Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1486 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-cache.c b/src/resolve/resolved-dns-cache.c
new file mode 100644
index 0000000..a9a6492
--- /dev/null
+++ b/src/resolve/resolved-dns-cache.c
@@ -0,0 +1,1486 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <net/if.h>
+
+#include "af-list.h"
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "format-util.h"
+#include "resolved-dns-answer.h"
+#include "resolved-dns-cache.h"
+#include "resolved-dns-packet.h"
+#include "string-util.h"
+
+/* Never cache more than 4K entries. RFC 1536, Section 5 suggests to
+ * leave DNS caches unbounded, but that's crazy. */
+#define CACHE_MAX 4096
+
+/* We never keep any item longer than 2h in our cache unless StaleRetentionSec is greater than zero. */
+#define CACHE_TTL_MAX_USEC (2 * USEC_PER_HOUR)
+
+/* The max TTL for stale data is set to 30 seconds. See RFC 8767, Section 6. */
+#define CACHE_STALE_TTL_MAX_USEC (30 * USEC_PER_SEC)
+
+/* How long to cache strange rcodes, i.e. rcodes != SUCCESS and != NXDOMAIN (specifically: that's only SERVFAIL for
+ * now) */
+#define CACHE_TTL_STRANGE_RCODE_USEC (10 * USEC_PER_SEC)
+
+#define CACHEABLE_QUERY_FLAGS (SD_RESOLVED_AUTHENTICATED|SD_RESOLVED_CONFIDENTIAL)
+
+typedef enum DnsCacheItemType DnsCacheItemType;
+typedef struct DnsCacheItem DnsCacheItem;
+
+enum DnsCacheItemType {
+        DNS_CACHE_POSITIVE,
+        DNS_CACHE_NODATA,
+        DNS_CACHE_NXDOMAIN,
+        DNS_CACHE_RCODE,      /* "strange" RCODE (effective only SERVFAIL for now) */
+};
+
+struct DnsCacheItem {
+        DnsCacheItemType type;
+        int rcode;
+        DnsResourceKey *key;     /* The key for this item, i.e. the lookup key */
+        DnsResourceRecord *rr;   /* The RR for this item, i.e. the lookup value for positive queries */
+        DnsAnswer *answer;       /* The full validated answer, if this is an RRset acquired via a "primary" lookup */
+        DnsPacket *full_packet;  /* The full packet this information was acquired with */
+
+        usec_t until;            /* If StaleRetentionSec is greater than zero, until is set to a duration of StaleRetentionSec from the time of TTL expiry. If StaleRetentionSec is zero, both until and until_valid will be set to ttl. */
+        usec_t until_valid;      /* The key is for storing the time when the TTL set to expire. */
+        uint64_t query_flags;    /* SD_RESOLVED_AUTHENTICATED and/or SD_RESOLVED_CONFIDENTIAL */
+        DnssecResult dnssec_result;
+
+        int ifindex;
+        int owner_family;
+        union in_addr_union owner_address;
+
+        unsigned prioq_idx;
+        LIST_FIELDS(DnsCacheItem, by_key);
+
+        bool shared_owner;
+};
+
+/* Returns true if this is a cache item created as result of an explicit lookup, or created as "side-effect"
+ * of another request. "Primary" entries will carry the full answer data (with NSEC, …) that can aso prove
+ * wildcard expansion, non-existence and such, while entries that were created as "side-effect" just contain
+ * immediate RR data for the specified RR key, but nothing else. */
+#define DNS_CACHE_ITEM_IS_PRIMARY(item) (!!(item)->answer)
+
+static const char *dns_cache_item_type_to_string(DnsCacheItem *item) {
+        assert(item);
+
+        switch (item->type) {
+
+        case DNS_CACHE_POSITIVE:
+                return "POSITIVE";
+
+        case DNS_CACHE_NODATA:
+                return "NODATA";
+
+        case DNS_CACHE_NXDOMAIN:
+                return "NXDOMAIN";
+
+        case DNS_CACHE_RCODE:
+                return dns_rcode_to_string(item->rcode);
+        }
+
+        return NULL;
+}
+
+static DnsCacheItem* dns_cache_item_free(DnsCacheItem *i) {
+        if (!i)
+                return NULL;
+
+        dns_resource_record_unref(i->rr);
+        dns_resource_key_unref(i->key);
+        dns_answer_unref(i->answer);
+        dns_packet_unref(i->full_packet);
+        return mfree(i);
+}
+DEFINE_TRIVIAL_CLEANUP_FUNC(DnsCacheItem*, dns_cache_item_free);
+
+static void dns_cache_item_unlink_and_free(DnsCache *c, DnsCacheItem *i) {
+        DnsCacheItem *first;
+
+        assert(c);
+
+        if (!i)
+                return;
+
+        first = hashmap_get(c->by_key, i->key);
+        LIST_REMOVE(by_key, first, i);
+
+        if (first)
+                assert_se(hashmap_replace(c->by_key, first->key, first) >= 0);
+        else
+                hashmap_remove(c->by_key, i->key);
+
+        prioq_remove(c->by_expiry, i, &i->prioq_idx);
+
+        dns_cache_item_free(i);
+}
+
+static bool dns_cache_remove_by_rr(DnsCache *c, DnsResourceRecord *rr) {
+        DnsCacheItem *first;
+        int r;
+
+        first = hashmap_get(c->by_key, rr->key);
+        LIST_FOREACH(by_key, i, first) {
+                r = dns_resource_record_equal(i->rr, rr);
+                if (r < 0)
+                        return r;
+                if (r > 0) {
+                        dns_cache_item_unlink_and_free(c, i);
+                        return true;
+                }
+        }
+
+        return false;
+}
+
+static bool dns_cache_remove_by_key(DnsCache *c, DnsResourceKey *key) {
+        DnsCacheItem *first;
+
+        assert(c);
+        assert(key);
+
+        first = hashmap_remove(c->by_key, key);
+        if (!first)
+                return false;
+
+        LIST_FOREACH(by_key, i, first) {
+                prioq_remove(c->by_expiry, i, &i->prioq_idx);
+                dns_cache_item_free(i);
+        }
+
+        return true;
+}
+
+void dns_cache_flush(DnsCache *c) {
+        DnsResourceKey *key;
+
+        assert(c);
+
+        while ((key = hashmap_first_key(c->by_key)))
+                dns_cache_remove_by_key(c, key);
+
+        assert(hashmap_size(c->by_key) == 0);
+        assert(prioq_size(c->by_expiry) == 0);
+
+        c->by_key = hashmap_free(c->by_key);
+        c->by_expiry = prioq_free(c->by_expiry);
+}
+
+static void dns_cache_make_space(DnsCache *c, unsigned add) {
+        assert(c);
+
+        if (add <= 0)
+                return;
+
+        /* Makes space for n new entries. Note that we actually allow
+         * the cache to grow beyond CACHE_MAX, but only when we shall
+         * add more RRs to the cache than CACHE_MAX at once. In that
+         * case the cache will be emptied completely otherwise. */
+
+        for (;;) {
+                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
+                DnsCacheItem *i;
+
+                if (prioq_size(c->by_expiry) <= 0)
+                        break;
+
+                if (prioq_size(c->by_expiry) + add < CACHE_MAX)
+                        break;
+
+                i = prioq_peek(c->by_expiry);
+                assert(i);
+
+                /* Take an extra reference to the key so that it
+                 * doesn't go away in the middle of the remove call */
+                key = dns_resource_key_ref(i->key);
+                dns_cache_remove_by_key(c, key);
+        }
+}
+
+void dns_cache_prune(DnsCache *c) {
+        usec_t t = 0;
+
+        assert(c);
+
+        /* Remove all entries that are past their TTL */
+
+        for (;;) {
+                DnsCacheItem *i;
