Update announce example

- Listen for correct record type (RR_PTR)
- Respond with all answer entries required to correctly announce a service
- Add IPv6 support to example

examples/announce.c

@@ -40,21 +40,66 @@ static bool stop(void *cbarg)
 
 static void callback(void *cbarg, int r, const struct mdns_ip *mdns_ip, const struct rr_entry *entry)
 {
+        if (entry->type != RR_PTR)
+        {
+                printf("Unsupported request type: %d\n", entry->type);
+                return;
+        }
         struct mdns_ctx *ctx = (struct mdns_ctx *) cbarg;
         struct mdns_hdr hdr = {0};
-        struct rr_entry answer = {0};
-
+        struct rr_entry answers[4] = {0}; // A/AAAA, SRV, TXT, PTR
         hdr.flags |= FLAG_QR;
         hdr.flags |= FLAG_AA;
-        hdr.num_ans_rr = 1;
+        hdr.num_ans_rr = sizeof(answers) / sizeof(answers[0]);
+
+        for (int i = 0; i < hdr.num_ans_rr; i++)
+        {
+
+                answers[i].rr_class = RR_IN;
+                answers[i].ttl      = 120;
+
+                if (i + 1 < hdr.num_ans_rr)
+                        answers[i].next = &answers[i + 1];
+        }
 
-        answer.name     = entry->name;
-        answer.type     = entry->type;
-        answer.rr_class = entry->rr_class;
-        answer.ttl      = 120;
+        char domain_name[] = "mdnshost.local";
+        char service_type[] = "_googlecast._tcp.local";
+        // link service type (_googlecast._tcp) to our domain (mdnshost.local) 
+        char service_type_link[] = "mdnshost mDNShost._googlecast._tcp.local";
+
+        // RR_PTR: point service type (_vlc._tcp._local) to local domain
+        answers[0].type     = RR_PTR;
+        answers[0].name     = service_type;
+        answers[0].data.PTR.domain = service_type_link;
+
+        // RR_TXT: provide additional information (HTTP server root directory etc.)
+        answers[1].type     = RR_TXT;
+        answers[1].name     = service_type_link;
+
+        // RR_SRV: provide info about the service we're announcing (port no, etc.)
+        answers[2].type     = RR_SRV;
+        answers[2].name     = service_type_link;
+        answers[2].data.SRV.port = 9001;
+        answers[2].data.SRV.priority = 0;
+        answers[2].data.SRV.weight = 0;
+        answers[2].data.SRV.target = domain_name;
+
+        // RR_A/AAAA: link .local domain to IP address
+        answers[3].name     = domain_name;
+        if (mdns_ip->family == AF_INET)
+        {
+                answers[3].type     = RR_A;
+                memcpy(&answers[3].data.A.addr, &mdns_ip->ipv4, 
+                        sizeof(answers[3].data.A.addr));
+        }
+        else
+        {
+                answers[3].type     = RR_AAAA;
+                memcpy(&answers[3].data.AAAA.addr, &mdns_ip->ipv6, 
+                        sizeof(answers[3].data.AAAA.addr));
+        }
 
-        memcpy(&answer.data.A.addr, &mdns_ip->ipv4, sizeof(answer.data.A.addr));
-        mdns_entries_send(ctx, &hdr, &answer);
+        mdns_entries_send(ctx, &hdr, answers);
 }
 
 int main(int argc, char *argv[])
@@ -69,8 +114,9 @@ int main(int argc, char *argv[])
         if ((r = mdns_init(&ctx, MDNS_ADDR_IPV4, MDNS_PORT)) < 0)
                 goto err;
 
-        // test with `ping mdnshost.local`
-        mdns_announce(ctx, "mdnshost.local", RR_A, callback, ctx);
+        // test with `ping mdnshost.local` after discovery (run ./test first)
+        // NB: a zeroconf service (eg Avahi) must be running for ping to work
+        mdns_announce(ctx, "_googlecast._tcp.local", RR_PTR, callback, ctx);
 
         if ((r = mdns_serve(ctx, stop, NULL)) < 0)
                 goto err;