resolved: add ResolveService() bus call for resolving SRV and DNS-SD services

This also adds client-side support for this to systemd-resolve-host.

Note that the ResolveService() API can deal both with DNS-SD service
(consisting of service name, type and domain), as well as classic SRV
services (consisting just of a type and a domain), all exposed in the
same call.

This patch also reworks CNAME handling in order to reuse it between
hostname, RR and service lookups.

In contrast to Avahi and Bonjour, this new API will actually reolve the
A/AAAA RRs the SRV RRs point to in one go (unless this is explicitly
disabled). This normally comes for free, as these RRs are sent along
the SRV responses anyway, hence let's make use of that. This makes the
API considerably easier to use, as a single ResolveService() invocation
will return all necessary data to pick a server and connect() to it.

Note that this only implements the DNS-SD resolving step, it does not
implement DNS-SD browsing, as that makes sense primarily on mDNS, due to
its continuous nature.

1 files changed, 652 insertions, 188 deletions

diff --git a/src/resolve/resolved-bus.c b/src/resolve/resolved-bus.c
index f0a3b607d4..1908cae2b7 100644
--- a/src/resolve/resolved-bus.c
+++ b/src/resolve/resolved-bus.c
@@ -31,15 +31,14 @@ static int reply_query_state(DnsQuery *q) {
         const char *name;
         int r;
 
-        if (q->request_hostname)
-                name = q->request_hostname;
-        else {
+        if (q->request_address_valid) {
                 r = in_addr_to_string(q->request_family, &q->request_address, &ip);
                 if (r < 0)
                         return r;
 
                 name = ip;
-        }
+        } else
+                name = dns_question_name(q->question);
 
         switch (q->state) {
 
@@ -132,10 +131,9 @@ static int append_address(sd_bus_message *reply, DnsResourceRecord *rr, int ifin
 }
 
 static void bus_method_resolve_hostname_complete(DnsQuery *q) {
-        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *cname = NULL, *canonical = NULL;
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *canonical = NULL;
         _cleanup_bus_message_unref_ sd_bus_message *reply = NULL;
-        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
-        unsigned added = 0, i;
+        unsigned added = 0;
         int r;
 
         assert(q);
@@ -145,6 +143,16 @@ static void bus_method_resolve_hostname_complete(DnsQuery *q) {
                 goto finish;
         }
 
+        r = dns_query_process_cname(q);
+        if (r == -ELOOP) {
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_question_name(q->question));
+                goto finish;
+        }
+        if (r < 0)
+                goto finish;
+        if (r > 0) /* This was a cname, and the query was restarted. */
+                return;
+
         r = sd_bus_message_new_method_return(q->request, &reply);
         if (r < 0)
                 goto finish;
@@ -154,92 +162,42 @@ static void bus_method_resolve_hostname_complete(DnsQuery *q) {
                 goto finish;
 
         if (q->answer) {
-                answer = dns_answer_ref(q->answer);
+                DnsResourceRecord *rr;
+                int ifindex;
 
-                for (i = 0; i < answer->n_rrs; i++) {
-                        r = dns_question_matches_rr(q->question, answer->items[i].rr);
+                DNS_ANSWER_FOREACH_IFINDEX(rr, ifindex, q->answer) {
+                        r = dns_question_matches_rr(q->question, rr);
                         if (r < 0)
                                 goto finish;
-                        if (r == 0) {
-                                /* Hmm, if this is not an address record,
-                                   maybe it's a cname? If so, remember this */
-                                r = dns_question_matches_cname(q->question, answer->items[i].rr);
-                                if (r < 0)
-                                        goto finish;
-                                if (r > 0)
-                                        cname = dns_resource_record_ref(answer->items[i].rr);
-
+                        if (r == 0)
                                 continue;
-                        }
 
-                        r = append_address(reply, answer->items[i].rr, answer->items[i].ifindex);
+                        r = append_address(reply, rr, ifindex);
                         if (r < 0)
                                 goto finish;
 
                         if (!canonical)
-                                canonical = dns_resource_record_ref(answer->items[i].rr);
+                                canonical = dns_resource_record_ref(rr);
 