+                char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+                i = prioq_peek(c->by_expiry);
+                if (!i)
+                        break;
+
+                if (t <= 0)
+                        t = now(CLOCK_BOOTTIME);
+
+                if (i->until > t)
+                        break;
+
+                /* Depending whether this is an mDNS shared entry
+                 * either remove only this one RR or the whole RRset */
+                log_debug("Removing %scache entry for %s (expired "USEC_FMT"s ago)",
+                          i->shared_owner ? "shared " : "",
+                          dns_resource_key_to_string(i->key, key_str, sizeof key_str),
+                          (t - i->until) / USEC_PER_SEC);
+
+                if (i->shared_owner)
+                        dns_cache_item_unlink_and_free(c, i);
+                else {
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
+
+                        /* Take an extra reference to the key so that it
+                         * doesn't go away in the middle of the remove call */
+                        key = dns_resource_key_ref(i->key);
+                        dns_cache_remove_by_key(c, key);
+                }
+        }
+}
+
+static int dns_cache_item_prioq_compare_func(const void *a, const void *b) {
+        const DnsCacheItem *x = a, *y = b;
+
+        return CMP(x->until, y->until);
+}
+
+static int dns_cache_init(DnsCache *c) {
+        int r;
+
+        assert(c);
+
+        r = prioq_ensure_allocated(&c->by_expiry, dns_cache_item_prioq_compare_func);
+        if (r < 0)
+                return r;
+
+        r = hashmap_ensure_allocated(&c->by_key, &dns_resource_key_hash_ops);
+        if (r < 0)
+                return r;
+
+        return r;
+}
+
+static int dns_cache_link_item(DnsCache *c, DnsCacheItem *i) {
+        DnsCacheItem *first;
+        int r;
+
+        assert(c);
+        assert(i);
+
+        r = prioq_put(c->by_expiry, i, &i->prioq_idx);
+        if (r < 0)
+                return r;
+
+        first = hashmap_get(c->by_key, i->key);
+        if (first) {
+                _unused_ _cleanup_(dns_resource_key_unrefp) DnsResourceKey *k = NULL;
+
+                /* Keep a reference to the original key, while we manipulate the list. */
+                k = dns_resource_key_ref(first->key);
+
+                /* Now, try to reduce the number of keys we keep */
+                dns_resource_key_reduce(&first->key, &i->key);
+
+                if (first->rr)
+                        dns_resource_key_reduce(&first->rr->key, &i->key);
+                if (i->rr)
+                        dns_resource_key_reduce(&i->rr->key, &i->key);
+
+                LIST_PREPEND(by_key, first, i);
+                assert_se(hashmap_replace(c->by_key, first->key, first) >= 0);
+        } else {
+                r = hashmap_put(c->by_key, i->key, i);
+                if (r < 0) {
+                        prioq_remove(c->by_expiry, i, &i->prioq_idx);
+                        return r;
+                }
+        }
+
+        return 0;
+}
+
+static DnsCacheItem* dns_cache_get(DnsCache *c, DnsResourceRecord *rr) {
+        assert(c);
+        assert(rr);
+
+        LIST_FOREACH(by_key, i, (DnsCacheItem*) hashmap_get(c->by_key, rr->key))
+                if (i->rr && dns_resource_record_equal(i->rr, rr) > 0)
+                        return i;
+
+        return NULL;
+}
+
+static usec_t calculate_until_valid(
+                DnsResourceRecord *rr,
+                uint32_t min_ttl,
+                uint32_t nsec_ttl,
+                usec_t timestamp,
+                bool use_soa_minimum) {
+
+        uint32_t ttl;
+        usec_t u;
+
+        assert(rr);
+
+        ttl = MIN(min_ttl, nsec_ttl);
+        if (rr->key->type == DNS_TYPE_SOA && use_soa_minimum) {
+                /* If this is a SOA RR, and it is requested, clamp to the SOA's minimum field. This is used
+                 * when we do negative caching, to determine the TTL for the negative caching entry. See RFC
+                 * 2308, Section 5. */
+
+                if (ttl > rr->soa.minimum)
+                        ttl = rr->soa.minimum;
+        }
+
+        u = ttl * USEC_PER_SEC;
+        if (u > CACHE_TTL_MAX_USEC)
+                u = CACHE_TTL_MAX_USEC;
+
+        if (rr->expiry != USEC_INFINITY) {
+                usec_t left;
+
+                /* Make use of the DNSSEC RRSIG expiry info, if we have it */
+
+                left = LESS_BY(rr->expiry, now(CLOCK_REALTIME));
+                if (u > left)
+                        u = left;
+        }
+
+        return timestamp + u;
+}
+
+static usec_t calculate_until(
+                usec_t until_valid,
+                usec_t stale_retention_usec) {
+
+        return stale_retention_usec > 0 ? usec_add(until_valid, stale_retention_usec) : until_valid;
+}
+
+static void dns_cache_item_update_positive(
+                DnsCache *c,
+                DnsCacheItem *i,
+                DnsResourceRecord *rr,
+                DnsAnswer *answer,
+                DnsPacket *full_packet,
+                uint32_t min_ttl,
+                uint64_t query_flags,
+                bool shared_owner,
+                DnssecResult dnssec_result,
+                usec_t timestamp,
+                int ifindex,
+                int owner_family,
+                const union in_addr_union *owner_address,
+                usec_t stale_retention_usec) {
+
+        assert(c);
+        assert(i);
+        assert(rr);
+        assert(owner_address);
+
+        i->type = DNS_CACHE_POSITIVE;
+
+        if (!i->by_key_prev)
+                /* We are the first item in the list, we need to
+                 * update the key used in the hashmap */
+
+                assert_se(hashmap_replace(c->by_key, rr->key, i) >= 0);
+
+        DNS_RR_REPLACE(i->rr, dns_resource_record_ref(rr));
+
+        DNS_RESOURCE_KEY_REPLACE(i->key, dns_resource_key_ref(rr->key));
+
+        DNS_ANSWER_REPLACE(i->answer, dns_answer_ref(answer));
+
+        DNS_PACKET_REPLACE(i->full_packet, dns_packet_ref(full_packet));
+
+        i->until_valid = calculate_until_valid(rr, min_ttl, UINT32_MAX, timestamp, false);
+        i->until = calculate_until(i->until_valid, stale_retention_usec);
+        i->query_flags = query_flags & CACHEABLE_QUERY_FLAGS;
+        i->shared_owner = shared_owner;
+        i->dnssec_result = dnssec_result;
+
+        i->ifindex = ifindex;
+
+        i->owner_family = owner_family;
+        i->owner_address = *owner_address;
+
+        prioq_reshuffle(c->by_expiry, i, &i->prioq_idx);
+}
+
+static int dns_cache_put_positive(
+                DnsCache *c,
+                DnsProtocol protocol,
+                DnsResourceRecord *rr,
+                DnsAnswer *answer,
+                DnsPacket *full_packet,
+                uint64_t query_flags,
+                bool shared_owner,
+                DnssecResult dnssec_result,
+                usec_t timestamp,
+                int ifindex,
+                int owner_family,
+                const union in_addr_union *owner_address,
+                usec_t stale_retention_usec) {
+
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+        DnsCacheItem *existing;
+        uint32_t min_ttl;
+        int r;
+
+        assert(c);
+        assert(rr);
+        assert(owner_address);
+
+        /* Never cache pseudo RRs */
+        if (dns_class_is_pseudo(rr->key->class))
+                return 0;
+        if (dns_type_is_pseudo(rr->key->type))
+                return 0;
+
+        /* Determine the minimal TTL of all RRs in the answer plus the one by the main RR we are supposed to
+         * cache. Since we cache whole answers to questions we should never return answers where only some
+         * RRs are still valid, hence find the lowest here */
+        min_ttl = MIN(dns_answer_min_ttl(answer), rr->ttl);
+
+        /* New TTL is 0? Delete this specific entry... */
+        if (min_ttl <= 0) {
+                r = dns_cache_remove_by_rr(c, rr);
+                log_debug("%s: %s",
+                          r > 0 ? "Removed zero TTL entry from cache" : "Not caching zero TTL cache entry",
+                          dns_resource_key_to_string(rr->key, key_str, sizeof key_str));
+                return 0;
+        }
+
+        /* Entry exists already? Update TTL, timestamp and owner */
+        existing = dns_cache_get(c, rr);
+        if (existing) {
+                dns_cache_item_update_positive(
+                                c,
+                                existing,
+                                rr,
+                                answer,
+                                full_packet,
+                                min_ttl,
+                                query_flags,
+                                shared_owner,
+                                dnssec_result,
+                                timestamp,
+                                ifindex,
+                                owner_family,
+                                owner_address,
+                                stale_retention_usec);
+                return 0;
+        }
+
+        /* Do not cache mDNS goodbye packet. */
+        if (protocol == DNS_PROTOCOL_MDNS && rr->ttl <= 1)
+                return 0;
+
+        /* Otherwise, add the new RR */
+        r = dns_cache_init(c);
+        if (r < 0)
+                return r;
+
+        dns_cache_make_space(c, 1);
+
+        _cleanup_(dns_cache_item_freep) DnsCacheItem *i = new(DnsCacheItem, 1);
+        if (!i)
+                return -ENOMEM;
+
+        /* If StaleRetentionSec is greater than zero, the 'until' property is set to a duration
+         * of StaleRetentionSec from the time of TTL expiry.
+         * If StaleRetentionSec is zero, both the 'until' and 'until_valid' are set to the TTL duration,
+         * leading to the eviction of the record once the TTL expires.*/
+        usec_t until_valid = calculate_until_valid(rr, min_ttl, UINT32_MAX, timestamp, false);
+        *i = (DnsCacheItem) {
+                .type = DNS_CACHE_POSITIVE,
+                .key = dns_resource_key_ref(rr->key),
+                .rr = dns_resource_record_ref(rr),
+                .answer = dns_answer_ref(answer),
+                .full_packet = dns_packet_ref(full_packet),
+                .until = calculate_until(until_valid, stale_retention_usec),
+                .until_valid = until_valid,
+                .query_flags = query_flags & CACHEABLE_QUERY_FLAGS,
+                .shared_owner = shared_owner,
+                .dnssec_result = dnssec_result,
+                .ifindex = ifindex,
+                .owner_family = owner_family,
+                .owner_address = *owner_address,
+                .prioq_idx = PRIOQ_IDX_NULL,
+        };
+
+        r = dns_cache_link_item(c, i);
+        if (r < 0)
+                return r;
+
+        log_debug("Added positive %s %s%s cache entry for %s "USEC_FMT"s on %s/%s/%s",
+                  FLAGS_SET(i->query_flags, SD_RESOLVED_AUTHENTICATED) ? "authenticated" : "unauthenticated",
+                  FLAGS_SET(i->query_flags, SD_RESOLVED_CONFIDENTIAL) ? "confidential" : "non-confidential",
+                  i->shared_owner ? " shared" : "",
+                  dns_resource_key_to_string(i->key, key_str, sizeof key_str),
+                  (i->until - timestamp) / USEC_PER_SEC,
+                  i->ifindex == 0 ? "*" : FORMAT_IFNAME(i->ifindex),
+                  af_to_name_short(i->owner_family),
+                  IN_ADDR_TO_STRING(i->owner_family, &i->owner_address));
+
+        TAKE_PTR(i);
+        return 0;
+}
+
+static int dns_cache_put_negative(
+                DnsCache *c,
+                DnsResourceKey *key,
+                int rcode,
+                DnsAnswer *answer,
+                DnsPacket *full_packet,
+                uint64_t query_flags,
+                DnssecResult dnssec_result,
+                uint32_t nsec_ttl,
+                usec_t timestamp,
+                DnsResourceRecord *soa,
+                int owner_family,
+                const union in_addr_union *owner_address) {
+
+        _cleanup_(dns_cache_item_freep) DnsCacheItem *i = NULL;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+        int r;
+
+        assert(c);
+        assert(key);
+        assert(owner_address);
+
+        /* Never cache pseudo RR keys. DNS_TYPE_ANY is particularly
+         * important to filter out as we use this as a pseudo-type for
+         * NXDOMAIN entries */
+        if (dns_class_is_pseudo(key->class))
+                return 0;
+        if (dns_type_is_pseudo(key->type))
+                return 0;
+
+        if (IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN)) {
+                if (!soa)
+                        return 0;
+
+                /* For negative replies, check if we have a TTL of a SOA */
+                if (nsec_ttl <= 0 || soa->soa.minimum <= 0 || soa->ttl <= 0) {
+                        log_debug("Not caching negative entry with zero SOA/NSEC/NSEC3 TTL: %s",
+                                  dns_resource_key_to_string(key, key_str, sizeof key_str));
+                        return 0;
+                }
+        } else if (rcode != DNS_RCODE_SERVFAIL)
+                return 0;
+
+        r = dns_cache_init(c);
+        if (r < 0)
+                return r;
+
+        dns_cache_make_space(c, 1);
+
+        i = new(DnsCacheItem, 1);
+        if (!i)
+                return -ENOMEM;
+
+        *i = (DnsCacheItem) {
+                .type =
+                        rcode == DNS_RCODE_SUCCESS ? DNS_CACHE_NODATA :
+                        rcode == DNS_RCODE_NXDOMAIN ? DNS_CACHE_NXDOMAIN : DNS_CACHE_RCODE,
+                .query_flags = query_flags & CACHEABLE_QUERY_FLAGS,
+                .dnssec_result = dnssec_result,
+                .owner_family = owner_family,
+                .owner_address = *owner_address,
+                .prioq_idx = PRIOQ_IDX_NULL,
+                .rcode = rcode,
+                .answer = dns_answer_ref(answer),
+                .full_packet = dns_packet_ref(full_packet),
+        };
+
+        /* Determine how long to cache this entry. In case we have some RRs in the answer use the lowest TTL
+         * of any of them. Typically that's the SOA's TTL, which is OK, but could possibly be lower because
+         * of some other RR. Let's better take the lowest option here than a needlessly high one */
