Adding upstream version 255.4.upstream/255.4

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

1 files changed, 2686 insertions, 0 deletions

diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c
new file mode 100644
index 0000000..426711b
--- /dev/null
+++ b/src/resolve/resolved-dns-packet.c
@@ -0,0 +1,2686 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#if HAVE_GCRYPT
+#  include <gcrypt.h>
+#endif
+
+#include "alloc-util.h"
+#include "dns-domain.h"
+#include "memory-util.h"
+#include "resolved-dns-packet.h"
+#include "set.h"
+#include "stdio-util.h"
+#include "string-table.h"
+#include "strv.h"
+#include "unaligned.h"
+#include "utf8.h"
+
+#define EDNS0_OPT_DO (1<<15)
+
+assert_cc(DNS_PACKET_SIZE_START > DNS_PACKET_HEADER_SIZE);
+
+typedef struct DnsPacketRewinder {
+        DnsPacket *packet;
+        size_t saved_rindex;
+} DnsPacketRewinder;
+
+static void rewind_dns_packet(DnsPacketRewinder *rewinder) {
+        if (rewinder->packet)
+                dns_packet_rewind(rewinder->packet, rewinder->saved_rindex);
+}
+
+#define REWINDER_INIT(p) {                              \
+                .packet = (p),                          \
+                .saved_rindex = (p)->rindex,            \
+        }
+#define CANCEL_REWINDER(rewinder) do { (rewinder).packet = NULL; } while (0)
+
+int dns_packet_new(
+                DnsPacket **ret,
+                DnsProtocol protocol,
+                size_t min_alloc_dsize,
+                size_t max_size) {
+
+        DnsPacket *p;
+        size_t a;
+
+        assert(ret);
+        assert(max_size >= DNS_PACKET_HEADER_SIZE);
+
+        if (max_size > DNS_PACKET_SIZE_MAX)
+                max_size = DNS_PACKET_SIZE_MAX;
+
+        /* The caller may not check what is going to be truly allocated, so do not allow to
+         * allocate a DNS packet bigger than DNS_PACKET_SIZE_MAX.
+         */
+        if (min_alloc_dsize > DNS_PACKET_SIZE_MAX)
+                return log_error_errno(SYNTHETIC_ERRNO(EFBIG),
+                                       "Requested packet data size too big: %zu",
+                                       min_alloc_dsize);
+
+        /* When dns_packet_new() is called with min_alloc_dsize == 0, allocate more than the
+         * absolute minimum (which is the dns packet header size), to avoid
+         * resizing immediately again after appending the first data to the packet.
+         */
+        if (min_alloc_dsize < DNS_PACKET_HEADER_SIZE)
+                a = DNS_PACKET_SIZE_START;
+        else
+                a = min_alloc_dsize;
+
+        /* round up to next page size */
+        a = PAGE_ALIGN(ALIGN(sizeof(DnsPacket)) + a) - ALIGN(sizeof(DnsPacket));
+
+        /* make sure we never allocate more than useful */
+        if (a > max_size)
+                a = max_size;
+
+        p = malloc0(ALIGN(sizeof(DnsPacket)) + a);
+        if (!p)
+                return -ENOMEM;
+
+        *p = (DnsPacket) {
+                .n_ref = 1,
+                .protocol = protocol,
+                .size = DNS_PACKET_HEADER_SIZE,
+                .rindex = DNS_PACKET_HEADER_SIZE,
+                .allocated = a,
+                .max_size = max_size,
+                .opt_start = SIZE_MAX,
+                .opt_size = SIZE_MAX,
+        };
+
+        *ret = p;
+
+        return 0;
+}
+
+void dns_packet_set_flags(DnsPacket *p, bool dnssec_checking_disabled, bool truncated) {
+
+        DnsPacketHeader *h;
+
+        assert(p);
+
+        h = DNS_PACKET_HEADER(p);
+
+        switch (p->protocol) {
+        case DNS_PROTOCOL_LLMNR:
+                assert(!truncated);
+
+                h->flags = htobe16(DNS_PACKET_MAKE_FLAGS(0 /* qr */,
+                                                         0 /* opcode */,
+                                                         0 /* c */,
+                                                         0 /* tc */,
+                                                         0 /* t */,
+                                                         0 /* ra */,
+                                                         0 /* ad */,
+                                                         0 /* cd */,
+                                                         0 /* rcode */));
+                break;
+
+        case DNS_PROTOCOL_MDNS:
+                h->flags = htobe16(DNS_PACKET_MAKE_FLAGS(0         /* qr */,
+                                                         0         /* opcode */,
+                                                         0         /* aa */,
+                                                         truncated /* tc */,
+                                                         0         /* rd (ask for recursion) */,
+                                                         0         /* ra */,
+                                                         0         /* ad */,
+                                                         0         /* cd */,
+                                                         0         /* rcode */));
+                break;
+
+        default:
+                assert(!truncated);
+
+                h->flags = htobe16(DNS_PACKET_MAKE_FLAGS(0 /* qr */,
+                                                         0 /* opcode */,
+                                                         0 /* aa */,
+                                                         0 /* tc */,
+                                                         1 /* rd (ask for recursion) */,
+                                                         0 /* ra */,
+                                                         0 /* ad */,
+                                                         dnssec_checking_disabled /* cd */,
+                                                         0 /* rcode */));
+        }
+}
+
+int dns_packet_new_query(DnsPacket **ret, DnsProtocol protocol, size_t min_alloc_dsize, bool dnssec_checking_disabled) {
+        DnsPacket *p;
+        int r;
+
+        assert(ret);
+
+        r = dns_packet_new(&p, protocol, min_alloc_dsize, DNS_PACKET_SIZE_MAX);
+        if (r < 0)
+                return r;
+
+        /* Always set the TC bit to 0 initially.
+         * If there are multiple packets later, we'll update the bit shortly before sending.
+         */
+        dns_packet_set_flags(p, dnssec_checking_disabled, false);
+
+        *ret = p;
+        return 0;
+}
+
+int dns_packet_dup(DnsPacket **ret, DnsPacket *p) {
+        DnsPacket *c;
+        int r;
+
+        assert(ret);
+        assert(p);
+
+        r = dns_packet_validate(p);
+        if (r < 0)
+                return r;
+
+        c = malloc(ALIGN(sizeof(DnsPacket)) + p->size);
+        if (!c)
+                return -ENOMEM;
+
+        *c = (DnsPacket) {
+                .n_ref = 1,
+                .protocol = p->protocol,
+                .size = p->size,
+                .rindex = DNS_PACKET_HEADER_SIZE,
+                .allocated = p->size,
+                .max_size = p->max_size,
+                .opt_start = SIZE_MAX,
+                .opt_size = SIZE_MAX,
+        };
+
+        memcpy(DNS_PACKET_DATA(c), DNS_PACKET_DATA(p), p->size);
+
+        *ret = c;
+        return 0;
+}
+
+DnsPacket *dns_packet_ref(DnsPacket *p) {
+
+        if (!p)
+                return NULL;
+
+        assert(!p->on_stack);
+
+        assert(p->n_ref > 0);
+        p->n_ref++;
+        return p;
+}
+
+static void dns_packet_free(DnsPacket *p) {
+        char *s;
+
+        assert(p);
+
+        dns_question_unref(p->question);
+        dns_answer_unref(p->answer);
+        dns_resource_record_unref(p->opt);
+
+        while ((s = hashmap_steal_first_key(p->names)))
+                free(s);
+        hashmap_free(p->names);
+
+        free(p->_data);
+
+        if (!p->on_stack)
+                free(p);
+}
+
+DnsPacket *dns_packet_unref(DnsPacket *p) {
+        if (!p)
+                return NULL;
+
+        assert(p->n_ref > 0);
+
+        dns_packet_unref(p->more);
+
+        if (p->n_ref == 1)
+                dns_packet_free(p);
+        else
+                p->n_ref--;
+
+        return NULL;
+}
+
+int dns_packet_validate(DnsPacket *p) {
+        assert(p);
+
+        if (p->size < DNS_PACKET_HEADER_SIZE)
+                return -EBADMSG;
+
+        if (p->size > DNS_PACKET_SIZE_MAX)
+                return -EBADMSG;
+
+        return 1;
+}
+
+int dns_packet_validate_reply(DnsPacket *p) {
+        int r;
+
+        assert(p);
+
+        r = dns_packet_validate(p);
+        if (r < 0)
+                return r;
+
+        if (DNS_PACKET_QR(p) != 1)
+                return 0;
+
+        if (DNS_PACKET_OPCODE(p) != 0)
+                return -EBADMSG;
+
+        switch (p->protocol) {
+
+        case DNS_PROTOCOL_LLMNR:
+                /* RFC 4795, Section 2.1.1. says to discard all replies with QDCOUNT != 1 */
+                if (DNS_PACKET_QDCOUNT(p) != 1)
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_PROTOCOL_MDNS:
+                /* RFC 6762, Section 18 */
+                if (DNS_PACKET_RCODE(p) != 0)
+                        return -EBADMSG;
+
+                break;
+
+        default:
+                break;
+        }
+
+        return 1;
+}
+
+int dns_packet_validate_query(DnsPacket *p) {
+        int r;
+
+        assert(p);
+
+        r = dns_packet_validate(p);
+        if (r < 0)
+                return r;
+
+        if (DNS_PACKET_QR(p) != 0)
+                return 0;
+
+        if (DNS_PACKET_OPCODE(p) != 0)
+                return -EBADMSG;
+
+        switch (p->protocol) {
+
+        case DNS_PROTOCOL_DNS:
+                if (DNS_PACKET_TC(p))
+                        return -EBADMSG;
+
+                if (DNS_PACKET_QDCOUNT(p) != 1)
+                        return -EBADMSG;
+
+                if (DNS_PACKET_ANCOUNT(p) > 0)
+                        return -EBADMSG;
+
+                /* Note, in most cases, DNS query packet does not have authority section. But some query
+                 * types, e.g. IXFR, have Authority sections. Hence, unlike the check for LLMNR, we do not
+                 * check DNS_PACKET_NSCOUNT(p) here. */
+                break;
+
+        case DNS_PROTOCOL_LLMNR:
+                if (DNS_PACKET_TC(p))
+                        return -EBADMSG;
+