                         added ++;
                 }
         }
 
-        if (added == 0) {
-                if (!cname) {
-                        r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "'%s' does not have any RR of requested type", q->request_hostname);
-                        goto finish;
-                }
-
-                /* This has a cname? Then update the query with the
-                 * new cname. */
-                r = dns_query_cname_redirect(q, cname);
-                if (r < 0) {
-                        if (r == -ELOOP)
-                                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_CNAME_LOOP, "CNAME loop on '%s'", q->request_hostname);
-                        else
-                                r = sd_bus_reply_method_errno(q->request, -r, NULL);
-
-                        goto finish;
-                }
-
-                /* Before we restart the query, let's see if any of
-                 * the RRs we already got already answers our query */
-                for (i = 0; i < answer->n_rrs; i++) {
-                        r = dns_question_matches_rr(q->question, answer->items[i].rr);
-                        if (r < 0)
-                                goto finish;
-                        if (r == 0)
-                                continue;
-
-                        r = append_address(reply, answer->items[i].rr, answer->items[i].ifindex);
-                        if (r < 0)
-                                goto finish;
-
-                        if (!canonical)
-                                canonical = dns_resource_record_ref(answer->items[i].rr);
-
-                        added++;
-                }
-
-                /* If we didn't find anything, then let's restart the
-                 * query, this time with the cname */
-                if (added <= 0) {
-                        r = dns_query_go(q);
-                        if (r < 0) {
-                                r = sd_bus_reply_method_errno(q->request, -r, NULL);
-                                goto finish;
-                        }
-
-                        return;
-                }
+        if (added <= 0) {
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "'%s' does not have any RR of the requested type", dns_question_name(q->question));
+                goto finish;
         }
 
         r = sd_bus_message_close_container(reply);
         if (r < 0)
                 goto finish;
 
-        /* Return the precise spelling and uppercasing reported by the server */
+        /* Return the precise spelling and uppercasing and CNAME target reported by the server */
         assert(canonical);
-        r = sd_bus_message_append(reply, "st", DNS_RESOURCE_KEY_NAME(canonical->key), SD_RESOLVED_FLAGS_MAKE(q->answer_protocol, q->answer_family));
+        r = sd_bus_message_append(
+                        reply, "st",
+                        DNS_RESOURCE_KEY_NAME(canonical->key),
+                        SD_RESOLVED_FLAGS_MAKE(q->answer_protocol, q->answer_family));
         if (r < 0)
                 goto finish;
 
@@ -248,23 +206,23 @@ static void bus_method_resolve_hostname_complete(DnsQuery *q) {
 finish:
         if (r < 0) {
                 log_error_errno(r, "Failed to send hostname reply: %m");
-                sd_bus_reply_method_errno(q->request, -r, NULL);
+                sd_bus_reply_method_errno(q->request, r, NULL);
         }
 
         dns_query_free(q);
 }
 
-static int check_ifindex_flags(int ifindex, uint64_t *flags, sd_bus_error *error) {
+static int check_ifindex_flags(int ifindex, uint64_t *flags, uint64_t ok, sd_bus_error *error) {
         assert(flags);
 
         if (ifindex < 0)
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid interface index");
 
-        if (*flags & ~SD_RESOLVED_FLAGS_ALL)
+        if (*flags & ~(SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_CNAME|ok))
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid flags parameter");
 
-        if (*flags == 0)
-                *flags = SD_RESOLVED_FLAGS_DEFAULT;
+        if ((*flags & SD_RESOLVED_PROTOCOLS_ALL) == 0) /* If no protocol is enabled, enable all */
+                *flags |= SD_RESOLVED_PROTOCOLS_ALL;
 
         return 0;
 }
@@ -281,6 +239,8 @@ static int bus_method_resolve_hostname(sd_bus_message *message, void *userdata,
         assert(message);
         assert(m);
 
+        assert_cc(sizeof(int) == sizeof(int32_t));
+
         r = sd_bus_message_read(message, "isit", &ifindex, &hostname, &family, &flags);
         if (r < 0)
                 return r;
@@ -288,41 +248,19 @@ static int bus_method_resolve_hostname(sd_bus_message *message, void *userdata,
         if (!IN_SET(family, AF_INET, AF_INET6, AF_UNSPEC))
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Unknown address family %i", family);
 
-        r = dns_name_normalize(hostname, NULL);
+        r = dns_name_is_valid(hostname);
         if (r < 0)
+                return r;
+        if (r == 0)
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid hostname '%s'", hostname);
 
-        r = check_ifindex_flags(ifindex, &flags, error);
+        r = check_ifindex_flags(ifindex, &flags, 0, error);
         if (r < 0)
                 return r;
 