+        i->until = i->until_valid =
+                i->type == DNS_CACHE_RCODE ? timestamp + CACHE_TTL_STRANGE_RCODE_USEC :
+                calculate_until_valid(soa, dns_answer_min_ttl(answer), nsec_ttl, timestamp, true);
+
+        if (i->type == DNS_CACHE_NXDOMAIN) {
+                /* NXDOMAIN entries should apply equally to all types, so we use ANY as
+                 * a pseudo type for this purpose here. */
+                i->key = dns_resource_key_new(key->class, DNS_TYPE_ANY, dns_resource_key_name(key));
+                if (!i->key)
+                        return -ENOMEM;
+
+                /* Make sure to remove any previous entry for this
+                 * specific ANY key. (For non-ANY keys the cache data
+                 * is already cleared by the caller.) Note that we
+                 * don't bother removing positive or NODATA cache
+                 * items in this case, because it would either be slow
+                 * or require explicit indexing by name */
+                dns_cache_remove_by_key(c, key);
+        } else
+                i->key = dns_resource_key_ref(key);
+
+        r = dns_cache_link_item(c, i);
+        if (r < 0)
+                return r;
+
+        log_debug("Added %s cache entry for %s "USEC_FMT"s",
+                  dns_cache_item_type_to_string(i),
+                  dns_resource_key_to_string(i->key, key_str, sizeof key_str),
+                  (i->until - timestamp) / USEC_PER_SEC);
+
+        i = NULL;
+        return 0;
+}
+
+static void dns_cache_remove_previous(
+                DnsCache *c,
+                DnsResourceKey *key,
+                DnsAnswer *answer) {
+
+        DnsResourceRecord *rr;
+        DnsAnswerFlags flags;
+
+        assert(c);
+
+        /* First, if we were passed a key (i.e. on LLMNR/DNS, but
+         * not on mDNS), delete all matching old RRs, so that we only
+         * keep complete by_key in place. */
+        if (key)
+                dns_cache_remove_by_key(c, key);
+
+        /* Second, flush all entries matching the answer, unless this
+         * is an RR that is explicitly marked to be "shared" between
+         * peers (i.e. mDNS RRs without the flush-cache bit set). */
+        DNS_ANSWER_FOREACH_FLAGS(rr, flags, answer) {
+                if ((flags & DNS_ANSWER_CACHEABLE) == 0)
+                        continue;
+
+                if (flags & DNS_ANSWER_SHARED_OWNER)
+                        continue;
+
+                dns_cache_remove_by_key(c, rr->key);
+        }
+}
+
+static bool rr_eligible(DnsResourceRecord *rr) {
+        assert(rr);
+
+        /* When we see an NSEC/NSEC3 RR, we'll only cache it if it is from the lower zone, not the upper zone, since
+         * that's where the interesting bits are (with exception of DS RRs). Of course, this way we cannot derive DS
+         * existence from any cached NSEC/NSEC3, but that should be fine. */
+
+        switch (rr->key->type) {
+
+        case DNS_TYPE_NSEC:
+                return !bitmap_isset(rr->nsec.types, DNS_TYPE_NS) ||
+                        bitmap_isset(rr->nsec.types, DNS_TYPE_SOA);
+
+        case DNS_TYPE_NSEC3:
+                return !bitmap_isset(rr->nsec3.types, DNS_TYPE_NS) ||
+                        bitmap_isset(rr->nsec3.types, DNS_TYPE_SOA);
+
+        default:
+                return true;
+        }
+}
+
+int dns_cache_put(
+                DnsCache *c,
+                DnsCacheMode cache_mode,
+                DnsProtocol protocol,
+                DnsResourceKey *key,
+                int rcode,
+                DnsAnswer *answer,
+                DnsPacket *full_packet,
+                uint64_t query_flags,
+                DnssecResult dnssec_result,
+                uint32_t nsec_ttl,
+                int owner_family,
+                const union in_addr_union *owner_address,
+                usec_t stale_retention_usec) {
+
+        DnsResourceRecord *soa = NULL;
+        bool weird_rcode = false;
+        DnsAnswerItem *item;
+        DnsAnswerFlags flags;
+        unsigned cache_keys;
+        usec_t timestamp;
+        int r;
+
+        assert(c);
+        assert(owner_address);
+
+        dns_cache_remove_previous(c, key, answer);
+
+        /* We only care for positive replies and NXDOMAINs, on all other replies we will simply flush the respective
+         * entries, and that's it. (Well, with one further exception: since some DNS zones (akamai!) return SERVFAIL
+         * consistently for some lookups, and forwarders tend to propagate that we'll cache that too, but only for a
+         * short time.) */
+
+        if (IN_SET(rcode, DNS_RCODE_SUCCESS, DNS_RCODE_NXDOMAIN)) {
+                if (dns_answer_isempty(answer)) {
+                        if (key) {
+                                char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+                                log_debug("Not caching negative entry without a SOA record: %s",
+                                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+                        }
+
+                        return 0;
+                }
+
+        } else {
+                /* Only cache SERVFAIL as "weird" rcode for now. We can add more later, should that turn out to be
+                 * beneficial. */
+                if (rcode != DNS_RCODE_SERVFAIL)
+                        return 0;
+
+                weird_rcode = true;
+        }
+
+        cache_keys = dns_answer_size(answer);
+        if (key)
+                cache_keys++;
+
+        /* Make some space for our new entries */
+        dns_cache_make_space(c, cache_keys);
+
+        timestamp = now(CLOCK_BOOTTIME);
+
+        /* Second, add in positive entries for all contained RRs */
+        DNS_ANSWER_FOREACH_ITEM(item, answer) {
+                int primary = false;
+
+                if (!FLAGS_SET(item->flags, DNS_ANSWER_CACHEABLE) ||
+                    !rr_eligible(item->rr))
+                        continue;
+
+                if (key) {
+                        /* We store the auxiliary RRs and packet data in the cache only if they were in
+                         * direct response to the original query. If we cache an RR we also received, and
+                         * that is just auxiliary information we can't use the data, hence don't. */
+
+                        primary = dns_resource_key_match_rr(key, item->rr, NULL);
+                        if (primary < 0)
+                                return primary;
+                        if (primary == 0) {
+                                primary = dns_resource_key_match_cname_or_dname(key, item->rr->key, NULL);
+                                if (primary < 0)
+                                        return primary;
+                        }
+                }
+
+                if (!primary) {
+                        DnsCacheItem *first;
+
+                        /* Do not replace existing cache items for primary lookups with non-primary
+                         * data. After all the primary lookup data is a lot more useful. */
+                        first = hashmap_get(c->by_key, item->rr->key);
+                        if (first && DNS_CACHE_ITEM_IS_PRIMARY(first))
+                                return 0;
+                }
+
+                r = dns_cache_put_positive(
+                                c,
+                                protocol,
+                                item->rr,
+                                primary ? answer : NULL,
+                                primary ? full_packet : NULL,
+                                ((item->flags & DNS_ANSWER_AUTHENTICATED) ? SD_RESOLVED_AUTHENTICATED : 0) |
+                                (query_flags & SD_RESOLVED_CONFIDENTIAL),
+                                item->flags & DNS_ANSWER_SHARED_OWNER,
+                                dnssec_result,
+                                timestamp,
+                                item->ifindex,
+                                owner_family,
+                                owner_address,
+                                stale_retention_usec);
+                if (r < 0)
+                        goto fail;
+        }
+
+        if (!key) /* mDNS doesn't know negative caching, really */
+                return 0;
+
+        /* Third, add in negative entries if the key has no RR */
+        r = dns_answer_match_key(answer, key, NULL);
+        if (r < 0)
+                goto fail;
+        if (r > 0)
+                return 0;
+
+        /* But not if it has a matching CNAME/DNAME (the negative caching will be done on the canonical name,
+         * not on the alias) */
+        r = dns_answer_find_cname_or_dname(answer, key, NULL, NULL);
+        if (r < 0)
+                goto fail;
+        if (r > 0)
+                return 0;
+
+        /* See https://tools.ietf.org/html/rfc2308, which say that a matching SOA record in the packet is used to
+         * enable negative caching. We apply one exception though: if we are about to cache a weird rcode we do so
+         * regardless of a SOA. */
+        r = dns_answer_find_soa(answer, key, &soa, &flags);
+        if (r < 0)
+                goto fail;
+        if (r == 0 && !weird_rcode)
+                return 0;
+        if (r > 0) {
+                /* Refuse using the SOA data if it is unsigned, but the key is signed */
+                if (FLAGS_SET(query_flags, SD_RESOLVED_AUTHENTICATED) &&
+                    (flags & DNS_ANSWER_AUTHENTICATED) == 0)
+                        return 0;
+        }
+
+        if (cache_mode == DNS_CACHE_MODE_NO_NEGATIVE) {
+                char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+                log_debug("Not caching negative entry for: %s, cache mode set to no-negative",
+                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+                return 0;
+        }
+
+        r = dns_cache_put_negative(
+                        c,
+                        key,
+                        rcode,
+                        answer,
+                        full_packet,
+                        query_flags,
+                        dnssec_result,
+                        nsec_ttl,
+                        timestamp,
+                        soa,
+                        owner_family,
+                        owner_address);
+        if (r < 0)
+                goto fail;
+
+        return 0;
+
+fail:
+        /* Adding all RRs failed. Let's clean up what we already
+         * added, just in case */
+
+        if (key)
+                dns_cache_remove_by_key(c, key);
+
+        DNS_ANSWER_FOREACH_ITEM(item, answer) {
+                if ((item->flags & DNS_ANSWER_CACHEABLE) == 0)
+                        continue;
+
+                dns_cache_remove_by_key(c, item->rr->key);
+        }
+
+        return r;
+}
+
+static DnsCacheItem *dns_cache_get_by_key_follow_cname_dname_nsec(DnsCache *c, DnsResourceKey *k) {
+        DnsCacheItem *i;
+        const char *n;
+        int r;
+
+        assert(c);
+        assert(k);
+
+        /* If we hit some OOM error, or suchlike, we don't care too
+         * much, after all this is just a cache */
+
+        i = hashmap_get(c->by_key, k);
+        if (i)
+                return i;
+
+        n = dns_resource_key_name(k);
+
+        /* Check if we have an NXDOMAIN cache item for the name, notice that we use
+         * the pseudo-type ANY for NXDOMAIN cache items. */
+        i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_ANY, n));
+        if (i && i->type == DNS_CACHE_NXDOMAIN)
+                return i;
+
+        if (dns_type_may_redirect(k->type)) {
+                /* Check if we have a CNAME record instead */
+                i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_CNAME, n));
+                if (i && i->type != DNS_CACHE_NODATA)
+                        return i;
+
+                /* OK, let's look for cached DNAME records. */
+                for (;;) {
+                        if (isempty(n))
+                                return NULL;
+
+                        i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_DNAME, n));
+                        if (i && i->type != DNS_CACHE_NODATA)
+                                return i;
+
+                        /* Jump one label ahead */
+                        r = dns_name_parent(&n);
+                        if (r <= 0)
+                                return NULL;
+                }
+        }
+
+        if (k->type != DNS_TYPE_NSEC) {
+                /* Check if we have an NSEC record instead for the name. */
+                i = hashmap_get(c->by_key, &DNS_RESOURCE_KEY_CONST(k->class, DNS_TYPE_NSEC, n));
+                if (i)
+                        return i;
+        }
+
+        return NULL;
+}
+
+static int answer_add_clamp_ttl(
+                DnsAnswer **answer,
+                DnsResourceRecord *rr,
+                int ifindex,
+                DnsAnswerFlags answer_flags,
+                DnsResourceRecord *rrsig,
+                uint64_t query_flags,
+                usec_t until,
+                usec_t current) {
+
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *patched = NULL, *patched_rrsig = NULL;
+        int r;
+
+        assert(answer);
+        assert(rr);
+
+        if (FLAGS_SET(query_flags, SD_RESOLVED_CLAMP_TTL)) {
+                uint32_t left_ttl;
+
+                assert(current > 0);
+
+                /* Let's determine how much time is left for this cache entry. Note that we round down, but
+                 * clamp this to be 1s at minimum, since we usually want records to remain cached better too
+                 * short a time than too long a time, but otoh don't want to return 0 ever, since that has
+                 * special semantics in various contexts — in particular in mDNS */
+
+                left_ttl = MAX(1U, LESS_BY(until, current) / USEC_PER_SEC);
+
+                patched = dns_resource_record_ref(rr);
+
+                r = dns_resource_record_clamp_ttl(&patched, left_ttl);
+                if (r < 0)
+                        return r;
+
+                rr = patched;
+
+                if (rrsig) {
+                        patched_rrsig = dns_resource_record_ref(rrsig);
+                        r = dns_resource_record_clamp_ttl(&patched_rrsig, left_ttl);
+                        if (r < 0)
