Java Soket 无法在 Raspberry Pi 上发送多播数据包

Question

我尝试在 Raspberry Pi 中运行这段代码。套接字可以从多播组接收数据，但是在尝试发送数据时显示以下错误：

pi@raspberrypi:~ $ java  Protocol
java.net.MulticastSocket@647e05
java.io.IOException: Cannot assign requested address
    at java.net.PlainDatagramSocketImpl.send(Native Method)
    at java.net.DatagramSocket.send(DatagramSocket.java:693)
    at Protocol.getSensorData(Protocol.java:201)
    at Protocol.main(Protocol.java:305)

代码如下：

import java.net.*;
import java.util.*;

public class Protocol {

    private MulticastSocket socket = null;
    private MulticastSocket socket_switchPanel = null;
    String MULTICAST_ADDRESS = "";
    int port = -1;

    public Protocol(String NIC, boolean isByIP, String multcastAddress, int port) {
        this.MULTICAST_ADDRESS = multcastAddress;
        this.port = port;
        try {
            InetAddress dstAddr = InetAddress.getByName(MULTICAST_ADDRESS);
            socket = new MulticastSocket(port);
            InetSocketAddress socketAddress = new InetSocketAddress(MULTICAST_ADDRESS, port);

            NetworkInterface ni = NetworkInterface.getByName(NIC);
            socket.setReuseAddress(true);
            socket.joinGroup(socketAddress, ni);
            System.out.println(ni);

        } catch (Exception e) {
            System.out.println(e);
            e.printStackTrace();
            if (socket != null) {
                socket.close();
            }
        }
    }

    public void close_socket() {
        if (socket != null) {
            socket.close();
        }
    }

    public Integer getSensorData() {

        byte[] msg = new byte[]{
                (byte) 0xAB, 0x04, (byte) 0x82, (byte) 0xCD, 0x00, (byte) 0x01};
        try {
            // get the IP address
            InetAddress dstAddr = InetAddress.getByName(MULTICAST_ADDRESS);

            final DatagramPacket out = new DatagramPacket(msg, msg.length, dstAddr, port);
            socket.send(out);
            // receive data until timeout or stop prematurely on users' request
            try {
                // process multi cast response(s)
                final byte[] inputBuffer = new byte[30];
                final DatagramPacket in = new DatagramPacket(inputBuffer, inputBuffer.length);
                socket.setSoTimeout(500);
                socket.receive(in);
                byte[] data = in.getData();
                return 1;

            } catch (Exception ste) {
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return 1;
    }


    public static void main(String[] args) {
//        tring NIC, boolean isByIP, String multcastAddress, int port
        Protocol dc = new Protocol("wlan0",
                false,
                "ff12:00:00:00:4479:00:00:00",
                50000);
        int ab = dc.getSensorData();
        System.out.println(ab);
        return;
    }
}

Answer 1

您的 java 可能正在获取 IP V4 而不是 IP V6（就像您的多播地址似乎指向的那样）。尝试从

开始

-Djava.net.preferIPv6Addresses=true

通常这种情况发生在 java 更喜欢 v6 而不是 v4 的情况下，但这里可能有特殊情况。或者，您只是使用了一个无效的多播地址（查看 https://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xhtml#ipv6-scope 似乎以 ff12 开头的地址对 ipv6 多播地址无效）。

Answer 2

我找到了解决办法。您必须禁用其他接口。例如，如果您使用 WIFI 发送多播消息。您可以使用禁用 eth0 ifconfig eth0 down。请注意，在 PI 重新启动后，eth0 会再次上线。

Java Soket 无法在 Raspberry Pi 上发送多播数据包

Java Soket cannot send multicast packet on Raspberry Pi

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raspberry-pi