resolved: split out RR synthesis logic into its own C file

Also, while we are at it, set the "authenticated" bit for everything we synthesize

3 files changed, 462 insertions, 368 deletions

diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c
index 47f1924702..2f9dd1c47b 100644
--- a/src/resolve/resolved-dns-query.c
+++ b/src/resolve/resolved-dns-query.c
@@ -24,6 +24,7 @@
 #include "hostname-util.h"
 #include "local-addresses.h"
 #include "resolved-dns-query.h"
+#include "resolved-dns-synthesize.h"
 #include "string-util.h"
 
 /* How long to wait for the query in total */
@@ -547,328 +548,15 @@ fail:
         return r;
 }
 
-static int SYNTHESIZE_IFINDEX(int ifindex) {
-
-        /* When the caller asked for resolving on a specific
-         * interface, we synthesize the answer for that
-         * interface. However, if nothing specific was claimed and we
-         * only return localhost RRs, we synthesize the answer for
-         * localhost. */
-
-        if (ifindex > 0)
-                return ifindex;
-
-        return LOOPBACK_IFINDEX;
-}
-
-static int SYNTHESIZE_FAMILY(uint64_t flags) {
-
-        /* Picks an address family depending on set flags. This is
-         * purely for synthesized answers, where the family we return
-         * for the reply should match what was requested in the
-         * question, even though we are synthesizing the answer
-         * here. */
-
-        if (!(flags & SD_RESOLVED_DNS)) {
-                if (flags & SD_RESOLVED_LLMNR_IPV4)
-                        return AF_INET;
-                if (flags & SD_RESOLVED_LLMNR_IPV6)
-                        return AF_INET6;
-        }
-
-        return AF_UNSPEC;
-}
-
-static DnsProtocol SYNTHESIZE_PROTOCOL(uint64_t flags) {
-
-        /* Similar as SYNTHESIZE_FAMILY() but does this for the
-         * protocol. If resolving via DNS was requested, we claim it
-         * was DNS. Similar, if nothing specific was
-         * requested. However, if only resolving via LLMNR was
-         * requested we return that. */
-
-        if (flags & SD_RESOLVED_DNS)
-                return DNS_PROTOCOL_DNS;
-        if (flags & SD_RESOLVED_LLMNR)
-                return DNS_PROTOCOL_LLMNR;
-
-        return DNS_PROTOCOL_DNS;
-}
-
-static int synthesize_localhost_rr(DnsQuery *q, const DnsResourceKey *key, DnsAnswer **answer) {
-        int r;
-
-        assert(q);
-        assert(key);
-        assert(answer);
-
-        r = dns_answer_reserve(answer, 2);
-        if (r < 0)
-                return r;
-
-        if (IN_SET(key->type, DNS_TYPE_A, DNS_TYPE_ANY)) {
-                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
-
-                rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, DNS_RESOURCE_KEY_NAME(key));
-                if (!rr)
-                        return -ENOMEM;
-
-                rr->a.in_addr.s_addr = htobe32(INADDR_LOOPBACK);
-
-                r = dns_answer_add(*answer, rr, SYNTHESIZE_IFINDEX(q->ifindex), DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-        }
-
-        if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY)) {
-                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
-
-                rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_AAAA, DNS_RESOURCE_KEY_NAME(key));
-                if (!rr)
-                        return -ENOMEM;
-
-                rr->aaaa.in6_addr = in6addr_loopback;
-
-                r = dns_answer_add(*answer, rr, SYNTHESIZE_IFINDEX(q->ifindex), DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-        }
-
-        return 0;
-}
-
-static int answer_add_ptr(DnsAnswer **answer, const char *from, const char *to, int ifindex, DnsAnswerFlags flags) {
-        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
-
-        rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_PTR, from);
-        if (!rr)
-                return -ENOMEM;
-
-        rr->ptr.name = strdup(to);
-        if (!rr->ptr.name)
-                return -ENOMEM;
-
-        return dns_answer_add(*answer, rr, ifindex, flags);
-}
-
-static int synthesize_localhost_ptr(DnsQuery *q, const DnsResourceKey *key, DnsAnswer **answer) {
-        int r;
-
-        assert(q);
-        assert(key);
-        assert(answer);
-
-        if (IN_SET(key->type, DNS_TYPE_PTR, DNS_TYPE_ANY)) {
-                r = dns_answer_reserve(answer, 1);
-                if (r < 0)
-                        return r;
-
-                r = answer_add_ptr(answer, DNS_RESOURCE_KEY_NAME(key), "localhost", SYNTHESIZE_IFINDEX(q->ifindex), DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-        }
-
-        return 0;
-}
-
-static int answer_add_addresses_rr(
-                DnsAnswer **answer,
-                const char *name,
-                struct local_address *addresses,
-                unsigned n_addresses) {
-
-        unsigned j;
-        int r;
-
-        assert(answer);
-        assert(name);
-
-        r = dns_answer_reserve(answer, n_addresses);
-        if (r < 0)
-                return r;
-
-        for (j = 0; j < n_addresses; j++) {
-                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
-
-                r = dns_resource_record_new_address(&rr, addresses[j].family, &addresses[j].address, name);
-                if (r < 0)
-                        return r;
-
-                r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-        }
-
-        return 0;
-}
-
-static int answer_add_addresses_ptr(
-                DnsAnswer **answer,
-                const char *name,
-                struct local_address *addresses,
