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, 16 insertions, 2 deletions

diff --git a/src/resolve/resolved-dns-query.h b/src/resolve/resolved-dns-query.h
index 2c28a7e284..256dddc00b 100644
--- a/src/resolve/resolved-dns-query.h
+++ b/src/resolve/resolved-dns-query.h
@@ -34,6 +34,16 @@ typedef struct DnsQuery DnsQuery;
 
 struct DnsQuery {
         Manager *manager;
+
+        /* When resolving a service, we first create a TXT+SRV query,
+         * and then for the hostnames we discover auxiliary A+AAAA
+         * queries. This pointer always points from the auxiliary
+         * queries back to the TXT+SRV query. */
+        DnsQuery *auxiliary_for;
+        LIST_HEAD(DnsQuery, auxiliary_queries);
+        unsigned n_auxiliary_queries;
+        int auxiliary_result;
+
         DnsQuestion *question;
 
         uint64_t flags;
@@ -53,8 +63,9 @@ struct DnsQuery {
         /* Bus client information */
         sd_bus_message *request;
         int request_family;
-        const char *request_hostname;
+        bool request_address_valid;
         union in_addr_union request_address;
+        unsigned block_all_complete;
 
         /* Completion callback */
         void (*complete)(DnsQuery* q);
@@ -65,15 +76,18 @@ struct DnsQuery {
         sd_bus_track *bus_track;
 
         LIST_FIELDS(DnsQuery, queries);
+        LIST_FIELDS(DnsQuery, auxiliary_queries);
 };
 
 int dns_query_new(Manager *m, DnsQuery **q, DnsQuestion *question, int family, uint64_t flags);
 DnsQuery *dns_query_free(DnsQuery *q);
 
+int dns_query_make_auxiliary(DnsQuery *q, DnsQuery *auxiliary_for);
+
 int dns_query_go(DnsQuery *q);
 void dns_query_ready(DnsQuery *q);
 
-int dns_query_cname_redirect(DnsQuery *q, const DnsResourceRecord *cname);
+int dns_query_process_cname(DnsQuery *q);
 
 int dns_query_bus_track(DnsQuery *q, sd_bus_message *m);