_BACKOFF);
+ to <<= pow;
+ return MIN(to, MAX_TIMEOUT);
+}
+
+/* This is verbatim (minus the default timeout value and minimal variance)
+ * RFC6298, sec. 2. */
+static unsigned calc_timeout(struct rtt_state state)
+{
+ int32_t timeout = state.srtt + MAX(4 * state.variance, MINIMAL_TIMEOUT_ADDITION);
+ return back_off_timeout(timeout, state.consecutive_timeouts);
+}
+
+/* This is verbatim RFC6298, sec. 2. */
+static struct rtt_state calc_rtt_state(struct rtt_state old, unsigned new_rtt)
+{
+ if (no_rtt_info(old)) {
+ return (struct rtt_state){ new_rtt, new_rtt / 2, 0 };
+ }
+
+ struct rtt_state ret = { 0 };
+ ret.variance = (3 * old.variance + abs(old.srtt - (int32_t)new_rtt)
+ + 2/*rounding*/) / 4;
+ ret.srtt = (7 * old.srtt + new_rtt + 4/*rounding*/) / 8;
+
+ return ret;
+}
+
+/**
+ * @internal Invalidate addresses which should be considered dead
+ */
+static void invalidate_dead_upstream(struct address_state *state,
+ unsigned int retry_timeout)
+{
+ struct rtt_state *rs = &state->rtt_state;
+ if (rs->dead_since) {
+ uint64_t now = kr_now();
+ if (now < rs->dead_since) {
+ // broken continuity of timestamp (reboot, different machine, etc.)
+ *rs = default_rtt_state;
+ } else if (now < rs->dead_since + retry_timeout) {
+ // period when we don't want to use the address
+ state->generation = -1;
+ } else {
+ kr_assert(now >= rs->dead_since + retry_timeout);
+ // we allow to retry the server now
+ // TODO: perhaps tweak *rs?
+ }
+ }
+}
+
+/**
+ * @internal Check if IP address is TLS capable.
+ *
+ * @p req has to have the selection_context properly initialized.
+ */
+static void check_tls_capable(struct address_state *address_state,
+ struct kr_request *req, struct sockaddr *address)
+{
+ address_state->tls_capable =
+ req->selection_context.is_tls_capable ?
+ req->selection_context.is_tls_capable(address) :
+ false;
+}
+
+#if 0
+/* TODO: uncomment these once we actually use the information it collects. */
+/**
+ * Check if there is a existing TCP connection to this address.
+ *
+ * @p req has to have the selection_context properly initialized.
+ */
+void check_tcp_connections(struct address_state *address_state, struct kr_request *req, struct sockaddr *address) {
+ address_state->tcp_connected = req->selection_context.is_tcp_connected ? req->selection_context.is_tcp_connected(address) : false;
+ address_state->tcp_waiting = req->selection_context.is_tcp_waiting ? req->selection_context.is_tcp_waiting(address) : false;
+}
+#endif
+
+/**
+ * @internal Invalidate address if the respective IP version is disabled.
+ */
+static void check_network_settings(struct address_state *address_state,
+ size_t address_len, bool no_ipv4, bool no_ipv6)
+{
+ if (no_ipv4 && address_len == sizeof(struct in_addr)) {
+ address_state->generation = -1;
+ }
+ if (no_ipv6 && address_len == sizeof(struct in6_addr)) {
+ address_state->generation = -1;
+ }
+}
+
+void update_address_state(struct address_state *state, union kr_sockaddr *address,
+ size_t address_len, struct kr_query *qry)
+{
+ check_tls_capable(state, qry->request, &address->ip);
+ /* TODO: uncomment this once we actually use the information it collects
+ check_tcp_connections(address_state, qry->request, &address->ip);
+ */
+ check_network_settings(state, address_len, qry->flags.NO_IPV4,
+ qry->flags.NO_IPV6);
+ state->rtt_state =
+ get_rtt_state(ip_to_bytes(address, address_len),
+ address_len, &qry->request->ctx->cache);
+ invalidate_dead_upstream(
+ state, qry->request->ctx->cache_rtt_tout_retry_interval);
+#ifdef SELECTION_CHOICE_LOGGING
+ // This is sometimes useful for debugging, but usually too verbose
+ if (kr_log_is_debug_qry(SELECTION, qry)) {
+ const char *ns_str = kr_straddr(&address->ip);
+ VERBOSE_MSG(qry, "rtt of %s is %d, variance is %d\n", ns_str,
+ state->rtt_state.srtt, state->rtt_state.variance);
+ }
+#endif
+}
+
+static int cmp_choices(const struct choice *a_, const struct choice *b_)
+{
+ int diff;
+ /* Prefer IPv4 if IPv6 appears to be generally broken. */
+ diff = (int)a_->address_len - (int)b_->address_len;
+ if (diff && no6_is_bad()) {
+ return diff;
+ }
+ /* Address with no RTT information is better than address
+ * with some information. */
+ if ((diff = no_rtt_info(b_->address_state->rtt_state) -
+ no_rtt_info(a_->address_state->rtt_state))) {
+ return diff;
+ }
+ /* Address with less errors is better. */
+ if ((diff = a_->address_state->error_count -
+ b_->address_state->error_count)) {
+ return diff;
+ }
+ /* Address with smaller expected timeout is better. */
+ if ((diff = calc_timeout(a_->address_state->rtt_state) -
+ calc_timeout(b_->address_state->rtt_state))) {
+ return diff;
+ }
+ return 0;
+}
+/** Select the best entry from choices[] according to cmp_choices() comparator.
