Question

我有一个多播套接字，我必须指定一个网络接口才能接收数据。但是，当我使用网络接口加入组时，Java将无法接收它。我有一个简单的python程序，在同一台服务器上执行完全相同的操作，并且工作正常。

在为Java中的MulticastSocket设置NetworkInterface时我缺少什么？

java是：

    SocketAddress socketAddress =  new InetSocketAddress("x.x.x.x", 40000);
    NetworkInterface networkInterface = NetworkInterface.getByInetAddress(InetAddress.getByName("z.z.z.z"));

    logger.info("Network interface is {} ", networkInterface);

    MulticastSocket s = new MulticastSocket();
    s.setInterface(InetAddress.getByName("z.z.z.z"));
    s.joinGroup(socketAddress,networkInterface);
    logger.info(s.getNetworkInterface());

while(true){

            try{

                logger.info("Waiting for message");
                byte[] size = new byte[2];

                DatagramPacket recv = new DatagramPacket(size, size.length);
                socket.receive(recv);

                logger.info("Received size message"); //Never get here
                ByteBuffer wrapped = ByteBuffer.wrap(size); // big-endian by default
                short messageSize = wrapped.getShort(); 

                byte[] buf = new byte[messageSize-2];
                DatagramPacket message = new DatagramPacket(buf, buf.length);
                socket.receive(message);

                logger.info("Received multicast message");
                dataQueue.put(buf);
            }catch(Exception e){ 
                logger.error("Failed to receive multicast message ",e);
            }
        }

结果是我从未收到任何数据包。我有一个简单的python程序，它做同样的事情，每次都很完美。

作为参考，python看起来像

MCAST_GRP = 'x.x.x.x'
MCAST_PORT = 40000

mcastsock = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
mcastsock.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
mcastsock.setsockopt(socket.SOL_IP,socket.IP_ADD_MEMBERSHIP,
                socket.inet_aton(MCAST_GRP)+socket.inet_aton('z.z.z.z'))
mcastsock.bind((MCAST_GRP,MCAST_PORT))

while True:
  print mcastsock.recv(1320)

Answer 1

使用nio包将其切换到MulticastChannel解决了该问题。不完全确定它是原因，但底层接口是igmp v3，在某些情况下，看起来上面的java多播代码不适用于该配置。

此处提供更多详细信息和代码示例： https://docs.oracle.com/javase/7/docs/api/java/nio/channels/MulticastChannel.html

 // join multicast group on this interface, and also use this
 // interface for outgoing multicast datagrams
 NetworkInterface ni = NetworkInterface.getByName("hme0");

 DatagramChannel dc = DatagramChannel.open(StandardProtocolFamily.INET)
     .setOption(StandardSocketOptions.SO_REUSEADDR, true)
     .bind(new InetSocketAddress(5000))
     .setOption(StandardSocketOptions.IP_MULTICAST_IF, ni);

 InetAddress group = InetAddress.getByName("225.4.5.6");

 MembershipKey key = dc.join(group, ni);

Java多播套接字未在特定网络接口

1 个答案: