add multicast

ios/UdpSocketClient.h

@@ -65,6 +65,22 @@ typedef enum RCTUDPError RCTUDPError;
  */
 - (BOOL)bind:(u_int16_t) port address:(NSString*) address error:(NSError**)error;
 
+/**
+ * Join multicast groupt
+ *
+ * @param address
+ * @return true if joined, false if there was an error
+ */
+- (BOOL)joinMulticastGroup:(NSString *)address error:(NSError **) error;
+
+/**
+ * leave multicast groupt
+ *
+ * @param address
+ * @return true if joined, false if there was an error
+ */
+- (BOOL)leaveMulticastGroup:(NSString *)address error:(NSError **) error;
+
 /**
  * send data to another host and port
  *

ios/UdpSocketClient.m

@@ -110,6 +110,24 @@ NSString *const RCTUDPErrorDomain = @"RCTUDPErrorDomain";
   return result && [_udpSocket beginReceiving:error];
 }
 
+- (BOOL)joinMulticastGroup:(NSString *)address error:(NSError **) error
+{
+    if(![_udpSocket joinMulticastGroup:address error:&error]){
+        NSLog(@"Error joining multicast group: %@", error);
+        return false;
+    }
+    return true;
+}
+
+- (BOOL)leaveMulticastGroup:(NSString *)address error:(NSError **) error
+{
+    if(![_udpSocket leaveMulticastGroup:address error:&error]){
+        NSLog(@"Error leaving multicast group: %@", error);
+        return false;
+    }
+    return true;
+}
+
 - (void)udpSocket:(GCDAsyncUdpSocket *)sock didSendDataWithTag:(long)msgTag
 {
   NSNumber* tagNum = [NSNumber numberWithLong:msgTag];

ios/UdpSockets.m

@@ -106,12 +106,22 @@ RCT_EXPORT_METHOD(setBroadcast:(nonnull NSNumber*)cId
 
 RCT_EXPORT_METHOD(addMembership:(nonnull NSNumber*)cId
                   multicastAddress:(NSString *)address) {
-    /* nop */
+     UdpSocketClient *client = _clients[cId];
+    
+    if (!client) return;
+    
+    NSError *error = nil;
+    [client joinMulticastGroup:address error:&error];
 }
 
 RCT_EXPORT_METHOD(dropMembership:(nonnull NSNumber*)cId
                   multicastAddress:(NSString *)address) {
-    /* nop */
+    UdpSocketClient *client = _clients[cId];
+    
+    if (!client) return;
+    
+    NSError *error = nil;
+    [client leaveMulticastGroup:address error:&error];
 }
 
 - (void) onData:(UdpSocketClient*) client data:(NSData *)data host:(NSString *)host port:(uint16_t)port