+ *
+ * Ties are decided in an (almost) uniformly random fashion.
+ */
+static const struct choice * select_best(const struct choice choices[], int choices_len)
+{
+ /* Deciding ties: it's as-if each index carries one byte of randomness.
+ * Ties get decided by comparing that byte, and the byte itself
+ * is computed lazily (negative until computed).
+ */
+ int best_i = 0;
+ int best_rnd = -1;
+ for (int i = 1; i < choices_len; ++i) {
+ int diff = cmp_choices(&choices[i], &choices[best_i]);
+ if (diff > 0)
+ continue;
+ if (diff < 0) {
+ best_i = i;
+ best_rnd = -1;
+ continue;
+ }
+ if (best_rnd < 0)
+ best_rnd = kr_rand_bytes(1);
+ int new_rnd = kr_rand_bytes(1);
+ if (new_rnd < best_rnd) {
+ best_i = i;
+ best_rnd = new_rnd;
+ }
+ }
+ return &choices[best_i];
+}
+
+/* Adjust choice from `unresolved` in case of NO6 (broken IPv6). */
+static struct kr_transport unresolved_adjust(const struct to_resolve unresolved[],
+ int unresolved_len, int index)
+{
+ if (unresolved[index].type != KR_TRANSPORT_RESOLVE_AAAA || !no6_is_bad())
+ goto finish;
+ /* AAAA is detected as bad; let's choose randomly from others, if there are any. */
+ int aaaa_count = 0;
+ for (int i = 0; i < unresolved_len; ++i)
+ aaaa_count += (unresolved[i].type == KR_TRANSPORT_RESOLVE_AAAA);
+ if (aaaa_count == unresolved_len)
+ goto finish;
+ /* Chosen index within non-AAAA items. */
+ int i_no6 = kr_rand_bytes(1) % (unresolved_len - aaaa_count);
+ for (int i = 0; i < unresolved_len; ++i) {
+ if (unresolved[i].type == KR_TRANSPORT_RESOLVE_AAAA) {
+ //continue
+ } else if (i_no6 == 0) {
+ index = i;
+ break;
+ } else {
+ --i_no6;
+ }
+ }
+finish:
+ return (struct kr_transport){
+ .protocol = unresolved[index].type,
+ .ns_name = unresolved[index].name
+ };
+}
+
+/* Performs the actual selection (currently variation on epsilon-greedy). */
+struct kr_transport *select_transport(const struct choice choices[], int choices_len,
+ const struct to_resolve unresolved[],
+ int unresolved_len, int timeouts,
+ struct knot_mm *mempool, bool tcp,
+ size_t *choice_index)
+{
+ if (!choices_len && !unresolved_len) {
+ /* There is nothing to choose from */
+ return NULL;
+ }
+
+ struct kr_transport *transport = mm_calloc(mempool, 1, sizeof(*transport));
+
+ /* If there are some addresses with no rtt_info we try them
+ * first (see cmp_choices). So unknown servers are chosen
+ * *before* the best know server. This ensures that every option
+ * is tried before going back to some that was tried before. */
+ const struct choice *best = select_best(choices, choices_len);
+ const struct choice *chosen;
+
+ const bool explore = choices_len == 0 || kr_rand_coin(EPSILON_NOMIN, EPSILON_DENOM)
+ /* We may need to explore to get at least one A record. */
+ || (no6_is_bad() && best->address.ip.sa_family == AF_INET6);
+ if (explore) {
+ /* "EXPLORE":
+ * randomly choose some option
+ * (including resolution of some new name). */
+ int index = kr_rand_bytes(1) % (choices_len + unresolved_len);
+ if (index < unresolved_len) {
+ // We will resolve a new NS name
+ *transport = unresolved_adjust(unresolved, unresolved_len, index);
+ return transport;
+ } else {
+ chosen = &choices[index - unresolved_len];
+ }
+ } else {
+ /* "EXPLOIT":
+ * choose a resolved address which seems best right now. */
+ chosen = best;
+ }
+
+ /* Don't try the same server again when there are other choices to be explored */
+ if (chosen->address_state->error_count && unresolved_len) {
+ int index = kr_rand_bytes(1) % unresolved_len;
+ *transport = unresolved_adjust(unresolved, unresolved_len, index);
+ return transport;
+ }
+
+ unsigned timeout;
