[mdns] Make connection test optional and only do it for Airplay (fixes #602)

Some remotes don't respond as expected to the test. Retune will give connection
refused, because the test is made too quickly, before the service is running.

Even if we delay the test it won't work because Retune crashes.

Since the false mdns advertisements are only seen on Airplay, we only do the
test there.

src/mdns.h

@@ -4,6 +4,12 @@
 
 #include "misc.h"
 
+enum mdns_options
+{
+  // Test connection to device and only call back if successful
+  MDNS_CONNECTION_TEST = (1 << 1),
+};
+
 typedef void (* mdns_browse_cb)(const char *name, const char *type, const char *domain, const char *hostname, int family, const char *address, int port, struct keyval *txt);
 
 /*
@@ -54,10 +60,11 @@ mdns_cname(char *name);
  * @in  type     Type of service to look for, e.g. "_raop._tcp"
  * @in  family   AF_INET to browse for ipv4 services, AF_INET6 for ipv6, 
                  AF_UNSPEC for both
+ * @in  flags    See mdns_options (only supported by Avahi implementation)
  * @in  cb       Callback when service state changes (e.g. appears/disappears)
  * @return       0 on success, -1 on error
  */
 int
-mdns_browse(char *type, int family, mdns_browse_cb cb);
+mdns_browse(char *type, int family, mdns_browse_cb cb, enum mdns_options flags);
 
 #endif /* !__MDNS_H__ */

src/mdns_avahi.c

@@ -348,6 +348,7 @@ struct mdns_browser
   char *type;
   AvahiProtocol protocol;
   mdns_browse_cb cb;
+  enum mdns_options flags;
 
   struct mdns_browser *next;
 };
@@ -567,7 +568,7 @@ connection_test(int family, const char *address, const char *address_log, int po
 // a connection to the address
 // - see also https://lists.freedesktop.org/archives/avahi/2012-September/002183.html
 static int
-address_check(AvahiProtocol proto, const char *hostname, const AvahiAddress *addr, int port)
+address_check(AvahiProtocol proto, const char *hostname, const AvahiAddress *addr, int port, enum mdns_options flags)
 {
   char address[AVAHI_ADDRESS_STR_MAX];
   char address_log[AVAHI_ADDRESS_STR_MAX + 2];
@@ -588,6 +589,9 @@ address_check(AvahiProtocol proto, const char *hostname, const AvahiAddress *add
       return -1;
     }
 
+  if (!(flags & MDNS_CONNECTION_TEST))
+    return 0; // All done
+
   ret = connection_test(family, address, address_log, port);
   if (ret < 0)
     {
@@ -633,7 +637,7 @@ browse_record_callback(AvahiRecordBrowser *b, AvahiIfIndex intf, AvahiProtocol p
 
   DPRINTF(E_DBG, L_MDNS, "Avahi Record Browser (%s, proto %d): NEW record %s for service type '%s'\n", hostname, proto, address, rb_data->mb->type);
 
-  ret = address_check(proto, hostname, &addr, rb_data->port);
+  ret = address_check(proto, hostname, &addr, rb_data->port, rb_data->mb->flags);
   if (ret < 0)
     return;
 
@@ -714,7 +718,7 @@ browse_resolve_callback(AvahiServiceResolver *r, AvahiIfIndex intf, AvahiProtoco
   // devices (e.g. ApEx 1 gen) will include multiple records, and we need to
   // filter out those records that won't work (notably link-local). The value of
   // *addr given by browse_resolve_callback is just the first record.
-  ret = address_check(proto, hostname, addr, port);
+  ret = address_check(proto, hostname, addr, port, mb->flags);
   if (ret < 0)
     {
       CHECK_NULL(L_MDNS, rb_data = calloc(1, sizeof(struct mdns_record_browser)));
@@ -1156,22 +1160,18 @@ mdns_cname(char *name)
 }
 
 int
-mdns_browse(char *type, int family, mdns_browse_cb cb)
+mdns_browse(char *type, int family, mdns_browse_cb cb, enum mdns_options flags)
 {
   struct mdns_browser *mb;
   AvahiServiceBrowser *b;
 
   DPRINTF(E_DBG, L_MDNS, "Adding service browser for type %s\n", type);
 
-  mb = calloc(1, sizeof(struct mdns_browser));
-  if (!mb)
-    {
-      DPRINTF(E_LOG, L_MDNS, "Out of memory for new mdns browser\n");
-      return -1;
-    }
+  CHECK_NULL(L_MDNS, mb = calloc(1, sizeof(struct mdns_browser)));
 
   mb->protocol = avahi_af_to_proto(family);
   mb->type = strdup(type);
+  mb->flags = flags;
   mb->cb = cb;
 
   mb->next = browser_list;

src/mdns_dnssd.c

@@ -116,6 +116,7 @@ struct mdns_browser
   struct mdns_resolver *resolvers;
   char *regtype;
   /* references */
+  enum mdns_options flags;
   mdns_browse_cb cb;
   DNSServiceProtocol protocol;
   void *res_uuid;
@@ -871,20 +872,16 @@ mdns_browse_callback(DNSServiceRef sdRef, DNSServiceFlags flags,
 }
 
 int
-mdns_browse(char *regtype, int family, mdns_browse_cb cb)
+mdns_browse(char *regtype, int family, mdns_browse_cb cb, enum mdns_options flags)
 {
   struct mdns_browser *mb;
   DNSServiceErrorType err;
 
   DPRINTF(E_DBG, L_MDNS, "Adding service browser for type %s\n", regtype);
 
-  mb = calloc(1, sizeof(*mb));
-  if (!mb)
-    {
-      DPRINTF(E_LOG, L_MDNS, "Out of memory creating service browser.\n");
-      return -1;
-    }
+  CHECK_NULL(L_MDNS, mb = calloc(1, sizeof(*mb)));
 
+  mb->flags = flags;
   mb->cb = cb;
 
   /* flags are ignored in DNS-SD implementation */

src/outputs/cast.c

@@ -1774,7 +1774,7 @@ cast_init(void)
   else
     family = AF_INET;
 
-  ret = mdns_browse("_googlecast._tcp", family, cast_device_cb);
+  ret = mdns_browse("_googlecast._tcp", family, cast_device_cb, 0);
   if (ret < 0)
     {
       DPRINTF(E_LOG, L_CAST, "Could not add mDNS browser for Chromecast devices\n");

src/outputs/raop.c

@@ -5025,7 +5025,7 @@ raop_init(void)
   else
     family = AF_INET;
 
-  ret = mdns_browse("_raop._tcp", family, raop_device_cb);
+  ret = mdns_browse("_raop._tcp", family, raop_device_cb, MDNS_CONNECTION_TEST);
   if (ret < 0)
     {
       DPRINTF(E_LOG, L_RAOP, "Could not add mDNS browser for AirPlay devices\n");

src/remote_pairing.c

@@ -818,7 +818,7 @@ remote_pairing_init(void)
 #endif /* HAVE_EVENTFD */
 
   // No ipv6 for remote at the moment
-  ret = mdns_browse("_touch-remote._tcp", AF_INET, touch_remote_cb);
+  ret = mdns_browse("_touch-remote._tcp", AF_INET, touch_remote_cb, 0);
   if (ret < 0)
     {
       DPRINTF(E_FATAL, L_REMOTE, "Could not browse for Remote services\n");