-        question = dns_question_new(family == AF_UNSPEC ? 2 : 1);
-        if (!question)
-                return -ENOMEM;
-
-        if (family != AF_INET6) {
-                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
-
-                key = dns_resource_key_new(DNS_CLASS_IN, DNS_TYPE_A, hostname);
-                if (!key)
-                        return -ENOMEM;
-
-                r = dns_question_add(question, key);
-                if (r < 0)
-                        return r;
-        }
-
-        if (family != AF_INET) {
-                _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
-
-                key = dns_resource_key_new(DNS_CLASS_IN, DNS_TYPE_AAAA, hostname);
-                if (!key)
-                        return -ENOMEM;
-
-                r = dns_question_add(question, key);
-                if (r < 0)
-                        return r;
-        }
+        r = dns_question_new_address(&question, family, hostname);
+        if (r < 0)
+                return r;
 
         r = dns_query_new(m, &q, question, ifindex, flags);
         if (r < 0)
@@ -330,27 +268,28 @@ static int bus_method_resolve_hostname(sd_bus_message *message, void *userdata,
 
         q->request = sd_bus_message_ref(message);
         q->request_family = family;
-        q->request_hostname = hostname;
         q->complete = bus_method_resolve_hostname_complete;
 
         r = dns_query_bus_track(q, message);
         if (r < 0)
-                return r;
+                goto fail;
 
         r = dns_query_go(q);
-        if (r < 0) {
-                dns_query_free(q);
-                return r;
-        }
+        if (r < 0)
+                goto fail;
 
         return 1;
+
+fail:
+        dns_query_free(q);
+        return r;
 }
 
 static void bus_method_resolve_address_complete(DnsQuery *q) {
         _cleanup_bus_message_unref_ sd_bus_message *reply = NULL;
-        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
-        unsigned added = 0, i;
-        int r;
+        DnsResourceRecord *rr;
+        unsigned added = 0;
+        int ifindex, r;
 
         assert(q);
 
@@ -359,6 +298,8 @@ static void bus_method_resolve_address_complete(DnsQuery *q) {
                 goto finish;
         }
 
+        /* We don't process CNAME for PTR lookups. */
+
         r = sd_bus_message_new_method_return(q->request, &reply);
         if (r < 0)
                 goto finish;
@@ -368,16 +309,14 @@ static void bus_method_resolve_address_complete(DnsQuery *q) {
                 goto finish;
 
         if (q->answer) {
-                answer = dns_answer_ref(q->answer);
-
-                for (i = 0; i < answer->n_rrs; i++) {
-                        r = dns_question_matches_rr(q->question, answer->items[i].rr);
+                DNS_ANSWER_FOREACH_IFINDEX(rr, ifindex, q->answer) {
+                        r = dns_question_matches_rr(q->question, rr);
                         if (r < 0)
                                 goto finish;
                         if (r == 0)
                                 continue;
 
-                        r = sd_bus_message_append(reply, "(is)", answer->items[i].ifindex, answer->items[i].rr->ptr.name);
+                        r = sd_bus_message_append(reply, "(is)", ifindex, rr->ptr.name);
                         if (r < 0)
                                 goto finish;
 
@@ -385,12 +324,11 @@ static void bus_method_resolve_address_complete(DnsQuery *q) {
                 }
         }
 
-        if (added == 0) {
+        if (added <= 0) {
                 _cleanup_free_ char *ip = NULL;
 
                 in_addr_to_string(q->request_family, &q->request_address, &ip);
-
-                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "Address '%s' does not have any RR of requested type", ip);
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "Address '%s' does not have any RR of requested type", strna(ip));
                 goto finish;
         }
 
@@ -407,16 +345,14 @@ static void bus_method_resolve_address_complete(DnsQuery *q) {
 finish:
         if (r < 0) {
                 log_error_errno(r, "Failed to send address reply: %m");
-                sd_bus_reply_method_errno(q->request, -r, NULL);
+                sd_bus_reply_method_errno(q->request, r, NULL);
         }
 
         dns_query_free(q);
 }
 
 static int bus_method_resolve_address(sd_bus_message *message, void *userdata, sd_bus_error *error) {
-        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
         _cleanup_(dns_question_unrefp) DnsQuestion *question = NULL;
-        _cleanup_free_ char *reverse = NULL;
         Manager *m = userdata;
         int family, ifindex;
         uint64_t flags;
@@ -428,6 +364,8 @@ static int bus_method_resolve_address(sd_bus_message *message, void *userdata, s
         assert(message);
         assert(m);
 