+ if (no_rtt_info(chosen->address_state->rtt_state)) {
+ /* Exponential back-off when retrying after timeout and choosing
+ * an unknown server. */
+ timeout = back_off_timeout(DEFAULT_TIMEOUT, timeouts);
+ } else {
+ timeout = calc_timeout(chosen->address_state->rtt_state);
+ if (explore) {
+ /* When trying a random server, we cap the timeout to EXPLORE_TIMEOUT_COEFFICIENT
+ * times the timeout for the best server. This is done so we don't spend
+ * unreasonable amounts of time probing really bad servers while still
+ * checking once in a while for e.g. big network change etc.
+ * We also note this capping was done and don't punish the bad server
+ * further if it fails to answer in the capped timeout. */
+ unsigned best_timeout = calc_timeout(best->address_state->rtt_state);
+ if (timeout > best_timeout * EXPLORE_TIMEOUT_COEFFICIENT) {
+ timeout = best_timeout * EXPLORE_TIMEOUT_COEFFICIENT;
+ transport->timeout_capped = true;
+ }
+ }
+ }
+
+ enum kr_transport_protocol protocol;
+ if (chosen->address_state->tls_capable) {
+ protocol = KR_TRANSPORT_TLS;
+ } else if (tcp ||
+ chosen->address_state->errors[KR_SELECTION_QUERY_TIMEOUT] >= TCP_TIMEOUT_THRESHOLD ||
+ timeout > TCP_RTT_THRESHOLD) {
+ protocol = KR_TRANSPORT_TCP;
+ } else {
+ protocol = KR_TRANSPORT_UDP;
+ }
+
+ *transport = (struct kr_transport){
+ .ns_name = chosen->address_state->ns_name,
+ .protocol = protocol,
+ .timeout = timeout,
+ };
+
+ int port = chosen->port;
+ if (!port) {
+ switch (transport->protocol) {
+ case KR_TRANSPORT_TLS:
+ port = KR_DNS_TLS_PORT;
+ break;
+ case KR_TRANSPORT_UDP:
+ case KR_TRANSPORT_TCP:
+ port = KR_DNS_PORT;
+ break;
+ default:
+ kr_assert(false);
+ return NULL;
+ }
+ }
+
+ switch (chosen->address_len)
+ {
+ case sizeof(struct in_addr):
+ transport->address.ip4 = chosen->address.ip4;
+ transport->address.ip4.sin_port = htons(port);
+ break;
+ case sizeof(struct in6_addr):
+ transport->address.ip6 = chosen->address.ip6;
+ transport->address.ip6.sin6_port = htons(port);
+ break;
+ default:
+ kr_assert(false);
+ return NULL;
+ }
+
+ transport->address_len = chosen->address_len;
+
+ if (choice_index) {
+ *choice_index = chosen->address_state->choice_array_index;
+ }
+
+ return transport;
+}
+
+void update_rtt(struct kr_query *qry, struct address_state *addr_state,
+ const struct kr_transport *transport, unsigned rtt)
+{
+ if (!transport || !addr_state) {
+ /* Answers from cache have NULL transport, ignore them. */
+ return;
+ }
+
+ struct kr_cache *cache = &qry->request->ctx->cache;
+
+ uint8_t *address = ip_to_bytes(&transport->address, transport->address_len);
+ /* This construct is a bit racy since the global state may change
+ * between calls to `get_rtt_state` and `put_rtt_state` but we don't
+ * care that much since it is rare and we only risk slightly suboptimal
+ * transport choice. */
+ struct rtt_state cur_rtt_state =
+ get_rtt_state(address, transport->address_len, cache);
+ struct rtt_state new_rtt_state = calc_rtt_state(cur_rtt_state, rtt);
+ put_rtt_state(address, transport->address_len, new_rtt_state, cache);
+
+ if (transport->address_len == sizeof(struct in6_addr))
+ no6_success(qry);
+
+ if (kr_log_is_debug_qry(SELECTION, qry)) {
+ KR_DNAME_GET_STR(ns_name, transport->ns_name);
+ KR_DNAME_GET_STR(zonecut_str, qry->zone_cut.name);
+ const char *ns_str = kr_straddr(&transport->address.ip);
+
+ VERBOSE_MSG(
+ qry,
+ "=> id: '%05u' updating: '%s'@'%s' zone cut: '%s'"
+ " with rtt %u to srtt: %d and variance: %d \n",
+ qry->id, ns_name, ns_str ? ns_str : "", zonecut_str,
+ rtt, new_rtt_state.srtt, new_rtt_state.variance);
+ }
+}
+
+/// Update rtt_state (including caching) after a server timed out.