+                                return r;
+
+                        rrsig = patched_rrsig;
+                }
+        }
+
+        r = dns_answer_add_extend(answer, rr, ifindex, answer_flags, rrsig);
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+int dns_cache_lookup(
+                DnsCache *c,
+                DnsResourceKey *key,
+                uint64_t query_flags,
+                int *ret_rcode,
+                DnsAnswer **ret_answer,
+                DnsPacket **ret_full_packet,
+                uint64_t *ret_query_flags,
+                DnssecResult *ret_dnssec_result) {
+
+        _cleanup_(dns_packet_unrefp) DnsPacket *full_packet = NULL;
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+        unsigned n = 0;
+        int r;
+        bool nxdomain = false;
+        DnsCacheItem *first, *nsec = NULL;
+        bool have_authenticated = false, have_non_authenticated = false, have_confidential = false, have_non_confidential = false;
+        usec_t current = 0;
+        int found_rcode = -1;
+        DnssecResult dnssec_result = -1;
+        int have_dnssec_result = -1;
+
+        assert(c);
+        assert(key);
+
+        if (key->type == DNS_TYPE_ANY || key->class == DNS_CLASS_ANY) {
+                /* If we have ANY lookups we don't use the cache, so that the caller refreshes via the
+                 * network. */
+
+                log_debug("Ignoring cache for ANY lookup: %s",
+                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+                goto miss;
+        }
+
+        first = dns_cache_get_by_key_follow_cname_dname_nsec(c, key);
+        if (!first) {
+                /* If one question cannot be answered we need to refresh */
+
+                log_debug("Cache miss for %s",
+                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+                goto miss;
+        }
+
+        if ((query_flags & (SD_RESOLVED_CLAMP_TTL | SD_RESOLVED_NO_STALE)) != 0) {
+                /* 'current' is always passed to answer_add_clamp_ttl(), but is only used conditionally.
+                 * We'll do the same assert there to make sure that it was initialized properly.
+                 * 'current' is also used below when SD_RESOLVED_NO_STALE is set. */
+                current = now(CLOCK_BOOTTIME);
+                assert(current > 0);
+        }
+
+        LIST_FOREACH(by_key, j, first) {
+                /* If the caller doesn't allow us to answer questions from cache data learned from
+                 * "side-effect", skip this entry. */
+                if (FLAGS_SET(query_flags, SD_RESOLVED_REQUIRE_PRIMARY) &&
+                    !DNS_CACHE_ITEM_IS_PRIMARY(j)) {
+                        log_debug("Primary answer was requested for cache lookup for %s, which we don't have.",
+                                  dns_resource_key_to_string(key, key_str, sizeof key_str));
+
+                        goto miss;
+                }
+
+                /* Skip the next part if ttl is expired and requested with no stale flag. */
+                if (FLAGS_SET(query_flags, SD_RESOLVED_NO_STALE) && j->until_valid < current) {
+                        log_debug("Requested with no stale and TTL expired for %s",
+                                                dns_resource_key_to_string(key, key_str, sizeof key_str));
+
+                        goto miss;
+                }
+
+                if (j->type == DNS_CACHE_NXDOMAIN)
+                        nxdomain = true;
+                else if (j->type == DNS_CACHE_RCODE)
+                        found_rcode = j->rcode;
+                else if (j->rr) {
+                        if (j->rr->key->type == DNS_TYPE_NSEC)
+                                nsec = j;
+
+                        n++;
+                }
+
+                if (FLAGS_SET(j->query_flags, SD_RESOLVED_AUTHENTICATED))
+                        have_authenticated = true;
+                else
+                        have_non_authenticated = true;
+
+                if (FLAGS_SET(j->query_flags, SD_RESOLVED_CONFIDENTIAL))
+                        have_confidential = true;
+                else
+                        have_non_confidential = true;
+
+                if (j->dnssec_result < 0) {
+                        have_dnssec_result = false; /* an entry without dnssec result? then invalidate things for good */
+                        dnssec_result = _DNSSEC_RESULT_INVALID;
+                } else if (have_dnssec_result < 0) {
+                        have_dnssec_result = true; /* So far no result seen, let's pick this one up */
+                        dnssec_result = j->dnssec_result;
+                } else if (have_dnssec_result > 0 && j->dnssec_result != dnssec_result) {
+                        have_dnssec_result = false; /* conflicting result seen? then invalidate for good */
+                        dnssec_result = _DNSSEC_RESULT_INVALID;
+                }
+
+                /* If the question is being resolved using stale data, the clamp TTL will be set to CACHE_STALE_TTL_MAX_USEC. */
+                usec_t until = FLAGS_SET(query_flags, SD_RESOLVED_NO_STALE) ? j->until_valid
+                                                                            : usec_add(current, CACHE_STALE_TTL_MAX_USEC);
+
+                /* Append the answer RRs to our answer. Ideally we have the answer object, which we
+                 * preferably use. But if the cached entry was generated as "side-effect" of a reply,
+                 * i.e. from validated auxiliary records rather than from the main reply, then we use the
+                 * individual RRs only instead. */
+                if (j->answer) {
+
+                        /* Minor optimization, if the full answer object of this and the previous RR is the
+                         * same, don't bother adding it again. Typically we store a full RRset here, hence
+                         * that should be the case. */
+                        if (!j->by_key_prev || j->answer != j->by_key_prev->answer) {
+                                DnsAnswerItem *item;
+
+                                DNS_ANSWER_FOREACH_ITEM(item, j->answer) {
+                                        r = answer_add_clamp_ttl(
+                                                        &answer,
+                                                        item->rr,
+                                                        item->ifindex,
+                                                        item->flags,
+                                                        item->rrsig,
+                                                        query_flags,
+                                                        until,
+                                                        current);
+                                        if (r < 0)
+                                                return r;
+                                }
+                        }
+
+                } else if (j->rr) {
+                        r = answer_add_clamp_ttl(
+                                        &answer,
+                                        j->rr,
+                                        j->ifindex,
