Fix for sending UDP multicast on IPv6

Source/GCD/GCDAsyncUdpSocket.h

@@ -490,6 +490,18 @@ typedef BOOL (^GCDAsyncUdpSocketSendFilterBlock)(NSData *data, NSData *address,
 - (BOOL)leaveMulticastGroup:(NSString *)group error:(NSError **)errPtr;
 - (BOOL)leaveMulticastGroup:(NSString *)group onInterface:(nullable NSString *)interface error:(NSError **)errPtr;
 
+/**
+ * Send multicast on a specified interface.
+ * For IPv4, interface should be the the IP address of the interface (eg @"192.168.10.1").
+ * For IPv6, interface should be the a network interface name (eg @"en0").
+ *
+ * On success, returns YES.
+ * Otherwise returns NO, and sets errPtr. If you don't care about the error, you can pass nil for errPtr.
+**/
+
+- (BOOL)sendIPv4MulticastOnInterface:(NSString*)interface error:(NSError **)errPtr;
+- (BOOL)sendIPv6MulticastOnInterface:(NSString*)interface error:(NSError **)errPtr;
+
 #pragma mark Reuse Port
 
 /**

Source/GCD/GCDAsyncUdpSocket.m

@@ -3531,6 +3531,121 @@ - (BOOL)performMulticastRequest:(int)requestType
 	return result;
 }
 
+- (BOOL)sendIPv4MulticastOnInterface:(NSString*)interface error:(NSError **)errPtr
+{
+    __block BOOL result = NO;
+    __block NSError *err = nil;
+
+    dispatch_block_t block = ^{ @autoreleasepool {
+
+        if (![self preOp:&err])
+        {
+            return_from_block;
+        }
+
+        if ((self->flags & kDidCreateSockets) == 0)
+        {
+            if (![self createSockets:&err])
+            {
+                return_from_block;
+            }
+        }
+
+        // Convert interface to address
+
+        NSData *interfaceAddr4 = nil;
+        NSData *interfaceAddr6 = nil;
+
+        [self convertIntefaceDescription:interface port:0 intoAddress4:&interfaceAddr4 address6:&interfaceAddr6];
+
+        if (interfaceAddr4 == nil)
+        {
+            NSString *msg = @"Unknown interface. Specify valid interface by IP address.";
+            err = [self badParamError:msg];
+            return_from_block;
+        }
+
+        if (self->socket4FD != SOCKET_NULL) {
+            const struct sockaddr_in *nativeIface = (struct sockaddr_in *)[interfaceAddr4 bytes];
+            struct in_addr interface_addr = nativeIface->sin_addr;
+            int status = setsockopt(self->socket4FD, IPPROTO_IP, IP_MULTICAST_IF, &interface_addr, sizeof(interface_addr));
+            if (status != 0) {
+                 err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
+                return_from_block;
+                result = YES;
+          }
+        }
+
+     }};
+
+    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
+        block();
+    else
+        dispatch_sync(socketQueue, block);
+
+    if (errPtr)
+        *errPtr = err;
+
+    return result;
+}
+
+- (BOOL)sendIPv6MulticastOnInterface:(NSString*)interface error:(NSError **)errPtr
+{
+    __block BOOL result = NO;
+    __block NSError *err = nil;
+
+    dispatch_block_t block = ^{ @autoreleasepool {
+
+        if (![self preOp:&err])
+        {
+            return_from_block;
+        }
+
+        if ((self->flags & kDidCreateSockets) == 0)
+        {
+            if (![self createSockets:&err])
+            {
+                return_from_block;
+            }
+        }
+
+        // Convert interface to address
+
+        NSData *interfaceAddr4 = nil;
+        NSData *interfaceAddr6 = nil;
+
+        [self convertIntefaceDescription:interface port:0 intoAddress4:&interfaceAddr4 address6:&interfaceAddr6];
+
+        if (interfaceAddr6 == nil)
+        {
+            NSString *msg = @"Unknown interface. Specify valid interface by name (e.g. \"en1\").";
+            err = [self badParamError:msg];
+            return_from_block;
+        }
+
+        if ((self->socket6FD != SOCKET_NULL)) {
+            uint32_t scope_id = [self indexOfInterfaceAddr6:interfaceAddr6];
+            int status = setsockopt(self->socket6FD, IPPROTO_IPV6, IPV6_MULTICAST_IF, &scope_id, sizeof(scope_id));
+            if (status != 0) {
+                 err = [self errnoErrorWithReason:@"Error in setsockopt() function"];
+                return_from_block;
+            }
+            result = YES;
+       }
+
+     }};
+
+    if (dispatch_get_specific(IsOnSocketQueueOrTargetQueueKey))
+        block();
+    else
+        dispatch_sync(socketQueue, block);
+
+    if (errPtr)
+        *errPtr = err;
+
+    return result;
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 #pragma mark Reuse port
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////