+static void server_timeout(const struct kr_query *qry, const struct kr_transport *transport,
+ struct address_state *addr_state, struct kr_cache *cache)
+{
+ // Make sure that the timeout wasn't capped; see kr_transport::timeout_capped
+ if (transport->timeout_capped)
+ return;
+
+ const uint8_t *address = ip_to_bytes(&transport->address, transport->address_len);
+ if (transport->address_len == sizeof(struct in6_addr))
+ no6_timed_out(qry, address);
+
+ struct rtt_state *state = &addr_state->rtt_state;
+ // While we were waiting for timeout, the stats might have changed considerably,
+ // so let's overwrite what we had by fresh cache contents.
+ // This is useful when the address is busy (we query it concurrently).
+ *state = get_rtt_state(address, transport->address_len, cache);
+
+ ++state->consecutive_timeouts;
+ // Avoid overflow; we don't utilize very high values anyway (arbitrary limit).
+ state->consecutive_timeouts = MIN(64, state->consecutive_timeouts);
+ if (state->consecutive_timeouts >= KR_NS_TIMEOUT_ROW_DEAD) {
+ // Only mark as dead if we waited long enough,
+ // so that many (concurrent) short attempts can't cause the dead state.
+ if (transport->timeout >= KR_NS_TIMEOUT_MIN_DEAD_TIMEOUT)
+ state->dead_since = kr_now();
+ }
+
+ // If transport was chosen by a different query, that one will cache it.
+ if (!transport->deduplicated) {
+ put_rtt_state(address, transport->address_len, *state, cache);
+ } else {
+ kr_cache_commit(cache); // Avoid any risk of long transaction.
+ }
+}
+// Not everything can be checked in nice ways like static_assert()
+static __attribute__((constructor)) void test_RTT_consts(void)
+{
+ // See KR_NS_TIMEOUT_MIN_DEAD_TIMEOUT above.
+ kr_require(
+ calc_timeout((struct rtt_state){ .consecutive_timeouts = MAX_BACKOFF, })
+ >= KR_NS_TIMEOUT_MIN_DEAD_TIMEOUT
+ );
+}
+
+void error(struct kr_query *qry, struct address_state *addr_state,
+ const struct kr_transport *transport,
+ enum kr_selection_error sel_error)
+{
+ if (!transport || !addr_state) {
+ /* Answers from cache have NULL transport, ignore them. */
+ return;
+ }
+
+ switch (sel_error) {
+ case KR_SELECTION_OK:
+ return;
+ case KR_SELECTION_TCP_CONNECT_FAILED:
+ case KR_SELECTION_TCP_CONNECT_TIMEOUT:
+ qry->server_selection.local_state->force_udp = true;
+ qry->flags.NO_0X20 = false;
+ /* Connection and handshake failures have properties similar
+ * to UDP timeouts, so we handle them (almost) the same way. */
+ /* fall-through */
+ case KR_SELECTION_TLS_HANDSHAKE_FAILED:
+ case KR_SELECTION_QUERY_TIMEOUT:
+ qry->server_selection.local_state->timeouts++;
+ server_timeout(qry, transport, addr_state, &qry->request->ctx->cache);
+ break;
+ case KR_SELECTION_FORMERR:
+ if (qry->flags.NO_EDNS) {
+ addr_state->broken = true;
+ } else {
+ qry->flags.NO_EDNS = true;
+ }
+ break;
+ case KR_SELECTION_FORMERR_EDNS:
+ addr_state->broken = true;
+ break;
+ case KR_SELECTION_MISMATCHED:
+ if (qry->flags.NO_0X20 && qry->flags.TCP) {
+ addr_state->broken = true;
+ } else {
+ qry->flags.TCP = true;
+ qry->flags.NO_0X20 = true;
+ }
+ break;
+ case KR_SELECTION_TRUNCATED:
+ if (transport->protocol == KR_TRANSPORT_UDP) {
+ qry->server_selection.local_state->truncated = true;
+ /* TC=1 over UDP is not an error, so we compensate. */
+ addr_state->error_count--;
+ } else {
+ addr_state->broken = true;
+ }
+ break;
+ case KR_SELECTION_REFUSED:
+ case KR_SELECTION_SERVFAIL:
+ if (qry->flags.NO_MINIMIZE && qry->flags.NO_0X20 && qry->flags.TCP) {
+ addr_state->broken = true;
+ } else if (qry->flags.NO_MINIMIZE) {
+ qry->flags.NO_0X20 = true;
+ qry->flags.TCP = true;
+ } else {
+ qry->flags.NO_MINIMIZE = true;
+ }
+ break;
+ case KR_SELECTION_LAME_DELEGATION:
+ if (qry->flags.NO_MINIMIZE) {
+ /* Lame delegations are weird, they breed more lame delegations on broken
+ * zones since trying another server from the same set usually doesn't help.