+        assert_cc(sizeof(int) == sizeof(int32_t));
+
         r = sd_bus_message_read(message, "ii", &ifindex, &family);
         if (r < 0)
                 return r;
@@ -446,25 +384,11 @@ static int bus_method_resolve_address(sd_bus_message *message, void *userdata, s
         if (r < 0)
                 return r;
 
-        r = check_ifindex_flags(ifindex, &flags, error);
-        if (r < 0)
-                return r;
-
-        r = dns_name_reverse(family, d, &reverse);
+        r = check_ifindex_flags(ifindex, &flags, 0, error);
         if (r < 0)
                 return r;
 
-        question = dns_question_new(1);
-        if (!question)
-                return -ENOMEM;
-
-        key = dns_resource_key_new_consume(DNS_CLASS_IN, DNS_TYPE_PTR, reverse);
-        if (!key)
-                return -ENOMEM;
-
-        reverse = NULL;
-
-        r = dns_question_add(question, key);
+        r = dns_question_new_reverse(&question, family, d);
         if (r < 0)
                 return r;
 
@@ -479,21 +403,58 @@ static int bus_method_resolve_address(sd_bus_message *message, void *userdata, s
 
         r = dns_query_bus_track(q, message);
         if (r < 0)
-                return r;
+                goto fail;
 
         r = dns_query_go(q);
-        if (r < 0) {
-                dns_query_free(q);
-                return r;
-        }
+        if (r < 0)
+                goto fail;
 
         return 1;
+
+fail:
+        dns_query_free(q);
+        return r;
+}
+
+static int bus_message_append_rr(sd_bus_message *m, DnsResourceRecord *rr, int ifindex) {
+        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
+        size_t start;
+        int r;
+
+        assert(m);
+        assert(rr);
+
+        r = sd_bus_message_open_container(m, 'r', "iqqay");
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_append(m, "iqq",
+                                  ifindex,
+                                  rr->key->class,
+                                  rr->key->type);
+        if (r < 0)
+                return r;
+
+        r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0);
+        if (r < 0)
+                return r;
+
+        p->refuse_compression = true;
+
+        r = dns_packet_append_rr(p, rr, &start);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_append_array(m, 'y', DNS_PACKET_DATA(p) + start, p->size - start);
+        if (r < 0)
+                return r;
+
+        return sd_bus_message_close_container(m);
 }
 
 static void bus_method_resolve_record_complete(DnsQuery *q) {
         _cleanup_bus_message_unref_ sd_bus_message *reply = NULL;
-        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
-        unsigned added = 0, i;
+        unsigned added = 0;
         int r;
 
         assert(q);
@@ -503,6 +464,16 @@ static void bus_method_resolve_record_complete(DnsQuery *q) {
                 goto finish;
         }
 
+        r = dns_query_process_cname(q);
+        if (r == -ELOOP) {
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_question_name(q->question));
+                goto finish;
+        }
+        if (r < 0)
+                goto finish;
+        if (r > 0) /* Following a CNAME */
+                return;
+
         r = sd_bus_message_new_method_return(q->request, &reply);
         if (r < 0)
                 goto finish;
@@ -512,44 +483,17 @@ static void bus_method_resolve_record_complete(DnsQuery *q) {
                 goto finish;
 
         if (q->answer) {
-                answer = dns_answer_ref(q->answer);
-
-                for (i = 0; i < answer->n_rrs; i++) {
-                        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
-                        size_t start;
+                DnsResourceRecord *rr;
+                int ifindex;
 
-                        r = dns_question_matches_rr(q->question, answer->items[i].rr);
+                DNS_ANSWER_FOREACH_IFINDEX(rr, ifindex, q->answer) {
+                        r = dns_question_matches_rr(q->question, rr);
                         if (r < 0)
                                 goto finish;
                         if (r == 0)
                                 continue;
 
-                        r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0);
-                        if (r < 0)
-                                goto finish;
-
-                        p->refuse_compression = true;
-
-                        r = dns_packet_append_rr(p, answer->items[i].rr, &start);
-                        if (r < 0)
-                                goto finish;
-
-                        r = sd_bus_message_open_container(reply, 'r', "iqqay");
-                        if (r < 0)
-                                goto finish;
-
-                        r = sd_bus_message_append(reply, "iqq",
-                                                  answer->items[i].ifindex,
-                                                  answer->items[i].rr->key->class,
-                                                  answer->items[i].rr->key->type);
-                        if (r < 0)
-                                goto finish;
-
-                        r = sd_bus_message_append_array(reply, 'y', DNS_PACKET_DATA(p) + start, p->size - start);
-                        if (r < 0)
-                                goto finish;
-
-                        r = sd_bus_message_close_container(reply);
+                        r = bus_message_append_rr(reply, rr, ifindex);
                         if (r < 0)
                                 goto finish;
 