+                /* RFC 4795, Section 2.1.1. says to discard all queries with QDCOUNT != 1 */
+                if (DNS_PACKET_QDCOUNT(p) != 1)
+                        return -EBADMSG;
+
+                /* RFC 4795, Section 2.1.1. says to discard all queries with ANCOUNT != 0 */
+                if (DNS_PACKET_ANCOUNT(p) > 0)
+                        return -EBADMSG;
+
+                /* RFC 4795, Section 2.1.1. says to discard all queries with NSCOUNT != 0 */
+                if (DNS_PACKET_NSCOUNT(p) > 0)
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_PROTOCOL_MDNS:
+                /* Note, mDNS query may have truncation flag. So, unlike the check for DNS and LLMNR,
+                 * we do not check DNS_PACKET_TC(p) here. */
+
+                /* RFC 6762, Section 18 specifies that messages with non-zero RCODE
+                 * must be silently ignored, and that we must ignore the values of
+                 * AA, RD, RA, AD, and CD bits. */
+                if (DNS_PACKET_RCODE(p) != 0)
+                        return -EBADMSG;
+
+                break;
+
+        default:
+                break;
+        }
+
+        return 1;
+}
+
+static int dns_packet_extend(DnsPacket *p, size_t add, void **ret, size_t *start) {
+        assert(p);
+
+        if (p->size + add > p->allocated) {
+                size_t a, ms;
+
+                a = PAGE_ALIGN((p->size + add) * 2);
+
+                ms = dns_packet_size_max(p);
+                if (a > ms)
+                        a = ms;
+
+                if (p->size + add > a)
+                        return -EMSGSIZE;
+
+                if (p->_data) {
+                        void *d;
+
+                        d = realloc(p->_data, a);
+                        if (!d)
+                                return -ENOMEM;
+
+                        p->_data = d;
+                } else {
+                        p->_data = malloc(a);
+                        if (!p->_data)
+                                return -ENOMEM;
+
+                        memcpy(p->_data, (uint8_t*) p + ALIGN(sizeof(DnsPacket)), p->size);
+                        memzero((uint8_t*) p->_data + p->size, a - p->size);
+                }
+
+                p->allocated = a;
+        }
+
+        if (start)
+                *start = p->size;
+
+        if (ret)
+                *ret = (uint8_t*) DNS_PACKET_DATA(p) + p->size;
+
+        p->size += add;
+        return 0;
+}
+
+void dns_packet_truncate(DnsPacket *p, size_t sz) {
+        char *s;
+        void *n;
+
+        assert(p);
+
+        if (p->size <= sz)
+                return;
+
+        HASHMAP_FOREACH_KEY(n, s, p->names) {
+
+                if (PTR_TO_SIZE(n) < sz)
+                        continue;
+
+                hashmap_remove(p->names, s);
+                free(s);
+        }
+
+        p->size = sz;
+}
+
+int dns_packet_append_blob(DnsPacket *p, const void *d, size_t l, size_t *start) {
+        void *q;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_extend(p, l, &q, start);
+        if (r < 0)
+                return r;
+
+        memcpy_safe(q, d, l);
+        return 0;
+}
+
+int dns_packet_append_uint8(DnsPacket *p, uint8_t v, size_t *start) {
+        void *d;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_extend(p, sizeof(uint8_t), &d, start);
+        if (r < 0)
+                return r;
+
+        ((uint8_t*) d)[0] = v;
+
+        return 0;
+}
+
+int dns_packet_append_uint16(DnsPacket *p, uint16_t v, size_t *start) {
+        void *d;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_extend(p, sizeof(uint16_t), &d, start);
+        if (r < 0)
+                return r;
+
+        unaligned_write_be16(d, v);
+
+        return 0;
+}
+
+int dns_packet_append_uint32(DnsPacket *p, uint32_t v, size_t *start) {
+        void *d;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_extend(p, sizeof(uint32_t), &d, start);
+        if (r < 0)
+                return r;
+
+        unaligned_write_be32(d, v);
+
+        return 0;
+}
+
+int dns_packet_append_string(DnsPacket *p, const char *s, size_t *start) {
+        assert(p);
+        assert(s);
+
+        return dns_packet_append_raw_string(p, s, strlen(s), start);
+}
+
+int dns_packet_append_raw_string(DnsPacket *p, const void *s, size_t size, size_t *start) {
+        void *d;
+        int r;
+
+        assert(p);
+        assert(s || size == 0);
+
+        if (size > 255)
+                return -E2BIG;
+
+        r = dns_packet_extend(p, 1 + size, &d, start);
+        if (r < 0)
+                return r;
+
+        ((uint8_t*) d)[0] = (uint8_t) size;
+
+        memcpy_safe(((uint8_t*) d) + 1, s, size);
+
+        return 0;
+}
+
+int dns_packet_append_label(DnsPacket *p, const char *d, size_t l, bool canonical_candidate, size_t *start) {
+        uint8_t *w;
+        int r;
+
+        /* Append a label to a packet. Optionally, does this in DNSSEC
+         * canonical form, if this label is marked as a candidate for
+         * it, and the canonical form logic is enabled for the
+         * packet */
+
+        assert(p);
+        assert(d);
+
+        if (l > DNS_LABEL_MAX)
+                return -E2BIG;
+
+        r = dns_packet_extend(p, 1 + l, (void**) &w, start);
+        if (r < 0)
+                return r;
+
+        *(w++) = (uint8_t) l;
+
+        if (p->canonical_form && canonical_candidate)
+                /* Generate in canonical form, as defined by DNSSEC
+                 * RFC 4034, Section 6.2, i.e. all lower-case. */
+                for (size_t i = 0; i < l; i++)
+                        w[i] = (uint8_t) ascii_tolower(d[i]);
+        else
+                /* Otherwise, just copy the string unaltered. This is
+                 * essential for DNS-SD, where the casing of labels
+                 * matters and needs to be retained. */
+                memcpy(w, d, l);
+
+        return 0;
+}
+
+int dns_packet_append_name(
+                DnsPacket *p,
+                const char *name,
+                bool allow_compression,
+                bool canonical_candidate,
+                size_t *start) {
+
+        size_t saved_size;
+        int r;
+
+        assert(p);
+        assert(name);
+
+        if (p->refuse_compression)
+                allow_compression = false;
+
+        saved_size = p->size;
+
+        while (!dns_name_is_root(name)) {
+                const char *z = name;
+                char label[DNS_LABEL_MAX];
+                size_t n = 0;
+
+                if (allow_compression)
+                        n = PTR_TO_SIZE(hashmap_get(p->names, name));
+                if (n > 0) {
+                        assert(n < p->size);
+
+                        if (n < 0x4000) {
+                                r = dns_packet_append_uint16(p, 0xC000 | n, NULL);
+                                if (r < 0)
+                                        goto fail;
+
+                                goto done;
+                        }
+                }
+
+                r = dns_label_unescape(&name, label, sizeof label, 0);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_label(p, label, r, canonical_candidate, &n);
+                if (r < 0)
+                        goto fail;
+
+                if (allow_compression) {
+                        _cleanup_free_ char *s = NULL;
+
+                        s = strdup(z);
+                        if (!s) {
+                                r = -ENOMEM;
+                                goto fail;
+                        }
+
+                        r = hashmap_ensure_put(&p->names, &dns_name_hash_ops, s, SIZE_TO_PTR(n));
+                        if (r < 0)
+                                goto fail;
+
+                        TAKE_PTR(s);
+                }
+        }
+
+        r = dns_packet_append_uint8(p, 0, NULL);
+        if (r < 0)
+                return r;
+
+done:
+        if (start)
+                *start = saved_size;
+
+        return 0;
+
+fail:
+        dns_packet_truncate(p, saved_size);
+        return r;
+}
+
+int dns_packet_append_key(DnsPacket *p, const DnsResourceKey *k, const DnsAnswerFlags flags, size_t *start) {
+        size_t saved_size;
+        uint16_t class;
+        int r;
+
+        assert(p);
+        assert(k);
+
+        saved_size = p->size;
+
+        r = dns_packet_append_name(p, dns_resource_key_name(k), true, true, NULL);
+        if (r < 0)
+                goto fail;
+
+        r = dns_packet_append_uint16(p, k->type, NULL);
+        if (r < 0)
+                goto fail;
+
+        class = flags & DNS_ANSWER_CACHE_FLUSH ? k->class | MDNS_RR_CACHE_FLUSH_OR_QU : k->class;
+        r = dns_packet_append_uint16(p, class, NULL);
+        if (r < 0)
+                goto fail;
+
+        if (start)
+                *start = saved_size;
+
+        return 0;
+
+fail:
+        dns_packet_truncate(p, saved_size);
+        return r;
+}
+
+static int dns_packet_append_type_window(DnsPacket *p, uint8_t window, uint8_t length, const uint8_t *types, size_t *start) {
+        size_t saved_size;
+        int r;
+
+        assert(p);
+        assert(types);
+        assert(length > 0);
+
+        saved_size = p->size;
+
+        r = dns_packet_append_uint8(p, window, NULL);
+        if (r < 0)
+                goto fail;
+
+        r = dns_packet_append_uint8(p, length, NULL);
+        if (r < 0)
+                goto fail;
+
+        r = dns_packet_append_blob(p, types, length, NULL);
+        if (r < 0)
+                goto fail;
+
+        if (start)
+                *start = saved_size;
+
+        return 0;
+fail:
+        dns_packet_truncate(p, saved_size);
+        return r;
+}
+
+static int dns_packet_append_types(DnsPacket *p, Bitmap *types, size_t *start) {
+        uint8_t window = 0;
+        uint8_t entry = 0;
+        uint8_t bitmaps[32] = {};
+        unsigned n;
+        size_t saved_size;
+        int r;
+
+        assert(p);
+
+        saved_size = p->size;
+
+        BITMAP_FOREACH(n, types) {
+                assert(n <= 0xffff);
+
+                if ((n >> 8) != window && bitmaps[entry / 8] != 0) {
+                        r = dns_packet_append_type_window(p, window, entry / 8 + 1, bitmaps, NULL);
+                        if (r < 0)
+                                goto fail;
+
+                        zero(bitmaps);
+                }
+
+                window = n >> 8;
+                entry = n & 255;
+
+                bitmaps[entry / 8] |= 1 << (7 - (entry % 8));
+        }
+
+        if (bitmaps[entry / 8] != 0) {
+                r = dns_packet_append_type_window(p, window, entry / 8 + 1, bitmaps, NULL);
+                if (r < 0)
+                        goto fail;
+        }
+
+        if (start)
+                *start = saved_size;
+
+        return 0;
+fail:
+        dns_packet_truncate(p, saved_size);
+        return r;
+}
+
+/* Append the OPT pseudo-RR described in RFC6891 */
+int dns_packet_append_opt(
+                DnsPacket *p,
+                uint16_t max_udp_size,
+                bool edns0_do,
+                bool include_rfc6975,
+                const char *nsid,
+                int rcode,
+                size_t *ret_start) {
+
+        size_t saved_size;
+        int r;
+
+        assert(p);
+        /* we must never advertise supported packet size smaller than the legacy max */
+        assert(max_udp_size >= DNS_PACKET_UNICAST_SIZE_MAX);
+        assert(rcode >= 0);
+        assert(rcode <= _DNS_RCODE_MAX);
+
+        if (p->opt_start != SIZE_MAX)
+                return -EBUSY;
+
+        assert(p->opt_size == SIZE_MAX);
+
+        saved_size = p->size;
+
+        /* empty name */
+        r = dns_packet_append_uint8(p, 0, NULL);
+        if (r < 0)
+                return r;
+
+        /* type */
+        r = dns_packet_append_uint16(p, DNS_TYPE_OPT, NULL);
+        if (r < 0)
+                goto fail;
+
+        /* class: maximum udp packet that can be received */
+        r = dns_packet_append_uint16(p, max_udp_size, NULL);
+        if (r < 0)
+                goto fail;
+
+        /* extended RCODE and VERSION */
+        r = dns_packet_append_uint16(p, ((uint16_t) rcode & 0x0FF0) << 4, NULL);
+        if (r < 0)
+                goto fail;
+
+        /* flags: DNSSEC OK (DO), see RFC3225 */
+        r = dns_packet_append_uint16(p, edns0_do ? EDNS0_OPT_DO : 0, NULL);
+        if (r < 0)
+                goto fail;
+
+        if (edns0_do && include_rfc6975) {
+                /* If DO is on and this is requested, also append RFC6975 Algorithm data. This is supposed to
+                 * be done on queries, not on replies, hencer callers should turn this off when finishing off
+                 * replies. */
+
+                static const uint8_t rfc6975[] = {
+
+                        0, 5, /* OPTION_CODE: DAU */
+#if PREFER_OPENSSL || (HAVE_GCRYPT && GCRYPT_VERSION_NUMBER >= 0x010600)
+                        0, 7, /* LIST_LENGTH */
+#else
+                        0, 6, /* LIST_LENGTH */
+#endif
+                        DNSSEC_ALGORITHM_RSASHA1,
+                        DNSSEC_ALGORITHM_RSASHA1_NSEC3_SHA1,
+                        DNSSEC_ALGORITHM_RSASHA256,
+                        DNSSEC_ALGORITHM_RSASHA512,
+                        DNSSEC_ALGORITHM_ECDSAP256SHA256,
+                        DNSSEC_ALGORITHM_ECDSAP384SHA384,
+#if PREFER_OPENSSL || (HAVE_GCRYPT && GCRYPT_VERSION_NUMBER >= 0x010600)
+                        DNSSEC_ALGORITHM_ED25519,
+#endif
+
+                        0, 6, /* OPTION_CODE: DHU */
+                        0, 3, /* LIST_LENGTH */
+                        DNSSEC_DIGEST_SHA1,
+                        DNSSEC_DIGEST_SHA256,
+                        DNSSEC_DIGEST_SHA384,
+
+                        0, 7, /* OPTION_CODE: N3U */
+                        0, 1, /* LIST_LENGTH */
+                        NSEC3_ALGORITHM_SHA1,
+                };
+
+                r = dns_packet_append_uint16(p, sizeof(rfc6975), NULL); /* RDLENGTH */
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rfc6975, sizeof(rfc6975), NULL); /* the payload, as defined above */
+
+        } else if (nsid) {
+
+                if (strlen(nsid) > UINT16_MAX - 4) {
+                        r = -E2BIG;
+                        goto fail;
+                }
+
+                r = dns_packet_append_uint16(p, 4 + strlen(nsid), NULL); /* RDLENGTH */
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint16(p, 3, NULL); /* OPTION-CODE: NSID */
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint16(p, strlen(nsid), NULL); /* OPTION-LENGTH */
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, nsid, strlen(nsid), NULL);
+        } else
+                r = dns_packet_append_uint16(p, 0, NULL);
+        if (r < 0)
+                goto fail;
+
+        DNS_PACKET_HEADER(p)->arcount = htobe16(DNS_PACKET_ARCOUNT(p) + 1);
+
+        p->opt_start = saved_size;
+        p->opt_size = p->size - saved_size;
+
+        if (ret_start)
+                *ret_start = saved_size;
+
+        return 0;
+
+fail:
+        dns_packet_truncate(p, saved_size);
+        return r;
+}
+
+int dns_packet_truncate_opt(DnsPacket *p) {
+        assert(p);
+
+        if (p->opt_start == SIZE_MAX) {
+                assert(p->opt_size == SIZE_MAX);
+                return 0;
+        }
+
+        assert(p->opt_size != SIZE_MAX);
+        assert(DNS_PACKET_ARCOUNT(p) > 0);
+
+        if (p->opt_start + p->opt_size != p->size)
+                return -EBUSY;
+
+        dns_packet_truncate(p, p->opt_start);
+        DNS_PACKET_HEADER(p)->arcount = htobe16(DNS_PACKET_ARCOUNT(p) - 1);
+        p->opt_start = p->opt_size = SIZE_MAX;
+
+        return 1;
+}
+
+int dns_packet_append_rr(DnsPacket *p, const DnsResourceRecord *rr, const DnsAnswerFlags flags, size_t *start, size_t *rdata_start) {
+
+        size_t saved_size, rdlength_offset, end, rdlength, rds;
+        uint32_t ttl;
+        int r;
+
+        assert(p);
+        assert(rr);
+
+        saved_size = p->size;
+
+        r = dns_packet_append_key(p, rr->key, flags, NULL);
+        if (r < 0)
+                goto fail;
+
+        ttl = flags & DNS_ANSWER_GOODBYE ? 0 : rr->ttl;
+        r = dns_packet_append_uint32(p, ttl, NULL);
+        if (r < 0)
+                goto fail;
+
+        /* Initially we write 0 here */
+        r = dns_packet_append_uint16(p, 0, &rdlength_offset);
+        if (r < 0)
+                goto fail;
+
+        rds = p->size - saved_size;
+
+        switch (rr->unparsable ? _DNS_TYPE_INVALID : rr->key->type) {
+
+        case DNS_TYPE_SRV:
+                r = dns_packet_append_uint16(p, rr->srv.priority, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint16(p, rr->srv.weight, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint16(p, rr->srv.port, NULL);
+                if (r < 0)
+                        goto fail;
+
+                /* RFC 2782 states "Unless and until permitted by future standards action, name compression
+                 * is not to be used for this field." Hence we turn off compression here. */
+                r = dns_packet_append_name(p, rr->srv.name, /* allow_compression= */ false, /* canonical_candidate= */ true, NULL);
+                break;
+
+        case DNS_TYPE_PTR:
+        case DNS_TYPE_NS:
+        case DNS_TYPE_CNAME:
+        case DNS_TYPE_DNAME:
+                r = dns_packet_append_name(p, rr->ptr.name, true, true, NULL);
+                break;
+
+        case DNS_TYPE_HINFO:
+                r = dns_packet_append_string(p, rr->hinfo.cpu, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_string(p, rr->hinfo.os, NULL);
+                break;
+
+        case DNS_TYPE_SPF: /* exactly the same as TXT */
+        case DNS_TYPE_TXT:
+
+                if (!rr->txt.items) {
+                        /* RFC 6763, section 6.1 suggests to generate
+                         * single empty string for an empty array. */
+
+                        r = dns_packet_append_raw_string(p, NULL, 0, NULL);
+                        if (r < 0)
+                                goto fail;
+                } else
+                        LIST_FOREACH(items, i, rr->txt.items) {
+                                r = dns_packet_append_raw_string(p, i->data, i->length, NULL);
+                                if (r < 0)
+                                        goto fail;
+                        }
+
+                r = 0;
+                break;
+
+        case DNS_TYPE_A:
+                r = dns_packet_append_blob(p, &rr->a.in_addr, sizeof(struct in_addr), NULL);
+                break;
+
+        case DNS_TYPE_AAAA:
+                r = dns_packet_append_blob(p, &rr->aaaa.in6_addr, sizeof(struct in6_addr), NULL);
+                break;
+
+        case DNS_TYPE_SOA:
+                r = dns_packet_append_name(p, rr->soa.mname, true, true, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_name(p, rr->soa.rname, true, true, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->soa.serial, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->soa.refresh, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->soa.retry, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->soa.expire, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->soa.minimum, NULL);
+                break;
+
+        case DNS_TYPE_MX:
+                r = dns_packet_append_uint16(p, rr->mx.priority, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_name(p, rr->mx.exchange, true, true, NULL);
+                break;
+
+        case DNS_TYPE_LOC:
+                r = dns_packet_append_uint8(p, rr->loc.version, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->loc.size, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->loc.horiz_pre, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->loc.vert_pre, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->loc.latitude, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->loc.longitude, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->loc.altitude, NULL);
+                break;
+
+        case DNS_TYPE_DS:
+                r = dns_packet_append_uint16(p, rr->ds.key_tag, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->ds.algorithm, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->ds.digest_type, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->ds.digest, rr->ds.digest_size, NULL);
+                break;
+
+        case DNS_TYPE_SSHFP:
+                r = dns_packet_append_uint8(p, rr->sshfp.algorithm, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->sshfp.fptype, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->sshfp.fingerprint, rr->sshfp.fingerprint_size, NULL);