-                unsigned n_addresses,
-                int af, const union in_addr_union *match) {
-
-        unsigned j;
-        int r;
-
-        assert(answer);
-        assert(name);
-
-        for (j = 0; j < n_addresses; j++) {
-                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
-
-                if (af != AF_UNSPEC) {
-
-                        if (addresses[j].family != af)
-                                continue;
-
-                        if (match && !in_addr_equal(af, match, &addresses[j].address))
-                                continue;
-                }
-
-                r = dns_answer_reserve(answer, 1);
-                if (r < 0)
-                        return r;
-
-                r = dns_resource_record_new_reverse(&rr, addresses[j].family, &addresses[j].address, name);
-                if (r < 0)
-                        return r;
-
-                r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-        }
-
-        return 0;
-}
-
-static int synthesize_system_hostname_rr(DnsQuery *q, const DnsResourceKey *key, DnsAnswer **answer) {
-        _cleanup_free_ struct local_address *addresses = NULL;
-        int n = 0, af;
-
-        assert(q);
-        assert(key);
-        assert(answer);
-
-        af = dns_type_to_af(key->type);
-        if (af >= 0) {
-                n = local_addresses(q->manager->rtnl, q->ifindex, af, &addresses);
-                if (n < 0)
-                        return n;
-
-                if (n == 0) {
-                        struct local_address buffer[2];
-
-                        /* If we have no local addresses then use ::1
-                         * and 127.0.0.2 as local ones. */
-
-                        if (af == AF_INET || af == AF_UNSPEC)
-                                buffer[n++] = (struct local_address) {
-                                        .family = AF_INET,
-                                        .ifindex = SYNTHESIZE_IFINDEX(q->ifindex),
-                                        .address.in.s_addr = htobe32(0x7F000002),
-                                };
-
-                        if (af == AF_INET6 || af == AF_UNSPEC)
-                                buffer[n++] = (struct local_address) {
-                                        .family = AF_INET6,
-                                        .ifindex = SYNTHESIZE_IFINDEX(q->ifindex),
-                                        .address.in6 = in6addr_loopback,
-                                };
-
-                        return answer_add_addresses_rr(answer, DNS_RESOURCE_KEY_NAME(key), buffer, n);
-                }
-        }
-
-        return answer_add_addresses_rr(answer, DNS_RESOURCE_KEY_NAME(key), addresses, n);
-}
-
-static int synthesize_system_hostname_ptr(DnsQuery *q, int af, const union in_addr_union *address, DnsAnswer **answer) {
-        _cleanup_free_ struct local_address *addresses = NULL;
-        int n, r;
-
-        assert(q);
-        assert(address);
-        assert(answer);
-
-        if (af == AF_INET && address->in.s_addr == htobe32(0x7F000002)) {
-
-                /* Always map the IPv4 address 127.0.0.2 to the local
-                 * hostname, in addition to "localhost": */
-
-                r = dns_answer_reserve(answer, 3);
-                if (r < 0)
-                        return r;
-
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", q->manager->llmnr_hostname, SYNTHESIZE_IFINDEX(q->ifindex), DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", q->manager->mdns_hostname, SYNTHESIZE_IFINDEX(q->ifindex), DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-
-                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", SYNTHESIZE_IFINDEX(q->ifindex), DNS_ANSWER_AUTHENTICATED);
-                if (r < 0)
-                        return r;
-
-                return 0;
-        }
-
-        n = local_addresses(q->manager->rtnl, q->ifindex, af, &addresses);
-        if (n < 0)
-                return n;
-
-        r = answer_add_addresses_ptr(answer, q->manager->llmnr_hostname, addresses, n, af, address);
-        if (r < 0)
-                return r;
-
-        return answer_add_addresses_ptr(answer, q->manager->mdns_hostname, addresses, n, af, address);
-}
-
-static int synthesize_gateway_rr(DnsQuery *q, const DnsResourceKey *key, DnsAnswer **answer) {
-        _cleanup_free_ struct local_address *addresses = NULL;
-        int n = 0, af;
-
-        assert(q);
-        assert(key);
-        assert(answer);
-
-        af = dns_type_to_af(key->type);
-        if (af >= 0) {
-                n = local_gateways(q->manager->rtnl, q->ifindex, af, &addresses);
-                if (n < 0)
-                        return n;
-        }
-
-        return answer_add_addresses_rr(answer, DNS_RESOURCE_KEY_NAME(key), addresses, n);
-}
-
-static int synthesize_gateway_ptr(DnsQuery *q, int af, const union in_addr_union *address, DnsAnswer **answer) {
-        _cleanup_free_ struct local_address *addresses = NULL;
-        int n;
-
-        assert(q);
-        assert(address);
-        assert(answer);
-
-        n = local_gateways(q->manager->rtnl, q->ifindex, af, &addresses);
-        if (n < 0)
-                return n;
-
-        return answer_add_addresses_ptr(answer, "gateway", addresses, n, af, address);
-}
-
 static int dns_query_synthesize_reply(DnsQuery *q, DnsTransactionState *state) {
         _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
-        DnsResourceKey *key;
-        int r;
+        DnsProtocol protocol;
+        int family, r;
 
