发送数据报 - 网络无法访问

Question

我试图在热点上的两个Android设备之间广播udp数据包。

我有一个设置热点的客户端，以及一个连接到热点的服务器。从客户端发送包并在服务器上接收该包正在运行。但是当我尝试从服务器回复时，我收到一个SocketException，说网络无法访问。我检查了IP地址和端口号，两者都应该是正确的（我假设端口是正确的，因为它是从数据包本身获取的）。

服务器和客户端的代码如下。任何人都可以看到代码出错的地方，或者它只是一个网络连接问题吗？

客户端：

    try {
            //Open a random port to send the package
            c = new DatagramSocket();
            c.setBroadcast(true);

            byte[] sendData = "DISCOVER_MV_REQUEST".getBytes();

            try {
                InetAddress addr = getIpAddress();
                DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, getBroadcast(addr), 8888);
                c.send(sendPacket);
            } catch (Exception e) {
                c.close();
                e.printStackTrace();
                return null;
            }

            // Broadcast the message over all the network interfaces
            Enumeration interfaces = NetworkInterface.getNetworkInterfaces();
            while (interfaces.hasMoreElements()) {
                NetworkInterface networkInterface = (NetworkInterface) interfaces.nextElement();

                if (networkInterface.isLoopback() || !networkInterface.isUp()) {
                    continue; // Don't want to broadcast to the loopback interface
                }

                for (InterfaceAddress interfaceAddress : networkInterface.getInterfaceAddresses()) {
                    InetAddress broadcast = interfaceAddress.getBroadcast();
                    if (broadcast == null) {
                        continue;
                    }

                    // Send the broadcast package!
                    try {
                        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, broadcast, 8888);
                        c.send(sendPacket);
                    } catch (Exception e) {
                        c.close();
                        e.printStackTrace();
                        return null;
                    }

                }
            }

            //Wait for a response
            byte[] recvBuf = new byte[15000];
            DatagramPacket receivePacket = new DatagramPacket(recvBuf, recvBuf.length);
            c.receive(receivePacket);

            //Check if the message is correct
            String message = new String(receivePacket.getData()).trim();
            if (message.equals("DISCOVER_MV_RESPONSE")) {
                //DO SOMETHING WITH THE SERVER'S IP (for example, store it in your controller)
                Log.v("SOCKET", "got correct response");
                c.close();
                return "correct";
            } else {
                c.close();
                Log.v("SOCKET", "wrong response");
                return "wrong";
            }

        } catch (Exception e) {
            c.close();
            e.printStackTrace();
            return null;
        }

服务器：

        try {
            //Keep a socket open to listen to all the UDP trafic that is destined for this port
            socket = new DatagramSocket(8888, InetAddress.getByName("0.0.0.0"));
            socket.setBroadcast(true);

            while (true) {
                //Receive a packet
                byte[] recvBuf = new byte[15000];
                DatagramPacket packet = new DatagramPacket(recvBuf, recvBuf.length);
                socket.receive(packet);

                //See if the packet holds the right command (message)
                String message = new String(packet.getData()).trim();
                if (message.equals("DISCOVER_MV_REQUEST")) {
                    byte[] sendData = "DISCOVER_MV_RESPONSE".getBytes();

                    //Send a response
                    DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, packet.getAddress(), packet.getPort());
                    socket.send(sendPacket); //where the error happens
                    socket.close();
                }

            }
        } catch (Exception e) {
            e.printStackTrace();
        }