@@ -558,7 +502,7 @@ static void bus_method_resolve_record_complete(DnsQuery *q) {
         }
 
         if (added <= 0) {
-                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "Name '%s' does not have any RR of the requested type", q->request_hostname);
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "Name '%s' does not have any RR of the requested type", dns_question_name(q->question));
                 goto finish;
         }
 
@@ -575,7 +519,7 @@ static void bus_method_resolve_record_complete(DnsQuery *q) {
 finish:
         if (r < 0) {
                 log_error_errno(r, "Failed to send record reply: %m");
-                sd_bus_reply_method_errno(q->request, -r, NULL);
+                sd_bus_reply_method_errno(q->request, r, NULL);
         }
 
         dns_query_free(q);
@@ -594,15 +538,19 @@ static int bus_method_resolve_record(sd_bus_message *message, void *userdata, sd
         assert(message);
         assert(m);
 
+        assert_cc(sizeof(int) == sizeof(int32_t));
+
         r = sd_bus_message_read(message, "isqqt", &ifindex, &name, &class, &type, &flags);
         if (r < 0)
                 return r;
 
-        r = dns_name_normalize(name, NULL);
+        r = dns_name_is_valid(name);
         if (r < 0)
+                return r;
+        if (r == 0)
                 return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid name '%s'", name);
 
-        r = check_ifindex_flags(ifindex, &flags, error);
+        r = check_ifindex_flags(ifindex, &flags, 0, error);
         if (r < 0)
                 return r;
 
@@ -623,20 +571,535 @@ static int bus_method_resolve_record(sd_bus_message *message, void *userdata, sd
                 return r;
 
         q->request = sd_bus_message_ref(message);
-        q->request_hostname = name;
         q->complete = bus_method_resolve_record_complete;
 
         r = dns_query_bus_track(q, message);
         if (r < 0)
-                return r;
+                goto fail;
 