         assert(q);
         assert(state);
 
-        /* Tries to synthesize localhost RR replies where appropriate */
+        /* Tries to synthesize localhost RR replies (and others) where appropriate */
 
         if (!IN_SET(*state,
                     DNS_TRANSACTION_RCODE_FAILURE,
@@ -878,64 +566,26 @@ static int dns_query_synthesize_reply(DnsQuery *q, DnsTransactionState *state) {
                     DNS_TRANSACTION_NETWORK_DOWN))
                 return 0;
 
-        DNS_QUESTION_FOREACH(key, q->question_utf8) {
-                union in_addr_union address;
-                const char *name;
-                int af;
-
-                if (key->class != DNS_CLASS_IN &&
-                    key->class != DNS_CLASS_ANY)
-                        continue;
-
-                name = DNS_RESOURCE_KEY_NAME(key);
+        r = dns_synthesize_answer(
+                        q->manager,
+                        q->question_utf8,
+                        q->ifindex,
+                        q->flags,
+                        &answer,
+                        &protocol,
+                        &family);
 
-                if (is_localhost(name)) {
-
-                        r = synthesize_localhost_rr(q, key, &answer);
-                        if (r < 0)
-                                return log_error_errno(r, "Failed to synthesize localhost RRs: %m");
-
-                } else if (manager_is_own_hostname(q->manager, name)) {
-
-                        r = synthesize_system_hostname_rr(q, key, &answer);
-                        if (r < 0)
-                                return log_error_errno(r, "Failed to synthesize system hostname RRs: %m");
-
-                } else if (is_gateway_hostname(name)) {
-
-                        r = synthesize_gateway_rr(q, key, &answer);
-                        if (r < 0)
-                                return log_error_errno(r, "Failed to synthesize gateway RRs: %m");
-
-                } else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 && dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0) ||
-                           dns_name_equal(name, "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa") > 0) {
-
-                        r = synthesize_localhost_ptr(q, key, &answer);
-                        if (r < 0)
-                                return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");
-
-                } else if (dns_name_address(name, &af, &address) > 0) {
-
-                        r = synthesize_system_hostname_ptr(q, af, &address, &answer);
-                        if (r < 0)
-                                return log_error_errno(r, "Failed to synthesize system hostname PTR RR: %m");
-
-                        r = synthesize_gateway_ptr(q, af, &address, &answer);
-                        if (r < 0)
-                                return log_error_errno(r, "Failed to synthesize gateway hostname PTR RR: %m");
-                }
-        }
+        if (r <= 0)
+                return r;
 