+                                        FLAGS_SET(j->query_flags, SD_RESOLVED_AUTHENTICATED) ? DNS_ANSWER_AUTHENTICATED : 0,
+                                        NULL,
+                                        query_flags,
+                                        until,
+                                        current);
+                        if (r < 0)
+                                return r;
+                }
+
+                /* We'll return any packet we have for this. Typically all cache entries for the same key
+                 * should come from the same packet anyway, hence it doesn't really matter which packet we
+                 * return here, they should all resolve to the same anyway. */
+                if (!full_packet && j->full_packet)
+                        full_packet = dns_packet_ref(j->full_packet);
+        }
+
+        if (found_rcode >= 0) {
+                log_debug("RCODE %s cache hit for %s",
+                          FORMAT_DNS_RCODE(found_rcode),
+                          dns_resource_key_to_string(key, key_str, sizeof(key_str)));
+
+                if (ret_rcode)
+                        *ret_rcode = found_rcode;
+                if (ret_answer)
+                        *ret_answer = TAKE_PTR(answer);
+                if (ret_full_packet)
+                        *ret_full_packet = TAKE_PTR(full_packet);
+                if (ret_query_flags)
+                        *ret_query_flags = 0;
+                if (ret_dnssec_result)
+                        *ret_dnssec_result = dnssec_result;
+
+                c->n_hit++;
+                return 1;
+        }
+
+        if (nsec && !IN_SET(key->type, DNS_TYPE_NSEC, DNS_TYPE_DS)) {
+                /* Note that we won't derive information for DS RRs from an NSEC, because we only cache NSEC
+                 * RRs from the lower-zone of a zone cut, but the DS RRs are on the upper zone. */
+
+                log_debug("NSEC NODATA cache hit for %s",
+                          dns_resource_key_to_string(key, key_str, sizeof key_str));
+
+                /* We only found an NSEC record that matches our name.  If it says the type doesn't exist
+                 * report NODATA. Otherwise report a cache miss. */
+
+                if (ret_rcode)
+                        *ret_rcode = DNS_RCODE_SUCCESS;
+                if (ret_answer)
+                        *ret_answer = TAKE_PTR(answer);
+                if (ret_full_packet)
+                        *ret_full_packet = TAKE_PTR(full_packet);
+                if (ret_query_flags)
+                        *ret_query_flags = nsec->query_flags;
+                if (ret_dnssec_result)
+                        *ret_dnssec_result = nsec->dnssec_result;
+
+                if (!bitmap_isset(nsec->rr->nsec.types, key->type) &&
+                    !bitmap_isset(nsec->rr->nsec.types, DNS_TYPE_CNAME) &&
+                    !bitmap_isset(nsec->rr->nsec.types, DNS_TYPE_DNAME)) {
+                        c->n_hit++;
+                        return 1;
+                }
+
+                c->n_miss++;
+                return 0;
+        }
+
+        log_debug("%s cache hit for %s",
+                  n > 0    ? "Positive" :
+                  nxdomain ? "NXDOMAIN" : "NODATA",
+                  dns_resource_key_to_string(key, key_str, sizeof key_str));
+
+        if (n <= 0) {
+                c->n_hit++;
+
+                if (ret_rcode)
+                        *ret_rcode = nxdomain ? DNS_RCODE_NXDOMAIN : DNS_RCODE_SUCCESS;
+                if (ret_answer)
+                        *ret_answer = TAKE_PTR(answer);
+                if (ret_full_packet)
+                        *ret_full_packet = TAKE_PTR(full_packet);
+                if (ret_query_flags)
+                        *ret_query_flags =
+                                ((have_authenticated && !have_non_authenticated) ? SD_RESOLVED_AUTHENTICATED : 0) |
+                                ((have_confidential && !have_non_confidential) ? SD_RESOLVED_CONFIDENTIAL : 0);
+                if (ret_dnssec_result)
+                        *ret_dnssec_result = dnssec_result;
+
+                return 1;
+        }
+
+        c->n_hit++;
+
+        if (ret_rcode)
+                *ret_rcode = DNS_RCODE_SUCCESS;
+        if (ret_answer)
+                *ret_answer = TAKE_PTR(answer);
+        if (ret_full_packet)
+                *ret_full_packet = TAKE_PTR(full_packet);
+        if (ret_query_flags)
+                *ret_query_flags =
+                        ((have_authenticated && !have_non_authenticated) ? SD_RESOLVED_AUTHENTICATED : 0) |
+                        ((have_confidential && !have_non_confidential) ? SD_RESOLVED_CONFIDENTIAL : 0);
+        if (ret_dnssec_result)
+                *ret_dnssec_result = dnssec_result;
+
+        return n;
+
+miss:
+        if (ret_rcode)
+                *ret_rcode = DNS_RCODE_SUCCESS;
+        if (ret_answer)
+                *ret_answer = NULL;
+        if (ret_full_packet)
+                *ret_full_packet = NULL;
+        if (ret_query_flags)
+                *ret_query_flags = 0;
+        if (ret_dnssec_result)
+                *ret_dnssec_result = _DNSSEC_RESULT_INVALID;
+
+        c->n_miss++;
+        return 0;
+}
+
+int dns_cache_check_conflicts(DnsCache *cache, DnsResourceRecord *rr, int owner_family, const union in_addr_union *owner_address) {
+        DnsCacheItem *first;
+        bool same_owner = true;
+
+        assert(cache);
+        assert(rr);
+
+        dns_cache_prune(cache);
+
+        /* See if there's a cache entry for the same key. If there
+         * isn't there's no conflict */
+        first = hashmap_get(cache->by_key, rr->key);
+        if (!first)
+                return 0;
+
+        /* See if the RR key is owned by the same owner, if so, there
+         * isn't a conflict either */
+        LIST_FOREACH(by_key, i, first) {
+                if (i->owner_family != owner_family ||
+                    !in_addr_equal(owner_family, &i->owner_address, owner_address)) {
+                        same_owner = false;
+                        break;
+                }
+        }
+        if (same_owner)
+                return 0;
+
+        /* See if there's the exact same RR in the cache. If yes, then
+         * there's no conflict. */
+        if (dns_cache_get(cache, rr))
+                return 0;
+
+        /* There's a conflict */
+        return 1;
+}
+
+int dns_cache_export_shared_to_packet(DnsCache *cache, DnsPacket *p, usec_t ts, unsigned max_rr) {
+        unsigned ancount = 0;
+        DnsCacheItem *i;
+        int r;
+
+        assert(cache);
+        assert(p);
+        assert(p->protocol == DNS_PROTOCOL_MDNS);
+
+        HASHMAP_FOREACH(i, cache->by_key)
+                LIST_FOREACH(by_key, j, i) {
+                        if (!j->rr)
+                                continue;
+
+                        if (!j->shared_owner)
+                                continue;
+
+                        /* Ignore cached goodby packet. See on_mdns_packet() and RFC 6762 section 10.1. */
+                        if (j->rr->ttl <= 1)
+                                continue;
+