+                break;
+
+        case DNS_TYPE_DNSKEY:
+                r = dns_packet_append_uint16(p, rr->dnskey.flags, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->dnskey.protocol, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->dnskey.algorithm, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->dnskey.key, rr->dnskey.key_size, NULL);
+                break;
+
+        case DNS_TYPE_RRSIG:
+                r = dns_packet_append_uint16(p, rr->rrsig.type_covered, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->rrsig.algorithm, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->rrsig.labels, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->rrsig.original_ttl, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->rrsig.expiration, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint32(p, rr->rrsig.inception, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint16(p, rr->rrsig.key_tag, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_name(p, rr->rrsig.signer, false, true, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->rrsig.signature, rr->rrsig.signature_size, NULL);
+                break;
+
+        case DNS_TYPE_NSEC:
+                r = dns_packet_append_name(p, rr->nsec.next_domain_name, false, false, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_types(p, rr->nsec.types, NULL);
+                if (r < 0)
+                        goto fail;
+
+                break;
+
+        case DNS_TYPE_NSEC3:
+                r = dns_packet_append_uint8(p, rr->nsec3.algorithm, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->nsec3.flags, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint16(p, rr->nsec3.iterations, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->nsec3.salt_size, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->nsec3.salt, rr->nsec3.salt_size, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->nsec3.next_hashed_name_size, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->nsec3.next_hashed_name, rr->nsec3.next_hashed_name_size, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_types(p, rr->nsec3.types, NULL);
+                if (r < 0)
+                        goto fail;
+
+                break;
+
+        case DNS_TYPE_TLSA:
+                r = dns_packet_append_uint8(p, rr->tlsa.cert_usage, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->tlsa.selector, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_uint8(p, rr->tlsa.matching_type, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->tlsa.data, rr->tlsa.data_size, NULL);
+                break;
+
+        case DNS_TYPE_CAA:
+                r = dns_packet_append_uint8(p, rr->caa.flags, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_string(p, rr->caa.tag, NULL);
+                if (r < 0)
+                        goto fail;
+
+                r = dns_packet_append_blob(p, rr->caa.value, rr->caa.value_size, NULL);
+                break;
+
+        case DNS_TYPE_OPT:
+        case DNS_TYPE_OPENPGPKEY:
+        case _DNS_TYPE_INVALID: /* unparsable */
+        default:
+
+                r = dns_packet_append_blob(p, rr->generic.data, rr->generic.data_size, NULL);
+                break;
+        }
+        if (r < 0)
+                goto fail;
+
+        /* Let's calculate the actual data size and update the field */
+        rdlength = p->size - rdlength_offset - sizeof(uint16_t);
+        if (rdlength > 0xFFFF) {
+                r = -ENOSPC;
+                goto fail;
+        }
+
+        end = p->size;
+        p->size = rdlength_offset;
+        r = dns_packet_append_uint16(p, rdlength, NULL);
+        if (r < 0)
+                goto fail;
+        p->size = end;
+
+        if (start)
+                *start = saved_size;
+
+        if (rdata_start)
+                *rdata_start = rds;
+
+        return 0;
+
+fail:
+        dns_packet_truncate(p, saved_size);
+        return r;
+}
+
+int dns_packet_append_question(DnsPacket *p, DnsQuestion *q) {
+        DnsResourceKey *key;
+        int r;
+
+        assert(p);
+
+        DNS_QUESTION_FOREACH(key, q) {
+                r = dns_packet_append_key(p, key, 0, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+int dns_packet_append_answer(DnsPacket *p, DnsAnswer *a, unsigned *completed) {
+        DnsResourceRecord *rr;
+        DnsAnswerFlags flags;
+        int r;
+
+        assert(p);
+
+        DNS_ANSWER_FOREACH_FLAGS(rr, flags, a) {
+                r = dns_packet_append_rr(p, rr, flags, NULL, NULL);
+                if (r < 0)
+                        return r;
+
+                if (completed)
+                        (*completed)++;
+        }
+
+        return 0;
+}
+
+int dns_packet_read(DnsPacket *p, size_t sz, const void **ret, size_t *start) {
+        assert(p);
+        assert(p->rindex <= p->size);
+
+        if (sz > p->size - p->rindex)
+                return -EMSGSIZE;
+
+        if (ret)
+                *ret = (uint8_t*) DNS_PACKET_DATA(p) + p->rindex;
+
+        if (start)
+                *start = p->rindex;
+
+        p->rindex += sz;
+        return 0;
+}
+
+void dns_packet_rewind(DnsPacket *p, size_t idx) {
+        assert(p);
+        assert(idx <= p->size);
+        assert(idx >= DNS_PACKET_HEADER_SIZE);
+
+        p->rindex = idx;
+}
+
+int dns_packet_read_blob(DnsPacket *p, void *d, size_t sz, size_t *start) {
+        const void *q;
+        int r;
+
+        assert(p);
+        assert(d);
+
+        r = dns_packet_read(p, sz, &q, start);
+        if (r < 0)
+                return r;
+
+        memcpy(d, q, sz);
+        return 0;
+}
+
+static int dns_packet_read_memdup(
+                DnsPacket *p, size_t size,
+                void **ret, size_t *ret_size,
+                size_t *ret_start) {
+
+        const void *src;
+        size_t start;
+        int r;
+
+        assert(p);
+        assert(ret);
+
+        r = dns_packet_read(p, size, &src, &start);
+        if (r < 0)
+                return r;
+
+        if (size <= 0)
+                *ret = NULL;
+        else {
+                void *copy;
+
+                copy = memdup(src, size);
+                if (!copy)
+                        return -ENOMEM;
+
+                *ret = copy;
+        }
+
+        if (ret_size)
+                *ret_size = size;
+        if (ret_start)
+                *ret_start = start;
+
+        return 0;
+}
+
+int dns_packet_read_uint8(DnsPacket *p, uint8_t *ret, size_t *start) {
+        const void *d;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_read(p, sizeof(uint8_t), &d, start);
+        if (r < 0)
+                return r;
+
+        *ret = ((uint8_t*) d)[0];
+        return 0;
+}
+
+int dns_packet_read_uint16(DnsPacket *p, uint16_t *ret, size_t *start) {
+        const void *d;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_read(p, sizeof(uint16_t), &d, start);
+        if (r < 0)
+                return r;
+
+        if (ret)
+                *ret = unaligned_read_be16(d);
+
+        return 0;
+}
+
+int dns_packet_read_uint32(DnsPacket *p, uint32_t *ret, size_t *start) {
+        const void *d;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_read(p, sizeof(uint32_t), &d, start);
+        if (r < 0)
+                return r;
+
+        *ret = unaligned_read_be32(d);
+
+        return 0;
+}
+
+int dns_packet_read_string(DnsPacket *p, char **ret, size_t *start) {
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        _cleanup_free_ char *t = NULL;
+        const void *d;
+        uint8_t c;
+        int r;
+
+        assert(p);
+
+        r = dns_packet_read_uint8(p, &c, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read(p, c, &d, NULL);
+        if (r < 0)
+                return r;
+
+        r = make_cstring(d, c, MAKE_CSTRING_REFUSE_TRAILING_NUL, &t);
+        if (r < 0)
+                return r;
+
+        if (!utf8_is_valid(t))
+                return -EBADMSG;
+
+        *ret = TAKE_PTR(t);
+
+        if (start)
+                *start = rewinder.saved_rindex;
+        CANCEL_REWINDER(rewinder);
+
+        return 0;
+}
+
+int dns_packet_read_raw_string(DnsPacket *p, const void **ret, size_t *size, size_t *start) {
+        assert(p);
+
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        uint8_t c;
+        int r;
+
+        r = dns_packet_read_uint8(p, &c, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read(p, c, ret, NULL);
+        if (r < 0)
+                return r;
+
+        if (size)
+                *size = c;
+        if (start)
+                *start = rewinder.saved_rindex;
+        CANCEL_REWINDER(rewinder);
+
+        return 0;
+}
+
+int dns_packet_read_name(
+                DnsPacket *p,
+                char **ret,
+                bool allow_compression,
+                size_t *ret_start) {
+
+        assert(p);
+
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        size_t after_rindex = 0, jump_barrier = p->rindex;
+        _cleanup_free_ char *name = NULL;
+        bool first = true;
+        size_t n = 0;
+        int r;
+
+        if (p->refuse_compression)
+                allow_compression = false;
+
+        for (;;) {
+                uint8_t c, d;
+
+                r = dns_packet_read_uint8(p, &c, NULL);
+                if (r < 0)
+                        return r;
+
+                if (c == 0)
+                        /* End of name */
+                        break;
+                else if (c <= 63) {
+                        const char *label;
+
+                        /* Literal label */
+                        r = dns_packet_read(p, c, (const void**) &label, NULL);
+                        if (r < 0)
+                                return r;
+
+                        if (!GREEDY_REALLOC(name, n + !first + DNS_LABEL_ESCAPED_MAX))
+                                return -ENOMEM;
+
+                        if (first)
+                                first = false;
+                        else
+                                name[n++] = '.';
+
+                        r = dns_label_escape(label, c, name + n, DNS_LABEL_ESCAPED_MAX);
+                        if (r < 0)
+                                return r;
+
+                        n += r;