-        if (!answer)
-                return 0;
+        dns_query_reset_answer(q);
 
-        dns_answer_unref(q->answer);
         q->answer = answer;
         answer = NULL;
-
         q->answer_rcode = DNS_RCODE_SUCCESS;
-        q->answer_protocol = SYNTHESIZE_PROTOCOL(q->flags);
-        q->answer_family = SYNTHESIZE_FAMILY(q->flags);
+        q->answer_protocol = protocol;
+        q->answer_family = family;
+        q->answer_authenticated = true;
 
         *state = DNS_TRANSACTION_SUCCESS;
 
diff --git a/src/resolve/resolved-dns-synthesize.c b/src/resolve/resolved-dns-synthesize.c
new file mode 100644
index 0000000000..e12bb6e828
--- /dev/null
+++ b/src/resolve/resolved-dns-synthesize.c
@@ -0,0 +1,418 @@
+/***
+  This file is part of systemd.
+
+  Copyright 2014 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "alloc-util.h"
+#include "hostname-util.h"
+#include "local-addresses.h"
+#include "resolved-dns-synthesize.h"
+
+static int SYNTHESIZE_IFINDEX(int ifindex) {
+
+        /* When the caller asked for resolving on a specific
+         * interface, we synthesize the answer for that
+         * interface. However, if nothing specific was claimed and we
+         * only return localhost RRs, we synthesize the answer for
+         * localhost. */
+
+        if (ifindex > 0)
+                return ifindex;
+
+        return LOOPBACK_IFINDEX;
+}
+
+static int SYNTHESIZE_FAMILY(uint64_t flags) {
+
+        /* Picks an address family depending on set flags. This is
+         * purely for synthesized answers, where the family we return
+         * for the reply should match what was requested in the
+         * question, even though we are synthesizing the answer
+         * here. */
+
+        if (!(flags & SD_RESOLVED_DNS)) {
+                if (flags & (SD_RESOLVED_LLMNR_IPV4|SD_RESOLVED_MDNS_IPV4))
+                        return AF_INET;
+                if (flags & (SD_RESOLVED_LLMNR_IPV6|SD_RESOLVED_MDNS_IPV6))
+                        return AF_INET6;
+        }
+
+        return AF_UNSPEC;
+}
+
+static DnsProtocol SYNTHESIZE_PROTOCOL(uint64_t flags) {
+
+        /* Similar as SYNTHESIZE_FAMILY() but does this for the
+         * protocol. If resolving via DNS was requested, we claim it
+         * was DNS. Similar, if nothing specific was
+         * requested. However, if only resolving via LLMNR was
+         * requested we return that. */
+
+        if (flags & SD_RESOLVED_DNS)
+                return DNS_PROTOCOL_DNS;
+        if (flags & SD_RESOLVED_LLMNR)
+                return DNS_PROTOCOL_LLMNR;
+        if (flags & SD_RESOLVED_MDNS)
+                return DNS_PROTOCOL_MDNS;
+
+        return DNS_PROTOCOL_DNS;
+}
+
+static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+        int r;
+
+        assert(m);
+        assert(key);
+        assert(answer);
+
+        r = dns_answer_reserve(answer, 2);
+        if (r < 0)
+                return r;
+
+        if (IN_SET(key->type, DNS_TYPE_A, DNS_TYPE_ANY)) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+                rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, DNS_RESOURCE_KEY_NAME(key));
+                if (!rr)
+                        return -ENOMEM;
+
+                rr->a.in_addr.s_addr = htobe32(INADDR_LOOPBACK);
+
+                r = dns_answer_add(*answer, rr, SYNTHESIZE_IFINDEX(ifindex), DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+        }
+
+        if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY)) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+                rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_AAAA, DNS_RESOURCE_KEY_NAME(key));
+                if (!rr)
+                        return -ENOMEM;
+
+                rr->aaaa.in6_addr = in6addr_loopback;
+
+                r = dns_answer_add(*answer, rr, SYNTHESIZE_IFINDEX(ifindex), DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int answer_add_ptr(DnsAnswer **answer, const char *from, const char *to, int ifindex, DnsAnswerFlags flags) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+        rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_PTR, from);
+        if (!rr)
+                return -ENOMEM;
+
+        rr->ptr.name = strdup(to);
+        if (!rr->ptr.name)
+                return -ENOMEM;
+
+        return dns_answer_add(*answer, rr, ifindex, flags);
+}
+
+static int synthesize_localhost_ptr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+        int r;
+
+        assert(m);
+        assert(key);
+        assert(answer);
+
+        if (IN_SET(key->type, DNS_TYPE_PTR, DNS_TYPE_ANY)) {
+                r = dns_answer_reserve(answer, 1);
+                if (r < 0)
+                        return r;
+