         r = dns_query_go(q);
+        if (r < 0)
+                goto fail;
+
+        return 1;
+
+fail:
+        dns_query_free(q);
+        return r;
+}
+
+static int append_srv(DnsQuery *q, sd_bus_message *reply, DnsResourceRecord *rr) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *canonical = NULL;
+        DnsQuery *aux;
+        int r;
+
+        assert(q);
+        assert(reply);
+        assert(rr);
+        assert(rr->key);
+
+        if (rr->key->type != DNS_TYPE_SRV)
+                return 0;
+
+        if ((q->flags & SD_RESOLVED_NO_ADDRESS) == 0) {
+                /* First, let's see if we could find an appropriate A or AAAA
+                 * record for the SRV record */
+                LIST_FOREACH(auxiliary_queries, aux, q->auxiliary_queries) {
+                        DnsResourceRecord *zz;
+
+                        if (aux->state != DNS_TRANSACTION_SUCCESS)
+                                continue;
+                        if (aux->auxiliary_result != 0)
+                                continue;
+
+                        r = dns_name_equal(dns_question_name(aux->question), rr->srv.name);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        DNS_ANSWER_FOREACH(zz, aux->answer) {
+
+                                r = dns_question_matches_rr(aux->question, zz);
+                                if (r < 0)
+                                        return r;
+                                if (r == 0)
+                                        continue;
+
+                                canonical = dns_resource_record_ref(zz);
+                                break;
+                        }
+
+                        if (canonical)
+                                break;
+                }
+
+                /* Is there are successful A/AAAA lookup for this SRV RR? If not, don't add it */
+                if (!canonical)
+                        return 0;
+        }
+
+        r = sd_bus_message_open_container(reply, 'r', "qqqsa(iiay)s");
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_append(
+                        reply,
+                        "qqqs",
+                        rr->srv.priority, rr->srv.weight, rr->srv.port, rr->srv.name);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_open_container(reply, 'a', "(iiay)");
+        if (r < 0)
+                return r;
+
+        if ((q->flags & SD_RESOLVED_NO_ADDRESS) == 0) {
+                LIST_FOREACH(auxiliary_queries, aux, q->auxiliary_queries) {
+                        DnsResourceRecord *zz;
+                        int ifindex;
+
+                        if (aux->state != DNS_TRANSACTION_SUCCESS)
+                                continue;
+                        if (aux->auxiliary_result != 0)
+                                continue;
+
+                        r = dns_name_equal(dns_question_name(aux->question), rr->srv.name);
+                        if (r < 0)
+                                return r;
+                        if (r == 0)
+                                continue;
+
+                        DNS_ANSWER_FOREACH_IFINDEX(zz, ifindex, aux->answer) {
+
+                                r = dns_question_matches_rr(aux->question, zz);
+                                if (r < 0)
+                                        return r;
+                                if (r == 0)
+                                        continue;
+
+                                r = append_address(reply, zz, ifindex);
+                                if (r < 0)
+                                        return r;
+                        }
+                }
+        }
+
+        r = sd_bus_message_close_container(reply);
+        if (r < 0)
+                return r;
+
+        /* Note that above we appended the hostname as encoded in the
+         * SRV, and here the canonical hostname this maps to. */
+        r = sd_bus_message_append(reply, "s", canonical ? DNS_RESOURCE_KEY_NAME(canonical->key) : rr->srv.name);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_close_container(reply);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static int append_txt(sd_bus_message *reply, DnsResourceRecord *rr) {
+        DnsTxtItem *i;
+        int r;
+
+        assert(reply);
+        assert(rr);
+        assert(rr->key);
+
+        if (rr->key->type != DNS_TYPE_TXT)
+                return 0;
+
+        LIST_FOREACH(items, i, rr->txt.items) {
+
+                if (i->length <= 0)
+                        continue;
+
+                r = sd_bus_message_append_array(reply, 'y', i->data, i->length);
+                if (r < 0)
+                        return r;
+        }
+
+        return 1;
+}
+
+static void resolve_service_all_complete(DnsQuery *q) {
+        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *canonical = NULL;
+        _cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
+        _cleanup_free_ char *name = NULL, *type = NULL, *domain = NULL;
+        DnsQuery *aux;
+        unsigned added = false;
+        int r;
+
+        assert(q);
+
+        if (q->block_all_complete > 0)
+                return;
+
+        if ((q->flags & SD_RESOLVED_NO_ADDRESS) == 0) {
+                DnsQuery *bad = NULL;
+                bool have_success = false;
+
+                LIST_FOREACH(auxiliary_queries, aux, q->auxiliary_queries) {
+
+                        switch (aux->state) {
+
+                        case DNS_TRANSACTION_PENDING:
+                                /* If an auxiliary query is still pending, let's wait */
+                                return;
+
+                        case DNS_TRANSACTION_SUCCESS:
+                                if (aux->auxiliary_result == 0)
+                                        have_success = true;
+                                else
+                                        bad = aux;
+                                break;
+
+                        default:
+                                bad = aux;
+                                break;
+                        }
+                }
+
+                if (!have_success) {
+                        /* We can only return one error, hence pick the last error we encountered */
+
+                        assert(bad);
+
+                        if (bad->state == DNS_TRANSACTION_SUCCESS) {
+                                assert(bad->auxiliary_result != 0);
+
+                                if (bad->auxiliary_result == -ELOOP) {
+                                        r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_question_name(bad->question));
+                                        goto finish;
+                                }
+
+                                r = bad->auxiliary_result;
+                                goto finish;
+                        }
+
+                        r = reply_query_state(bad);
+                        goto finish;
+                }
+        }
+
+        r = sd_bus_message_new_method_return(q->request, &reply);
+        if (r < 0)
+                goto finish;
+
+        r = sd_bus_message_open_container(reply, 'a', "(qqqsa(iiay)s)");
+        if (r < 0)
+                goto finish;
+
+        if (q->answer) {
+                DnsResourceRecord *rr;
+
+                DNS_ANSWER_FOREACH(rr, q->answer) {
+                        r = dns_question_matches_rr(q->question, rr);
+                        if (r < 0)
+                                goto finish;
+                        if (r == 0)
+                                continue;
+
+                        r = append_srv(q, reply, rr);