+                        continue;
+                } else if (allow_compression && FLAGS_SET(c, 0xc0)) {
+                        uint16_t ptr;
+
+                        /* Pointer */
+                        r = dns_packet_read_uint8(p, &d, NULL);
+                        if (r < 0)
+                                return r;
+
+                        ptr = (uint16_t) (c & ~0xc0) << 8 | (uint16_t) d;
+                        if (ptr < DNS_PACKET_HEADER_SIZE || ptr >= jump_barrier)
+                                return -EBADMSG;
+
+                        if (after_rindex == 0)
+                                after_rindex = p->rindex;
+
+                        /* Jumps are limited to a "prior occurrence" (RFC-1035 4.1.4) */
+                        jump_barrier = ptr;
+                        p->rindex = ptr;
+                } else
+                        return -EBADMSG;
+        }
+
+        if (!GREEDY_REALLOC(name, n + 1))
+                return -ENOMEM;
+
+        name[n] = 0;
+
+        if (after_rindex != 0)
+                p->rindex= after_rindex;
+
+        if (ret)
+                *ret = TAKE_PTR(name);
+        if (ret_start)
+                *ret_start = rewinder.saved_rindex;
+
+        CANCEL_REWINDER(rewinder);
+
+        return 0;
+}
+
+static int dns_packet_read_type_window(DnsPacket *p, Bitmap **types, size_t *start) {
+        assert(p);
+        assert(types);
+
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        uint8_t window, length;
+        const uint8_t *bitmap;
+        uint8_t bit = 0;
+        bool found = false;
+        int r;
+
+        r = bitmap_ensure_allocated(types);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint8(p, &window, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint8(p, &length, NULL);
+        if (r < 0)
+                return r;
+
+        if (length == 0 || length > 32)
+                return -EBADMSG;
+
+        r = dns_packet_read(p, length, (const void **)&bitmap, NULL);
+        if (r < 0)
+                return r;
+
+        for (uint8_t i = 0; i < length; i++) {
+                uint8_t bitmask = 1 << 7;
+
+                if (!bitmap[i]) {
+                        found = false;
+                        bit += 8;
+                        continue;
+                }
+
+                found = true;
+
+                for (; bitmask; bit++, bitmask >>= 1)
+                        if (bitmap[i] & bitmask) {
+                                uint16_t n;
+
+                                n = (uint16_t) window << 8 | (uint16_t) bit;
+
+                                /* Ignore pseudo-types. see RFC4034 section 4.1.2 */
+                                if (dns_type_is_pseudo(n))
+                                        continue;
+
+                                r = bitmap_set(*types, n);
+                                if (r < 0)
+                                        return r;
+                        }
+        }
+
+        if (!found)
+                return -EBADMSG;
+
+        if (start)
+                *start = rewinder.saved_rindex;
+        CANCEL_REWINDER(rewinder);
+
+        return 0;
+}
+
+static int dns_packet_read_type_windows(DnsPacket *p, Bitmap **types, size_t size, size_t *start) {
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        int r;
+
+        while (p->rindex - rewinder.saved_rindex < size) {
+                r = dns_packet_read_type_window(p, types, NULL);
+                if (r < 0)
+                        return r;
+
+                assert(p->rindex >= rewinder.saved_rindex);
+
+                /* don't read past end of current RR */
+                if (p->rindex - rewinder.saved_rindex > size)
+                        return -EBADMSG;
+        }
+
+        if (p->rindex - rewinder.saved_rindex != size)
+                return -EBADMSG;
+
+        if (start)
+                *start = rewinder.saved_rindex;
+        CANCEL_REWINDER(rewinder);
+
+        return 0;
+}
+
+int dns_packet_read_key(
+                DnsPacket *p,
+                DnsResourceKey **ret,
+                bool *ret_cache_flush_or_qu,
+                size_t *ret_start) {
+
+        assert(p);
+
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        _cleanup_free_ char *name = NULL;
+        bool cache_flush_or_qu = false;
+        uint16_t class, type;
+        int r;
+
+        r = dns_packet_read_name(p, &name, true, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint16(p, &type, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint16(p, &class, NULL);
+        if (r < 0)
+                return r;
+
+        if (p->protocol == DNS_PROTOCOL_MDNS) {
+                /* See RFC6762, sections 5.4 and 10.2 */
+
+                if (type != DNS_TYPE_OPT && (class & MDNS_RR_CACHE_FLUSH_OR_QU)) {
+                        class &= ~MDNS_RR_CACHE_FLUSH_OR_QU;
+                        cache_flush_or_qu = true;
+                }
+        }
+
+        if (ret) {
+                DnsResourceKey *key;
+
+                key = dns_resource_key_new_consume(class, type, name);
+                if (!key)
+                        return -ENOMEM;
+
+                TAKE_PTR(name);
+                *ret = key;
+        }
+
+        if (ret_cache_flush_or_qu)
+                *ret_cache_flush_or_qu = cache_flush_or_qu;
+        if (ret_start)
+                *ret_start = rewinder.saved_rindex;
+
+        CANCEL_REWINDER(rewinder);
+        return 0;
+}
+
+static bool loc_size_ok(uint8_t size) {
+        uint8_t m = size >> 4, e = size & 0xF;
+
+        return m <= 9 && e <= 9 && (m > 0 || e == 0);
+}
+
+int dns_packet_read_rr(
+                DnsPacket *p,
+                DnsResourceRecord **ret,
+                bool *ret_cache_flush,
+                size_t *ret_start) {
+
+        assert(p);
+
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
+        size_t offset;
+        uint16_t rdlength;
+        bool cache_flush;
+        int r;
+
+        r = dns_packet_read_key(p, &key, &cache_flush, NULL);
+        if (r < 0)
+                return r;
+
+        if (!dns_class_is_valid_rr(key->class) || !dns_type_is_valid_rr(key->type))
+                return -EBADMSG;
+
+        rr = dns_resource_record_new(key);
+        if (!rr)
+                return -ENOMEM;
+
+        r = dns_packet_read_uint32(p, &rr->ttl, NULL);
+        if (r < 0)
+                return r;
+
+        /* RFC 2181, Section 8, suggests to
+         * treat a TTL with the MSB set as a zero TTL. */
+        if (rr->ttl & UINT32_C(0x80000000))
+                rr->ttl = 0;
+
+        r = dns_packet_read_uint16(p, &rdlength, NULL);
+        if (r < 0)
+                return r;
+
+        if (rdlength > p->size - p->rindex)
+                return -EBADMSG;
+
+        offset = p->rindex;
+
+        switch (rr->key->type) {
+
+        case DNS_TYPE_SRV:
+                r = dns_packet_read_uint16(p, &rr->srv.priority, NULL);
+                if (r < 0)
+                        return r;
+                r = dns_packet_read_uint16(p, &rr->srv.weight, NULL);
+                if (r < 0)
+                        return r;
+                r = dns_packet_read_uint16(p, &rr->srv.port, NULL);
+                if (r < 0)
+                        return r;
+
+                /* RFC 2782 states "Unless and until permitted by future standards action, name compression
+                 * is not to be used for this field." Nonetheless, we support it here, in the interest of
+                 * increasing compatibility with implementations that do not implement this correctly. After
+                 * all we didn't do this right once upon a time ourselves (see
+                 * https://github.com/systemd/systemd/issues/9793). */
+                r = dns_packet_read_name(p, &rr->srv.name, /* allow_compression= */ true, NULL);
+                break;
+
+        case DNS_TYPE_PTR:
+        case DNS_TYPE_NS:
+        case DNS_TYPE_CNAME:
+        case DNS_TYPE_DNAME:
+                r = dns_packet_read_name(p, &rr->ptr.name, true, NULL);
+                break;
+
+        case DNS_TYPE_HINFO:
+                r = dns_packet_read_string(p, &rr->hinfo.cpu, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_string(p, &rr->hinfo.os, NULL);
+                break;
+
+        case DNS_TYPE_SPF: /* exactly the same as TXT */
+        case DNS_TYPE_TXT:
+                if (rdlength <= 0) {
+                        r = dns_txt_item_new_empty(&rr->txt.items);
+                        if (r < 0)
+                                return r;
+                } else {
+                        DnsTxtItem *last = NULL;
+
+                        while (p->rindex - offset < rdlength) {
+                                DnsTxtItem *i;
+                                const void *data;
+                                size_t sz;
+
+                                r = dns_packet_read_raw_string(p, &data, &sz, NULL);
+                                if (r < 0)
+                                        return r;
+
+                                i = malloc0(offsetof(DnsTxtItem, data) + sz + 1); /* extra NUL byte at the end */
+                                if (!i)
+                                        return -ENOMEM;
+
+                                memcpy(i->data, data, sz);
+                                i->length = sz;
+
+                                LIST_INSERT_AFTER(items, rr->txt.items, last, i);
+                                last = i;
+                        }
+                }
+
+                r = 0;
+                break;
+
+        case DNS_TYPE_A:
+                r = dns_packet_read_blob(p, &rr->a.in_addr, sizeof(struct in_addr), NULL);
+                break;
+
+        case DNS_TYPE_AAAA:
+                r = dns_packet_read_blob(p, &rr->aaaa.in6_addr, sizeof(struct in6_addr), NULL);
+                break;
+
+        case DNS_TYPE_SOA:
+                r = dns_packet_read_name(p, &rr->soa.mname, true, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_name(p, &rr->soa.rname, true, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->soa.serial, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->soa.refresh, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->soa.retry, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->soa.expire, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->soa.minimum, NULL);