+                r = answer_add_ptr(answer, DNS_RESOURCE_KEY_NAME(key), "localhost", SYNTHESIZE_IFINDEX(ifindex), DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int answer_add_addresses_rr(
+                DnsAnswer **answer,
+                const char *name,
+                struct local_address *addresses,
+                unsigned n_addresses) {
+
+        unsigned j;
+        int r;
+
+        assert(answer);
+        assert(name);
+
+        r = dns_answer_reserve(answer, n_addresses);
+        if (r < 0)
+                return r;
+
+        for (j = 0; j < n_addresses; j++) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+                r = dns_resource_record_new_address(&rr, addresses[j].family, &addresses[j].address, name);
+                if (r < 0)
+                        return r;
+
+                r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int answer_add_addresses_ptr(
+                DnsAnswer **answer,
+                const char *name,
+                struct local_address *addresses,
+                unsigned n_addresses,
+                int af, const union in_addr_union *match) {
+
+        unsigned j;
+        int r;
+
+        assert(answer);
+        assert(name);
+
+        for (j = 0; j < n_addresses; j++) {
+                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
+
+                if (af != AF_UNSPEC) {
+
+                        if (addresses[j].family != af)
+                                continue;
+
+                        if (match && !in_addr_equal(af, match, &addresses[j].address))
+                                continue;
+                }
+
+                r = dns_answer_reserve(answer, 1);
+                if (r < 0)
+                        return r;
+
+                r = dns_resource_record_new_reverse(&rr, addresses[j].family, &addresses[j].address, name);
+                if (r < 0)
+                        return r;
+
+                r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+        }
+
+        return 0;
+}
+
+static int synthesize_system_hostname_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+        _cleanup_free_ struct local_address *addresses = NULL;
+        int n = 0, af;
+
+        assert(m);
+        assert(key);
+        assert(answer);
+
+        af = dns_type_to_af(key->type);
+        if (af >= 0) {
+                n = local_addresses(m->rtnl, ifindex, af, &addresses);
+                if (n < 0)
+                        return n;
+
+                if (n == 0) {
+                        struct local_address buffer[2];
+
+                        /* If we have no local addresses then use ::1
+                         * and 127.0.0.2 as local ones. */
+
+                        if (af == AF_INET || af == AF_UNSPEC)
+                                buffer[n++] = (struct local_address) {
+                                        .family = AF_INET,
+                                        .ifindex = SYNTHESIZE_IFINDEX(ifindex),
+                                        .address.in.s_addr = htobe32(0x7F000002),
+                                };
+
+                        if (af == AF_INET6 || af == AF_UNSPEC)
+                                buffer[n++] = (struct local_address) {
+                                        .family = AF_INET6,
+                                        .ifindex = SYNTHESIZE_IFINDEX(ifindex),
+                                        .address.in6 = in6addr_loopback,
+                                };
+
+                        return answer_add_addresses_rr(answer, DNS_RESOURCE_KEY_NAME(key), buffer, n);
+                }
+        }
+
+        return answer_add_addresses_rr(answer, DNS_RESOURCE_KEY_NAME(key), addresses, n);
+}
+
+static int synthesize_system_hostname_ptr(Manager *m, int af, const union in_addr_union *address, int ifindex, DnsAnswer **answer) {
+        _cleanup_free_ struct local_address *addresses = NULL;
+        int n, r;
+
+        assert(m);
+        assert(address);
+        assert(answer);
+
+        if (af == AF_INET && address->in.s_addr == htobe32(0x7F000002)) {
+
+                /* Always map the IPv4 address 127.0.0.2 to the local
+                 * hostname, in addition to "localhost": */
+
+                r = dns_answer_reserve(answer, 3);
+                if (r < 0)
+                        return r;
+
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->llmnr_hostname, SYNTHESIZE_IFINDEX(ifindex), DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->mdns_hostname, SYNTHESIZE_IFINDEX(ifindex), DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+
+                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", SYNTHESIZE_IFINDEX(ifindex), DNS_ANSWER_AUTHENTICATED);
+                if (r < 0)