+                        /* RFC6762 7.1: Don't append records with less than half the TTL remaining
+                         * as known answers. */
+                        if (usec_sub_unsigned(j->until, ts) < j->rr->ttl * USEC_PER_SEC / 2)
+                                continue;
+
+                        if (max_rr > 0 && ancount >= max_rr) {
+                                DNS_PACKET_HEADER(p)->ancount = htobe16(ancount);
+                                ancount = 0;
+
+                                r = dns_packet_new_query(&p->more, p->protocol, 0, true);
+                                if (r < 0)
+                                        return r;
+
+                                p = p->more;
+
+                                max_rr = UINT_MAX;
+                        }
+
+                        r = dns_packet_append_rr(p, j->rr, 0, NULL, NULL);
+                        if (r == -EMSGSIZE) {
+                                if (max_rr == 0)
+                                        /* If max_rr == 0, do not allocate more packets. */
+                                        goto finalize;
+
+                                /* If we're unable to stuff all known answers into the given packet, allocate
+                                 * a new one, push the RR into that one and link it to the current one. */
+
+                                DNS_PACKET_HEADER(p)->ancount = htobe16(ancount);
+                                ancount = 0;
+
+                                r = dns_packet_new_query(&p->more, p->protocol, 0, true);
+                                if (r < 0)
+                                        return r;
+
+                                /* continue with new packet */
+                                p = p->more;
+                                r = dns_packet_append_rr(p, j->rr, 0, NULL, NULL);
+                        }
+
+                        if (r < 0)
+                                return r;
+
+                        ancount++;
+                }
+
+finalize:
+        DNS_PACKET_HEADER(p)->ancount = htobe16(ancount);
+
+        return 0;
+}
+
+void dns_cache_dump(DnsCache *cache, FILE *f) {
+        DnsCacheItem *i;
+
+        if (!cache)
+                return;
+
+        if (!f)
+                f = stdout;
+
+        HASHMAP_FOREACH(i, cache->by_key)
+                LIST_FOREACH(by_key, j, i) {
+
+                        fputc('\t', f);
+
+                        if (j->rr) {
+                                const char *t;
+                                t = dns_resource_record_to_string(j->rr);
+                                if (!t) {
+                                        log_oom();
+                                        continue;
+                                }
+
+                                fputs(t, f);
+                                fputc('\n', f);
+                        } else {
+                                char key_str[DNS_RESOURCE_KEY_STRING_MAX];
+
+                                fputs(dns_resource_key_to_string(j->key, key_str, sizeof key_str), f);
+                                fputs(" -- ", f);
+                                fputs(dns_cache_item_type_to_string(j), f);
+                                fputc('\n', f);
+                        }
+                }
+}
+
+int dns_cache_dump_to_json(DnsCache *cache, JsonVariant **ret) {
+        _cleanup_(json_variant_unrefp) JsonVariant *c = NULL;
+        DnsCacheItem *i;
+        int r;
+
+        assert(cache);
+        assert(ret);
+
+        HASHMAP_FOREACH(i, cache->by_key) {
+                _cleanup_(json_variant_unrefp) JsonVariant *d = NULL, *k = NULL;
+
+                r = dns_resource_key_to_json(i->key, &k);
+                if (r < 0)
+                        return r;
+
+                if (i->rr) {
+                        _cleanup_(json_variant_unrefp) JsonVariant *l = NULL;
+
+                        LIST_FOREACH(by_key, j, i) {
+                                _cleanup_(json_variant_unrefp) JsonVariant *rj = NULL;
+
+                                assert(j->rr);
+
+                                r = dns_resource_record_to_json(j->rr, &rj);
+                                if (r < 0)
+                                        return r;
+
+                                r = dns_resource_record_to_wire_format(j->rr, /* canonical= */ false); /* don't use DNSSEC canonical format, since it removes casing, but we want that for DNS_SD compat */
+                                if (r < 0)
+                                        return r;
+
+                                r = json_variant_append_arrayb(
+                                                &l,
+                                                JSON_BUILD_OBJECT(
+                                                                JSON_BUILD_PAIR_VARIANT("rr", rj),
+                                                                JSON_BUILD_PAIR_BASE64("raw", j->rr->wire_format, j->rr->wire_format_size)));
+                                if (r < 0)
+                                        return r;
+                        }
+
+                        if (!l) {
+                                r = json_variant_new_array(&l, NULL, 0);
+                                if (r < 0)
+                                        return r;
+                        }
+
+                        r = json_build(&d,
+                                       JSON_BUILD_OBJECT(
+                                                       JSON_BUILD_PAIR_VARIANT("key", k),
+                                                       JSON_BUILD_PAIR_VARIANT("rrs", l),
+                                                       JSON_BUILD_PAIR_UNSIGNED("until", i->until)));
+                } else if (i->type == DNS_CACHE_NODATA) {
+                        r = json_build(&d,
+                                       JSON_BUILD_OBJECT(
+                                                       JSON_BUILD_PAIR_VARIANT("key", k),
+                                                       JSON_BUILD_PAIR_EMPTY_ARRAY("rrs"),
+                                                       JSON_BUILD_PAIR_UNSIGNED("until", i->until)));
+                } else
+                        r = json_build(&d,
+                                       JSON_BUILD_OBJECT(
+                                                       JSON_BUILD_PAIR_VARIANT("key", k),
+                                                       JSON_BUILD_PAIR_STRING("type", dns_cache_item_type_to_string(i)),
+                                                       JSON_BUILD_PAIR_UNSIGNED("until", i->until)));
+                if (r < 0)
+                        return r;
+
+                r = json_variant_append_array(&c, d);
+                if (r < 0)
+                        return r;
+        }
+
+        if (!c)
+                return json_variant_new_array(ret, NULL, 0);
+
+        *ret = TAKE_PTR(c);
+        return 0;
+}
+
+bool dns_cache_is_empty(DnsCache *cache) {
+        if (!cache)
+                return true;
+
+        return hashmap_isempty(cache->by_key);
+}
+
+unsigned dns_cache_size(DnsCache *cache) {
+        if (!cache)
+                return 0;
+
+        return hashmap_size(cache->by_key);
+}