+                break;
+
+        case DNS_TYPE_MX:
+                r = dns_packet_read_uint16(p, &rr->mx.priority, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_name(p, &rr->mx.exchange, true, NULL);
+                break;
+
+        case DNS_TYPE_LOC: {
+                uint8_t t;
+                size_t pos;
+
+                r = dns_packet_read_uint8(p, &t, &pos);
+                if (r < 0)
+                        return r;
+
+                if (t == 0) {
+                        rr->loc.version = t;
+
+                        r = dns_packet_read_uint8(p, &rr->loc.size, NULL);
+                        if (r < 0)
+                                return r;
+
+                        if (!loc_size_ok(rr->loc.size))
+                                return -EBADMSG;
+
+                        r = dns_packet_read_uint8(p, &rr->loc.horiz_pre, NULL);
+                        if (r < 0)
+                                return r;
+
+                        if (!loc_size_ok(rr->loc.horiz_pre))
+                                return -EBADMSG;
+
+                        r = dns_packet_read_uint8(p, &rr->loc.vert_pre, NULL);
+                        if (r < 0)
+                                return r;
+
+                        if (!loc_size_ok(rr->loc.vert_pre))
+                                return -EBADMSG;
+
+                        r = dns_packet_read_uint32(p, &rr->loc.latitude, NULL);
+                        if (r < 0)
+                                return r;
+
+                        r = dns_packet_read_uint32(p, &rr->loc.longitude, NULL);
+                        if (r < 0)
+                                return r;
+
+                        r = dns_packet_read_uint32(p, &rr->loc.altitude, NULL);
+                        if (r < 0)
+                                return r;
+
+                        break;
+                } else {
+                        dns_packet_rewind(p, pos);
+                        rr->unparsable = true;
+                        goto unparsable;
+                }
+        }
+
+        case DNS_TYPE_DS:
+                r = dns_packet_read_uint16(p, &rr->ds.key_tag, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->ds.algorithm, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->ds.digest_type, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < 4)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p, rdlength - 4,
+                                           &rr->ds.digest, &rr->ds.digest_size,
+                                           NULL);
+                if (r < 0)
+                        return r;
+
+                if (rr->ds.digest_size <= 0)
+                        /* the accepted size depends on the algorithm, but for now
+                           just ensure that the value is greater than zero */
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_TYPE_SSHFP:
+                r = dns_packet_read_uint8(p, &rr->sshfp.algorithm, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->sshfp.fptype, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < 2)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p, rdlength - 2,
+                                           &rr->sshfp.fingerprint, &rr->sshfp.fingerprint_size,
+                                           NULL);
+
+                if (rr->sshfp.fingerprint_size <= 0)
+                        /* the accepted size depends on the algorithm, but for now
+                           just ensure that the value is greater than zero */
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_TYPE_DNSKEY:
+                r = dns_packet_read_uint16(p, &rr->dnskey.flags, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->dnskey.protocol, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->dnskey.algorithm, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < 4)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p, rdlength - 4,
+                                           &rr->dnskey.key, &rr->dnskey.key_size,
+                                           NULL);
+
+                if (rr->dnskey.key_size <= 0)
+                        /* the accepted size depends on the algorithm, but for now
+                           just ensure that the value is greater than zero */
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_TYPE_RRSIG:
+                r = dns_packet_read_uint16(p, &rr->rrsig.type_covered, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->rrsig.algorithm, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->rrsig.labels, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->rrsig.original_ttl, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->rrsig.expiration, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint32(p, &rr->rrsig.inception, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint16(p, &rr->rrsig.key_tag, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_name(p, &rr->rrsig.signer, false, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < p->rindex - offset)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p, offset + rdlength - p->rindex,
+                                           &rr->rrsig.signature, &rr->rrsig.signature_size,
+                                           NULL);
+
+                if (rr->rrsig.signature_size <= 0)
+                        /* the accepted size depends on the algorithm, but for now
+                           just ensure that the value is greater than zero */
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_TYPE_NSEC: {
+
+                /*
+                 * RFC6762, section 18.14 explicitly states mDNS should use name compression.
+                 * This contradicts RFC3845, section 2.1.1
+                 */
+
+                bool allow_compressed = p->protocol == DNS_PROTOCOL_MDNS;
+
+                r = dns_packet_read_name(p, &rr->nsec.next_domain_name, allow_compressed, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < p->rindex - offset)
+                        return -EBADMSG;
+
+                r = dns_packet_read_type_windows(p, &rr->nsec.types, offset + rdlength - p->rindex, NULL);
+
+                /* We accept empty NSEC bitmaps. The bit indicating the presence of the NSEC record itself
+                 * is redundant and in e.g., RFC4956 this fact is used to define a use for NSEC records
+                 * without the NSEC bit set. */
+
+                break;
+        }
+        case DNS_TYPE_NSEC3: {
+                uint8_t size;
+
+                r = dns_packet_read_uint8(p, &rr->nsec3.algorithm, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->nsec3.flags, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint16(p, &rr->nsec3.iterations, NULL);
+                if (r < 0)
+                        return r;
+
+                /* this may be zero */
+                r = dns_packet_read_uint8(p, &size, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_memdup(p, size, &rr->nsec3.salt, &rr->nsec3.salt_size, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &size, NULL);
+                if (r < 0)
+                        return r;
+
+                if (size <= 0)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p, size,
+                                           &rr->nsec3.next_hashed_name, &rr->nsec3.next_hashed_name_size,
+                                           NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < p->rindex - offset)
+                        return -EBADMSG;
+
+                r = dns_packet_read_type_windows(p, &rr->nsec3.types, offset + rdlength - p->rindex, NULL);
+
+                /* empty non-terminals can have NSEC3 records, so empty bitmaps are allowed */
+
+                break;
+        }
+
+        case DNS_TYPE_TLSA:
+                r = dns_packet_read_uint8(p, &rr->tlsa.cert_usage, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->tlsa.selector, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_uint8(p, &rr->tlsa.matching_type, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < 3)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p, rdlength - 3,
+                                           &rr->tlsa.data, &rr->tlsa.data_size,
+                                           NULL);
+
+                if (rr->tlsa.data_size <= 0)
+                        /* the accepted size depends on the algorithm, but for now
+                           just ensure that the value is greater than zero */
+                        return -EBADMSG;
+
+                break;
+
+        case DNS_TYPE_CAA:
+                r = dns_packet_read_uint8(p, &rr->caa.flags, NULL);
+                if (r < 0)
+                        return r;
+
+                r = dns_packet_read_string(p, &rr->caa.tag, NULL);
+                if (r < 0)
+                        return r;
+
+                if (rdlength < p->rindex - offset)
+                        return -EBADMSG;
+
+                r = dns_packet_read_memdup(p,
+                                           rdlength + offset - p->rindex,
+                                           &rr->caa.value, &rr->caa.value_size, NULL);
+
+                break;
+
+        case DNS_TYPE_OPT: /* we only care about the header of OPT for now. */
+        case DNS_TYPE_OPENPGPKEY:
+        default:
+        unparsable:
+                r = dns_packet_read_memdup(p, rdlength, &rr->generic.data, &rr->generic.data_size, NULL);
+
+                break;
+        }
+        if (r < 0)
+                return r;
+        if (p->rindex - offset != rdlength)
+                return -EBADMSG;
+
+        if (ret)
+                *ret = TAKE_PTR(rr);
+        if (ret_cache_flush)
+                *ret_cache_flush = cache_flush;
+        if (ret_start)
+                *ret_start = rewinder.saved_rindex;
+
+        CANCEL_REWINDER(rewinder);
+        return 0;
+}
+
+static bool opt_is_good(DnsResourceRecord *rr, bool *rfc6975) {
+        const uint8_t* p;
+        bool found_dau_dhu_n3u = false;
+        size_t l;
+
+        /* Checks whether the specified OPT RR is well-formed and whether it contains RFC6975 data (which is not OK in
+         * a reply). */
+
+        assert(rr);