+ * We force resolution of another NS name in hope of getting somewhere. */
+ qry->server_selection.local_state->force_resolve = true;
+ addr_state->broken = true;
+ } else {
+ qry->flags.NO_MINIMIZE = true;
+ }
+ break;
+ case KR_SELECTION_NOTIMPL:
+ case KR_SELECTION_OTHER_RCODE:
+ case KR_SELECTION_DNSSEC_ERROR:
+ case KR_SELECTION_BAD_CNAME:
+ case KR_SELECTION_MALFORMED:
+ /* These errors are fatal, no point in trying this server again. */
+ addr_state->broken = true;
+ break;
+ default:
+ kr_assert(false);
+ return;
+ }
+
+ addr_state->error_count++;
+ addr_state->errors[sel_error]++;
+
+ if (kr_log_is_debug_qry(SELECTION, qry)) {
+ KR_DNAME_GET_STR(ns_name, transport->ns_name);
+ KR_DNAME_GET_STR(zonecut_str, qry->zone_cut.name);
+ const char *ns_str = kr_straddr(&transport->address.ip);
+ const char *err_str = kr_selection_error_str(sel_error);
+
+ VERBOSE_MSG(
+ qry,
+ "=> id: '%05u' noting selection error: '%s'@'%s'"
+ " zone cut: '%s' error: %d %s\n",
+ qry->id, ns_name, ns_str ? ns_str : "",
+ zonecut_str, sel_error, err_str ? err_str : "??");
+ }
+}
+
+void kr_server_selection_init(struct kr_query *qry)
+{
+ struct knot_mm *mempool = &qry->request->pool;
+ struct local_state *local_state = mm_calloc(mempool, 1, sizeof(*local_state));
+
+ if (qry->flags.FORWARD || qry->flags.STUB) {
+ qry->server_selection = (struct kr_server_selection){
+ .initialized = true,
+ .choose_transport = forward_choose_transport,
+ .update_rtt = forward_update_rtt,
+ .error = forward_error,
+ .local_state = local_state,
+ };
+ forward_local_state_alloc(
+ mempool, &qry->server_selection.local_state->private,
+ qry->request);
+ } else {
+ qry->server_selection = (struct kr_server_selection){
+ .initialized = true,
+ .choose_transport = iter_choose_transport,
+ .update_rtt = iter_update_rtt,
+ .error = iter_error,
+ .local_state = local_state,
+ };
+ iter_local_state_alloc(
+ mempool, &qry->server_selection.local_state->private);
+ }
+}
+
+int kr_forward_add_target(struct kr_request *req, const struct sockaddr *sock)
+{
+ if (!req->selection_context.forwarding_targets.at) {
+ return kr_error(EINVAL);
+ }
+
+ union kr_sockaddr address;
+
+ switch (sock->sa_family) {
+ case AF_INET:
+ if (req->options.NO_IPV4)
+ return kr_error(EINVAL);
+ address.ip4 = *(const struct sockaddr_in *)sock;
+ break;
+ case AF_INET6:
+ if (req->options.NO_IPV6)
+ return kr_error(EINVAL);
+ address.ip6 = *(const struct sockaddr_in6 *)sock;
+ break;
+ default:
+ return kr_error(EINVAL);
+ }
+
+ array_push_mm(req->selection_context.forwarding_targets, address,
+ kr_memreserve, &req->pool);
+ return kr_ok();
+}