+                        if (r < 0)
+                                goto finish;
+                        if (r == 0) /* not an SRV record */
+                                continue;
+
+                        if (!canonical)
+                                canonical = dns_resource_record_ref(rr);
+
+                        added++;
+                }
+        }
+
+        if (added <= 0) {
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "'%s' does not have any RR of the requested type", dns_question_name(q->question));
+                goto finish;
+        }
+
+        r = sd_bus_message_close_container(reply);
+        if (r < 0)
+                goto finish;
+
+        r = sd_bus_message_open_container(reply, 'a', "ay");
+        if (r < 0)
+                goto finish;
+
+        if (q->answer) {
+                DnsResourceRecord *rr;
+
+                DNS_ANSWER_FOREACH(rr, q->answer) {
+                        r = dns_question_matches_rr(q->question, rr);
+                        if (r < 0)
+                                goto finish;
+                        if (r == 0)
+                                continue;
+
+                        r = append_txt(reply, rr);
+                        if (r < 0)
+                                goto finish;
+                }
+        }
+
+        r = sd_bus_message_close_container(reply);
+        if (r < 0)
+                goto finish;
+
+        assert(canonical);
+        r = dns_service_split(DNS_RESOURCE_KEY_NAME(canonical->key), &name, &type, &domain);
+        if (r < 0)
+                goto finish;
+
+        r = sd_bus_message_append(
+                        reply,
+                        "ssst",
+                        name, type, domain,
+                        SD_RESOLVED_FLAGS_MAKE(q->answer_protocol, q->answer_family));
+        if (r < 0)
+                goto finish;
+
+        r = sd_bus_send(q->manager->bus, reply, NULL);
+
+finish:
+        if (r < 0) {
+                log_error_errno(r, "Failed to send service reply: %m");
+                sd_bus_reply_method_errno(q->request, r, NULL);
+        }
+
+        dns_query_free(q);
+}
+
+static void resolve_service_hostname_complete(DnsQuery *q) {
+        int r;
+
+        assert(q);
+        assert(q->auxiliary_for);
+
+        if (q->state != DNS_TRANSACTION_SUCCESS) {
+                resolve_service_all_complete(q->auxiliary_for);
+                return;
+        }
+
+        r = dns_query_process_cname(q);
+        if (r > 0) /* This was a cname, and the query was restarted. */
+                return;
+
+        /* This auxiliary lookup is finished or failed, let's see if all are finished now. */
+        q->auxiliary_result = r;
+        resolve_service_all_complete(q->auxiliary_for);
+}
+
+static int resolve_service_hostname(DnsQuery *q, DnsResourceRecord *rr, int ifindex) {
+        _cleanup_(dns_question_unrefp) DnsQuestion *question = NULL;
+        DnsQuery *aux;
+        int r;
+
+        assert(q);
+        assert(rr);
+        assert(rr->key);
+        assert(rr->key->type == DNS_TYPE_SRV);
+
+        /* OK, we found an SRV record for the service. Let's resolve
+         * the hostname included in it */
+
+        r = dns_question_new_address(&question, q->request_family, rr->srv.name);
+        if (r < 0)
+                return r;
+
+        r = dns_query_new(q->manager, &aux, question, ifindex, q->flags);
+        if (r < 0)
+                return r;
+
+        aux->request_family = q->request_family;
+        aux->complete = resolve_service_hostname_complete;
+
+        r = dns_query_make_auxiliary(aux, q);
+        if (r == -EAGAIN) {
+                /* Too many auxiliary lookups? If so, don't complain,
+                 * let's just not add this one, we already have more
+                 * than enough */
+
+                dns_query_free(aux);
+                return 0;
+        }
+        if (r < 0)
+                goto fail;
+
+        /* Note that auxiliary queries do not track the original bus
+         * client, only the primary request does that. */
+
+        r = dns_query_go(aux);
+        if (r < 0)
+                goto fail;
+
+        return 1;
+
+fail:
+        dns_query_free(aux);
+        return r;
+}
+
+static void bus_method_resolve_service_complete(DnsQuery *q) {
+        unsigned found = 0;
+        int r;
+
+        assert(q);
+
+        if (q->state != DNS_TRANSACTION_SUCCESS) {
+                r = reply_query_state(q);
+                goto finish;
+        }
+
+        r = dns_query_process_cname(q);
+        if (r == -ELOOP) {
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_CNAME_LOOP, "CNAME loop detected, or CNAME resolving disabled on '%s'", dns_question_name(q->question));
+                goto finish;
+        }
+        if (r < 0)
+                goto finish;
+        if (r > 0) /* This was a cname, and the query was restarted. */
+                return;
+
+        if (q->answer) {
+                DnsResourceRecord *rr;
+                int ifindex;
+
+                DNS_ANSWER_FOREACH_IFINDEX(rr, ifindex, q->answer) {
+                        r = dns_question_matches_rr(q->question, rr);
+                        if (r < 0)
+                                goto finish;
+                        if (r == 0)
+                                continue;
+
+                        if (rr->key->type != DNS_TYPE_SRV)
+                                continue;
+
+                        if ((q->flags & SD_RESOLVED_NO_ADDRESS) == 0) {
+                                q->block_all_complete ++;
+                                r = resolve_service_hostname(q, rr, ifindex);
+                                q->block_all_complete --;
+
+                                if (r < 0)
+                                        goto finish;
+                        }
+
+                        found++;
+                }
+        }
+
+        if (found <= 0) {
+                r = sd_bus_reply_method_errorf(q->request, BUS_ERROR_NO_SUCH_RR, "'%s' does not have any RR of the requested type", dns_question_name(q->question));
+                goto finish;
+        }
+
+        /* Maybe we are already finished? check now... */
+        resolve_service_all_complete(q);
+        return;
+
+finish:
         if (r < 0) {
-                dns_query_free(q);
+                log_error_errno(r, "Failed to send service reply: %m");
+                sd_bus_reply_method_errno(q->request, r, NULL);
+        }
+
+        dns_query_free(q);
+}
+
+static int bus_method_resolve_service(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        _cleanup_(dns_resource_key_unrefp) DnsResourceKey *key = NULL;
+        _cleanup_(dns_question_unrefp) DnsQuestion *question = NULL;
+        const char *name, *type, *domain, *joined;
+        _cleanup_free_ char *n = NULL;
+        Manager *m = userdata;
+        int family, ifindex;
+        uint64_t flags;
+        DnsQuery *q;
+        int r;
+
+        assert(message);
+        assert(m);
+
+        assert_cc(sizeof(int) == sizeof(int32_t));
+
+        r = sd_bus_message_read(message, "isssit", &ifindex, &name, &type, &domain, &family, &flags);
+        if (r < 0)
                 return r;
+
+        if (!IN_SET(family, AF_INET, AF_INET6, AF_UNSPEC))
+                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Unknown address family %i", family);
+
+        if (isempty(name))
+                name = NULL;
+        else {
+                if (!dns_service_name_is_valid(name))
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid service name '%s'", name);
         }
 