+                        return r;
+
+                return 0;
+        }
+
+        n = local_addresses(m->rtnl, ifindex, af, &addresses);
+        if (n < 0)
+                return n;
+
+        r = answer_add_addresses_ptr(answer, m->llmnr_hostname, addresses, n, af, address);
+        if (r < 0)
+                return r;
+
+        return answer_add_addresses_ptr(answer, m->mdns_hostname, addresses, n, af, address);
+}
+
+static int synthesize_gateway_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
+        _cleanup_free_ struct local_address *addresses = NULL;
+        int n = 0, af;
+
+        assert(m);
+        assert(key);
+        assert(answer);
+
+        af = dns_type_to_af(key->type);
+        if (af >= 0) {
+                n = local_gateways(m->rtnl, ifindex, af, &addresses);
+                if (n < 0)
+                        return n;
+        }
+
+        return answer_add_addresses_rr(answer, DNS_RESOURCE_KEY_NAME(key), addresses, n);
+}
+
+static int synthesize_gateway_ptr(Manager *m, int af, const union in_addr_union *address, int ifindex, DnsAnswer **answer) {
+        _cleanup_free_ struct local_address *addresses = NULL;
+        int n;
+
+        assert(m);
+        assert(address);
+        assert(answer);
+
+        n = local_gateways(m->rtnl, ifindex, af, &addresses);
+        if (n < 0)
+                return n;
+
+        return answer_add_addresses_ptr(answer, "gateway", addresses, n, af, address);
+}
+
+int dns_synthesize_answer(
+                Manager *m,
+                DnsQuestion *q,
+                int ifindex,
+                uint64_t flags,
+                DnsAnswer **ret,
+                DnsProtocol *ret_protocol,
+                int *ret_family) {
+
+        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
+        DnsResourceKey *key;
+        int r;
+
+        assert(m);
+        assert(q);
+
+        DNS_QUESTION_FOREACH(key, q) {
+                union in_addr_union address;
+                const char *name;
+                int af;
+
+                if (key->class != DNS_CLASS_IN &&
+                    key->class != DNS_CLASS_ANY)
+                        continue;
+
+                name = DNS_RESOURCE_KEY_NAME(key);
+
+                if (is_localhost(name)) {
+
+                        r = synthesize_localhost_rr(m, key, ifindex, &answer);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to synthesize localhost RRs: %m");
+
+                } else if (manager_is_own_hostname(m, name)) {
+
+                        r = synthesize_system_hostname_rr(m, key, ifindex, &answer);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to synthesize system hostname RRs: %m");
+
+                } else if (is_gateway_hostname(name)) {
+
+                        r = synthesize_gateway_rr(m, key, ifindex, &answer);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to synthesize gateway RRs: %m");
+
+                } else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 && dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0) ||
+                           dns_name_equal(name, "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa") > 0) {
+
+                        r = synthesize_localhost_ptr(m, key, ifindex, &answer);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");
+
+                } else if (dns_name_address(name, &af, &address) > 0) {
+
+                        r = synthesize_system_hostname_ptr(m, af, &address, ifindex, &answer);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to synthesize system hostname PTR RR: %m");
+
+                        r = synthesize_gateway_ptr(m, af, &address, ifindex, &answer);
+                        if (r < 0)
+                                return log_error_errno(r, "Failed to synthesize gateway hostname PTR RR: %m");
+                }
+        }
+
+        r = dns_answer_size(answer) > 0;
+
+        if (ret) {
+                *ret = answer;
+                answer = NULL;
+        }
+
+        if (ret_protocol)
+                *ret_protocol = SYNTHESIZE_PROTOCOL(flags);
+
+        if (ret_family)
+                *ret_family = SYNTHESIZE_FAMILY(flags);
+
+        return r;
+}
diff --git a/src/resolve/resolved-dns-synthesize.h b/src/resolve/resolved-dns-synthesize.h
new file mode 100644
index 0000000000..e43d96cb2c
--- /dev/null
+++ b/src/resolve/resolved-dns-synthesize.h
@@ -0,0 +1,26 @@
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2016 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "resolved-dns-answer.h"
+#include "resolved-dns-question.h"
+#include "resolved-manager.h"
+
+int dns_synthesize_answer(Manager *m, DnsQuestion *q, int ifindex, uint64_t flags, DnsAnswer **ret, DnsProtocol *ret_protocol, int *ret_family);