+        assert(rr->key->type == DNS_TYPE_OPT);
+
+        /* Check that the version is 0 */
+        if (((rr->ttl >> 16) & UINT32_C(0xFF)) != 0) {
+                *rfc6975 = false;
+                return true; /* if it's not version 0, it's OK, but we will ignore the OPT field contents */
+        }
+
+        p = rr->opt.data;
+        l = rr->opt.data_size;
+        while (l > 0) {
+                uint16_t option_code, option_length;
+
+                /* At least four bytes for OPTION-CODE and OPTION-LENGTH are required */
+                if (l < 4U)
+                        return false;
+
+                option_code = unaligned_read_be16(p);
+                option_length = unaligned_read_be16(p + 2);
+
+                if (l < option_length + 4U)
+                        return false;
+
+                /* RFC 6975 DAU, DHU or N3U fields found. */
+                if (IN_SET(option_code, 5, 6, 7))
+                        found_dau_dhu_n3u = true;
+
+                p += option_length + 4U;
+                l -= option_length + 4U;
+        }
+
+        *rfc6975 = found_dau_dhu_n3u;
+        return true;
+}
+
+static int dns_packet_extract_question(DnsPacket *p, DnsQuestion **ret_question) {
+        _cleanup_(dns_question_unrefp) DnsQuestion *question = NULL;
+        unsigned n;
+        int r;
+
+        n = DNS_PACKET_QDCOUNT(p);
+        if (n > 0) {
+                question = dns_question_new(n);
+                if (!question)
+                        return -ENOMEM;
+
+                _cleanup_set_free_ Set *keys = NULL; /* references to keys are kept by Question */
+
+                keys = set_new(&dns_resource_key_hash_ops);
+                if (!keys)
+                        return log_oom();
+
+                r = set_reserve(keys, n * 2); /* Higher multipliers give slightly higher efficiency through
+                                               * hash collisions, but the gains quickly drop off after 2. */
+                if (r < 0)
+                        return r;
+
+                for (unsigned i = 0; i < n; i++) {
+                        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
+                        bool qu;
+
+                        r = dns_packet_read_key(p, &key, &qu, NULL);
+                        if (r < 0)
+                                return r;
+
+                        if (!dns_type_is_valid_query(key->type))
+                                return -EBADMSG;
+
+                        r = set_put(keys, key);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                /* Already in the Question, let's skip */
+                                continue;
+
+                        r = dns_question_add_raw(question, key, qu ? DNS_QUESTION_WANTS_UNICAST_REPLY : 0);
+                        if (r < 0)
+                                return r;
+                }
+        }
+
+        *ret_question = TAKE_PTR(question);
+
+        return 0;
+}
+
+static int dns_packet_extract_answer(DnsPacket *p, DnsAnswer **ret_answer) {
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        unsigned n;
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *previous = NULL;
+        bool bad_opt = false;
+        int r;
+
+        n = DNS_PACKET_RRCOUNT(p);
+        if (n == 0)
+                return 0;
+
+        answer = dns_answer_new(n);
+        if (!answer)
+                return -ENOMEM;
+
+        for (unsigned i = 0; i < n; i++) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+                bool cache_flush = false;
+                size_t start;
+
+                if (p->rindex == p->size && p->opt) {
+                        /* If we reached the end of the packet already, but there are still more RRs
+                         * declared, then that's a corrupt packet. Let's accept the packet anyway, since it's
+                         * apparently a common bug in routers. Let's however suppress OPT support in this
+                         * case, so that we force the rest of the logic into lowest DNS baseline support. Or
+                         * to say this differently: if the DNS server doesn't even get the RR counts right,
+                         * it's highly unlikely it gets EDNS right. */
+                        log_debug("More resource records declared in packet than included, suppressing OPT.");
+                        bad_opt = true;
+                        break;
+                }
+
+                r = dns_packet_read_rr(p, &rr, &cache_flush, &start);
+                if (r < 0)
+                        return r;
+
+                /* Try to reduce memory usage a bit */
+                if (previous)
+                        dns_resource_key_reduce(&rr->key, &previous->key);
+
+                if (rr->key->type == DNS_TYPE_OPT) {
+                        bool has_rfc6975;
+
+                        if (p->opt || bad_opt) {
+                                /* Multiple OPT RRs? if so, let's ignore all, because there's
+                                 * something wrong with the server, and if one is valid we wouldn't
+                                 * know which one. */
+                                log_debug("Multiple OPT RRs detected, ignoring all.");
+                                bad_opt = true;
+                                continue;
+                        }
+
+                        if (!dns_name_is_root(dns_resource_key_name(rr->key))) {
+                                /* If the OPT RR is not owned by the root domain, then it is bad,
+                                 * let's ignore it. */
+                                log_debug("OPT RR is not owned by root domain, ignoring.");
+                                bad_opt = true;
+                                continue;
+                        }
+
+                        if (i < DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p)) {
+                                /* OPT RR is in the wrong section? Some Belkin routers do this. This
+                                 * is a hint the EDNS implementation is borked, like the Belkin one
+                                 * is, hence ignore it. */
+                                log_debug("OPT RR in wrong section, ignoring.");
+                                bad_opt = true;
+                                continue;
+                        }
+
+                        if (!opt_is_good(rr, &has_rfc6975)) {
+                                log_debug("Malformed OPT RR, ignoring.");
+                                bad_opt = true;
+                                continue;
+                        }
+
+                        if (DNS_PACKET_QR(p)) {
+                                /* Additional checks for responses */
+
+                                if (!DNS_RESOURCE_RECORD_OPT_VERSION_SUPPORTED(rr))
+                                        /* If this is a reply and we don't know the EDNS version
+                                         * then something is weird... */
+                                        return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG),
+                                                               "EDNS version newer that our request, bad server.");
+
+                                if (has_rfc6975) {
+                                        /* If the OPT RR contains RFC6975 algorithm data, then this
+                                         * is indication that the server just copied the OPT it got
+                                         * from us (which contained that data) back into the reply.
+                                         * If so, then it doesn't properly support EDNS, as RFC6975
+                                         * makes it very clear that the algorithm data should only
+                                         * be contained in questions, never in replies. Crappy
+                                         * Belkin routers copy the OPT data for example, hence let's
+                                         * detect this so that we downgrade early. */
+                                        log_debug("OPT RR contains RFC6975 data, ignoring.");
+                                        bad_opt = true;
+                                        continue;
+                                }
+                        }
+
+                        p->opt = dns_resource_record_ref(rr);
+                        p->opt_start = start;
+                        assert(p->rindex >= start);
+                        p->opt_size = p->rindex - start;
+                } else {
+                        DnsAnswerFlags flags = 0;
+
+                        if (p->protocol == DNS_PROTOCOL_MDNS) {
+                                flags |= DNS_ANSWER_REFUSE_TTL_NO_MATCH;
+                                if (!cache_flush)
+                                        flags |= DNS_ANSWER_SHARED_OWNER;
+                        }
+
+                        /* According to RFC 4795, section 2.9. only the RRs from the Answer section shall be
+                         * cached. Hence mark only those RRs as cacheable by default, but not the ones from
+                         * the Additional or Authority sections.
+                         * This restriction does not apply to mDNS records (RFC 6762). */
+                        if (i < DNS_PACKET_ANCOUNT(p))
+                                flags |= DNS_ANSWER_CACHEABLE|DNS_ANSWER_SECTION_ANSWER;
+                        else if (i < DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p))
+                                flags |= DNS_ANSWER_SECTION_AUTHORITY;
+                        else {
+                                flags |= DNS_ANSWER_SECTION_ADDITIONAL;
+                                if (p->protocol == DNS_PROTOCOL_MDNS)
+                                        flags |= DNS_ANSWER_CACHEABLE;
+                        }
+
+                        r = dns_answer_add(answer, rr, p->ifindex, flags, NULL);
+                        if (r < 0)
+                                return r;
+                }
+
+                /* Remember this RR, so that we can potentially merge its ->key object with the
+                 * next RR. Note that we only do this if we actually decided to keep the RR around.
+                 */
+                DNS_RR_REPLACE(previous, dns_resource_record_ref(rr));
+        }
+
+        if (bad_opt) {
+                p->opt = dns_resource_record_unref(p->opt);
+                p->opt_start = p->opt_size = SIZE_MAX;
+        }
+
+        *ret_answer = TAKE_PTR(answer);
+
+        return 0;
+}
+
+int dns_packet_extract(DnsPacket *p) {
+        assert(p);
+
+        if (p->extracted)
+                return 0;
+
+        _cleanup_(dns_question_unrefp) DnsQuestion *question = NULL;
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        _unused_ _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        int r;
+
+        dns_packet_rewind(p, DNS_PACKET_HEADER_SIZE);
+
+        r = dns_packet_extract_question(p, &question);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_extract_answer(p, &answer);
+        if (r < 0)
+                return r;
+
+        if (p->rindex < p->size)  {
+                log_debug("Trailing garbage in packet, suppressing OPT.");
+                p->opt = dns_resource_record_unref(p->opt);
+                p->opt_start = p->opt_size = SIZE_MAX;
+        }
+
+        p->question = TAKE_PTR(question);
+        p->answer = TAKE_PTR(answer);
+        p->extracted = true;
+
+        /* no CANCEL, always rewind */
+        return 0;
+}
+
+int dns_packet_is_reply_for(DnsPacket *p, const DnsResourceKey *key) {
+        int r;
+
+        assert(p);
+        assert(key);
+
+        /* Checks if the specified packet is a reply for the specified
+         * key and the specified key is the only one in the question
+         * section. */
+
+        if (DNS_PACKET_QR(p) != 1)
+                return 0;
+
+        /* Let's unpack the packet, if that hasn't happened yet. */
+        r = dns_packet_extract(p);
+        if (r < 0)
+                return r;
+
+        if (!p->question)
+                return 0;
+
+        if (p->question->n_keys != 1)
+                return 0;
+
+        return dns_resource_key_equal(dns_question_first_key(p->question), key);
+}
+
+int dns_packet_patch_max_udp_size(DnsPacket *p, uint16_t max_udp_size) {
+        assert(p);
+        assert(max_udp_size >= DNS_PACKET_UNICAST_SIZE_MAX);
+
+        if (p->opt_start == SIZE_MAX) /* No OPT section, nothing to patch */
+                return 0;
+
+        assert(p->opt_size != SIZE_MAX);
+        assert(p->opt_size >= 5);
+
+        unaligned_write_be16(DNS_PACKET_DATA(p) + p->opt_start + 3, max_udp_size);
+        return 1;
+}
+
+static int patch_rr(DnsPacket *p, usec_t age) {
+        _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        size_t ttl_index;
+        uint32_t ttl;
+        uint16_t type, rdlength;
+        int r;
+
+        /* Patches the RR at the current rindex, subtracts the specified time from the TTL */
+
+        r = dns_packet_read_name(p, NULL, true, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint16(p, &type, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint16(p, NULL, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read_uint32(p, &ttl, &ttl_index);
+        if (r < 0)
+                return r;
+
+        if (type != DNS_TYPE_OPT) { /* The TTL of the OPT field is not actually a TTL, skip it */
+                ttl = LESS_BY(ttl * USEC_PER_SEC, age) / USEC_PER_SEC;
+                unaligned_write_be32(DNS_PACKET_DATA(p) + ttl_index, ttl);
+        }
+
+        r = dns_packet_read_uint16(p, &rdlength, NULL);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_read(p, rdlength, NULL, NULL);
+        if (r < 0)
+                return r;
+
+        CANCEL_REWINDER(rewinder);
+        return 0;
+}
+
+int dns_packet_patch_ttls(DnsPacket *p, usec_t timestamp) {
+        assert(p);
+        assert(timestamp_is_set(timestamp));
+
+        /* Adjusts all TTLs in the packet by subtracting the time difference between now and the specified timestamp */
+
+        _unused_ _cleanup_(rewind_dns_packet) DnsPacketRewinder rewinder = REWINDER_INIT(p);
+        unsigned n;
+        usec_t k;
+        int r;
+
+        k = now(CLOCK_BOOTTIME);
+        assert(k >= timestamp);
+        k -= timestamp;
+
+        dns_packet_rewind(p, DNS_PACKET_HEADER_SIZE);
+
+        n = DNS_PACKET_QDCOUNT(p);
+        for (unsigned i = 0; i < n; i++) {
+                r = dns_packet_read_key(p, NULL, NULL, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        n = DNS_PACKET_RRCOUNT(p);
+        for (unsigned i = 0; i < n; i++) {
+
+                /* DNS servers suck, hence the RR count is in many servers off. If we reached the end
+                 * prematurely, accept that, exit early */
+                if (p->rindex == p->size)
+                        break;
+
+                r = patch_rr(p, k);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static void dns_packet_hash_func(const DnsPacket *s, struct siphash *state) {
+        assert(s);
+
+        siphash24_compress(&s->size, sizeof(s->size), state);
+        siphash24_compress(DNS_PACKET_DATA((DnsPacket*) s), s->size, state);
+}
+
+static int dns_packet_compare_func(const DnsPacket *x, const DnsPacket *y) {
+        int r;
+
+        r = CMP(x->size, y->size);
+        if (r != 0)
+                return r;
+
+        return memcmp(DNS_PACKET_DATA((DnsPacket*) x), DNS_PACKET_DATA((DnsPacket*) y), x->size);
+}
+
+DEFINE_HASH_OPS(dns_packet_hash_ops, DnsPacket, dns_packet_hash_func, dns_packet_compare_func);
+
+bool dns_packet_equal(const DnsPacket *a, const DnsPacket *b) {
+        return dns_packet_compare_func(a, b) == 0;
+}
+
+int dns_packet_has_nsid_request(DnsPacket *p) {
+        bool has_nsid = false;
+        const uint8_t *d;
+        size_t l;
+
+        assert(p);
+
+        if (!p->opt)
+                return false;
+
+        d = p->opt->opt.data;
+        l = p->opt->opt.data_size;
+
+        while (l > 0) {
+                uint16_t code, length;
+
+                if (l < 4U)
+                        return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG),
+                                               "EDNS0 variable part has invalid size.");
+
+                code = unaligned_read_be16(d);
+                length = unaligned_read_be16(d + 2);
+
+                if (l < 4U + length)
+                        return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG),
+                                               "Truncated option in EDNS0 variable part.");
+
+                if (code == 3) {
+                        if (has_nsid)
+                                return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG),
+                                                       "Duplicate NSID option in EDNS0 variable part.");
+
+                        if (length != 0)
+                                return log_debug_errno(SYNTHETIC_ERRNO(EBADMSG),
+                                                       "Non-empty NSID option in DNS request.");
+
+                        has_nsid = true;
+                }
+
+                d += 4U + length;
+                l -= 4U + length;
+        }
+
+        return has_nsid;
+}
+
+size_t dns_packet_size_unfragmented(DnsPacket *p) {
+        assert(p);
+
+        if (p->fragsize == 0) /* Wasn't fragmented */
+                return p->size;
+
+        /* The fragment size (p->fragsize) covers the whole (fragmented) IP packet, while the regular packet
+         * size (p->size) only covers the DNS part. Thus, subtract the UDP header from the largest fragment
+         * size, in order to determine which size of DNS packet would have gone through without
+         * fragmenting. */
+
+        return LESS_BY(p->fragsize, udp_header_size(p->family));
+}
+
+static const char* const dns_rcode_table[_DNS_RCODE_MAX_DEFINED] = {
+        [DNS_RCODE_SUCCESS]   = "SUCCESS",
+        [DNS_RCODE_FORMERR]   = "FORMERR",
+        [DNS_RCODE_SERVFAIL]  = "SERVFAIL",
+        [DNS_RCODE_NXDOMAIN]  = "NXDOMAIN",
+        [DNS_RCODE_NOTIMP]    = "NOTIMP",
+        [DNS_RCODE_REFUSED]   = "REFUSED",
+        [DNS_RCODE_YXDOMAIN]  = "YXDOMAIN",
+        [DNS_RCODE_YXRRSET]   = "YRRSET",
+        [DNS_RCODE_NXRRSET]   = "NXRRSET",
+        [DNS_RCODE_NOTAUTH]   = "NOTAUTH",
+        [DNS_RCODE_NOTZONE]   = "NOTZONE",
+        [DNS_RCODE_BADVERS]   = "BADVERS",
+        [DNS_RCODE_BADKEY]    = "BADKEY",
+        [DNS_RCODE_BADTIME]   = "BADTIME",
+        [DNS_RCODE_BADMODE]   = "BADMODE",
+        [DNS_RCODE_BADNAME]   = "BADNAME",
+        [DNS_RCODE_BADALG]    = "BADALG",
+        [DNS_RCODE_BADTRUNC]  = "BADTRUNC",
+        [DNS_RCODE_BADCOOKIE] = "BADCOOKIE",
+};
+DEFINE_STRING_TABLE_LOOKUP(dns_rcode, int);
+
+const char *format_dns_rcode(int i, char buf[static DECIMAL_STR_MAX(int)]) {
+        const char *p = dns_rcode_to_string(i);
+        if (p)
+                return p;
+
+        return snprintf_ok(buf, DECIMAL_STR_MAX(int), "%i", i);
+}
+
+static const char* const dns_protocol_table[_DNS_PROTOCOL_MAX] = {
+        [DNS_PROTOCOL_DNS]   = "dns",
+        [DNS_PROTOCOL_MDNS]  = "mdns",
+        [DNS_PROTOCOL_LLMNR] = "llmnr",
+};
+DEFINE_STRING_TABLE_LOOKUP(dns_protocol, DnsProtocol);