+        if (isempty(type))
+                type = NULL;
+        else {
+                r = dns_srv_type_verify(type);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid SRV service type '%s'", type);
+        }
+
+        r = dns_name_is_valid(domain);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid domain '%s'", domain);
+
+        if (name && !type)
+                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Service name cannot be specified without service type.");
+
+        r = check_ifindex_flags(ifindex, &flags, SD_RESOLVED_NO_TXT|SD_RESOLVED_NO_ADDRESS, error);
+        if (r < 0)
+                return r;
+
+        if (type) {
+                /* If the type is specified, we generate the full domain name to look up ourselves */
+                r = dns_service_join(name, type, domain, &n);
+                if (r < 0)
+                        return r;
+
+                joined = n;
+        } else
+                /* If no type is specified, we assume the domain
+                 * contains the full domain name to lookup already */
+                joined = domain;
+
+        r = dns_question_new_service(&question, joined, !(flags & SD_RESOLVED_NO_TXT));
+        if (r < 0)
+                return r;
+
+        r = dns_query_new(m, &q, question, ifindex, flags);
+        if (r < 0)
+                return r;
+
+        q->request = sd_bus_message_ref(message);
+        q->request_family = family;
+        q->complete = bus_method_resolve_service_complete;
+
+        r = dns_query_bus_track(q, message);
+        if (r < 0)
+                goto fail;
+
+        r = dns_query_go(q);
+        if (r < 0)
+                goto fail;
+
         return 1;
+
+fail:
+        dns_query_free(q);
+        return r;
 }
 
 static const sd_bus_vtable resolve_vtable[] = {
@@ -644,6 +1107,7 @@ static const sd_bus_vtable resolve_vtable[] = {
         SD_BUS_METHOD("ResolveHostname", "isit", "a(iiay)st", bus_method_resolve_hostname, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("ResolveAddress", "iiayt", "a(is)t", bus_method_resolve_address, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("ResolveRecord", "isqqt", "a(iqqay)t", bus_method_resolve_record, SD_BUS_VTABLE_UNPRIVILEGED),
+        SD_BUS_METHOD("ResolveService", "isssit", "a(qqqsa(iiay)s)aayssst", bus_method_resolve_service, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_VTABLE_END,
 };