How to send broadcast on a specific UDP port? (Getting error: `sendto failed: EINVAL`)

Question

免责声明：我知道已经有相同主题的问题，但下面的问题与其他问题不同。

我正在尝试在某个端口上广播数据包。

这不起作用。我的代码：（我运行这个在我实际的 phone 上）

//Creating the socket (It's a class field, not a private element)
bcSock = new DatagramSocket(DEVICE_PORT, bcAddress);//bcAddress is explained below
bcSock.setBroadcast(true);
bcSock.setSoTimeout(LISTEN_TIMEOUT);
//Somewhere else in the code, creating the packet/sending it
 byte[] buf = PACKET_CONTENT.getBytes();
    DatagramPacket dp = new DatagramPacket(buf, buf.length, bcAddress, PORT);
    new SendUDPTask() {
        @Override
        public void handleException(Exception e) {
            //TODO Handle
            e.printStackTrace();
        }
    }.execute(bcSock, dp, LISTEN_TIMEOUT);

其中 SendUDPTask 是一个 public class，它就是这样做的：sock.send(dp);.

bcAddress是使用此方法生成的默认广播IP：

public static InetAddress getBroadcastAddress(Activity activity) throws IOException {
    WifiManager wifi = (WifiManager) activity.getSystemService(Context.WIFI_SERVICE);
    DhcpInfo dhcp = wifi.getDhcpInfo();
    // handle null somehow

    int broadcast = (dhcp.ipAddress & dhcp.netmask) | ~dhcp.netmask;
    byte[] quads = new byte[4];
    for (int k = 0; k < 4; k++)
        quads[k] = (byte) (broadcast >> (k * 8));
    return InetAddress.getByAddress(quads);
}

这样我得到这个错误：

java.net.SocketException: sendto failed: EINVAL (Invalid argument)
    at libcore.io.IoBridge.maybeThrowAfterSendto(IoBridge.java:542)
    at libcore.io.IoBridge.sendto(IoBridge.java:511)
    at java.net.PlainDatagramSocketImpl.send(PlainDatagramSocketImpl.java:184)
    at java.net.DatagramSocket.send(DatagramSocket.java:305)
    at me.nonamesldev.smarthouse.SendUDPTask.doInBackground(SendUDPTask.java:27)
    at me.nonamesldev.smarthouse.SendUDPTask.doInBackground(SendUDPTask.java:17)

（第 27 行是 socket.send(packet) 部分。）

尝试像这样创建套接字 DatagramSocket s = new DatagramSocket(8888); 也不起作用并且在 DatagramSocket.send 上抛出 NullPointerException - null buffer || null address，即使文档说这应该没事:

DatagramSocket s = new DatagramSocket(null); s.bind(new InetSocketAddress(8888)); Which is equivalent to: DatagramSocket s = new DatagramSocket(8888); Both cases will create a DatagramSocket able to receive broadcasts on UDP port 8888.

我该怎么办？我只想在 Android 中的某个端口上的 UDP 上广播。为什么一定要这么难？

提前致谢！

编辑：我也试过这样创建套接字：

DatagramChannel channel = DatagramChannel.open();
DatagramSocket socket = channel.socket();
bcSock.bind(new InetSocketAddress(bcAddress, PORT));

而不是 bcSock = new DatagramSocket(DEVICE_PORT, bcAddress);，它会产生相同的错误。

Answer 1

对我有用：

发件人

bcSock = new DatagramSocket();
bcSock.setBroadcast(true);
byte[] buf = PACKET_CONTENT.getBytes();
DatagramPacket dp = new DatagramPacket(buf, buf.length, bcAddress, PORT);
bcSock.send(dp);

接收方

DatagramSocket ds = new DatagramSocket(PORT);
byte[] buf = new byte[PACKET_CONTENT.getBytes().length];
DatagramPacket dp = new DatagramPacket(buf, buf.length);
ds.receive(dp);

Answer 2

您不应尝试将套接字绑定到广播地址。使用 INADDR_ANY，在 Java 中是 null 的 InetAddress。

How to send broadcast on a specific UDP port? (Getting error: `sendto failed: EINVAL`)

How to send broadcast on a specific UDP port? (Getting error: `sendto failed: EINVAL`)

java

sockets

networking

android

broadcast

发件人

接收方